xref: /openbmc/linux/net/ipv4/tcp_input.c (revision feeeeb4c)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * INET		An implementation of the TCP/IP protocol suite for the LINUX
4  *		operating system.  INET is implemented using the  BSD Socket
5  *		interface as the means of communication with the user level.
6  *
7  *		Implementation of the Transmission Control Protocol(TCP).
8  *
9  * Authors:	Ross Biro
10  *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11  *		Mark Evans, <evansmp@uhura.aston.ac.uk>
12  *		Corey Minyard <wf-rch!minyard@relay.EU.net>
13  *		Florian La Roche, <flla@stud.uni-sb.de>
14  *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15  *		Linus Torvalds, <torvalds@cs.helsinki.fi>
16  *		Alan Cox, <gw4pts@gw4pts.ampr.org>
17  *		Matthew Dillon, <dillon@apollo.west.oic.com>
18  *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19  *		Jorge Cwik, <jorge@laser.satlink.net>
20  */
21 
22 /*
23  * Changes:
24  *		Pedro Roque	:	Fast Retransmit/Recovery.
25  *					Two receive queues.
26  *					Retransmit queue handled by TCP.
27  *					Better retransmit timer handling.
28  *					New congestion avoidance.
29  *					Header prediction.
30  *					Variable renaming.
31  *
32  *		Eric		:	Fast Retransmit.
33  *		Randy Scott	:	MSS option defines.
34  *		Eric Schenk	:	Fixes to slow start algorithm.
35  *		Eric Schenk	:	Yet another double ACK bug.
36  *		Eric Schenk	:	Delayed ACK bug fixes.
37  *		Eric Schenk	:	Floyd style fast retrans war avoidance.
38  *		David S. Miller	:	Don't allow zero congestion window.
39  *		Eric Schenk	:	Fix retransmitter so that it sends
40  *					next packet on ack of previous packet.
41  *		Andi Kleen	:	Moved open_request checking here
42  *					and process RSTs for open_requests.
43  *		Andi Kleen	:	Better prune_queue, and other fixes.
44  *		Andrey Savochkin:	Fix RTT measurements in the presence of
45  *					timestamps.
46  *		Andrey Savochkin:	Check sequence numbers correctly when
47  *					removing SACKs due to in sequence incoming
48  *					data segments.
49  *		Andi Kleen:		Make sure we never ack data there is not
50  *					enough room for. Also make this condition
51  *					a fatal error if it might still happen.
52  *		Andi Kleen:		Add tcp_measure_rcv_mss to make
53  *					connections with MSS<min(MTU,ann. MSS)
54  *					work without delayed acks.
55  *		Andi Kleen:		Process packets with PSH set in the
56  *					fast path.
57  *		J Hadi Salim:		ECN support
58  *	 	Andrei Gurtov,
59  *		Pasi Sarolahti,
60  *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
61  *					engine. Lots of bugs are found.
62  *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
63  */
64 
65 #define pr_fmt(fmt) "TCP: " fmt
66 
67 #include <linux/mm.h>
68 #include <linux/slab.h>
69 #include <linux/module.h>
70 #include <linux/sysctl.h>
71 #include <linux/kernel.h>
72 #include <linux/prefetch.h>
73 #include <net/dst.h>
74 #include <net/tcp.h>
75 #include <net/inet_common.h>
76 #include <linux/ipsec.h>
77 #include <asm/unaligned.h>
78 #include <linux/errqueue.h>
79 #include <trace/events/tcp.h>
80 #include <linux/jump_label_ratelimit.h>
81 #include <net/busy_poll.h>
82 #include <net/mptcp.h>
83 
84 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
85 
86 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
87 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
88 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
89 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
90 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
91 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
92 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
93 #define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
94 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
95 #define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
96 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
97 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
98 #define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */
99 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
100 #define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
101 #define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
102 #define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */
103 #define FLAG_DSACK_TLP		0x20000 /* DSACK for tail loss probe */
104 
105 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
106 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
107 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
108 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
109 
110 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
111 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
112 
113 #define REXMIT_NONE	0 /* no loss recovery to do */
114 #define REXMIT_LOST	1 /* retransmit packets marked lost */
115 #define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
116 
117 #if IS_ENABLED(CONFIG_TLS_DEVICE)
118 static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
119 
120 void clean_acked_data_enable(struct inet_connection_sock *icsk,
121 			     void (*cad)(struct sock *sk, u32 ack_seq))
122 {
123 	icsk->icsk_clean_acked = cad;
124 	static_branch_deferred_inc(&clean_acked_data_enabled);
125 }
126 EXPORT_SYMBOL_GPL(clean_acked_data_enable);
127 
128 void clean_acked_data_disable(struct inet_connection_sock *icsk)
129 {
130 	static_branch_slow_dec_deferred(&clean_acked_data_enabled);
131 	icsk->icsk_clean_acked = NULL;
132 }
133 EXPORT_SYMBOL_GPL(clean_acked_data_disable);
134 
135 void clean_acked_data_flush(void)
136 {
137 	static_key_deferred_flush(&clean_acked_data_enabled);
138 }
139 EXPORT_SYMBOL_GPL(clean_acked_data_flush);
140 #endif
141 
142 #ifdef CONFIG_CGROUP_BPF
143 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
144 {
145 	bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown &&
146 		BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
147 				       BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG);
148 	bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
149 						    BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG);
150 	struct bpf_sock_ops_kern sock_ops;
151 
152 	if (likely(!unknown_opt && !parse_all_opt))
153 		return;
154 
155 	/* The skb will be handled in the
156 	 * bpf_skops_established() or
157 	 * bpf_skops_write_hdr_opt().
158 	 */
159 	switch (sk->sk_state) {
160 	case TCP_SYN_RECV:
161 	case TCP_SYN_SENT:
162 	case TCP_LISTEN:
163 		return;
164 	}
165 
166 	sock_owned_by_me(sk);
167 
168 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
169 	sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
170 	sock_ops.is_fullsock = 1;
171 	sock_ops.sk = sk;
172 	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
173 
174 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
175 }
176 
177 static void bpf_skops_established(struct sock *sk, int bpf_op,
178 				  struct sk_buff *skb)
179 {
180 	struct bpf_sock_ops_kern sock_ops;
181 
182 	sock_owned_by_me(sk);
183 
184 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
185 	sock_ops.op = bpf_op;
186 	sock_ops.is_fullsock = 1;
187 	sock_ops.sk = sk;
188 	/* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
189 	if (skb)
190 		bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
191 
192 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
193 }
194 #else
195 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
196 {
197 }
198 
199 static void bpf_skops_established(struct sock *sk, int bpf_op,
200 				  struct sk_buff *skb)
201 {
202 }
203 #endif
204 
205 static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
206 			     unsigned int len)
207 {
208 	static bool __once __read_mostly;
209 
210 	if (!__once) {
211 		struct net_device *dev;
212 
213 		__once = true;
214 
215 		rcu_read_lock();
216 		dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
217 		if (!dev || len >= dev->mtu)
218 			pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
219 				dev ? dev->name : "Unknown driver");
220 		rcu_read_unlock();
221 	}
222 }
223 
224 /* Adapt the MSS value used to make delayed ack decision to the
225  * real world.
226  */
227 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
228 {
229 	struct inet_connection_sock *icsk = inet_csk(sk);
230 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
231 	unsigned int len;
232 
233 	icsk->icsk_ack.last_seg_size = 0;
234 
235 	/* skb->len may jitter because of SACKs, even if peer
236 	 * sends good full-sized frames.
237 	 */
238 	len = skb_shinfo(skb)->gso_size ? : skb->len;
239 	if (len >= icsk->icsk_ack.rcv_mss) {
240 		/* Note: divides are still a bit expensive.
241 		 * For the moment, only adjust scaling_ratio
242 		 * when we update icsk_ack.rcv_mss.
243 		 */
244 		if (unlikely(len != icsk->icsk_ack.rcv_mss)) {
245 			u64 val = (u64)skb->len << TCP_RMEM_TO_WIN_SCALE;
246 
247 			do_div(val, skb->truesize);
248 			tcp_sk(sk)->scaling_ratio = val ? val : 1;
249 		}
250 		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
251 					       tcp_sk(sk)->advmss);
252 		/* Account for possibly-removed options */
253 		if (unlikely(len > icsk->icsk_ack.rcv_mss +
254 				   MAX_TCP_OPTION_SPACE))
255 			tcp_gro_dev_warn(sk, skb, len);
256 		/* If the skb has a len of exactly 1*MSS and has the PSH bit
257 		 * set then it is likely the end of an application write. So
258 		 * more data may not be arriving soon, and yet the data sender
259 		 * may be waiting for an ACK if cwnd-bound or using TX zero
260 		 * copy. So we set ICSK_ACK_PUSHED here so that
261 		 * tcp_cleanup_rbuf() will send an ACK immediately if the app
262 		 * reads all of the data and is not ping-pong. If len > MSS
263 		 * then this logic does not matter (and does not hurt) because
264 		 * tcp_cleanup_rbuf() will always ACK immediately if the app
265 		 * reads data and there is more than an MSS of unACKed data.
266 		 */
267 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_PSH)
268 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
269 	} else {
270 		/* Otherwise, we make more careful check taking into account,
271 		 * that SACKs block is variable.
272 		 *
273 		 * "len" is invariant segment length, including TCP header.
274 		 */
275 		len += skb->data - skb_transport_header(skb);
276 		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
277 		    /* If PSH is not set, packet should be
278 		     * full sized, provided peer TCP is not badly broken.
279 		     * This observation (if it is correct 8)) allows
280 		     * to handle super-low mtu links fairly.
281 		     */
282 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
283 		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
284 			/* Subtract also invariant (if peer is RFC compliant),
285 			 * tcp header plus fixed timestamp option length.
286 			 * Resulting "len" is MSS free of SACK jitter.
287 			 */
288 			len -= tcp_sk(sk)->tcp_header_len;
289 			icsk->icsk_ack.last_seg_size = len;
290 			if (len == lss) {
291 				icsk->icsk_ack.rcv_mss = len;
292 				return;
293 			}
294 		}
295 		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
296 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
297 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
298 	}
299 }
300 
301 static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
302 {
303 	struct inet_connection_sock *icsk = inet_csk(sk);
304 	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
305 
306 	if (quickacks == 0)
307 		quickacks = 2;
308 	quickacks = min(quickacks, max_quickacks);
309 	if (quickacks > icsk->icsk_ack.quick)
310 		icsk->icsk_ack.quick = quickacks;
311 }
312 
313 static void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
314 {
315 	struct inet_connection_sock *icsk = inet_csk(sk);
316 
317 	tcp_incr_quickack(sk, max_quickacks);
318 	inet_csk_exit_pingpong_mode(sk);
319 	icsk->icsk_ack.ato = TCP_ATO_MIN;
320 }
321 
322 /* Send ACKs quickly, if "quick" count is not exhausted
323  * and the session is not interactive.
324  */
325 
326 static bool tcp_in_quickack_mode(struct sock *sk)
327 {
328 	const struct inet_connection_sock *icsk = inet_csk(sk);
329 	const struct dst_entry *dst = __sk_dst_get(sk);
330 
331 	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
332 		(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
333 }
334 
335 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
336 {
337 	if (tp->ecn_flags & TCP_ECN_OK)
338 		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
339 }
340 
341 static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
342 {
343 	if (tcp_hdr(skb)->cwr) {
344 		tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
345 
346 		/* If the sender is telling us it has entered CWR, then its
347 		 * cwnd may be very low (even just 1 packet), so we should ACK
348 		 * immediately.
349 		 */
350 		if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq)
351 			inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
352 	}
353 }
354 
355 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
356 {
357 	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
358 }
359 
360 static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
361 {
362 	struct tcp_sock *tp = tcp_sk(sk);
363 
364 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
365 	case INET_ECN_NOT_ECT:
366 		/* Funny extension: if ECT is not set on a segment,
367 		 * and we already seen ECT on a previous segment,
368 		 * it is probably a retransmit.
369 		 */
370 		if (tp->ecn_flags & TCP_ECN_SEEN)
371 			tcp_enter_quickack_mode(sk, 2);
372 		break;
373 	case INET_ECN_CE:
374 		if (tcp_ca_needs_ecn(sk))
375 			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
376 
377 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
378 			/* Better not delay acks, sender can have a very low cwnd */
379 			tcp_enter_quickack_mode(sk, 2);
380 			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
381 		}
382 		tp->ecn_flags |= TCP_ECN_SEEN;
383 		break;
384 	default:
385 		if (tcp_ca_needs_ecn(sk))
386 			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
387 		tp->ecn_flags |= TCP_ECN_SEEN;
388 		break;
389 	}
390 }
391 
392 static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
393 {
394 	if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
395 		__tcp_ecn_check_ce(sk, skb);
396 }
397 
398 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
399 {
400 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
401 		tp->ecn_flags &= ~TCP_ECN_OK;
402 }
403 
404 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
405 {
406 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
407 		tp->ecn_flags &= ~TCP_ECN_OK;
408 }
409 
410 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
411 {
412 	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
413 		return true;
414 	return false;
415 }
416 
417 /* Buffer size and advertised window tuning.
418  *
419  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
420  */
421 
422 static void tcp_sndbuf_expand(struct sock *sk)
423 {
424 	const struct tcp_sock *tp = tcp_sk(sk);
425 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
426 	int sndmem, per_mss;
427 	u32 nr_segs;
428 
429 	/* Worst case is non GSO/TSO : each frame consumes one skb
430 	 * and skb->head is kmalloced using power of two area of memory
431 	 */
432 	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
433 		  MAX_TCP_HEADER +
434 		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
435 
436 	per_mss = roundup_pow_of_two(per_mss) +
437 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
438 
439 	nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
440 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
441 
442 	/* Fast Recovery (RFC 5681 3.2) :
443 	 * Cubic needs 1.7 factor, rounded to 2 to include
444 	 * extra cushion (application might react slowly to EPOLLOUT)
445 	 */
446 	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
447 	sndmem *= nr_segs * per_mss;
448 
449 	if (sk->sk_sndbuf < sndmem)
450 		WRITE_ONCE(sk->sk_sndbuf,
451 			   min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2])));
452 }
453 
454 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
455  *
456  * All tcp_full_space() is split to two parts: "network" buffer, allocated
457  * forward and advertised in receiver window (tp->rcv_wnd) and
458  * "application buffer", required to isolate scheduling/application
459  * latencies from network.
460  * window_clamp is maximal advertised window. It can be less than
461  * tcp_full_space(), in this case tcp_full_space() - window_clamp
462  * is reserved for "application" buffer. The less window_clamp is
463  * the smoother our behaviour from viewpoint of network, but the lower
464  * throughput and the higher sensitivity of the connection to losses. 8)
465  *
466  * rcv_ssthresh is more strict window_clamp used at "slow start"
467  * phase to predict further behaviour of this connection.
468  * It is used for two goals:
469  * - to enforce header prediction at sender, even when application
470  *   requires some significant "application buffer". It is check #1.
471  * - to prevent pruning of receive queue because of misprediction
472  *   of receiver window. Check #2.
473  *
474  * The scheme does not work when sender sends good segments opening
475  * window and then starts to feed us spaghetti. But it should work
476  * in common situations. Otherwise, we have to rely on queue collapsing.
477  */
478 
479 /* Slow part of check#2. */
480 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb,
481 			     unsigned int skbtruesize)
482 {
483 	const struct tcp_sock *tp = tcp_sk(sk);
484 	/* Optimize this! */
485 	int truesize = tcp_win_from_space(sk, skbtruesize) >> 1;
486 	int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1;
487 
488 	while (tp->rcv_ssthresh <= window) {
489 		if (truesize <= skb->len)
490 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
491 
492 		truesize >>= 1;
493 		window >>= 1;
494 	}
495 	return 0;
496 }
497 
498 /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing
499  * can play nice with us, as sk_buff and skb->head might be either
500  * freed or shared with up to MAX_SKB_FRAGS segments.
501  * Only give a boost to drivers using page frag(s) to hold the frame(s),
502  * and if no payload was pulled in skb->head before reaching us.
503  */
504 static u32 truesize_adjust(bool adjust, const struct sk_buff *skb)
505 {
506 	u32 truesize = skb->truesize;
507 
508 	if (adjust && !skb_headlen(skb)) {
509 		truesize -= SKB_TRUESIZE(skb_end_offset(skb));
510 		/* paranoid check, some drivers might be buggy */
511 		if (unlikely((int)truesize < (int)skb->len))
512 			truesize = skb->truesize;
513 	}
514 	return truesize;
515 }
516 
517 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
518 			    bool adjust)
519 {
520 	struct tcp_sock *tp = tcp_sk(sk);
521 	int room;
522 
523 	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
524 
525 	if (room <= 0)
526 		return;
527 
528 	/* Check #1 */
529 	if (!tcp_under_memory_pressure(sk)) {
530 		unsigned int truesize = truesize_adjust(adjust, skb);
531 		int incr;
532 
533 		/* Check #2. Increase window, if skb with such overhead
534 		 * will fit to rcvbuf in future.
535 		 */
536 		if (tcp_win_from_space(sk, truesize) <= skb->len)
537 			incr = 2 * tp->advmss;
538 		else
539 			incr = __tcp_grow_window(sk, skb, truesize);
540 
541 		if (incr) {
542 			incr = max_t(int, incr, 2 * skb->len);
543 			tp->rcv_ssthresh += min(room, incr);
544 			inet_csk(sk)->icsk_ack.quick |= 1;
545 		}
546 	} else {
547 		/* Under pressure:
548 		 * Adjust rcv_ssthresh according to reserved mem
549 		 */
550 		tcp_adjust_rcv_ssthresh(sk);
551 	}
552 }
553 
554 /* 3. Try to fixup all. It is made immediately after connection enters
555  *    established state.
556  */
557 static void tcp_init_buffer_space(struct sock *sk)
558 {
559 	int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win);
560 	struct tcp_sock *tp = tcp_sk(sk);
561 	int maxwin;
562 
563 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
564 		tcp_sndbuf_expand(sk);
565 
566 	tcp_mstamp_refresh(tp);
567 	tp->rcvq_space.time = tp->tcp_mstamp;
568 	tp->rcvq_space.seq = tp->copied_seq;
569 
570 	maxwin = tcp_full_space(sk);
571 
572 	if (tp->window_clamp >= maxwin) {
573 		tp->window_clamp = maxwin;
574 
575 		if (tcp_app_win && maxwin > 4 * tp->advmss)
576 			tp->window_clamp = max(maxwin -
577 					       (maxwin >> tcp_app_win),
578 					       4 * tp->advmss);
579 	}
580 
581 	/* Force reservation of one segment. */
582 	if (tcp_app_win &&
583 	    tp->window_clamp > 2 * tp->advmss &&
584 	    tp->window_clamp + tp->advmss > maxwin)
585 		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
586 
587 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
588 	tp->snd_cwnd_stamp = tcp_jiffies32;
589 	tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
590 				    (u32)TCP_INIT_CWND * tp->advmss);
591 }
592 
593 /* 4. Recalculate window clamp after socket hit its memory bounds. */
594 static void tcp_clamp_window(struct sock *sk)
595 {
596 	struct tcp_sock *tp = tcp_sk(sk);
597 	struct inet_connection_sock *icsk = inet_csk(sk);
598 	struct net *net = sock_net(sk);
599 	int rmem2;
600 
601 	icsk->icsk_ack.quick = 0;
602 	rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
603 
604 	if (sk->sk_rcvbuf < rmem2 &&
605 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
606 	    !tcp_under_memory_pressure(sk) &&
607 	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
608 		WRITE_ONCE(sk->sk_rcvbuf,
609 			   min(atomic_read(&sk->sk_rmem_alloc), rmem2));
610 	}
611 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
612 		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
613 }
614 
615 /* Initialize RCV_MSS value.
616  * RCV_MSS is an our guess about MSS used by the peer.
617  * We haven't any direct information about the MSS.
618  * It's better to underestimate the RCV_MSS rather than overestimate.
619  * Overestimations make us ACKing less frequently than needed.
620  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
621  */
622 void tcp_initialize_rcv_mss(struct sock *sk)
623 {
624 	const struct tcp_sock *tp = tcp_sk(sk);
625 	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
626 
627 	hint = min(hint, tp->rcv_wnd / 2);
628 	hint = min(hint, TCP_MSS_DEFAULT);
629 	hint = max(hint, TCP_MIN_MSS);
630 
631 	inet_csk(sk)->icsk_ack.rcv_mss = hint;
632 }
633 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
634 
635 /* Receiver "autotuning" code.
636  *
637  * The algorithm for RTT estimation w/o timestamps is based on
638  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
639  * <https://public.lanl.gov/radiant/pubs.html#DRS>
640  *
641  * More detail on this code can be found at
642  * <http://staff.psc.edu/jheffner/>,
643  * though this reference is out of date.  A new paper
644  * is pending.
645  */
646 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
647 {
648 	u32 new_sample = tp->rcv_rtt_est.rtt_us;
649 	long m = sample;
650 
651 	if (new_sample != 0) {
652 		/* If we sample in larger samples in the non-timestamp
653 		 * case, we could grossly overestimate the RTT especially
654 		 * with chatty applications or bulk transfer apps which
655 		 * are stalled on filesystem I/O.
656 		 *
657 		 * Also, since we are only going for a minimum in the
658 		 * non-timestamp case, we do not smooth things out
659 		 * else with timestamps disabled convergence takes too
660 		 * long.
661 		 */
662 		if (!win_dep) {
663 			m -= (new_sample >> 3);
664 			new_sample += m;
665 		} else {
666 			m <<= 3;
667 			if (m < new_sample)
668 				new_sample = m;
669 		}
670 	} else {
671 		/* No previous measure. */
672 		new_sample = m << 3;
673 	}
674 
675 	tp->rcv_rtt_est.rtt_us = new_sample;
676 }
677 
678 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
679 {
680 	u32 delta_us;
681 
682 	if (tp->rcv_rtt_est.time == 0)
683 		goto new_measure;
684 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
685 		return;
686 	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
687 	if (!delta_us)
688 		delta_us = 1;
689 	tcp_rcv_rtt_update(tp, delta_us, 1);
690 
691 new_measure:
692 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
693 	tp->rcv_rtt_est.time = tp->tcp_mstamp;
694 }
695 
696 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
697 					  const struct sk_buff *skb)
698 {
699 	struct tcp_sock *tp = tcp_sk(sk);
700 
701 	if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
702 		return;
703 	tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
704 
705 	if (TCP_SKB_CB(skb)->end_seq -
706 	    TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
707 		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
708 		u32 delta_us;
709 
710 		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
711 			if (!delta)
712 				delta = 1;
713 			delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
714 			tcp_rcv_rtt_update(tp, delta_us, 0);
715 		}
716 	}
717 }
718 
719 /*
720  * This function should be called every time data is copied to user space.
721  * It calculates the appropriate TCP receive buffer space.
722  */
723 void tcp_rcv_space_adjust(struct sock *sk)
724 {
725 	struct tcp_sock *tp = tcp_sk(sk);
726 	u32 copied;
727 	int time;
728 
729 	trace_tcp_rcv_space_adjust(sk);
730 
731 	tcp_mstamp_refresh(tp);
732 	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
733 	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
734 		return;
735 
736 	/* Number of bytes copied to user in last RTT */
737 	copied = tp->copied_seq - tp->rcvq_space.seq;
738 	if (copied <= tp->rcvq_space.space)
739 		goto new_measure;
740 
741 	/* A bit of theory :
742 	 * copied = bytes received in previous RTT, our base window
743 	 * To cope with packet losses, we need a 2x factor
744 	 * To cope with slow start, and sender growing its cwin by 100 %
745 	 * every RTT, we need a 4x factor, because the ACK we are sending
746 	 * now is for the next RTT, not the current one :
747 	 * <prev RTT . ><current RTT .. ><next RTT .... >
748 	 */
749 
750 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
751 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
752 		u64 rcvwin, grow;
753 		int rcvbuf;
754 
755 		/* minimal window to cope with packet losses, assuming
756 		 * steady state. Add some cushion because of small variations.
757 		 */
758 		rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
759 
760 		/* Accommodate for sender rate increase (eg. slow start) */
761 		grow = rcvwin * (copied - tp->rcvq_space.space);
762 		do_div(grow, tp->rcvq_space.space);
763 		rcvwin += (grow << 1);
764 
765 		rcvbuf = min_t(u64, tcp_space_from_win(sk, rcvwin),
766 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
767 		if (rcvbuf > sk->sk_rcvbuf) {
768 			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
769 
770 			/* Make the window clamp follow along.  */
771 			tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
772 		}
773 	}
774 	tp->rcvq_space.space = copied;
775 
776 new_measure:
777 	tp->rcvq_space.seq = tp->copied_seq;
778 	tp->rcvq_space.time = tp->tcp_mstamp;
779 }
780 
781 /* There is something which you must keep in mind when you analyze the
782  * behavior of the tp->ato delayed ack timeout interval.  When a
783  * connection starts up, we want to ack as quickly as possible.  The
784  * problem is that "good" TCP's do slow start at the beginning of data
785  * transmission.  The means that until we send the first few ACK's the
786  * sender will sit on his end and only queue most of his data, because
787  * he can only send snd_cwnd unacked packets at any given time.  For
788  * each ACK we send, he increments snd_cwnd and transmits more of his
789  * queue.  -DaveM
790  */
791 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
792 {
793 	struct tcp_sock *tp = tcp_sk(sk);
794 	struct inet_connection_sock *icsk = inet_csk(sk);
795 	u32 now;
796 
797 	inet_csk_schedule_ack(sk);
798 
799 	tcp_measure_rcv_mss(sk, skb);
800 
801 	tcp_rcv_rtt_measure(tp);
802 
803 	now = tcp_jiffies32;
804 
805 	if (!icsk->icsk_ack.ato) {
806 		/* The _first_ data packet received, initialize
807 		 * delayed ACK engine.
808 		 */
809 		tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
810 		icsk->icsk_ack.ato = TCP_ATO_MIN;
811 	} else {
812 		int m = now - icsk->icsk_ack.lrcvtime;
813 
814 		if (m <= TCP_ATO_MIN / 2) {
815 			/* The fastest case is the first. */
816 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
817 		} else if (m < icsk->icsk_ack.ato) {
818 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
819 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
820 				icsk->icsk_ack.ato = icsk->icsk_rto;
821 		} else if (m > icsk->icsk_rto) {
822 			/* Too long gap. Apparently sender failed to
823 			 * restart window, so that we send ACKs quickly.
824 			 */
825 			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
826 		}
827 	}
828 	icsk->icsk_ack.lrcvtime = now;
829 
830 	tcp_ecn_check_ce(sk, skb);
831 
832 	if (skb->len >= 128)
833 		tcp_grow_window(sk, skb, true);
834 }
835 
836 /* Called to compute a smoothed rtt estimate. The data fed to this
837  * routine either comes from timestamps, or from segments that were
838  * known _not_ to have been retransmitted [see Karn/Partridge
839  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
840  * piece by Van Jacobson.
841  * NOTE: the next three routines used to be one big routine.
842  * To save cycles in the RFC 1323 implementation it was better to break
843  * it up into three procedures. -- erics
844  */
845 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
846 {
847 	struct tcp_sock *tp = tcp_sk(sk);
848 	long m = mrtt_us; /* RTT */
849 	u32 srtt = tp->srtt_us;
850 
851 	/*	The following amusing code comes from Jacobson's
852 	 *	article in SIGCOMM '88.  Note that rtt and mdev
853 	 *	are scaled versions of rtt and mean deviation.
854 	 *	This is designed to be as fast as possible
855 	 *	m stands for "measurement".
856 	 *
857 	 *	On a 1990 paper the rto value is changed to:
858 	 *	RTO = rtt + 4 * mdev
859 	 *
860 	 * Funny. This algorithm seems to be very broken.
861 	 * These formulae increase RTO, when it should be decreased, increase
862 	 * too slowly, when it should be increased quickly, decrease too quickly
863 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
864 	 * does not matter how to _calculate_ it. Seems, it was trap
865 	 * that VJ failed to avoid. 8)
866 	 */
867 	if (srtt != 0) {
868 		m -= (srtt >> 3);	/* m is now error in rtt est */
869 		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
870 		if (m < 0) {
871 			m = -m;		/* m is now abs(error) */
872 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
873 			/* This is similar to one of Eifel findings.
874 			 * Eifel blocks mdev updates when rtt decreases.
875 			 * This solution is a bit different: we use finer gain
876 			 * for mdev in this case (alpha*beta).
877 			 * Like Eifel it also prevents growth of rto,
878 			 * but also it limits too fast rto decreases,
879 			 * happening in pure Eifel.
880 			 */
881 			if (m > 0)
882 				m >>= 3;
883 		} else {
884 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
885 		}
886 		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
887 		if (tp->mdev_us > tp->mdev_max_us) {
888 			tp->mdev_max_us = tp->mdev_us;
889 			if (tp->mdev_max_us > tp->rttvar_us)
890 				tp->rttvar_us = tp->mdev_max_us;
891 		}
892 		if (after(tp->snd_una, tp->rtt_seq)) {
893 			if (tp->mdev_max_us < tp->rttvar_us)
894 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
895 			tp->rtt_seq = tp->snd_nxt;
896 			tp->mdev_max_us = tcp_rto_min_us(sk);
897 
898 			tcp_bpf_rtt(sk);
899 		}
900 	} else {
901 		/* no previous measure. */
902 		srtt = m << 3;		/* take the measured time to be rtt */
903 		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
904 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
905 		tp->mdev_max_us = tp->rttvar_us;
906 		tp->rtt_seq = tp->snd_nxt;
907 
908 		tcp_bpf_rtt(sk);
909 	}
910 	tp->srtt_us = max(1U, srtt);
911 }
912 
913 static void tcp_update_pacing_rate(struct sock *sk)
914 {
915 	const struct tcp_sock *tp = tcp_sk(sk);
916 	u64 rate;
917 
918 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
919 	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
920 
921 	/* current rate is (cwnd * mss) / srtt
922 	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
923 	 * In Congestion Avoidance phase, set it to 120 % the current rate.
924 	 *
925 	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
926 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
927 	 *	 end of slow start and should slow down.
928 	 */
929 	if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
930 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio);
931 	else
932 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio);
933 
934 	rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
935 
936 	if (likely(tp->srtt_us))
937 		do_div(rate, tp->srtt_us);
938 
939 	/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
940 	 * without any lock. We want to make sure compiler wont store
941 	 * intermediate values in this location.
942 	 */
943 	WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
944 					     sk->sk_max_pacing_rate));
945 }
946 
947 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
948  * routine referred to above.
949  */
950 static void tcp_set_rto(struct sock *sk)
951 {
952 	const struct tcp_sock *tp = tcp_sk(sk);
953 	/* Old crap is replaced with new one. 8)
954 	 *
955 	 * More seriously:
956 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
957 	 *    It cannot be less due to utterly erratic ACK generation made
958 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
959 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
960 	 *    is invisible. Actually, Linux-2.4 also generates erratic
961 	 *    ACKs in some circumstances.
962 	 */
963 	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
964 
965 	/* 2. Fixups made earlier cannot be right.
966 	 *    If we do not estimate RTO correctly without them,
967 	 *    all the algo is pure shit and should be replaced
968 	 *    with correct one. It is exactly, which we pretend to do.
969 	 */
970 
971 	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
972 	 * guarantees that rto is higher.
973 	 */
974 	tcp_bound_rto(sk);
975 }
976 
977 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
978 {
979 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
980 
981 	if (!cwnd)
982 		cwnd = TCP_INIT_CWND;
983 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
984 }
985 
986 struct tcp_sacktag_state {
987 	/* Timestamps for earliest and latest never-retransmitted segment
988 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
989 	 * but congestion control should still get an accurate delay signal.
990 	 */
991 	u64	first_sackt;
992 	u64	last_sackt;
993 	u32	reord;
994 	u32	sack_delivered;
995 	int	flag;
996 	unsigned int mss_now;
997 	struct rate_sample *rate;
998 };
999 
1000 /* Take a notice that peer is sending D-SACKs. Skip update of data delivery
1001  * and spurious retransmission information if this DSACK is unlikely caused by
1002  * sender's action:
1003  * - DSACKed sequence range is larger than maximum receiver's window.
1004  * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
1005  */
1006 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
1007 			  u32 end_seq, struct tcp_sacktag_state *state)
1008 {
1009 	u32 seq_len, dup_segs = 1;
1010 
1011 	if (!before(start_seq, end_seq))
1012 		return 0;
1013 
1014 	seq_len = end_seq - start_seq;
1015 	/* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
1016 	if (seq_len > tp->max_window)
1017 		return 0;
1018 	if (seq_len > tp->mss_cache)
1019 		dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
1020 	else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
1021 		state->flag |= FLAG_DSACK_TLP;
1022 
1023 	tp->dsack_dups += dup_segs;
1024 	/* Skip the DSACK if dup segs weren't retransmitted by sender */
1025 	if (tp->dsack_dups > tp->total_retrans)
1026 		return 0;
1027 
1028 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
1029 	/* We increase the RACK ordering window in rounds where we receive
1030 	 * DSACKs that may have been due to reordering causing RACK to trigger
1031 	 * a spurious fast recovery. Thus RACK ignores DSACKs that happen
1032 	 * without having seen reordering, or that match TLP probes (TLP
1033 	 * is timer-driven, not triggered by RACK).
1034 	 */
1035 	if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
1036 		tp->rack.dsack_seen = 1;
1037 
1038 	state->flag |= FLAG_DSACKING_ACK;
1039 	/* A spurious retransmission is delivered */
1040 	state->sack_delivered += dup_segs;
1041 
1042 	return dup_segs;
1043 }
1044 
1045 /* It's reordering when higher sequence was delivered (i.e. sacked) before
1046  * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
1047  * distance is approximated in full-mss packet distance ("reordering").
1048  */
1049 static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
1050 				      const int ts)
1051 {
1052 	struct tcp_sock *tp = tcp_sk(sk);
1053 	const u32 mss = tp->mss_cache;
1054 	u32 fack, metric;
1055 
1056 	fack = tcp_highest_sack_seq(tp);
1057 	if (!before(low_seq, fack))
1058 		return;
1059 
1060 	metric = fack - low_seq;
1061 	if ((metric > tp->reordering * mss) && mss) {
1062 #if FASTRETRANS_DEBUG > 1
1063 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
1064 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
1065 			 tp->reordering,
1066 			 0,
1067 			 tp->sacked_out,
1068 			 tp->undo_marker ? tp->undo_retrans : 0);
1069 #endif
1070 		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
1071 				       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
1072 	}
1073 
1074 	/* This exciting event is worth to be remembered. 8) */
1075 	tp->reord_seen++;
1076 	NET_INC_STATS(sock_net(sk),
1077 		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
1078 }
1079 
1080  /* This must be called before lost_out or retrans_out are updated
1081   * on a new loss, because we want to know if all skbs previously
1082   * known to be lost have already been retransmitted, indicating
1083   * that this newly lost skb is our next skb to retransmit.
1084   */
1085 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1086 {
1087 	if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
1088 	    (tp->retransmit_skb_hint &&
1089 	     before(TCP_SKB_CB(skb)->seq,
1090 		    TCP_SKB_CB(tp->retransmit_skb_hint)->seq)))
1091 		tp->retransmit_skb_hint = skb;
1092 }
1093 
1094 /* Sum the number of packets on the wire we have marked as lost, and
1095  * notify the congestion control module that the given skb was marked lost.
1096  */
1097 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
1098 {
1099 	tp->lost += tcp_skb_pcount(skb);
1100 }
1101 
1102 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
1103 {
1104 	__u8 sacked = TCP_SKB_CB(skb)->sacked;
1105 	struct tcp_sock *tp = tcp_sk(sk);
1106 
1107 	if (sacked & TCPCB_SACKED_ACKED)
1108 		return;
1109 
1110 	tcp_verify_retransmit_hint(tp, skb);
1111 	if (sacked & TCPCB_LOST) {
1112 		if (sacked & TCPCB_SACKED_RETRANS) {
1113 			/* Account for retransmits that are lost again */
1114 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1115 			tp->retrans_out -= tcp_skb_pcount(skb);
1116 			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
1117 				      tcp_skb_pcount(skb));
1118 			tcp_notify_skb_loss_event(tp, skb);
1119 		}
1120 	} else {
1121 		tp->lost_out += tcp_skb_pcount(skb);
1122 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1123 		tcp_notify_skb_loss_event(tp, skb);
1124 	}
1125 }
1126 
1127 /* Updates the delivered and delivered_ce counts */
1128 static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
1129 				bool ece_ack)
1130 {
1131 	tp->delivered += delivered;
1132 	if (ece_ack)
1133 		tp->delivered_ce += delivered;
1134 }
1135 
1136 /* This procedure tags the retransmission queue when SACKs arrive.
1137  *
1138  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1139  * Packets in queue with these bits set are counted in variables
1140  * sacked_out, retrans_out and lost_out, correspondingly.
1141  *
1142  * Valid combinations are:
1143  * Tag  InFlight	Description
1144  * 0	1		- orig segment is in flight.
1145  * S	0		- nothing flies, orig reached receiver.
1146  * L	0		- nothing flies, orig lost by net.
1147  * R	2		- both orig and retransmit are in flight.
1148  * L|R	1		- orig is lost, retransmit is in flight.
1149  * S|R  1		- orig reached receiver, retrans is still in flight.
1150  * (L|S|R is logically valid, it could occur when L|R is sacked,
1151  *  but it is equivalent to plain S and code short-curcuits it to S.
1152  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1153  *
1154  * These 6 states form finite state machine, controlled by the following events:
1155  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1156  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1157  * 3. Loss detection event of two flavors:
1158  *	A. Scoreboard estimator decided the packet is lost.
1159  *	   A'. Reno "three dupacks" marks head of queue lost.
1160  *	B. SACK arrives sacking SND.NXT at the moment, when the
1161  *	   segment was retransmitted.
1162  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1163  *
1164  * It is pleasant to note, that state diagram turns out to be commutative,
1165  * so that we are allowed not to be bothered by order of our actions,
1166  * when multiple events arrive simultaneously. (see the function below).
1167  *
1168  * Reordering detection.
1169  * --------------------
1170  * Reordering metric is maximal distance, which a packet can be displaced
1171  * in packet stream. With SACKs we can estimate it:
1172  *
1173  * 1. SACK fills old hole and the corresponding segment was not
1174  *    ever retransmitted -> reordering. Alas, we cannot use it
1175  *    when segment was retransmitted.
1176  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1177  *    for retransmitted and already SACKed segment -> reordering..
1178  * Both of these heuristics are not used in Loss state, when we cannot
1179  * account for retransmits accurately.
1180  *
1181  * SACK block validation.
1182  * ----------------------
1183  *
1184  * SACK block range validation checks that the received SACK block fits to
1185  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1186  * Note that SND.UNA is not included to the range though being valid because
1187  * it means that the receiver is rather inconsistent with itself reporting
1188  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1189  * perfectly valid, however, in light of RFC2018 which explicitly states
1190  * that "SACK block MUST reflect the newest segment.  Even if the newest
1191  * segment is going to be discarded ...", not that it looks very clever
1192  * in case of head skb. Due to potentional receiver driven attacks, we
1193  * choose to avoid immediate execution of a walk in write queue due to
1194  * reneging and defer head skb's loss recovery to standard loss recovery
1195  * procedure that will eventually trigger (nothing forbids us doing this).
1196  *
1197  * Implements also blockage to start_seq wrap-around. Problem lies in the
1198  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1199  * there's no guarantee that it will be before snd_nxt (n). The problem
1200  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1201  * wrap (s_w):
1202  *
1203  *         <- outs wnd ->                          <- wrapzone ->
1204  *         u     e      n                         u_w   e_w  s n_w
1205  *         |     |      |                          |     |   |  |
1206  * |<------------+------+----- TCP seqno space --------------+---------->|
1207  * ...-- <2^31 ->|                                           |<--------...
1208  * ...---- >2^31 ------>|                                    |<--------...
1209  *
1210  * Current code wouldn't be vulnerable but it's better still to discard such
1211  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1212  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1213  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1214  * equal to the ideal case (infinite seqno space without wrap caused issues).
1215  *
1216  * With D-SACK the lower bound is extended to cover sequence space below
1217  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1218  * again, D-SACK block must not to go across snd_una (for the same reason as
1219  * for the normal SACK blocks, explained above). But there all simplicity
1220  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1221  * fully below undo_marker they do not affect behavior in anyway and can
1222  * therefore be safely ignored. In rare cases (which are more or less
1223  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1224  * fragmentation and packet reordering past skb's retransmission. To consider
1225  * them correctly, the acceptable range must be extended even more though
1226  * the exact amount is rather hard to quantify. However, tp->max_window can
1227  * be used as an exaggerated estimate.
1228  */
1229 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1230 				   u32 start_seq, u32 end_seq)
1231 {
1232 	/* Too far in future, or reversed (interpretation is ambiguous) */
1233 	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1234 		return false;
1235 
1236 	/* Nasty start_seq wrap-around check (see comments above) */
1237 	if (!before(start_seq, tp->snd_nxt))
1238 		return false;
1239 
1240 	/* In outstanding window? ...This is valid exit for D-SACKs too.
1241 	 * start_seq == snd_una is non-sensical (see comments above)
1242 	 */
1243 	if (after(start_seq, tp->snd_una))
1244 		return true;
1245 
1246 	if (!is_dsack || !tp->undo_marker)
1247 		return false;
1248 
1249 	/* ...Then it's D-SACK, and must reside below snd_una completely */
1250 	if (after(end_seq, tp->snd_una))
1251 		return false;
1252 
1253 	if (!before(start_seq, tp->undo_marker))
1254 		return true;
1255 
1256 	/* Too old */
1257 	if (!after(end_seq, tp->undo_marker))
1258 		return false;
1259 
1260 	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1261 	 *   start_seq < undo_marker and end_seq >= undo_marker.
1262 	 */
1263 	return !before(start_seq, end_seq - tp->max_window);
1264 }
1265 
1266 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1267 			    struct tcp_sack_block_wire *sp, int num_sacks,
1268 			    u32 prior_snd_una, struct tcp_sacktag_state *state)
1269 {
1270 	struct tcp_sock *tp = tcp_sk(sk);
1271 	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1272 	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1273 	u32 dup_segs;
1274 
1275 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1276 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1277 	} else if (num_sacks > 1) {
1278 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1279 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1280 
1281 		if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1))
1282 			return false;
1283 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV);
1284 	} else {
1285 		return false;
1286 	}
1287 
1288 	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
1289 	if (!dup_segs) {	/* Skip dubious DSACK */
1290 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
1291 		return false;
1292 	}
1293 
1294 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
1295 
1296 	/* D-SACK for already forgotten data... Do dumb counting. */
1297 	if (tp->undo_marker && tp->undo_retrans > 0 &&
1298 	    !after(end_seq_0, prior_snd_una) &&
1299 	    after(end_seq_0, tp->undo_marker))
1300 		tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs);
1301 
1302 	return true;
1303 }
1304 
1305 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1306  * the incoming SACK may not exactly match but we can find smaller MSS
1307  * aligned portion of it that matches. Therefore we might need to fragment
1308  * which may fail and creates some hassle (caller must handle error case
1309  * returns).
1310  *
1311  * FIXME: this could be merged to shift decision code
1312  */
1313 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1314 				  u32 start_seq, u32 end_seq)
1315 {
1316 	int err;
1317 	bool in_sack;
1318 	unsigned int pkt_len;
1319 	unsigned int mss;
1320 
1321 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1322 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1323 
1324 	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1325 	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1326 		mss = tcp_skb_mss(skb);
1327 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1328 
1329 		if (!in_sack) {
1330 			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1331 			if (pkt_len < mss)
1332 				pkt_len = mss;
1333 		} else {
1334 			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1335 			if (pkt_len < mss)
1336 				return -EINVAL;
1337 		}
1338 
1339 		/* Round if necessary so that SACKs cover only full MSSes
1340 		 * and/or the remaining small portion (if present)
1341 		 */
1342 		if (pkt_len > mss) {
1343 			unsigned int new_len = (pkt_len / mss) * mss;
1344 			if (!in_sack && new_len < pkt_len)
1345 				new_len += mss;
1346 			pkt_len = new_len;
1347 		}
1348 
1349 		if (pkt_len >= skb->len && !in_sack)
1350 			return 0;
1351 
1352 		err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1353 				   pkt_len, mss, GFP_ATOMIC);
1354 		if (err < 0)
1355 			return err;
1356 	}
1357 
1358 	return in_sack;
1359 }
1360 
1361 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1362 static u8 tcp_sacktag_one(struct sock *sk,
1363 			  struct tcp_sacktag_state *state, u8 sacked,
1364 			  u32 start_seq, u32 end_seq,
1365 			  int dup_sack, int pcount,
1366 			  u64 xmit_time)
1367 {
1368 	struct tcp_sock *tp = tcp_sk(sk);
1369 
1370 	/* Account D-SACK for retransmitted packet. */
1371 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1372 		if (tp->undo_marker && tp->undo_retrans > 0 &&
1373 		    after(end_seq, tp->undo_marker))
1374 			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
1375 		if ((sacked & TCPCB_SACKED_ACKED) &&
1376 		    before(start_seq, state->reord))
1377 				state->reord = start_seq;
1378 	}
1379 
1380 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1381 	if (!after(end_seq, tp->snd_una))
1382 		return sacked;
1383 
1384 	if (!(sacked & TCPCB_SACKED_ACKED)) {
1385 		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1386 
1387 		if (sacked & TCPCB_SACKED_RETRANS) {
1388 			/* If the segment is not tagged as lost,
1389 			 * we do not clear RETRANS, believing
1390 			 * that retransmission is still in flight.
1391 			 */
1392 			if (sacked & TCPCB_LOST) {
1393 				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1394 				tp->lost_out -= pcount;
1395 				tp->retrans_out -= pcount;
1396 			}
1397 		} else {
1398 			if (!(sacked & TCPCB_RETRANS)) {
1399 				/* New sack for not retransmitted frame,
1400 				 * which was in hole. It is reordering.
1401 				 */
1402 				if (before(start_seq,
1403 					   tcp_highest_sack_seq(tp)) &&
1404 				    before(start_seq, state->reord))
1405 					state->reord = start_seq;
1406 
1407 				if (!after(end_seq, tp->high_seq))
1408 					state->flag |= FLAG_ORIG_SACK_ACKED;
1409 				if (state->first_sackt == 0)
1410 					state->first_sackt = xmit_time;
1411 				state->last_sackt = xmit_time;
1412 			}
1413 
1414 			if (sacked & TCPCB_LOST) {
1415 				sacked &= ~TCPCB_LOST;
1416 				tp->lost_out -= pcount;
1417 			}
1418 		}
1419 
1420 		sacked |= TCPCB_SACKED_ACKED;
1421 		state->flag |= FLAG_DATA_SACKED;
1422 		tp->sacked_out += pcount;
1423 		/* Out-of-order packets delivered */
1424 		state->sack_delivered += pcount;
1425 
1426 		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1427 		if (tp->lost_skb_hint &&
1428 		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1429 			tp->lost_cnt_hint += pcount;
1430 	}
1431 
1432 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1433 	 * frames and clear it. undo_retrans is decreased above, L|R frames
1434 	 * are accounted above as well.
1435 	 */
1436 	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1437 		sacked &= ~TCPCB_SACKED_RETRANS;
1438 		tp->retrans_out -= pcount;
1439 	}
1440 
1441 	return sacked;
1442 }
1443 
1444 /* Shift newly-SACKed bytes from this skb to the immediately previous
1445  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1446  */
1447 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1448 			    struct sk_buff *skb,
1449 			    struct tcp_sacktag_state *state,
1450 			    unsigned int pcount, int shifted, int mss,
1451 			    bool dup_sack)
1452 {
1453 	struct tcp_sock *tp = tcp_sk(sk);
1454 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1455 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1456 
1457 	BUG_ON(!pcount);
1458 
1459 	/* Adjust counters and hints for the newly sacked sequence
1460 	 * range but discard the return value since prev is already
1461 	 * marked. We must tag the range first because the seq
1462 	 * advancement below implicitly advances
1463 	 * tcp_highest_sack_seq() when skb is highest_sack.
1464 	 */
1465 	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1466 			start_seq, end_seq, dup_sack, pcount,
1467 			tcp_skb_timestamp_us(skb));
1468 	tcp_rate_skb_delivered(sk, skb, state->rate);
1469 
1470 	if (skb == tp->lost_skb_hint)
1471 		tp->lost_cnt_hint += pcount;
1472 
1473 	TCP_SKB_CB(prev)->end_seq += shifted;
1474 	TCP_SKB_CB(skb)->seq += shifted;
1475 
1476 	tcp_skb_pcount_add(prev, pcount);
1477 	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1478 	tcp_skb_pcount_add(skb, -pcount);
1479 
1480 	/* When we're adding to gso_segs == 1, gso_size will be zero,
1481 	 * in theory this shouldn't be necessary but as long as DSACK
1482 	 * code can come after this skb later on it's better to keep
1483 	 * setting gso_size to something.
1484 	 */
1485 	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1486 		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1487 
1488 	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1489 	if (tcp_skb_pcount(skb) <= 1)
1490 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1491 
1492 	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1493 	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1494 
1495 	if (skb->len > 0) {
1496 		BUG_ON(!tcp_skb_pcount(skb));
1497 		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1498 		return false;
1499 	}
1500 
1501 	/* Whole SKB was eaten :-) */
1502 
1503 	if (skb == tp->retransmit_skb_hint)
1504 		tp->retransmit_skb_hint = prev;
1505 	if (skb == tp->lost_skb_hint) {
1506 		tp->lost_skb_hint = prev;
1507 		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1508 	}
1509 
1510 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1511 	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1512 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1513 		TCP_SKB_CB(prev)->end_seq++;
1514 
1515 	if (skb == tcp_highest_sack(sk))
1516 		tcp_advance_highest_sack(sk, skb);
1517 
1518 	tcp_skb_collapse_tstamp(prev, skb);
1519 	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1520 		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1521 
1522 	tcp_rtx_queue_unlink_and_free(skb, sk);
1523 
1524 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1525 
1526 	return true;
1527 }
1528 
1529 /* I wish gso_size would have a bit more sane initialization than
1530  * something-or-zero which complicates things
1531  */
1532 static int tcp_skb_seglen(const struct sk_buff *skb)
1533 {
1534 	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1535 }
1536 
1537 /* Shifting pages past head area doesn't work */
1538 static int skb_can_shift(const struct sk_buff *skb)
1539 {
1540 	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1541 }
1542 
1543 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1544 		  int pcount, int shiftlen)
1545 {
1546 	/* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1547 	 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1548 	 * to make sure not storing more than 65535 * 8 bytes per skb,
1549 	 * even if current MSS is bigger.
1550 	 */
1551 	if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1552 		return 0;
1553 	if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1554 		return 0;
1555 	return skb_shift(to, from, shiftlen);
1556 }
1557 
1558 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1559  * skb.
1560  */
1561 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1562 					  struct tcp_sacktag_state *state,
1563 					  u32 start_seq, u32 end_seq,
1564 					  bool dup_sack)
1565 {
1566 	struct tcp_sock *tp = tcp_sk(sk);
1567 	struct sk_buff *prev;
1568 	int mss;
1569 	int pcount = 0;
1570 	int len;
1571 	int in_sack;
1572 
1573 	/* Normally R but no L won't result in plain S */
1574 	if (!dup_sack &&
1575 	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1576 		goto fallback;
1577 	if (!skb_can_shift(skb))
1578 		goto fallback;
1579 	/* This frame is about to be dropped (was ACKed). */
1580 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1581 		goto fallback;
1582 
1583 	/* Can only happen with delayed DSACK + discard craziness */
1584 	prev = skb_rb_prev(skb);
1585 	if (!prev)
1586 		goto fallback;
1587 
1588 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1589 		goto fallback;
1590 
1591 	if (!tcp_skb_can_collapse(prev, skb))
1592 		goto fallback;
1593 
1594 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1595 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1596 
1597 	if (in_sack) {
1598 		len = skb->len;
1599 		pcount = tcp_skb_pcount(skb);
1600 		mss = tcp_skb_seglen(skb);
1601 
1602 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1603 		 * drop this restriction as unnecessary
1604 		 */
1605 		if (mss != tcp_skb_seglen(prev))
1606 			goto fallback;
1607 	} else {
1608 		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1609 			goto noop;
1610 		/* CHECKME: This is non-MSS split case only?, this will
1611 		 * cause skipped skbs due to advancing loop btw, original
1612 		 * has that feature too
1613 		 */
1614 		if (tcp_skb_pcount(skb) <= 1)
1615 			goto noop;
1616 
1617 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1618 		if (!in_sack) {
1619 			/* TODO: head merge to next could be attempted here
1620 			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1621 			 * though it might not be worth of the additional hassle
1622 			 *
1623 			 * ...we can probably just fallback to what was done
1624 			 * previously. We could try merging non-SACKed ones
1625 			 * as well but it probably isn't going to buy off
1626 			 * because later SACKs might again split them, and
1627 			 * it would make skb timestamp tracking considerably
1628 			 * harder problem.
1629 			 */
1630 			goto fallback;
1631 		}
1632 
1633 		len = end_seq - TCP_SKB_CB(skb)->seq;
1634 		BUG_ON(len < 0);
1635 		BUG_ON(len > skb->len);
1636 
1637 		/* MSS boundaries should be honoured or else pcount will
1638 		 * severely break even though it makes things bit trickier.
1639 		 * Optimize common case to avoid most of the divides
1640 		 */
1641 		mss = tcp_skb_mss(skb);
1642 
1643 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1644 		 * drop this restriction as unnecessary
1645 		 */
1646 		if (mss != tcp_skb_seglen(prev))
1647 			goto fallback;
1648 
1649 		if (len == mss) {
1650 			pcount = 1;
1651 		} else if (len < mss) {
1652 			goto noop;
1653 		} else {
1654 			pcount = len / mss;
1655 			len = pcount * mss;
1656 		}
1657 	}
1658 
1659 	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1660 	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1661 		goto fallback;
1662 
1663 	if (!tcp_skb_shift(prev, skb, pcount, len))
1664 		goto fallback;
1665 	if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1666 		goto out;
1667 
1668 	/* Hole filled allows collapsing with the next as well, this is very
1669 	 * useful when hole on every nth skb pattern happens
1670 	 */
1671 	skb = skb_rb_next(prev);
1672 	if (!skb)
1673 		goto out;
1674 
1675 	if (!skb_can_shift(skb) ||
1676 	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1677 	    (mss != tcp_skb_seglen(skb)))
1678 		goto out;
1679 
1680 	if (!tcp_skb_can_collapse(prev, skb))
1681 		goto out;
1682 	len = skb->len;
1683 	pcount = tcp_skb_pcount(skb);
1684 	if (tcp_skb_shift(prev, skb, pcount, len))
1685 		tcp_shifted_skb(sk, prev, skb, state, pcount,
1686 				len, mss, 0);
1687 
1688 out:
1689 	return prev;
1690 
1691 noop:
1692 	return skb;
1693 
1694 fallback:
1695 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1696 	return NULL;
1697 }
1698 
1699 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1700 					struct tcp_sack_block *next_dup,
1701 					struct tcp_sacktag_state *state,
1702 					u32 start_seq, u32 end_seq,
1703 					bool dup_sack_in)
1704 {
1705 	struct tcp_sock *tp = tcp_sk(sk);
1706 	struct sk_buff *tmp;
1707 
1708 	skb_rbtree_walk_from(skb) {
1709 		int in_sack = 0;
1710 		bool dup_sack = dup_sack_in;
1711 
1712 		/* queue is in-order => we can short-circuit the walk early */
1713 		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1714 			break;
1715 
1716 		if (next_dup  &&
1717 		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1718 			in_sack = tcp_match_skb_to_sack(sk, skb,
1719 							next_dup->start_seq,
1720 							next_dup->end_seq);
1721 			if (in_sack > 0)
1722 				dup_sack = true;
1723 		}
1724 
1725 		/* skb reference here is a bit tricky to get right, since
1726 		 * shifting can eat and free both this skb and the next,
1727 		 * so not even _safe variant of the loop is enough.
1728 		 */
1729 		if (in_sack <= 0) {
1730 			tmp = tcp_shift_skb_data(sk, skb, state,
1731 						 start_seq, end_seq, dup_sack);
1732 			if (tmp) {
1733 				if (tmp != skb) {
1734 					skb = tmp;
1735 					continue;
1736 				}
1737 
1738 				in_sack = 0;
1739 			} else {
1740 				in_sack = tcp_match_skb_to_sack(sk, skb,
1741 								start_seq,
1742 								end_seq);
1743 			}
1744 		}
1745 
1746 		if (unlikely(in_sack < 0))
1747 			break;
1748 
1749 		if (in_sack) {
1750 			TCP_SKB_CB(skb)->sacked =
1751 				tcp_sacktag_one(sk,
1752 						state,
1753 						TCP_SKB_CB(skb)->sacked,
1754 						TCP_SKB_CB(skb)->seq,
1755 						TCP_SKB_CB(skb)->end_seq,
1756 						dup_sack,
1757 						tcp_skb_pcount(skb),
1758 						tcp_skb_timestamp_us(skb));
1759 			tcp_rate_skb_delivered(sk, skb, state->rate);
1760 			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1761 				list_del_init(&skb->tcp_tsorted_anchor);
1762 
1763 			if (!before(TCP_SKB_CB(skb)->seq,
1764 				    tcp_highest_sack_seq(tp)))
1765 				tcp_advance_highest_sack(sk, skb);
1766 		}
1767 	}
1768 	return skb;
1769 }
1770 
1771 static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1772 {
1773 	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1774 	struct sk_buff *skb;
1775 
1776 	while (*p) {
1777 		parent = *p;
1778 		skb = rb_to_skb(parent);
1779 		if (before(seq, TCP_SKB_CB(skb)->seq)) {
1780 			p = &parent->rb_left;
1781 			continue;
1782 		}
1783 		if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1784 			p = &parent->rb_right;
1785 			continue;
1786 		}
1787 		return skb;
1788 	}
1789 	return NULL;
1790 }
1791 
1792 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1793 					u32 skip_to_seq)
1794 {
1795 	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1796 		return skb;
1797 
1798 	return tcp_sacktag_bsearch(sk, skip_to_seq);
1799 }
1800 
1801 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1802 						struct sock *sk,
1803 						struct tcp_sack_block *next_dup,
1804 						struct tcp_sacktag_state *state,
1805 						u32 skip_to_seq)
1806 {
1807 	if (!next_dup)
1808 		return skb;
1809 
1810 	if (before(next_dup->start_seq, skip_to_seq)) {
1811 		skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1812 		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1813 				       next_dup->start_seq, next_dup->end_seq,
1814 				       1);
1815 	}
1816 
1817 	return skb;
1818 }
1819 
1820 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1821 {
1822 	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1823 }
1824 
1825 static int
1826 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1827 			u32 prior_snd_una, struct tcp_sacktag_state *state)
1828 {
1829 	struct tcp_sock *tp = tcp_sk(sk);
1830 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1831 				    TCP_SKB_CB(ack_skb)->sacked);
1832 	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1833 	struct tcp_sack_block sp[TCP_NUM_SACKS];
1834 	struct tcp_sack_block *cache;
1835 	struct sk_buff *skb;
1836 	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1837 	int used_sacks;
1838 	bool found_dup_sack = false;
1839 	int i, j;
1840 	int first_sack_index;
1841 
1842 	state->flag = 0;
1843 	state->reord = tp->snd_nxt;
1844 
1845 	if (!tp->sacked_out)
1846 		tcp_highest_sack_reset(sk);
1847 
1848 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1849 					 num_sacks, prior_snd_una, state);
1850 
1851 	/* Eliminate too old ACKs, but take into
1852 	 * account more or less fresh ones, they can
1853 	 * contain valid SACK info.
1854 	 */
1855 	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1856 		return 0;
1857 
1858 	if (!tp->packets_out)
1859 		goto out;
1860 
1861 	used_sacks = 0;
1862 	first_sack_index = 0;
1863 	for (i = 0; i < num_sacks; i++) {
1864 		bool dup_sack = !i && found_dup_sack;
1865 
1866 		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1867 		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1868 
1869 		if (!tcp_is_sackblock_valid(tp, dup_sack,
1870 					    sp[used_sacks].start_seq,
1871 					    sp[used_sacks].end_seq)) {
1872 			int mib_idx;
1873 
1874 			if (dup_sack) {
1875 				if (!tp->undo_marker)
1876 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1877 				else
1878 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1879 			} else {
1880 				/* Don't count olds caused by ACK reordering */
1881 				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1882 				    !after(sp[used_sacks].end_seq, tp->snd_una))
1883 					continue;
1884 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1885 			}
1886 
1887 			NET_INC_STATS(sock_net(sk), mib_idx);
1888 			if (i == 0)
1889 				first_sack_index = -1;
1890 			continue;
1891 		}
1892 
1893 		/* Ignore very old stuff early */
1894 		if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
1895 			if (i == 0)
1896 				first_sack_index = -1;
1897 			continue;
1898 		}
1899 
1900 		used_sacks++;
1901 	}
1902 
1903 	/* order SACK blocks to allow in order walk of the retrans queue */
1904 	for (i = used_sacks - 1; i > 0; i--) {
1905 		for (j = 0; j < i; j++) {
1906 			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1907 				swap(sp[j], sp[j + 1]);
1908 
1909 				/* Track where the first SACK block goes to */
1910 				if (j == first_sack_index)
1911 					first_sack_index = j + 1;
1912 			}
1913 		}
1914 	}
1915 
1916 	state->mss_now = tcp_current_mss(sk);
1917 	skb = NULL;
1918 	i = 0;
1919 
1920 	if (!tp->sacked_out) {
1921 		/* It's already past, so skip checking against it */
1922 		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1923 	} else {
1924 		cache = tp->recv_sack_cache;
1925 		/* Skip empty blocks in at head of the cache */
1926 		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1927 		       !cache->end_seq)
1928 			cache++;
1929 	}
1930 
1931 	while (i < used_sacks) {
1932 		u32 start_seq = sp[i].start_seq;
1933 		u32 end_seq = sp[i].end_seq;
1934 		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1935 		struct tcp_sack_block *next_dup = NULL;
1936 
1937 		if (found_dup_sack && ((i + 1) == first_sack_index))
1938 			next_dup = &sp[i + 1];
1939 
1940 		/* Skip too early cached blocks */
1941 		while (tcp_sack_cache_ok(tp, cache) &&
1942 		       !before(start_seq, cache->end_seq))
1943 			cache++;
1944 
1945 		/* Can skip some work by looking recv_sack_cache? */
1946 		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1947 		    after(end_seq, cache->start_seq)) {
1948 
1949 			/* Head todo? */
1950 			if (before(start_seq, cache->start_seq)) {
1951 				skb = tcp_sacktag_skip(skb, sk, start_seq);
1952 				skb = tcp_sacktag_walk(skb, sk, next_dup,
1953 						       state,
1954 						       start_seq,
1955 						       cache->start_seq,
1956 						       dup_sack);
1957 			}
1958 
1959 			/* Rest of the block already fully processed? */
1960 			if (!after(end_seq, cache->end_seq))
1961 				goto advance_sp;
1962 
1963 			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1964 						       state,
1965 						       cache->end_seq);
1966 
1967 			/* ...tail remains todo... */
1968 			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1969 				/* ...but better entrypoint exists! */
1970 				skb = tcp_highest_sack(sk);
1971 				if (!skb)
1972 					break;
1973 				cache++;
1974 				goto walk;
1975 			}
1976 
1977 			skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1978 			/* Check overlap against next cached too (past this one already) */
1979 			cache++;
1980 			continue;
1981 		}
1982 
1983 		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1984 			skb = tcp_highest_sack(sk);
1985 			if (!skb)
1986 				break;
1987 		}
1988 		skb = tcp_sacktag_skip(skb, sk, start_seq);
1989 
1990 walk:
1991 		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1992 				       start_seq, end_seq, dup_sack);
1993 
1994 advance_sp:
1995 		i++;
1996 	}
1997 
1998 	/* Clear the head of the cache sack blocks so we can skip it next time */
1999 	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
2000 		tp->recv_sack_cache[i].start_seq = 0;
2001 		tp->recv_sack_cache[i].end_seq = 0;
2002 	}
2003 	for (j = 0; j < used_sacks; j++)
2004 		tp->recv_sack_cache[i++] = sp[j];
2005 
2006 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
2007 		tcp_check_sack_reordering(sk, state->reord, 0);
2008 
2009 	tcp_verify_left_out(tp);
2010 out:
2011 
2012 #if FASTRETRANS_DEBUG > 0
2013 	WARN_ON((int)tp->sacked_out < 0);
2014 	WARN_ON((int)tp->lost_out < 0);
2015 	WARN_ON((int)tp->retrans_out < 0);
2016 	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
2017 #endif
2018 	return state->flag;
2019 }
2020 
2021 /* Limits sacked_out so that sum with lost_out isn't ever larger than
2022  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
2023  */
2024 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
2025 {
2026 	u32 holes;
2027 
2028 	holes = max(tp->lost_out, 1U);
2029 	holes = min(holes, tp->packets_out);
2030 
2031 	if ((tp->sacked_out + holes) > tp->packets_out) {
2032 		tp->sacked_out = tp->packets_out - holes;
2033 		return true;
2034 	}
2035 	return false;
2036 }
2037 
2038 /* If we receive more dupacks than we expected counting segments
2039  * in assumption of absent reordering, interpret this as reordering.
2040  * The only another reason could be bug in receiver TCP.
2041  */
2042 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
2043 {
2044 	struct tcp_sock *tp = tcp_sk(sk);
2045 
2046 	if (!tcp_limit_reno_sacked(tp))
2047 		return;
2048 
2049 	tp->reordering = min_t(u32, tp->packets_out + addend,
2050 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
2051 	tp->reord_seen++;
2052 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
2053 }
2054 
2055 /* Emulate SACKs for SACKless connection: account for a new dupack. */
2056 
2057 static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack)
2058 {
2059 	if (num_dupack) {
2060 		struct tcp_sock *tp = tcp_sk(sk);
2061 		u32 prior_sacked = tp->sacked_out;
2062 		s32 delivered;
2063 
2064 		tp->sacked_out += num_dupack;
2065 		tcp_check_reno_reordering(sk, 0);
2066 		delivered = tp->sacked_out - prior_sacked;
2067 		if (delivered > 0)
2068 			tcp_count_delivered(tp, delivered, ece_ack);
2069 		tcp_verify_left_out(tp);
2070 	}
2071 }
2072 
2073 /* Account for ACK, ACKing some data in Reno Recovery phase. */
2074 
2075 static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack)
2076 {
2077 	struct tcp_sock *tp = tcp_sk(sk);
2078 
2079 	if (acked > 0) {
2080 		/* One ACK acked hole. The rest eat duplicate ACKs. */
2081 		tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1),
2082 				    ece_ack);
2083 		if (acked - 1 >= tp->sacked_out)
2084 			tp->sacked_out = 0;
2085 		else
2086 			tp->sacked_out -= acked - 1;
2087 	}
2088 	tcp_check_reno_reordering(sk, acked);
2089 	tcp_verify_left_out(tp);
2090 }
2091 
2092 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2093 {
2094 	tp->sacked_out = 0;
2095 }
2096 
2097 void tcp_clear_retrans(struct tcp_sock *tp)
2098 {
2099 	tp->retrans_out = 0;
2100 	tp->lost_out = 0;
2101 	tp->undo_marker = 0;
2102 	tp->undo_retrans = -1;
2103 	tp->sacked_out = 0;
2104 }
2105 
2106 static inline void tcp_init_undo(struct tcp_sock *tp)
2107 {
2108 	tp->undo_marker = tp->snd_una;
2109 
2110 	/* Retransmission still in flight may cause DSACKs later. */
2111 	/* First, account for regular retransmits in flight: */
2112 	tp->undo_retrans = tp->retrans_out;
2113 	/* Next, account for TLP retransmits in flight: */
2114 	if (tp->tlp_high_seq && tp->tlp_retrans)
2115 		tp->undo_retrans++;
2116 	/* Finally, avoid 0, because undo_retrans==0 means "can undo now": */
2117 	if (!tp->undo_retrans)
2118 		tp->undo_retrans = -1;
2119 }
2120 
2121 static bool tcp_is_rack(const struct sock *sk)
2122 {
2123 	return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
2124 		TCP_RACK_LOSS_DETECTION;
2125 }
2126 
2127 /* If we detect SACK reneging, forget all SACK information
2128  * and reset tags completely, otherwise preserve SACKs. If receiver
2129  * dropped its ofo queue, we will know this due to reneging detection.
2130  */
2131 static void tcp_timeout_mark_lost(struct sock *sk)
2132 {
2133 	struct tcp_sock *tp = tcp_sk(sk);
2134 	struct sk_buff *skb, *head;
2135 	bool is_reneg;			/* is receiver reneging on SACKs? */
2136 
2137 	head = tcp_rtx_queue_head(sk);
2138 	is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
2139 	if (is_reneg) {
2140 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2141 		tp->sacked_out = 0;
2142 		/* Mark SACK reneging until we recover from this loss event. */
2143 		tp->is_sack_reneg = 1;
2144 	} else if (tcp_is_reno(tp)) {
2145 		tcp_reset_reno_sack(tp);
2146 	}
2147 
2148 	skb = head;
2149 	skb_rbtree_walk_from(skb) {
2150 		if (is_reneg)
2151 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2152 		else if (tcp_is_rack(sk) && skb != head &&
2153 			 tcp_rack_skb_timeout(tp, skb, 0) > 0)
2154 			continue; /* Don't mark recently sent ones lost yet */
2155 		tcp_mark_skb_lost(sk, skb);
2156 	}
2157 	tcp_verify_left_out(tp);
2158 	tcp_clear_all_retrans_hints(tp);
2159 }
2160 
2161 /* Enter Loss state. */
2162 void tcp_enter_loss(struct sock *sk)
2163 {
2164 	const struct inet_connection_sock *icsk = inet_csk(sk);
2165 	struct tcp_sock *tp = tcp_sk(sk);
2166 	struct net *net = sock_net(sk);
2167 	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
2168 	u8 reordering;
2169 
2170 	tcp_timeout_mark_lost(sk);
2171 
2172 	/* Reduce ssthresh if it has not yet been made inside this window. */
2173 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
2174 	    !after(tp->high_seq, tp->snd_una) ||
2175 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2176 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2177 		tp->prior_cwnd = tcp_snd_cwnd(tp);
2178 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2179 		tcp_ca_event(sk, CA_EVENT_LOSS);
2180 		tcp_init_undo(tp);
2181 	}
2182 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
2183 	tp->snd_cwnd_cnt   = 0;
2184 	tp->snd_cwnd_stamp = tcp_jiffies32;
2185 
2186 	/* Timeout in disordered state after receiving substantial DUPACKs
2187 	 * suggests that the degree of reordering is over-estimated.
2188 	 */
2189 	reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering);
2190 	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2191 	    tp->sacked_out >= reordering)
2192 		tp->reordering = min_t(unsigned int, tp->reordering,
2193 				       reordering);
2194 
2195 	tcp_set_ca_state(sk, TCP_CA_Loss);
2196 	tp->high_seq = tp->snd_nxt;
2197 	tp->tlp_high_seq = 0;
2198 	tcp_ecn_queue_cwr(tp);
2199 
2200 	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2201 	 * loss recovery is underway except recurring timeout(s) on
2202 	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2203 	 */
2204 	tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) &&
2205 		   (new_recovery || icsk->icsk_retransmits) &&
2206 		   !inet_csk(sk)->icsk_mtup.probe_size;
2207 }
2208 
2209 /* If ACK arrived pointing to a remembered SACK, it means that our
2210  * remembered SACKs do not reflect real state of receiver i.e.
2211  * receiver _host_ is heavily congested (or buggy).
2212  *
2213  * To avoid big spurious retransmission bursts due to transient SACK
2214  * scoreboard oddities that look like reneging, we give the receiver a
2215  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2216  * restore sanity to the SACK scoreboard. If the apparent reneging
2217  * persists until this RTO then we'll clear the SACK scoreboard.
2218  */
2219 static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag)
2220 {
2221 	if (*ack_flag & FLAG_SACK_RENEGING &&
2222 	    *ack_flag & FLAG_SND_UNA_ADVANCED) {
2223 		struct tcp_sock *tp = tcp_sk(sk);
2224 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2225 					  msecs_to_jiffies(10));
2226 
2227 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2228 					  delay, TCP_RTO_MAX);
2229 		*ack_flag &= ~FLAG_SET_XMIT_TIMER;
2230 		return true;
2231 	}
2232 	return false;
2233 }
2234 
2235 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2236  * counter when SACK is enabled (without SACK, sacked_out is used for
2237  * that purpose).
2238  *
2239  * With reordering, holes may still be in flight, so RFC3517 recovery
2240  * uses pure sacked_out (total number of SACKed segments) even though
2241  * it violates the RFC that uses duplicate ACKs, often these are equal
2242  * but when e.g. out-of-window ACKs or packet duplication occurs,
2243  * they differ. Since neither occurs due to loss, TCP should really
2244  * ignore them.
2245  */
2246 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2247 {
2248 	return tp->sacked_out + 1;
2249 }
2250 
2251 /* Linux NewReno/SACK/ECN state machine.
2252  * --------------------------------------
2253  *
2254  * "Open"	Normal state, no dubious events, fast path.
2255  * "Disorder"   In all the respects it is "Open",
2256  *		but requires a bit more attention. It is entered when
2257  *		we see some SACKs or dupacks. It is split of "Open"
2258  *		mainly to move some processing from fast path to slow one.
2259  * "CWR"	CWND was reduced due to some Congestion Notification event.
2260  *		It can be ECN, ICMP source quench, local device congestion.
2261  * "Recovery"	CWND was reduced, we are fast-retransmitting.
2262  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2263  *
2264  * tcp_fastretrans_alert() is entered:
2265  * - each incoming ACK, if state is not "Open"
2266  * - when arrived ACK is unusual, namely:
2267  *	* SACK
2268  *	* Duplicate ACK.
2269  *	* ECN ECE.
2270  *
2271  * Counting packets in flight is pretty simple.
2272  *
2273  *	in_flight = packets_out - left_out + retrans_out
2274  *
2275  *	packets_out is SND.NXT-SND.UNA counted in packets.
2276  *
2277  *	retrans_out is number of retransmitted segments.
2278  *
2279  *	left_out is number of segments left network, but not ACKed yet.
2280  *
2281  *		left_out = sacked_out + lost_out
2282  *
2283  *     sacked_out: Packets, which arrived to receiver out of order
2284  *		   and hence not ACKed. With SACKs this number is simply
2285  *		   amount of SACKed data. Even without SACKs
2286  *		   it is easy to give pretty reliable estimate of this number,
2287  *		   counting duplicate ACKs.
2288  *
2289  *       lost_out: Packets lost by network. TCP has no explicit
2290  *		   "loss notification" feedback from network (for now).
2291  *		   It means that this number can be only _guessed_.
2292  *		   Actually, it is the heuristics to predict lossage that
2293  *		   distinguishes different algorithms.
2294  *
2295  *	F.e. after RTO, when all the queue is considered as lost,
2296  *	lost_out = packets_out and in_flight = retrans_out.
2297  *
2298  *		Essentially, we have now a few algorithms detecting
2299  *		lost packets.
2300  *
2301  *		If the receiver supports SACK:
2302  *
2303  *		RFC6675/3517: It is the conventional algorithm. A packet is
2304  *		considered lost if the number of higher sequence packets
2305  *		SACKed is greater than or equal the DUPACK thoreshold
2306  *		(reordering). This is implemented in tcp_mark_head_lost and
2307  *		tcp_update_scoreboard.
2308  *
2309  *		RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2310  *		(2017-) that checks timing instead of counting DUPACKs.
2311  *		Essentially a packet is considered lost if it's not S/ACKed
2312  *		after RTT + reordering_window, where both metrics are
2313  *		dynamically measured and adjusted. This is implemented in
2314  *		tcp_rack_mark_lost.
2315  *
2316  *		If the receiver does not support SACK:
2317  *
2318  *		NewReno (RFC6582): in Recovery we assume that one segment
2319  *		is lost (classic Reno). While we are in Recovery and
2320  *		a partial ACK arrives, we assume that one more packet
2321  *		is lost (NewReno). This heuristics are the same in NewReno
2322  *		and SACK.
2323  *
2324  * Really tricky (and requiring careful tuning) part of algorithm
2325  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2326  * The first determines the moment _when_ we should reduce CWND and,
2327  * hence, slow down forward transmission. In fact, it determines the moment
2328  * when we decide that hole is caused by loss, rather than by a reorder.
2329  *
2330  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2331  * holes, caused by lost packets.
2332  *
2333  * And the most logically complicated part of algorithm is undo
2334  * heuristics. We detect false retransmits due to both too early
2335  * fast retransmit (reordering) and underestimated RTO, analyzing
2336  * timestamps and D-SACKs. When we detect that some segments were
2337  * retransmitted by mistake and CWND reduction was wrong, we undo
2338  * window reduction and abort recovery phase. This logic is hidden
2339  * inside several functions named tcp_try_undo_<something>.
2340  */
2341 
2342 /* This function decides, when we should leave Disordered state
2343  * and enter Recovery phase, reducing congestion window.
2344  *
2345  * Main question: may we further continue forward transmission
2346  * with the same cwnd?
2347  */
2348 static bool tcp_time_to_recover(struct sock *sk, int flag)
2349 {
2350 	struct tcp_sock *tp = tcp_sk(sk);
2351 
2352 	/* Trick#1: The loss is proven. */
2353 	if (tp->lost_out)
2354 		return true;
2355 
2356 	/* Not-A-Trick#2 : Classic rule... */
2357 	if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2358 		return true;
2359 
2360 	return false;
2361 }
2362 
2363 /* Detect loss in event "A" above by marking head of queue up as lost.
2364  * For RFC3517 SACK, a segment is considered lost if it
2365  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2366  * the maximum SACKed segments to pass before reaching this limit.
2367  */
2368 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2369 {
2370 	struct tcp_sock *tp = tcp_sk(sk);
2371 	struct sk_buff *skb;
2372 	int cnt;
2373 	/* Use SACK to deduce losses of new sequences sent during recovery */
2374 	const u32 loss_high = tp->snd_nxt;
2375 
2376 	WARN_ON(packets > tp->packets_out);
2377 	skb = tp->lost_skb_hint;
2378 	if (skb) {
2379 		/* Head already handled? */
2380 		if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2381 			return;
2382 		cnt = tp->lost_cnt_hint;
2383 	} else {
2384 		skb = tcp_rtx_queue_head(sk);
2385 		cnt = 0;
2386 	}
2387 
2388 	skb_rbtree_walk_from(skb) {
2389 		/* TODO: do this better */
2390 		/* this is not the most efficient way to do this... */
2391 		tp->lost_skb_hint = skb;
2392 		tp->lost_cnt_hint = cnt;
2393 
2394 		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2395 			break;
2396 
2397 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2398 			cnt += tcp_skb_pcount(skb);
2399 
2400 		if (cnt > packets)
2401 			break;
2402 
2403 		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST))
2404 			tcp_mark_skb_lost(sk, skb);
2405 
2406 		if (mark_head)
2407 			break;
2408 	}
2409 	tcp_verify_left_out(tp);
2410 }
2411 
2412 /* Account newly detected lost packet(s) */
2413 
2414 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2415 {
2416 	struct tcp_sock *tp = tcp_sk(sk);
2417 
2418 	if (tcp_is_sack(tp)) {
2419 		int sacked_upto = tp->sacked_out - tp->reordering;
2420 		if (sacked_upto >= 0)
2421 			tcp_mark_head_lost(sk, sacked_upto, 0);
2422 		else if (fast_rexmit)
2423 			tcp_mark_head_lost(sk, 1, 1);
2424 	}
2425 }
2426 
2427 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2428 {
2429 	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2430 	       before(tp->rx_opt.rcv_tsecr, when);
2431 }
2432 
2433 /* skb is spurious retransmitted if the returned timestamp echo
2434  * reply is prior to the skb transmission time
2435  */
2436 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2437 				     const struct sk_buff *skb)
2438 {
2439 	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2440 	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2441 }
2442 
2443 /* Nothing was retransmitted or returned timestamp is less
2444  * than timestamp of the first retransmission.
2445  */
2446 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2447 {
2448 	return tp->retrans_stamp &&
2449 	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2450 }
2451 
2452 /* Undo procedures. */
2453 
2454 /* We can clear retrans_stamp when there are no retransmissions in the
2455  * window. It would seem that it is trivially available for us in
2456  * tp->retrans_out, however, that kind of assumptions doesn't consider
2457  * what will happen if errors occur when sending retransmission for the
2458  * second time. ...It could the that such segment has only
2459  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2460  * the head skb is enough except for some reneging corner cases that
2461  * are not worth the effort.
2462  *
2463  * Main reason for all this complexity is the fact that connection dying
2464  * time now depends on the validity of the retrans_stamp, in particular,
2465  * that successive retransmissions of a segment must not advance
2466  * retrans_stamp under any conditions.
2467  */
2468 static bool tcp_any_retrans_done(const struct sock *sk)
2469 {
2470 	const struct tcp_sock *tp = tcp_sk(sk);
2471 	struct sk_buff *skb;
2472 
2473 	if (tp->retrans_out)
2474 		return true;
2475 
2476 	skb = tcp_rtx_queue_head(sk);
2477 	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2478 		return true;
2479 
2480 	return false;
2481 }
2482 
2483 static void DBGUNDO(struct sock *sk, const char *msg)
2484 {
2485 #if FASTRETRANS_DEBUG > 1
2486 	struct tcp_sock *tp = tcp_sk(sk);
2487 	struct inet_sock *inet = inet_sk(sk);
2488 
2489 	if (sk->sk_family == AF_INET) {
2490 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2491 			 msg,
2492 			 &inet->inet_daddr, ntohs(inet->inet_dport),
2493 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2494 			 tp->snd_ssthresh, tp->prior_ssthresh,
2495 			 tp->packets_out);
2496 	}
2497 #if IS_ENABLED(CONFIG_IPV6)
2498 	else if (sk->sk_family == AF_INET6) {
2499 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2500 			 msg,
2501 			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2502 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2503 			 tp->snd_ssthresh, tp->prior_ssthresh,
2504 			 tp->packets_out);
2505 	}
2506 #endif
2507 #endif
2508 }
2509 
2510 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2511 {
2512 	struct tcp_sock *tp = tcp_sk(sk);
2513 
2514 	if (unmark_loss) {
2515 		struct sk_buff *skb;
2516 
2517 		skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2518 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2519 		}
2520 		tp->lost_out = 0;
2521 		tcp_clear_all_retrans_hints(tp);
2522 	}
2523 
2524 	if (tp->prior_ssthresh) {
2525 		const struct inet_connection_sock *icsk = inet_csk(sk);
2526 
2527 		tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
2528 
2529 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2530 			tp->snd_ssthresh = tp->prior_ssthresh;
2531 			tcp_ecn_withdraw_cwr(tp);
2532 		}
2533 	}
2534 	tp->snd_cwnd_stamp = tcp_jiffies32;
2535 	tp->undo_marker = 0;
2536 	tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2537 }
2538 
2539 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2540 {
2541 	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2542 }
2543 
2544 static bool tcp_is_non_sack_preventing_reopen(struct sock *sk)
2545 {
2546 	struct tcp_sock *tp = tcp_sk(sk);
2547 
2548 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2549 		/* Hold old state until something *above* high_seq
2550 		 * is ACKed. For Reno it is MUST to prevent false
2551 		 * fast retransmits (RFC2582). SACK TCP is safe. */
2552 		if (!tcp_any_retrans_done(sk))
2553 			tp->retrans_stamp = 0;
2554 		return true;
2555 	}
2556 	return false;
2557 }
2558 
2559 /* People celebrate: "We love our President!" */
2560 static bool tcp_try_undo_recovery(struct sock *sk)
2561 {
2562 	struct tcp_sock *tp = tcp_sk(sk);
2563 
2564 	if (tcp_may_undo(tp)) {
2565 		int mib_idx;
2566 
2567 		/* Happy end! We did not retransmit anything
2568 		 * or our original transmission succeeded.
2569 		 */
2570 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2571 		tcp_undo_cwnd_reduction(sk, false);
2572 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2573 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2574 		else
2575 			mib_idx = LINUX_MIB_TCPFULLUNDO;
2576 
2577 		NET_INC_STATS(sock_net(sk), mib_idx);
2578 	} else if (tp->rack.reo_wnd_persist) {
2579 		tp->rack.reo_wnd_persist--;
2580 	}
2581 	if (tcp_is_non_sack_preventing_reopen(sk))
2582 		return true;
2583 	tcp_set_ca_state(sk, TCP_CA_Open);
2584 	tp->is_sack_reneg = 0;
2585 	return false;
2586 }
2587 
2588 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2589 static bool tcp_try_undo_dsack(struct sock *sk)
2590 {
2591 	struct tcp_sock *tp = tcp_sk(sk);
2592 
2593 	if (tp->undo_marker && !tp->undo_retrans) {
2594 		tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2595 					       tp->rack.reo_wnd_persist + 1);
2596 		DBGUNDO(sk, "D-SACK");
2597 		tcp_undo_cwnd_reduction(sk, false);
2598 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2599 		return true;
2600 	}
2601 	return false;
2602 }
2603 
2604 /* Undo during loss recovery after partial ACK or using F-RTO. */
2605 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2606 {
2607 	struct tcp_sock *tp = tcp_sk(sk);
2608 
2609 	if (frto_undo || tcp_may_undo(tp)) {
2610 		tcp_undo_cwnd_reduction(sk, true);
2611 
2612 		DBGUNDO(sk, "partial loss");
2613 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2614 		if (frto_undo)
2615 			NET_INC_STATS(sock_net(sk),
2616 					LINUX_MIB_TCPSPURIOUSRTOS);
2617 		inet_csk(sk)->icsk_retransmits = 0;
2618 		if (tcp_is_non_sack_preventing_reopen(sk))
2619 			return true;
2620 		if (frto_undo || tcp_is_sack(tp)) {
2621 			tcp_set_ca_state(sk, TCP_CA_Open);
2622 			tp->is_sack_reneg = 0;
2623 		}
2624 		return true;
2625 	}
2626 	return false;
2627 }
2628 
2629 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2630  * It computes the number of packets to send (sndcnt) based on packets newly
2631  * delivered:
2632  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2633  *	cwnd reductions across a full RTT.
2634  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2635  *      But when SND_UNA is acked without further losses,
2636  *      slow starts cwnd up to ssthresh to speed up the recovery.
2637  */
2638 static void tcp_init_cwnd_reduction(struct sock *sk)
2639 {
2640 	struct tcp_sock *tp = tcp_sk(sk);
2641 
2642 	tp->high_seq = tp->snd_nxt;
2643 	tp->tlp_high_seq = 0;
2644 	tp->snd_cwnd_cnt = 0;
2645 	tp->prior_cwnd = tcp_snd_cwnd(tp);
2646 	tp->prr_delivered = 0;
2647 	tp->prr_out = 0;
2648 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2649 	tcp_ecn_queue_cwr(tp);
2650 }
2651 
2652 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag)
2653 {
2654 	struct tcp_sock *tp = tcp_sk(sk);
2655 	int sndcnt = 0;
2656 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2657 
2658 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2659 		return;
2660 
2661 	tp->prr_delivered += newly_acked_sacked;
2662 	if (delta < 0) {
2663 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2664 			       tp->prior_cwnd - 1;
2665 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2666 	} else {
2667 		sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
2668 			       newly_acked_sacked);
2669 		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
2670 			sndcnt++;
2671 		sndcnt = min(delta, sndcnt);
2672 	}
2673 	/* Force a fast retransmit upon entering fast recovery */
2674 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2675 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
2676 }
2677 
2678 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2679 {
2680 	struct tcp_sock *tp = tcp_sk(sk);
2681 
2682 	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2683 		return;
2684 
2685 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2686 	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2687 	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2688 		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
2689 		tp->snd_cwnd_stamp = tcp_jiffies32;
2690 	}
2691 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2692 }
2693 
2694 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2695 void tcp_enter_cwr(struct sock *sk)
2696 {
2697 	struct tcp_sock *tp = tcp_sk(sk);
2698 
2699 	tp->prior_ssthresh = 0;
2700 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2701 		tp->undo_marker = 0;
2702 		tcp_init_cwnd_reduction(sk);
2703 		tcp_set_ca_state(sk, TCP_CA_CWR);
2704 	}
2705 }
2706 EXPORT_SYMBOL(tcp_enter_cwr);
2707 
2708 static void tcp_try_keep_open(struct sock *sk)
2709 {
2710 	struct tcp_sock *tp = tcp_sk(sk);
2711 	int state = TCP_CA_Open;
2712 
2713 	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2714 		state = TCP_CA_Disorder;
2715 
2716 	if (inet_csk(sk)->icsk_ca_state != state) {
2717 		tcp_set_ca_state(sk, state);
2718 		tp->high_seq = tp->snd_nxt;
2719 	}
2720 }
2721 
2722 static void tcp_try_to_open(struct sock *sk, int flag)
2723 {
2724 	struct tcp_sock *tp = tcp_sk(sk);
2725 
2726 	tcp_verify_left_out(tp);
2727 
2728 	if (!tcp_any_retrans_done(sk))
2729 		tp->retrans_stamp = 0;
2730 
2731 	if (flag & FLAG_ECE)
2732 		tcp_enter_cwr(sk);
2733 
2734 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2735 		tcp_try_keep_open(sk);
2736 	}
2737 }
2738 
2739 static void tcp_mtup_probe_failed(struct sock *sk)
2740 {
2741 	struct inet_connection_sock *icsk = inet_csk(sk);
2742 
2743 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2744 	icsk->icsk_mtup.probe_size = 0;
2745 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2746 }
2747 
2748 static void tcp_mtup_probe_success(struct sock *sk)
2749 {
2750 	struct tcp_sock *tp = tcp_sk(sk);
2751 	struct inet_connection_sock *icsk = inet_csk(sk);
2752 	u64 val;
2753 
2754 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2755 
2756 	val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache);
2757 	do_div(val, icsk->icsk_mtup.probe_size);
2758 	DEBUG_NET_WARN_ON_ONCE((u32)val != val);
2759 	tcp_snd_cwnd_set(tp, max_t(u32, 1U, val));
2760 
2761 	tp->snd_cwnd_cnt = 0;
2762 	tp->snd_cwnd_stamp = tcp_jiffies32;
2763 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2764 
2765 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2766 	icsk->icsk_mtup.probe_size = 0;
2767 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2768 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2769 }
2770 
2771 /* Sometimes we deduce that packets have been dropped due to reasons other than
2772  * congestion, like path MTU reductions or failed client TFO attempts. In these
2773  * cases we call this function to retransmit as many packets as cwnd allows,
2774  * without reducing cwnd. Given that retransmits will set retrans_stamp to a
2775  * non-zero value (and may do so in a later calling context due to TSQ), we
2776  * also enter CA_Loss so that we track when all retransmitted packets are ACKed
2777  * and clear retrans_stamp when that happens (to ensure later recurring RTOs
2778  * are using the correct retrans_stamp and don't declare ETIMEDOUT
2779  * prematurely).
2780  */
2781 static void tcp_non_congestion_loss_retransmit(struct sock *sk)
2782 {
2783 	const struct inet_connection_sock *icsk = inet_csk(sk);
2784 	struct tcp_sock *tp = tcp_sk(sk);
2785 
2786 	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2787 		tp->high_seq = tp->snd_nxt;
2788 		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2789 		tp->prior_ssthresh = 0;
2790 		tp->undo_marker = 0;
2791 		tcp_set_ca_state(sk, TCP_CA_Loss);
2792 	}
2793 	tcp_xmit_retransmit_queue(sk);
2794 }
2795 
2796 /* Do a simple retransmit without using the backoff mechanisms in
2797  * tcp_timer. This is used for path mtu discovery.
2798  * The socket is already locked here.
2799  */
2800 void tcp_simple_retransmit(struct sock *sk)
2801 {
2802 	struct tcp_sock *tp = tcp_sk(sk);
2803 	struct sk_buff *skb;
2804 	int mss;
2805 
2806 	/* A fastopen SYN request is stored as two separate packets within
2807 	 * the retransmit queue, this is done by tcp_send_syn_data().
2808 	 * As a result simply checking the MSS of the frames in the queue
2809 	 * will not work for the SYN packet.
2810 	 *
2811 	 * Us being here is an indication of a path MTU issue so we can
2812 	 * assume that the fastopen SYN was lost and just mark all the
2813 	 * frames in the retransmit queue as lost. We will use an MSS of
2814 	 * -1 to mark all frames as lost, otherwise compute the current MSS.
2815 	 */
2816 	if (tp->syn_data && sk->sk_state == TCP_SYN_SENT)
2817 		mss = -1;
2818 	else
2819 		mss = tcp_current_mss(sk);
2820 
2821 	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2822 		if (tcp_skb_seglen(skb) > mss)
2823 			tcp_mark_skb_lost(sk, skb);
2824 	}
2825 
2826 	tcp_clear_retrans_hints_partial(tp);
2827 
2828 	if (!tp->lost_out)
2829 		return;
2830 
2831 	if (tcp_is_reno(tp))
2832 		tcp_limit_reno_sacked(tp);
2833 
2834 	tcp_verify_left_out(tp);
2835 
2836 	/* Don't muck with the congestion window here.
2837 	 * Reason is that we do not increase amount of _data_
2838 	 * in network, but units changed and effective
2839 	 * cwnd/ssthresh really reduced now.
2840 	 */
2841 	tcp_non_congestion_loss_retransmit(sk);
2842 }
2843 EXPORT_SYMBOL(tcp_simple_retransmit);
2844 
2845 void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2846 {
2847 	struct tcp_sock *tp = tcp_sk(sk);
2848 	int mib_idx;
2849 
2850 	if (tcp_is_reno(tp))
2851 		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2852 	else
2853 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2854 
2855 	NET_INC_STATS(sock_net(sk), mib_idx);
2856 
2857 	tp->prior_ssthresh = 0;
2858 	tcp_init_undo(tp);
2859 
2860 	if (!tcp_in_cwnd_reduction(sk)) {
2861 		if (!ece_ack)
2862 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2863 		tcp_init_cwnd_reduction(sk);
2864 	}
2865 	tcp_set_ca_state(sk, TCP_CA_Recovery);
2866 }
2867 
2868 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2869  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2870  */
2871 static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2872 			     int *rexmit)
2873 {
2874 	struct tcp_sock *tp = tcp_sk(sk);
2875 	bool recovered = !before(tp->snd_una, tp->high_seq);
2876 
2877 	if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2878 	    tcp_try_undo_loss(sk, false))
2879 		return;
2880 
2881 	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2882 		/* Step 3.b. A timeout is spurious if not all data are
2883 		 * lost, i.e., never-retransmitted data are (s)acked.
2884 		 */
2885 		if ((flag & FLAG_ORIG_SACK_ACKED) &&
2886 		    tcp_try_undo_loss(sk, true))
2887 			return;
2888 
2889 		if (after(tp->snd_nxt, tp->high_seq)) {
2890 			if (flag & FLAG_DATA_SACKED || num_dupack)
2891 				tp->frto = 0; /* Step 3.a. loss was real */
2892 		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2893 			tp->high_seq = tp->snd_nxt;
2894 			/* Step 2.b. Try send new data (but deferred until cwnd
2895 			 * is updated in tcp_ack()). Otherwise fall back to
2896 			 * the conventional recovery.
2897 			 */
2898 			if (!tcp_write_queue_empty(sk) &&
2899 			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
2900 				*rexmit = REXMIT_NEW;
2901 				return;
2902 			}
2903 			tp->frto = 0;
2904 		}
2905 	}
2906 
2907 	if (recovered) {
2908 		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2909 		tcp_try_undo_recovery(sk);
2910 		return;
2911 	}
2912 	if (tcp_is_reno(tp)) {
2913 		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2914 		 * delivered. Lower inflight to clock out (re)transmissions.
2915 		 */
2916 		if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2917 			tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE);
2918 		else if (flag & FLAG_SND_UNA_ADVANCED)
2919 			tcp_reset_reno_sack(tp);
2920 	}
2921 	*rexmit = REXMIT_LOST;
2922 }
2923 
2924 static bool tcp_force_fast_retransmit(struct sock *sk)
2925 {
2926 	struct tcp_sock *tp = tcp_sk(sk);
2927 
2928 	return after(tcp_highest_sack_seq(tp),
2929 		     tp->snd_una + tp->reordering * tp->mss_cache);
2930 }
2931 
2932 /* Undo during fast recovery after partial ACK. */
2933 static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una,
2934 				 bool *do_lost)
2935 {
2936 	struct tcp_sock *tp = tcp_sk(sk);
2937 
2938 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
2939 		/* Plain luck! Hole if filled with delayed
2940 		 * packet, rather than with a retransmit. Check reordering.
2941 		 */
2942 		tcp_check_sack_reordering(sk, prior_snd_una, 1);
2943 
2944 		/* We are getting evidence that the reordering degree is higher
2945 		 * than we realized. If there are no retransmits out then we
2946 		 * can undo. Otherwise we clock out new packets but do not
2947 		 * mark more packets lost or retransmit more.
2948 		 */
2949 		if (tp->retrans_out)
2950 			return true;
2951 
2952 		if (!tcp_any_retrans_done(sk))
2953 			tp->retrans_stamp = 0;
2954 
2955 		DBGUNDO(sk, "partial recovery");
2956 		tcp_undo_cwnd_reduction(sk, true);
2957 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2958 		tcp_try_keep_open(sk);
2959 	} else {
2960 		/* Partial ACK arrived. Force fast retransmit. */
2961 		*do_lost = tcp_force_fast_retransmit(sk);
2962 	}
2963 	return false;
2964 }
2965 
2966 static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
2967 {
2968 	struct tcp_sock *tp = tcp_sk(sk);
2969 
2970 	if (tcp_rtx_queue_empty(sk))
2971 		return;
2972 
2973 	if (unlikely(tcp_is_reno(tp))) {
2974 		tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
2975 	} else if (tcp_is_rack(sk)) {
2976 		u32 prior_retrans = tp->retrans_out;
2977 
2978 		if (tcp_rack_mark_lost(sk))
2979 			*ack_flag &= ~FLAG_SET_XMIT_TIMER;
2980 		if (prior_retrans > tp->retrans_out)
2981 			*ack_flag |= FLAG_LOST_RETRANS;
2982 	}
2983 }
2984 
2985 /* Process an event, which can update packets-in-flight not trivially.
2986  * Main goal of this function is to calculate new estimate for left_out,
2987  * taking into account both packets sitting in receiver's buffer and
2988  * packets lost by network.
2989  *
2990  * Besides that it updates the congestion state when packet loss or ECN
2991  * is detected. But it does not reduce the cwnd, it is done by the
2992  * congestion control later.
2993  *
2994  * It does _not_ decide what to send, it is made in function
2995  * tcp_xmit_retransmit_queue().
2996  */
2997 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
2998 				  int num_dupack, int *ack_flag, int *rexmit)
2999 {
3000 	struct inet_connection_sock *icsk = inet_csk(sk);
3001 	struct tcp_sock *tp = tcp_sk(sk);
3002 	int fast_rexmit = 0, flag = *ack_flag;
3003 	bool ece_ack = flag & FLAG_ECE;
3004 	bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
3005 				      tcp_force_fast_retransmit(sk));
3006 
3007 	if (!tp->packets_out && tp->sacked_out)
3008 		tp->sacked_out = 0;
3009 
3010 	/* Now state machine starts.
3011 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
3012 	if (ece_ack)
3013 		tp->prior_ssthresh = 0;
3014 
3015 	/* B. In all the states check for reneging SACKs. */
3016 	if (tcp_check_sack_reneging(sk, ack_flag))
3017 		return;
3018 
3019 	/* C. Check consistency of the current state. */
3020 	tcp_verify_left_out(tp);
3021 
3022 	/* D. Check state exit conditions. State can be terminated
3023 	 *    when high_seq is ACKed. */
3024 	if (icsk->icsk_ca_state == TCP_CA_Open) {
3025 		WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
3026 		tp->retrans_stamp = 0;
3027 	} else if (!before(tp->snd_una, tp->high_seq)) {
3028 		switch (icsk->icsk_ca_state) {
3029 		case TCP_CA_CWR:
3030 			/* CWR is to be held something *above* high_seq
3031 			 * is ACKed for CWR bit to reach receiver. */
3032 			if (tp->snd_una != tp->high_seq) {
3033 				tcp_end_cwnd_reduction(sk);
3034 				tcp_set_ca_state(sk, TCP_CA_Open);
3035 			}
3036 			break;
3037 
3038 		case TCP_CA_Recovery:
3039 			if (tcp_is_reno(tp))
3040 				tcp_reset_reno_sack(tp);
3041 			if (tcp_try_undo_recovery(sk))
3042 				return;
3043 			tcp_end_cwnd_reduction(sk);
3044 			break;
3045 		}
3046 	}
3047 
3048 	/* E. Process state. */
3049 	switch (icsk->icsk_ca_state) {
3050 	case TCP_CA_Recovery:
3051 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3052 			if (tcp_is_reno(tp))
3053 				tcp_add_reno_sack(sk, num_dupack, ece_ack);
3054 		} else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost))
3055 			return;
3056 
3057 		if (tcp_try_undo_dsack(sk))
3058 			tcp_try_to_open(sk, flag);
3059 
3060 		tcp_identify_packet_loss(sk, ack_flag);
3061 		if (icsk->icsk_ca_state != TCP_CA_Recovery) {
3062 			if (!tcp_time_to_recover(sk, flag))
3063 				return;
3064 			/* Undo reverts the recovery state. If loss is evident,
3065 			 * starts a new recovery (e.g. reordering then loss);
3066 			 */
3067 			tcp_enter_recovery(sk, ece_ack);
3068 		}
3069 		break;
3070 	case TCP_CA_Loss:
3071 		tcp_process_loss(sk, flag, num_dupack, rexmit);
3072 		tcp_identify_packet_loss(sk, ack_flag);
3073 		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
3074 		      (*ack_flag & FLAG_LOST_RETRANS)))
3075 			return;
3076 		/* Change state if cwnd is undone or retransmits are lost */
3077 		fallthrough;
3078 	default:
3079 		if (tcp_is_reno(tp)) {
3080 			if (flag & FLAG_SND_UNA_ADVANCED)
3081 				tcp_reset_reno_sack(tp);
3082 			tcp_add_reno_sack(sk, num_dupack, ece_ack);
3083 		}
3084 
3085 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3086 			tcp_try_undo_dsack(sk);
3087 
3088 		tcp_identify_packet_loss(sk, ack_flag);
3089 		if (!tcp_time_to_recover(sk, flag)) {
3090 			tcp_try_to_open(sk, flag);
3091 			return;
3092 		}
3093 
3094 		/* MTU probe failure: don't reduce cwnd */
3095 		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3096 		    icsk->icsk_mtup.probe_size &&
3097 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3098 			tcp_mtup_probe_failed(sk);
3099 			/* Restores the reduction we did in tcp_mtup_probe() */
3100 			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
3101 			tcp_simple_retransmit(sk);
3102 			return;
3103 		}
3104 
3105 		/* Otherwise enter Recovery state */
3106 		tcp_enter_recovery(sk, ece_ack);
3107 		fast_rexmit = 1;
3108 	}
3109 
3110 	if (!tcp_is_rack(sk) && do_lost)
3111 		tcp_update_scoreboard(sk, fast_rexmit);
3112 	*rexmit = REXMIT_LOST;
3113 }
3114 
3115 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
3116 {
3117 	u32 wlen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen) * HZ;
3118 	struct tcp_sock *tp = tcp_sk(sk);
3119 
3120 	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
3121 		/* If the remote keeps returning delayed ACKs, eventually
3122 		 * the min filter would pick it up and overestimate the
3123 		 * prop. delay when it expires. Skip suspected delayed ACKs.
3124 		 */
3125 		return;
3126 	}
3127 	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
3128 			   rtt_us ? : jiffies_to_usecs(1));
3129 }
3130 
3131 static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
3132 			       long seq_rtt_us, long sack_rtt_us,
3133 			       long ca_rtt_us, struct rate_sample *rs)
3134 {
3135 	const struct tcp_sock *tp = tcp_sk(sk);
3136 
3137 	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
3138 	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
3139 	 * Karn's algorithm forbids taking RTT if some retransmitted data
3140 	 * is acked (RFC6298).
3141 	 */
3142 	if (seq_rtt_us < 0)
3143 		seq_rtt_us = sack_rtt_us;
3144 
3145 	/* RTTM Rule: A TSecr value received in a segment is used to
3146 	 * update the averaged RTT measurement only if the segment
3147 	 * acknowledges some new data, i.e., only if it advances the
3148 	 * left edge of the send window.
3149 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3150 	 */
3151 	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3152 	    flag & FLAG_ACKED) {
3153 		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
3154 
3155 		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
3156 			if (!delta)
3157 				delta = 1;
3158 			seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
3159 			ca_rtt_us = seq_rtt_us;
3160 		}
3161 	}
3162 	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
3163 	if (seq_rtt_us < 0)
3164 		return false;
3165 
3166 	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
3167 	 * always taken together with ACK, SACK, or TS-opts. Any negative
3168 	 * values will be skipped with the seq_rtt_us < 0 check above.
3169 	 */
3170 	tcp_update_rtt_min(sk, ca_rtt_us, flag);
3171 	tcp_rtt_estimator(sk, seq_rtt_us);
3172 	tcp_set_rto(sk);
3173 
3174 	/* RFC6298: only reset backoff on valid RTT measurement. */
3175 	inet_csk(sk)->icsk_backoff = 0;
3176 	return true;
3177 }
3178 
3179 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
3180 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
3181 {
3182 	struct rate_sample rs;
3183 	long rtt_us = -1L;
3184 
3185 	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
3186 		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
3187 
3188 	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
3189 }
3190 
3191 
3192 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3193 {
3194 	const struct inet_connection_sock *icsk = inet_csk(sk);
3195 
3196 	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3197 	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
3198 }
3199 
3200 /* Restart timer after forward progress on connection.
3201  * RFC2988 recommends to restart timer to now+rto.
3202  */
3203 void tcp_rearm_rto(struct sock *sk)
3204 {
3205 	const struct inet_connection_sock *icsk = inet_csk(sk);
3206 	struct tcp_sock *tp = tcp_sk(sk);
3207 
3208 	/* If the retrans timer is currently being used by Fast Open
3209 	 * for SYN-ACK retrans purpose, stay put.
3210 	 */
3211 	if (rcu_access_pointer(tp->fastopen_rsk))
3212 		return;
3213 
3214 	if (!tp->packets_out) {
3215 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3216 	} else {
3217 		u32 rto = inet_csk(sk)->icsk_rto;
3218 		/* Offset the time elapsed after installing regular RTO */
3219 		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3220 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3221 			s64 delta_us = tcp_rto_delta_us(sk);
3222 			/* delta_us may not be positive if the socket is locked
3223 			 * when the retrans timer fires and is rescheduled.
3224 			 */
3225 			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3226 		}
3227 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3228 				     TCP_RTO_MAX);
3229 	}
3230 }
3231 
3232 /* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
3233 static void tcp_set_xmit_timer(struct sock *sk)
3234 {
3235 	if (!tcp_schedule_loss_probe(sk, true))
3236 		tcp_rearm_rto(sk);
3237 }
3238 
3239 /* If we get here, the whole TSO packet has not been acked. */
3240 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3241 {
3242 	struct tcp_sock *tp = tcp_sk(sk);
3243 	u32 packets_acked;
3244 
3245 	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3246 
3247 	packets_acked = tcp_skb_pcount(skb);
3248 	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3249 		return 0;
3250 	packets_acked -= tcp_skb_pcount(skb);
3251 
3252 	if (packets_acked) {
3253 		BUG_ON(tcp_skb_pcount(skb) == 0);
3254 		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3255 	}
3256 
3257 	return packets_acked;
3258 }
3259 
3260 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3261 			   const struct sk_buff *ack_skb, u32 prior_snd_una)
3262 {
3263 	const struct skb_shared_info *shinfo;
3264 
3265 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3266 	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3267 		return;
3268 
3269 	shinfo = skb_shinfo(skb);
3270 	if (!before(shinfo->tskey, prior_snd_una) &&
3271 	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3272 		tcp_skb_tsorted_save(skb) {
3273 			__skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
3274 		} tcp_skb_tsorted_restore(skb);
3275 	}
3276 }
3277 
3278 /* Remove acknowledged frames from the retransmission queue. If our packet
3279  * is before the ack sequence we can discard it as it's confirmed to have
3280  * arrived at the other end.
3281  */
3282 static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
3283 			       u32 prior_fack, u32 prior_snd_una,
3284 			       struct tcp_sacktag_state *sack, bool ece_ack)
3285 {
3286 	const struct inet_connection_sock *icsk = inet_csk(sk);
3287 	u64 first_ackt, last_ackt;
3288 	struct tcp_sock *tp = tcp_sk(sk);
3289 	u32 prior_sacked = tp->sacked_out;
3290 	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3291 	struct sk_buff *skb, *next;
3292 	bool fully_acked = true;
3293 	long sack_rtt_us = -1L;
3294 	long seq_rtt_us = -1L;
3295 	long ca_rtt_us = -1L;
3296 	u32 pkts_acked = 0;
3297 	bool rtt_update;
3298 	int flag = 0;
3299 
3300 	first_ackt = 0;
3301 
3302 	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3303 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3304 		const u32 start_seq = scb->seq;
3305 		u8 sacked = scb->sacked;
3306 		u32 acked_pcount;
3307 
3308 		/* Determine how many packets and what bytes were acked, tso and else */
3309 		if (after(scb->end_seq, tp->snd_una)) {
3310 			if (tcp_skb_pcount(skb) == 1 ||
3311 			    !after(tp->snd_una, scb->seq))
3312 				break;
3313 
3314 			acked_pcount = tcp_tso_acked(sk, skb);
3315 			if (!acked_pcount)
3316 				break;
3317 			fully_acked = false;
3318 		} else {
3319 			acked_pcount = tcp_skb_pcount(skb);
3320 		}
3321 
3322 		if (unlikely(sacked & TCPCB_RETRANS)) {
3323 			if (sacked & TCPCB_SACKED_RETRANS)
3324 				tp->retrans_out -= acked_pcount;
3325 			flag |= FLAG_RETRANS_DATA_ACKED;
3326 		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3327 			last_ackt = tcp_skb_timestamp_us(skb);
3328 			WARN_ON_ONCE(last_ackt == 0);
3329 			if (!first_ackt)
3330 				first_ackt = last_ackt;
3331 
3332 			if (before(start_seq, reord))
3333 				reord = start_seq;
3334 			if (!after(scb->end_seq, tp->high_seq))
3335 				flag |= FLAG_ORIG_SACK_ACKED;
3336 		}
3337 
3338 		if (sacked & TCPCB_SACKED_ACKED) {
3339 			tp->sacked_out -= acked_pcount;
3340 		} else if (tcp_is_sack(tp)) {
3341 			tcp_count_delivered(tp, acked_pcount, ece_ack);
3342 			if (!tcp_skb_spurious_retrans(tp, skb))
3343 				tcp_rack_advance(tp, sacked, scb->end_seq,
3344 						 tcp_skb_timestamp_us(skb));
3345 		}
3346 		if (sacked & TCPCB_LOST)
3347 			tp->lost_out -= acked_pcount;
3348 
3349 		tp->packets_out -= acked_pcount;
3350 		pkts_acked += acked_pcount;
3351 		tcp_rate_skb_delivered(sk, skb, sack->rate);
3352 
3353 		/* Initial outgoing SYN's get put onto the write_queue
3354 		 * just like anything else we transmit.  It is not
3355 		 * true data, and if we misinform our callers that
3356 		 * this ACK acks real data, we will erroneously exit
3357 		 * connection startup slow start one packet too
3358 		 * quickly.  This is severely frowned upon behavior.
3359 		 */
3360 		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3361 			flag |= FLAG_DATA_ACKED;
3362 		} else {
3363 			flag |= FLAG_SYN_ACKED;
3364 			tp->retrans_stamp = 0;
3365 		}
3366 
3367 		if (!fully_acked)
3368 			break;
3369 
3370 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3371 
3372 		next = skb_rb_next(skb);
3373 		if (unlikely(skb == tp->retransmit_skb_hint))
3374 			tp->retransmit_skb_hint = NULL;
3375 		if (unlikely(skb == tp->lost_skb_hint))
3376 			tp->lost_skb_hint = NULL;
3377 		tcp_highest_sack_replace(sk, skb, next);
3378 		tcp_rtx_queue_unlink_and_free(skb, sk);
3379 	}
3380 
3381 	if (!skb)
3382 		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3383 
3384 	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3385 		tp->snd_up = tp->snd_una;
3386 
3387 	if (skb) {
3388 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3389 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3390 			flag |= FLAG_SACK_RENEGING;
3391 	}
3392 
3393 	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3394 		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3395 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3396 
3397 		if (pkts_acked == 1 && fully_acked && !prior_sacked &&
3398 		    (tp->snd_una - prior_snd_una) < tp->mss_cache &&
3399 		    sack->rate->prior_delivered + 1 == tp->delivered &&
3400 		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3401 			/* Conservatively mark a delayed ACK. It's typically
3402 			 * from a lone runt packet over the round trip to
3403 			 * a receiver w/o out-of-order or CE events.
3404 			 */
3405 			flag |= FLAG_ACK_MAYBE_DELAYED;
3406 		}
3407 	}
3408 	if (sack->first_sackt) {
3409 		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3410 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3411 	}
3412 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3413 					ca_rtt_us, sack->rate);
3414 
3415 	if (flag & FLAG_ACKED) {
3416 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3417 		if (unlikely(icsk->icsk_mtup.probe_size &&
3418 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3419 			tcp_mtup_probe_success(sk);
3420 		}
3421 
3422 		if (tcp_is_reno(tp)) {
3423 			tcp_remove_reno_sacks(sk, pkts_acked, ece_ack);
3424 
3425 			/* If any of the cumulatively ACKed segments was
3426 			 * retransmitted, non-SACK case cannot confirm that
3427 			 * progress was due to original transmission due to
3428 			 * lack of TCPCB_SACKED_ACKED bits even if some of
3429 			 * the packets may have been never retransmitted.
3430 			 */
3431 			if (flag & FLAG_RETRANS_DATA_ACKED)
3432 				flag &= ~FLAG_ORIG_SACK_ACKED;
3433 		} else {
3434 			int delta;
3435 
3436 			/* Non-retransmitted hole got filled? That's reordering */
3437 			if (before(reord, prior_fack))
3438 				tcp_check_sack_reordering(sk, reord, 0);
3439 
3440 			delta = prior_sacked - tp->sacked_out;
3441 			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3442 		}
3443 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3444 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3445 						    tcp_skb_timestamp_us(skb))) {
3446 		/* Do not re-arm RTO if the sack RTT is measured from data sent
3447 		 * after when the head was last (re)transmitted. Otherwise the
3448 		 * timeout may continue to extend in loss recovery.
3449 		 */
3450 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3451 	}
3452 
3453 	if (icsk->icsk_ca_ops->pkts_acked) {
3454 		struct ack_sample sample = { .pkts_acked = pkts_acked,
3455 					     .rtt_us = sack->rate->rtt_us };
3456 
3457 		sample.in_flight = tp->mss_cache *
3458 			(tp->delivered - sack->rate->prior_delivered);
3459 		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3460 	}
3461 
3462 #if FASTRETRANS_DEBUG > 0
3463 	WARN_ON((int)tp->sacked_out < 0);
3464 	WARN_ON((int)tp->lost_out < 0);
3465 	WARN_ON((int)tp->retrans_out < 0);
3466 	if (!tp->packets_out && tcp_is_sack(tp)) {
3467 		icsk = inet_csk(sk);
3468 		if (tp->lost_out) {
3469 			pr_debug("Leak l=%u %d\n",
3470 				 tp->lost_out, icsk->icsk_ca_state);
3471 			tp->lost_out = 0;
3472 		}
3473 		if (tp->sacked_out) {
3474 			pr_debug("Leak s=%u %d\n",
3475 				 tp->sacked_out, icsk->icsk_ca_state);
3476 			tp->sacked_out = 0;
3477 		}
3478 		if (tp->retrans_out) {
3479 			pr_debug("Leak r=%u %d\n",
3480 				 tp->retrans_out, icsk->icsk_ca_state);
3481 			tp->retrans_out = 0;
3482 		}
3483 	}
3484 #endif
3485 	return flag;
3486 }
3487 
3488 static void tcp_ack_probe(struct sock *sk)
3489 {
3490 	struct inet_connection_sock *icsk = inet_csk(sk);
3491 	struct sk_buff *head = tcp_send_head(sk);
3492 	const struct tcp_sock *tp = tcp_sk(sk);
3493 
3494 	/* Was it a usable window open? */
3495 	if (!head)
3496 		return;
3497 	if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3498 		icsk->icsk_backoff = 0;
3499 		icsk->icsk_probes_tstamp = 0;
3500 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3501 		/* Socket must be waked up by subsequent tcp_data_snd_check().
3502 		 * This function is not for random using!
3503 		 */
3504 	} else {
3505 		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3506 
3507 		when = tcp_clamp_probe0_to_user_timeout(sk, when);
3508 		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX);
3509 	}
3510 }
3511 
3512 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3513 {
3514 	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3515 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3516 }
3517 
3518 /* Decide wheather to run the increase function of congestion control. */
3519 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3520 {
3521 	/* If reordering is high then always grow cwnd whenever data is
3522 	 * delivered regardless of its ordering. Otherwise stay conservative
3523 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3524 	 * new SACK or ECE mark may first advance cwnd here and later reduce
3525 	 * cwnd in tcp_fastretrans_alert() based on more states.
3526 	 */
3527 	if (tcp_sk(sk)->reordering >
3528 	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering))
3529 		return flag & FLAG_FORWARD_PROGRESS;
3530 
3531 	return flag & FLAG_DATA_ACKED;
3532 }
3533 
3534 /* The "ultimate" congestion control function that aims to replace the rigid
3535  * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3536  * It's called toward the end of processing an ACK with precise rate
3537  * information. All transmission or retransmission are delayed afterwards.
3538  */
3539 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3540 			     int flag, const struct rate_sample *rs)
3541 {
3542 	const struct inet_connection_sock *icsk = inet_csk(sk);
3543 
3544 	if (icsk->icsk_ca_ops->cong_control) {
3545 		icsk->icsk_ca_ops->cong_control(sk, rs);
3546 		return;
3547 	}
3548 
3549 	if (tcp_in_cwnd_reduction(sk)) {
3550 		/* Reduce cwnd if state mandates */
3551 		tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag);
3552 	} else if (tcp_may_raise_cwnd(sk, flag)) {
3553 		/* Advance cwnd if state allows */
3554 		tcp_cong_avoid(sk, ack, acked_sacked);
3555 	}
3556 	tcp_update_pacing_rate(sk);
3557 }
3558 
3559 /* Check that window update is acceptable.
3560  * The function assumes that snd_una<=ack<=snd_next.
3561  */
3562 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3563 					const u32 ack, const u32 ack_seq,
3564 					const u32 nwin)
3565 {
3566 	return	after(ack, tp->snd_una) ||
3567 		after(ack_seq, tp->snd_wl1) ||
3568 		(ack_seq == tp->snd_wl1 && (nwin > tp->snd_wnd || !nwin));
3569 }
3570 
3571 /* If we update tp->snd_una, also update tp->bytes_acked */
3572 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3573 {
3574 	u32 delta = ack - tp->snd_una;
3575 
3576 	sock_owned_by_me((struct sock *)tp);
3577 	tp->bytes_acked += delta;
3578 	tp->snd_una = ack;
3579 }
3580 
3581 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3582 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3583 {
3584 	u32 delta = seq - tp->rcv_nxt;
3585 
3586 	sock_owned_by_me((struct sock *)tp);
3587 	tp->bytes_received += delta;
3588 	WRITE_ONCE(tp->rcv_nxt, seq);
3589 }
3590 
3591 /* Update our send window.
3592  *
3593  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3594  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3595  */
3596 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3597 				 u32 ack_seq)
3598 {
3599 	struct tcp_sock *tp = tcp_sk(sk);
3600 	int flag = 0;
3601 	u32 nwin = ntohs(tcp_hdr(skb)->window);
3602 
3603 	if (likely(!tcp_hdr(skb)->syn))
3604 		nwin <<= tp->rx_opt.snd_wscale;
3605 
3606 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3607 		flag |= FLAG_WIN_UPDATE;
3608 		tcp_update_wl(tp, ack_seq);
3609 
3610 		if (tp->snd_wnd != nwin) {
3611 			tp->snd_wnd = nwin;
3612 
3613 			/* Note, it is the only place, where
3614 			 * fast path is recovered for sending TCP.
3615 			 */
3616 			tp->pred_flags = 0;
3617 			tcp_fast_path_check(sk);
3618 
3619 			if (!tcp_write_queue_empty(sk))
3620 				tcp_slow_start_after_idle_check(sk);
3621 
3622 			if (nwin > tp->max_window) {
3623 				tp->max_window = nwin;
3624 				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3625 			}
3626 		}
3627 	}
3628 
3629 	tcp_snd_una_update(tp, ack);
3630 
3631 	return flag;
3632 }
3633 
3634 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3635 				   u32 *last_oow_ack_time)
3636 {
3637 	/* Paired with the WRITE_ONCE() in this function. */
3638 	u32 val = READ_ONCE(*last_oow_ack_time);
3639 
3640 	if (val) {
3641 		s32 elapsed = (s32)(tcp_jiffies32 - val);
3642 
3643 		if (0 <= elapsed &&
3644 		    elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
3645 			NET_INC_STATS(net, mib_idx);
3646 			return true;	/* rate-limited: don't send yet! */
3647 		}
3648 	}
3649 
3650 	/* Paired with the prior READ_ONCE() and with itself,
3651 	 * as we might be lockless.
3652 	 */
3653 	WRITE_ONCE(*last_oow_ack_time, tcp_jiffies32);
3654 
3655 	return false;	/* not rate-limited: go ahead, send dupack now! */
3656 }
3657 
3658 /* Return true if we're currently rate-limiting out-of-window ACKs and
3659  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3660  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3661  * attacks that send repeated SYNs or ACKs for the same connection. To
3662  * do this, we do not send a duplicate SYNACK or ACK if the remote
3663  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3664  */
3665 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3666 			  int mib_idx, u32 *last_oow_ack_time)
3667 {
3668 	/* Data packets without SYNs are not likely part of an ACK loop. */
3669 	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3670 	    !tcp_hdr(skb)->syn)
3671 		return false;
3672 
3673 	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3674 }
3675 
3676 /* RFC 5961 7 [ACK Throttling] */
3677 static void tcp_send_challenge_ack(struct sock *sk)
3678 {
3679 	struct tcp_sock *tp = tcp_sk(sk);
3680 	struct net *net = sock_net(sk);
3681 	u32 count, now, ack_limit;
3682 
3683 	/* First check our per-socket dupack rate limit. */
3684 	if (__tcp_oow_rate_limited(net,
3685 				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3686 				   &tp->last_oow_ack_time))
3687 		return;
3688 
3689 	ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
3690 	if (ack_limit == INT_MAX)
3691 		goto send_ack;
3692 
3693 	/* Then check host-wide RFC 5961 rate limit. */
3694 	now = jiffies / HZ;
3695 	if (now != READ_ONCE(net->ipv4.tcp_challenge_timestamp)) {
3696 		u32 half = (ack_limit + 1) >> 1;
3697 
3698 		WRITE_ONCE(net->ipv4.tcp_challenge_timestamp, now);
3699 		WRITE_ONCE(net->ipv4.tcp_challenge_count,
3700 			   get_random_u32_inclusive(half, ack_limit + half - 1));
3701 	}
3702 	count = READ_ONCE(net->ipv4.tcp_challenge_count);
3703 	if (count > 0) {
3704 		WRITE_ONCE(net->ipv4.tcp_challenge_count, count - 1);
3705 send_ack:
3706 		NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3707 		tcp_send_ack(sk);
3708 	}
3709 }
3710 
3711 static void tcp_store_ts_recent(struct tcp_sock *tp)
3712 {
3713 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3714 	tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3715 }
3716 
3717 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3718 {
3719 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3720 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3721 		 * extra check below makes sure this can only happen
3722 		 * for pure ACK frames.  -DaveM
3723 		 *
3724 		 * Not only, also it occurs for expired timestamps.
3725 		 */
3726 
3727 		if (tcp_paws_check(&tp->rx_opt, 0))
3728 			tcp_store_ts_recent(tp);
3729 	}
3730 }
3731 
3732 /* This routine deals with acks during a TLP episode and ends an episode by
3733  * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack
3734  */
3735 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3736 {
3737 	struct tcp_sock *tp = tcp_sk(sk);
3738 
3739 	if (before(ack, tp->tlp_high_seq))
3740 		return;
3741 
3742 	if (!tp->tlp_retrans) {
3743 		/* TLP of new data has been acknowledged */
3744 		tp->tlp_high_seq = 0;
3745 	} else if (flag & FLAG_DSACK_TLP) {
3746 		/* This DSACK means original and TLP probe arrived; no loss */
3747 		tp->tlp_high_seq = 0;
3748 	} else if (after(ack, tp->tlp_high_seq)) {
3749 		/* ACK advances: there was a loss, so reduce cwnd. Reset
3750 		 * tlp_high_seq in tcp_init_cwnd_reduction()
3751 		 */
3752 		tcp_init_cwnd_reduction(sk);
3753 		tcp_set_ca_state(sk, TCP_CA_CWR);
3754 		tcp_end_cwnd_reduction(sk);
3755 		tcp_try_keep_open(sk);
3756 		NET_INC_STATS(sock_net(sk),
3757 				LINUX_MIB_TCPLOSSPROBERECOVERY);
3758 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3759 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3760 		/* Pure dupack: original and TLP probe arrived; no loss */
3761 		tp->tlp_high_seq = 0;
3762 	}
3763 }
3764 
3765 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3766 {
3767 	const struct inet_connection_sock *icsk = inet_csk(sk);
3768 
3769 	if (icsk->icsk_ca_ops->in_ack_event)
3770 		icsk->icsk_ca_ops->in_ack_event(sk, flags);
3771 }
3772 
3773 /* Congestion control has updated the cwnd already. So if we're in
3774  * loss recovery then now we do any new sends (for FRTO) or
3775  * retransmits (for CA_Loss or CA_recovery) that make sense.
3776  */
3777 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3778 {
3779 	struct tcp_sock *tp = tcp_sk(sk);
3780 
3781 	if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3782 		return;
3783 
3784 	if (unlikely(rexmit == REXMIT_NEW)) {
3785 		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3786 					  TCP_NAGLE_OFF);
3787 		if (after(tp->snd_nxt, tp->high_seq))
3788 			return;
3789 		tp->frto = 0;
3790 	}
3791 	tcp_xmit_retransmit_queue(sk);
3792 }
3793 
3794 /* Returns the number of packets newly acked or sacked by the current ACK */
3795 static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3796 {
3797 	const struct net *net = sock_net(sk);
3798 	struct tcp_sock *tp = tcp_sk(sk);
3799 	u32 delivered;
3800 
3801 	delivered = tp->delivered - prior_delivered;
3802 	NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3803 	if (flag & FLAG_ECE)
3804 		NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3805 
3806 	return delivered;
3807 }
3808 
3809 /* This routine deals with incoming acks, but not outgoing ones. */
3810 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3811 {
3812 	struct inet_connection_sock *icsk = inet_csk(sk);
3813 	struct tcp_sock *tp = tcp_sk(sk);
3814 	struct tcp_sacktag_state sack_state;
3815 	struct rate_sample rs = { .prior_delivered = 0 };
3816 	u32 prior_snd_una = tp->snd_una;
3817 	bool is_sack_reneg = tp->is_sack_reneg;
3818 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3819 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3820 	int num_dupack = 0;
3821 	int prior_packets = tp->packets_out;
3822 	u32 delivered = tp->delivered;
3823 	u32 lost = tp->lost;
3824 	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3825 	u32 prior_fack;
3826 
3827 	sack_state.first_sackt = 0;
3828 	sack_state.rate = &rs;
3829 	sack_state.sack_delivered = 0;
3830 
3831 	/* We very likely will need to access rtx queue. */
3832 	prefetch(sk->tcp_rtx_queue.rb_node);
3833 
3834 	/* If the ack is older than previous acks
3835 	 * then we can probably ignore it.
3836 	 */
3837 	if (before(ack, prior_snd_una)) {
3838 		u32 max_window;
3839 
3840 		/* do not accept ACK for bytes we never sent. */
3841 		max_window = min_t(u64, tp->max_window, tp->bytes_acked);
3842 		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3843 		if (before(ack, prior_snd_una - max_window)) {
3844 			if (!(flag & FLAG_NO_CHALLENGE_ACK))
3845 				tcp_send_challenge_ack(sk);
3846 			return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
3847 		}
3848 		goto old_ack;
3849 	}
3850 
3851 	/* If the ack includes data we haven't sent yet, discard
3852 	 * this segment (RFC793 Section 3.9).
3853 	 */
3854 	if (after(ack, tp->snd_nxt))
3855 		return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
3856 
3857 	if (after(ack, prior_snd_una)) {
3858 		flag |= FLAG_SND_UNA_ADVANCED;
3859 		icsk->icsk_retransmits = 0;
3860 
3861 #if IS_ENABLED(CONFIG_TLS_DEVICE)
3862 		if (static_branch_unlikely(&clean_acked_data_enabled.key))
3863 			if (icsk->icsk_clean_acked)
3864 				icsk->icsk_clean_acked(sk, ack);
3865 #endif
3866 	}
3867 
3868 	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3869 	rs.prior_in_flight = tcp_packets_in_flight(tp);
3870 
3871 	/* ts_recent update must be made after we are sure that the packet
3872 	 * is in window.
3873 	 */
3874 	if (flag & FLAG_UPDATE_TS_RECENT)
3875 		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3876 
3877 	if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
3878 	    FLAG_SND_UNA_ADVANCED) {
3879 		/* Window is constant, pure forward advance.
3880 		 * No more checks are required.
3881 		 * Note, we use the fact that SND.UNA>=SND.WL2.
3882 		 */
3883 		tcp_update_wl(tp, ack_seq);
3884 		tcp_snd_una_update(tp, ack);
3885 		flag |= FLAG_WIN_UPDATE;
3886 
3887 		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3888 
3889 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3890 	} else {
3891 		u32 ack_ev_flags = CA_ACK_SLOWPATH;
3892 
3893 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3894 			flag |= FLAG_DATA;
3895 		else
3896 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3897 
3898 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3899 
3900 		if (TCP_SKB_CB(skb)->sacked)
3901 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3902 							&sack_state);
3903 
3904 		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3905 			flag |= FLAG_ECE;
3906 			ack_ev_flags |= CA_ACK_ECE;
3907 		}
3908 
3909 		if (sack_state.sack_delivered)
3910 			tcp_count_delivered(tp, sack_state.sack_delivered,
3911 					    flag & FLAG_ECE);
3912 
3913 		if (flag & FLAG_WIN_UPDATE)
3914 			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3915 
3916 		tcp_in_ack_event(sk, ack_ev_flags);
3917 	}
3918 
3919 	/* This is a deviation from RFC3168 since it states that:
3920 	 * "When the TCP data sender is ready to set the CWR bit after reducing
3921 	 * the congestion window, it SHOULD set the CWR bit only on the first
3922 	 * new data packet that it transmits."
3923 	 * We accept CWR on pure ACKs to be more robust
3924 	 * with widely-deployed TCP implementations that do this.
3925 	 */
3926 	tcp_ecn_accept_cwr(sk, skb);
3927 
3928 	/* We passed data and got it acked, remove any soft error
3929 	 * log. Something worked...
3930 	 */
3931 	WRITE_ONCE(sk->sk_err_soft, 0);
3932 	icsk->icsk_probes_out = 0;
3933 	tp->rcv_tstamp = tcp_jiffies32;
3934 	if (!prior_packets)
3935 		goto no_queue;
3936 
3937 	/* See if we can take anything off of the retransmit queue. */
3938 	flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una,
3939 				    &sack_state, flag & FLAG_ECE);
3940 
3941 	tcp_rack_update_reo_wnd(sk, &rs);
3942 
3943 	if (tp->tlp_high_seq)
3944 		tcp_process_tlp_ack(sk, ack, flag);
3945 
3946 	if (tcp_ack_is_dubious(sk, flag)) {
3947 		if (!(flag & (FLAG_SND_UNA_ADVANCED |
3948 			      FLAG_NOT_DUP | FLAG_DSACKING_ACK))) {
3949 			num_dupack = 1;
3950 			/* Consider if pure acks were aggregated in tcp_add_backlog() */
3951 			if (!(flag & FLAG_DATA))
3952 				num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
3953 		}
3954 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3955 				      &rexmit);
3956 	}
3957 
3958 	/* If needed, reset TLP/RTO timer when RACK doesn't set. */
3959 	if (flag & FLAG_SET_XMIT_TIMER)
3960 		tcp_set_xmit_timer(sk);
3961 
3962 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3963 		sk_dst_confirm(sk);
3964 
3965 	delivered = tcp_newly_delivered(sk, delivered, flag);
3966 	lost = tp->lost - lost;			/* freshly marked lost */
3967 	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
3968 	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
3969 	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3970 	tcp_xmit_recovery(sk, rexmit);
3971 	return 1;
3972 
3973 no_queue:
3974 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3975 	if (flag & FLAG_DSACKING_ACK) {
3976 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3977 				      &rexmit);
3978 		tcp_newly_delivered(sk, delivered, flag);
3979 	}
3980 	/* If this ack opens up a zero window, clear backoff.  It was
3981 	 * being used to time the probes, and is probably far higher than
3982 	 * it needs to be for normal retransmission.
3983 	 */
3984 	tcp_ack_probe(sk);
3985 
3986 	if (tp->tlp_high_seq)
3987 		tcp_process_tlp_ack(sk, ack, flag);
3988 	return 1;
3989 
3990 old_ack:
3991 	/* If data was SACKed, tag it and see if we should send more data.
3992 	 * If data was DSACKed, see if we can undo a cwnd reduction.
3993 	 */
3994 	if (TCP_SKB_CB(skb)->sacked) {
3995 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3996 						&sack_state);
3997 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3998 				      &rexmit);
3999 		tcp_newly_delivered(sk, delivered, flag);
4000 		tcp_xmit_recovery(sk, rexmit);
4001 	}
4002 
4003 	return 0;
4004 }
4005 
4006 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
4007 				      bool syn, struct tcp_fastopen_cookie *foc,
4008 				      bool exp_opt)
4009 {
4010 	/* Valid only in SYN or SYN-ACK with an even length.  */
4011 	if (!foc || !syn || len < 0 || (len & 1))
4012 		return;
4013 
4014 	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
4015 	    len <= TCP_FASTOPEN_COOKIE_MAX)
4016 		memcpy(foc->val, cookie, len);
4017 	else if (len != 0)
4018 		len = -1;
4019 	foc->len = len;
4020 	foc->exp = exp_opt;
4021 }
4022 
4023 static bool smc_parse_options(const struct tcphdr *th,
4024 			      struct tcp_options_received *opt_rx,
4025 			      const unsigned char *ptr,
4026 			      int opsize)
4027 {
4028 #if IS_ENABLED(CONFIG_SMC)
4029 	if (static_branch_unlikely(&tcp_have_smc)) {
4030 		if (th->syn && !(opsize & 1) &&
4031 		    opsize >= TCPOLEN_EXP_SMC_BASE &&
4032 		    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
4033 			opt_rx->smc_ok = 1;
4034 			return true;
4035 		}
4036 	}
4037 #endif
4038 	return false;
4039 }
4040 
4041 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
4042  * value on success.
4043  */
4044 u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
4045 {
4046 	const unsigned char *ptr = (const unsigned char *)(th + 1);
4047 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4048 	u16 mss = 0;
4049 
4050 	while (length > 0) {
4051 		int opcode = *ptr++;
4052 		int opsize;
4053 
4054 		switch (opcode) {
4055 		case TCPOPT_EOL:
4056 			return mss;
4057 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4058 			length--;
4059 			continue;
4060 		default:
4061 			if (length < 2)
4062 				return mss;
4063 			opsize = *ptr++;
4064 			if (opsize < 2) /* "silly options" */
4065 				return mss;
4066 			if (opsize > length)
4067 				return mss;	/* fail on partial options */
4068 			if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
4069 				u16 in_mss = get_unaligned_be16(ptr);
4070 
4071 				if (in_mss) {
4072 					if (user_mss && user_mss < in_mss)
4073 						in_mss = user_mss;
4074 					mss = in_mss;
4075 				}
4076 			}
4077 			ptr += opsize - 2;
4078 			length -= opsize;
4079 		}
4080 	}
4081 	return mss;
4082 }
4083 EXPORT_SYMBOL_GPL(tcp_parse_mss_option);
4084 
4085 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
4086  * But, this can also be called on packets in the established flow when
4087  * the fast version below fails.
4088  */
4089 void tcp_parse_options(const struct net *net,
4090 		       const struct sk_buff *skb,
4091 		       struct tcp_options_received *opt_rx, int estab,
4092 		       struct tcp_fastopen_cookie *foc)
4093 {
4094 	const unsigned char *ptr;
4095 	const struct tcphdr *th = tcp_hdr(skb);
4096 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4097 
4098 	ptr = (const unsigned char *)(th + 1);
4099 	opt_rx->saw_tstamp = 0;
4100 	opt_rx->saw_unknown = 0;
4101 
4102 	while (length > 0) {
4103 		int opcode = *ptr++;
4104 		int opsize;
4105 
4106 		switch (opcode) {
4107 		case TCPOPT_EOL:
4108 			return;
4109 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4110 			length--;
4111 			continue;
4112 		default:
4113 			if (length < 2)
4114 				return;
4115 			opsize = *ptr++;
4116 			if (opsize < 2) /* "silly options" */
4117 				return;
4118 			if (opsize > length)
4119 				return;	/* don't parse partial options */
4120 			switch (opcode) {
4121 			case TCPOPT_MSS:
4122 				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
4123 					u16 in_mss = get_unaligned_be16(ptr);
4124 					if (in_mss) {
4125 						if (opt_rx->user_mss &&
4126 						    opt_rx->user_mss < in_mss)
4127 							in_mss = opt_rx->user_mss;
4128 						opt_rx->mss_clamp = in_mss;
4129 					}
4130 				}
4131 				break;
4132 			case TCPOPT_WINDOW:
4133 				if (opsize == TCPOLEN_WINDOW && th->syn &&
4134 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) {
4135 					__u8 snd_wscale = *(__u8 *)ptr;
4136 					opt_rx->wscale_ok = 1;
4137 					if (snd_wscale > TCP_MAX_WSCALE) {
4138 						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
4139 								     __func__,
4140 								     snd_wscale,
4141 								     TCP_MAX_WSCALE);
4142 						snd_wscale = TCP_MAX_WSCALE;
4143 					}
4144 					opt_rx->snd_wscale = snd_wscale;
4145 				}
4146 				break;
4147 			case TCPOPT_TIMESTAMP:
4148 				if ((opsize == TCPOLEN_TIMESTAMP) &&
4149 				    ((estab && opt_rx->tstamp_ok) ||
4150 				     (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) {
4151 					opt_rx->saw_tstamp = 1;
4152 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
4153 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
4154 				}
4155 				break;
4156 			case TCPOPT_SACK_PERM:
4157 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
4158 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) {
4159 					opt_rx->sack_ok = TCP_SACK_SEEN;
4160 					tcp_sack_reset(opt_rx);
4161 				}
4162 				break;
4163 
4164 			case TCPOPT_SACK:
4165 				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
4166 				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
4167 				   opt_rx->sack_ok) {
4168 					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
4169 				}
4170 				break;
4171 #ifdef CONFIG_TCP_MD5SIG
4172 			case TCPOPT_MD5SIG:
4173 				/* The MD5 Hash has already been
4174 				 * checked (see tcp_v{4,6}_rcv()).
4175 				 */
4176 				break;
4177 #endif
4178 			case TCPOPT_FASTOPEN:
4179 				tcp_parse_fastopen_option(
4180 					opsize - TCPOLEN_FASTOPEN_BASE,
4181 					ptr, th->syn, foc, false);
4182 				break;
4183 
4184 			case TCPOPT_EXP:
4185 				/* Fast Open option shares code 254 using a
4186 				 * 16 bits magic number.
4187 				 */
4188 				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
4189 				    get_unaligned_be16(ptr) ==
4190 				    TCPOPT_FASTOPEN_MAGIC) {
4191 					tcp_parse_fastopen_option(opsize -
4192 						TCPOLEN_EXP_FASTOPEN_BASE,
4193 						ptr + 2, th->syn, foc, true);
4194 					break;
4195 				}
4196 
4197 				if (smc_parse_options(th, opt_rx, ptr, opsize))
4198 					break;
4199 
4200 				opt_rx->saw_unknown = 1;
4201 				break;
4202 
4203 			default:
4204 				opt_rx->saw_unknown = 1;
4205 			}
4206 			ptr += opsize-2;
4207 			length -= opsize;
4208 		}
4209 	}
4210 }
4211 EXPORT_SYMBOL(tcp_parse_options);
4212 
4213 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4214 {
4215 	const __be32 *ptr = (const __be32 *)(th + 1);
4216 
4217 	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4218 			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4219 		tp->rx_opt.saw_tstamp = 1;
4220 		++ptr;
4221 		tp->rx_opt.rcv_tsval = ntohl(*ptr);
4222 		++ptr;
4223 		if (*ptr)
4224 			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
4225 		else
4226 			tp->rx_opt.rcv_tsecr = 0;
4227 		return true;
4228 	}
4229 	return false;
4230 }
4231 
4232 /* Fast parse options. This hopes to only see timestamps.
4233  * If it is wrong it falls back on tcp_parse_options().
4234  */
4235 static bool tcp_fast_parse_options(const struct net *net,
4236 				   const struct sk_buff *skb,
4237 				   const struct tcphdr *th, struct tcp_sock *tp)
4238 {
4239 	/* In the spirit of fast parsing, compare doff directly to constant
4240 	 * values.  Because equality is used, short doff can be ignored here.
4241 	 */
4242 	if (th->doff == (sizeof(*th) / 4)) {
4243 		tp->rx_opt.saw_tstamp = 0;
4244 		return false;
4245 	} else if (tp->rx_opt.tstamp_ok &&
4246 		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4247 		if (tcp_parse_aligned_timestamp(tp, th))
4248 			return true;
4249 	}
4250 
4251 	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
4252 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
4253 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
4254 
4255 	return true;
4256 }
4257 
4258 #ifdef CONFIG_TCP_MD5SIG
4259 /*
4260  * Parse MD5 Signature option
4261  */
4262 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4263 {
4264 	int length = (th->doff << 2) - sizeof(*th);
4265 	const u8 *ptr = (const u8 *)(th + 1);
4266 
4267 	/* If not enough data remaining, we can short cut */
4268 	while (length >= TCPOLEN_MD5SIG) {
4269 		int opcode = *ptr++;
4270 		int opsize;
4271 
4272 		switch (opcode) {
4273 		case TCPOPT_EOL:
4274 			return NULL;
4275 		case TCPOPT_NOP:
4276 			length--;
4277 			continue;
4278 		default:
4279 			opsize = *ptr++;
4280 			if (opsize < 2 || opsize > length)
4281 				return NULL;
4282 			if (opcode == TCPOPT_MD5SIG)
4283 				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4284 		}
4285 		ptr += opsize - 2;
4286 		length -= opsize;
4287 	}
4288 	return NULL;
4289 }
4290 EXPORT_SYMBOL(tcp_parse_md5sig_option);
4291 #endif
4292 
4293 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4294  *
4295  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4296  * it can pass through stack. So, the following predicate verifies that
4297  * this segment is not used for anything but congestion avoidance or
4298  * fast retransmit. Moreover, we even are able to eliminate most of such
4299  * second order effects, if we apply some small "replay" window (~RTO)
4300  * to timestamp space.
4301  *
4302  * All these measures still do not guarantee that we reject wrapped ACKs
4303  * on networks with high bandwidth, when sequence space is recycled fastly,
4304  * but it guarantees that such events will be very rare and do not affect
4305  * connection seriously. This doesn't look nice, but alas, PAWS is really
4306  * buggy extension.
4307  *
4308  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4309  * states that events when retransmit arrives after original data are rare.
4310  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4311  * the biggest problem on large power networks even with minor reordering.
4312  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4313  * up to bandwidth of 18Gigabit/sec. 8) ]
4314  */
4315 
4316 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4317 {
4318 	const struct tcp_sock *tp = tcp_sk(sk);
4319 	const struct tcphdr *th = tcp_hdr(skb);
4320 	u32 seq = TCP_SKB_CB(skb)->seq;
4321 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4322 
4323 	return (/* 1. Pure ACK with correct sequence number. */
4324 		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4325 
4326 		/* 2. ... and duplicate ACK. */
4327 		ack == tp->snd_una &&
4328 
4329 		/* 3. ... and does not update window. */
4330 		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4331 
4332 		/* 4. ... and sits in replay window. */
4333 		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4334 }
4335 
4336 static inline bool tcp_paws_discard(const struct sock *sk,
4337 				   const struct sk_buff *skb)
4338 {
4339 	const struct tcp_sock *tp = tcp_sk(sk);
4340 
4341 	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4342 	       !tcp_disordered_ack(sk, skb);
4343 }
4344 
4345 /* Check segment sequence number for validity.
4346  *
4347  * Segment controls are considered valid, if the segment
4348  * fits to the window after truncation to the window. Acceptability
4349  * of data (and SYN, FIN, of course) is checked separately.
4350  * See tcp_data_queue(), for example.
4351  *
4352  * Also, controls (RST is main one) are accepted using RCV.WUP instead
4353  * of RCV.NXT. Peer still did not advance his SND.UNA when we
4354  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4355  * (borrowed from freebsd)
4356  */
4357 
4358 static enum skb_drop_reason tcp_sequence(const struct tcp_sock *tp,
4359 					 u32 seq, u32 end_seq)
4360 {
4361 	if (before(end_seq, tp->rcv_wup))
4362 		return SKB_DROP_REASON_TCP_OLD_SEQUENCE;
4363 
4364 	if (after(seq, tp->rcv_nxt + tcp_receive_window(tp)))
4365 		return SKB_DROP_REASON_TCP_INVALID_SEQUENCE;
4366 
4367 	return SKB_NOT_DROPPED_YET;
4368 }
4369 
4370 /* When we get a reset we do this. */
4371 void tcp_reset(struct sock *sk, struct sk_buff *skb)
4372 {
4373 	trace_tcp_receive_reset(sk);
4374 
4375 	/* mptcp can't tell us to ignore reset pkts,
4376 	 * so just ignore the return value of mptcp_incoming_options().
4377 	 */
4378 	if (sk_is_mptcp(sk))
4379 		mptcp_incoming_options(sk, skb);
4380 
4381 	/* We want the right error as BSD sees it (and indeed as we do). */
4382 	switch (sk->sk_state) {
4383 	case TCP_SYN_SENT:
4384 		WRITE_ONCE(sk->sk_err, ECONNREFUSED);
4385 		break;
4386 	case TCP_CLOSE_WAIT:
4387 		WRITE_ONCE(sk->sk_err, EPIPE);
4388 		break;
4389 	case TCP_CLOSE:
4390 		return;
4391 	default:
4392 		WRITE_ONCE(sk->sk_err, ECONNRESET);
4393 	}
4394 	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4395 	smp_wmb();
4396 
4397 	tcp_write_queue_purge(sk);
4398 	tcp_done(sk);
4399 
4400 	if (!sock_flag(sk, SOCK_DEAD))
4401 		sk_error_report(sk);
4402 }
4403 
4404 /*
4405  * 	Process the FIN bit. This now behaves as it is supposed to work
4406  *	and the FIN takes effect when it is validly part of sequence
4407  *	space. Not before when we get holes.
4408  *
4409  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4410  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4411  *	TIME-WAIT)
4412  *
4413  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4414  *	close and we go into CLOSING (and later onto TIME-WAIT)
4415  *
4416  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4417  */
4418 void tcp_fin(struct sock *sk)
4419 {
4420 	struct tcp_sock *tp = tcp_sk(sk);
4421 
4422 	inet_csk_schedule_ack(sk);
4423 
4424 	WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | RCV_SHUTDOWN);
4425 	sock_set_flag(sk, SOCK_DONE);
4426 
4427 	switch (sk->sk_state) {
4428 	case TCP_SYN_RECV:
4429 	case TCP_ESTABLISHED:
4430 		/* Move to CLOSE_WAIT */
4431 		tcp_set_state(sk, TCP_CLOSE_WAIT);
4432 		inet_csk_enter_pingpong_mode(sk);
4433 		break;
4434 
4435 	case TCP_CLOSE_WAIT:
4436 	case TCP_CLOSING:
4437 		/* Received a retransmission of the FIN, do
4438 		 * nothing.
4439 		 */
4440 		break;
4441 	case TCP_LAST_ACK:
4442 		/* RFC793: Remain in the LAST-ACK state. */
4443 		break;
4444 
4445 	case TCP_FIN_WAIT1:
4446 		/* This case occurs when a simultaneous close
4447 		 * happens, we must ack the received FIN and
4448 		 * enter the CLOSING state.
4449 		 */
4450 		tcp_send_ack(sk);
4451 		tcp_set_state(sk, TCP_CLOSING);
4452 		break;
4453 	case TCP_FIN_WAIT2:
4454 		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4455 		tcp_send_ack(sk);
4456 		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4457 		break;
4458 	default:
4459 		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4460 		 * cases we should never reach this piece of code.
4461 		 */
4462 		pr_err("%s: Impossible, sk->sk_state=%d\n",
4463 		       __func__, sk->sk_state);
4464 		break;
4465 	}
4466 
4467 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4468 	 * Probably, we should reset in this case. For now drop them.
4469 	 */
4470 	skb_rbtree_purge(&tp->out_of_order_queue);
4471 	if (tcp_is_sack(tp))
4472 		tcp_sack_reset(&tp->rx_opt);
4473 
4474 	if (!sock_flag(sk, SOCK_DEAD)) {
4475 		sk->sk_state_change(sk);
4476 
4477 		/* Do not send POLL_HUP for half duplex close. */
4478 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4479 		    sk->sk_state == TCP_CLOSE)
4480 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4481 		else
4482 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4483 	}
4484 }
4485 
4486 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4487 				  u32 end_seq)
4488 {
4489 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4490 		if (before(seq, sp->start_seq))
4491 			sp->start_seq = seq;
4492 		if (after(end_seq, sp->end_seq))
4493 			sp->end_seq = end_seq;
4494 		return true;
4495 	}
4496 	return false;
4497 }
4498 
4499 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4500 {
4501 	struct tcp_sock *tp = tcp_sk(sk);
4502 
4503 	if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4504 		int mib_idx;
4505 
4506 		if (before(seq, tp->rcv_nxt))
4507 			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4508 		else
4509 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4510 
4511 		NET_INC_STATS(sock_net(sk), mib_idx);
4512 
4513 		tp->rx_opt.dsack = 1;
4514 		tp->duplicate_sack[0].start_seq = seq;
4515 		tp->duplicate_sack[0].end_seq = end_seq;
4516 	}
4517 }
4518 
4519 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4520 {
4521 	struct tcp_sock *tp = tcp_sk(sk);
4522 
4523 	if (!tp->rx_opt.dsack)
4524 		tcp_dsack_set(sk, seq, end_seq);
4525 	else
4526 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4527 }
4528 
4529 static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4530 {
4531 	/* When the ACK path fails or drops most ACKs, the sender would
4532 	 * timeout and spuriously retransmit the same segment repeatedly.
4533 	 * The receiver remembers and reflects via DSACKs. Leverage the
4534 	 * DSACK state and change the txhash to re-route speculatively.
4535 	 */
4536 	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
4537 	    sk_rethink_txhash(sk))
4538 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
4539 }
4540 
4541 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4542 {
4543 	struct tcp_sock *tp = tcp_sk(sk);
4544 
4545 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4546 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4547 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4548 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4549 
4550 		if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4551 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4552 
4553 			tcp_rcv_spurious_retrans(sk, skb);
4554 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4555 				end_seq = tp->rcv_nxt;
4556 			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4557 		}
4558 	}
4559 
4560 	tcp_send_ack(sk);
4561 }
4562 
4563 /* These routines update the SACK block as out-of-order packets arrive or
4564  * in-order packets close up the sequence space.
4565  */
4566 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4567 {
4568 	int this_sack;
4569 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4570 	struct tcp_sack_block *swalk = sp + 1;
4571 
4572 	/* See if the recent change to the first SACK eats into
4573 	 * or hits the sequence space of other SACK blocks, if so coalesce.
4574 	 */
4575 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4576 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4577 			int i;
4578 
4579 			/* Zap SWALK, by moving every further SACK up by one slot.
4580 			 * Decrease num_sacks.
4581 			 */
4582 			tp->rx_opt.num_sacks--;
4583 			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4584 				sp[i] = sp[i + 1];
4585 			continue;
4586 		}
4587 		this_sack++;
4588 		swalk++;
4589 	}
4590 }
4591 
4592 void tcp_sack_compress_send_ack(struct sock *sk)
4593 {
4594 	struct tcp_sock *tp = tcp_sk(sk);
4595 
4596 	if (!tp->compressed_ack)
4597 		return;
4598 
4599 	if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
4600 		__sock_put(sk);
4601 
4602 	/* Since we have to send one ack finally,
4603 	 * substract one from tp->compressed_ack to keep
4604 	 * LINUX_MIB_TCPACKCOMPRESSED accurate.
4605 	 */
4606 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
4607 		      tp->compressed_ack - 1);
4608 
4609 	tp->compressed_ack = 0;
4610 	tcp_send_ack(sk);
4611 }
4612 
4613 /* Reasonable amount of sack blocks included in TCP SACK option
4614  * The max is 4, but this becomes 3 if TCP timestamps are there.
4615  * Given that SACK packets might be lost, be conservative and use 2.
4616  */
4617 #define TCP_SACK_BLOCKS_EXPECTED 2
4618 
4619 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4620 {
4621 	struct tcp_sock *tp = tcp_sk(sk);
4622 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4623 	int cur_sacks = tp->rx_opt.num_sacks;
4624 	int this_sack;
4625 
4626 	if (!cur_sacks)
4627 		goto new_sack;
4628 
4629 	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4630 		if (tcp_sack_extend(sp, seq, end_seq)) {
4631 			if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4632 				tcp_sack_compress_send_ack(sk);
4633 			/* Rotate this_sack to the first one. */
4634 			for (; this_sack > 0; this_sack--, sp--)
4635 				swap(*sp, *(sp - 1));
4636 			if (cur_sacks > 1)
4637 				tcp_sack_maybe_coalesce(tp);
4638 			return;
4639 		}
4640 	}
4641 
4642 	if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4643 		tcp_sack_compress_send_ack(sk);
4644 
4645 	/* Could not find an adjacent existing SACK, build a new one,
4646 	 * put it at the front, and shift everyone else down.  We
4647 	 * always know there is at least one SACK present already here.
4648 	 *
4649 	 * If the sack array is full, forget about the last one.
4650 	 */
4651 	if (this_sack >= TCP_NUM_SACKS) {
4652 		this_sack--;
4653 		tp->rx_opt.num_sacks--;
4654 		sp--;
4655 	}
4656 	for (; this_sack > 0; this_sack--, sp--)
4657 		*sp = *(sp - 1);
4658 
4659 new_sack:
4660 	/* Build the new head SACK, and we're done. */
4661 	sp->start_seq = seq;
4662 	sp->end_seq = end_seq;
4663 	tp->rx_opt.num_sacks++;
4664 }
4665 
4666 /* RCV.NXT advances, some SACKs should be eaten. */
4667 
4668 static void tcp_sack_remove(struct tcp_sock *tp)
4669 {
4670 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4671 	int num_sacks = tp->rx_opt.num_sacks;
4672 	int this_sack;
4673 
4674 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4675 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4676 		tp->rx_opt.num_sacks = 0;
4677 		return;
4678 	}
4679 
4680 	for (this_sack = 0; this_sack < num_sacks;) {
4681 		/* Check if the start of the sack is covered by RCV.NXT. */
4682 		if (!before(tp->rcv_nxt, sp->start_seq)) {
4683 			int i;
4684 
4685 			/* RCV.NXT must cover all the block! */
4686 			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4687 
4688 			/* Zap this SACK, by moving forward any other SACKS. */
4689 			for (i = this_sack+1; i < num_sacks; i++)
4690 				tp->selective_acks[i-1] = tp->selective_acks[i];
4691 			num_sacks--;
4692 			continue;
4693 		}
4694 		this_sack++;
4695 		sp++;
4696 	}
4697 	tp->rx_opt.num_sacks = num_sacks;
4698 }
4699 
4700 /**
4701  * tcp_try_coalesce - try to merge skb to prior one
4702  * @sk: socket
4703  * @to: prior buffer
4704  * @from: buffer to add in queue
4705  * @fragstolen: pointer to boolean
4706  *
4707  * Before queueing skb @from after @to, try to merge them
4708  * to reduce overall memory use and queue lengths, if cost is small.
4709  * Packets in ofo or receive queues can stay a long time.
4710  * Better try to coalesce them right now to avoid future collapses.
4711  * Returns true if caller should free @from instead of queueing it
4712  */
4713 static bool tcp_try_coalesce(struct sock *sk,
4714 			     struct sk_buff *to,
4715 			     struct sk_buff *from,
4716 			     bool *fragstolen)
4717 {
4718 	int delta;
4719 
4720 	*fragstolen = false;
4721 
4722 	/* Its possible this segment overlaps with prior segment in queue */
4723 	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4724 		return false;
4725 
4726 	if (!mptcp_skb_can_collapse(to, from))
4727 		return false;
4728 
4729 #ifdef CONFIG_TLS_DEVICE
4730 	if (from->decrypted != to->decrypted)
4731 		return false;
4732 #endif
4733 
4734 	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4735 		return false;
4736 
4737 	atomic_add(delta, &sk->sk_rmem_alloc);
4738 	sk_mem_charge(sk, delta);
4739 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4740 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4741 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4742 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4743 
4744 	if (TCP_SKB_CB(from)->has_rxtstamp) {
4745 		TCP_SKB_CB(to)->has_rxtstamp = true;
4746 		to->tstamp = from->tstamp;
4747 		skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4748 	}
4749 
4750 	return true;
4751 }
4752 
4753 static bool tcp_ooo_try_coalesce(struct sock *sk,
4754 			     struct sk_buff *to,
4755 			     struct sk_buff *from,
4756 			     bool *fragstolen)
4757 {
4758 	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4759 
4760 	/* In case tcp_drop_reason() is called later, update to->gso_segs */
4761 	if (res) {
4762 		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4763 			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
4764 
4765 		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4766 	}
4767 	return res;
4768 }
4769 
4770 static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
4771 			    enum skb_drop_reason reason)
4772 {
4773 	sk_drops_add(sk, skb);
4774 	kfree_skb_reason(skb, reason);
4775 }
4776 
4777 /* This one checks to see if we can put data from the
4778  * out_of_order queue into the receive_queue.
4779  */
4780 static void tcp_ofo_queue(struct sock *sk)
4781 {
4782 	struct tcp_sock *tp = tcp_sk(sk);
4783 	__u32 dsack_high = tp->rcv_nxt;
4784 	bool fin, fragstolen, eaten;
4785 	struct sk_buff *skb, *tail;
4786 	struct rb_node *p;
4787 
4788 	p = rb_first(&tp->out_of_order_queue);
4789 	while (p) {
4790 		skb = rb_to_skb(p);
4791 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4792 			break;
4793 
4794 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4795 			__u32 dsack = dsack_high;
4796 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4797 				dsack_high = TCP_SKB_CB(skb)->end_seq;
4798 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4799 		}
4800 		p = rb_next(p);
4801 		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4802 
4803 		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4804 			tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP);
4805 			continue;
4806 		}
4807 
4808 		tail = skb_peek_tail(&sk->sk_receive_queue);
4809 		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4810 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4811 		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4812 		if (!eaten)
4813 			__skb_queue_tail(&sk->sk_receive_queue, skb);
4814 		else
4815 			kfree_skb_partial(skb, fragstolen);
4816 
4817 		if (unlikely(fin)) {
4818 			tcp_fin(sk);
4819 			/* tcp_fin() purges tp->out_of_order_queue,
4820 			 * so we must end this loop right now.
4821 			 */
4822 			break;
4823 		}
4824 	}
4825 }
4826 
4827 static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb);
4828 static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb);
4829 
4830 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4831 				 unsigned int size)
4832 {
4833 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4834 	    !sk_rmem_schedule(sk, skb, size)) {
4835 
4836 		if (tcp_prune_queue(sk, skb) < 0)
4837 			return -1;
4838 
4839 		while (!sk_rmem_schedule(sk, skb, size)) {
4840 			if (!tcp_prune_ofo_queue(sk, skb))
4841 				return -1;
4842 		}
4843 	}
4844 	return 0;
4845 }
4846 
4847 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4848 {
4849 	struct tcp_sock *tp = tcp_sk(sk);
4850 	struct rb_node **p, *parent;
4851 	struct sk_buff *skb1;
4852 	u32 seq, end_seq;
4853 	bool fragstolen;
4854 
4855 	tcp_ecn_check_ce(sk, skb);
4856 
4857 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4858 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4859 		sk->sk_data_ready(sk);
4860 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM);
4861 		return;
4862 	}
4863 
4864 	/* Disable header prediction. */
4865 	tp->pred_flags = 0;
4866 	inet_csk_schedule_ack(sk);
4867 
4868 	tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4869 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4870 	seq = TCP_SKB_CB(skb)->seq;
4871 	end_seq = TCP_SKB_CB(skb)->end_seq;
4872 
4873 	p = &tp->out_of_order_queue.rb_node;
4874 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4875 		/* Initial out of order segment, build 1 SACK. */
4876 		if (tcp_is_sack(tp)) {
4877 			tp->rx_opt.num_sacks = 1;
4878 			tp->selective_acks[0].start_seq = seq;
4879 			tp->selective_acks[0].end_seq = end_seq;
4880 		}
4881 		rb_link_node(&skb->rbnode, NULL, p);
4882 		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4883 		tp->ooo_last_skb = skb;
4884 		goto end;
4885 	}
4886 
4887 	/* In the typical case, we are adding an skb to the end of the list.
4888 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4889 	 */
4890 	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
4891 				 skb, &fragstolen)) {
4892 coalesce_done:
4893 		/* For non sack flows, do not grow window to force DUPACK
4894 		 * and trigger fast retransmit.
4895 		 */
4896 		if (tcp_is_sack(tp))
4897 			tcp_grow_window(sk, skb, true);
4898 		kfree_skb_partial(skb, fragstolen);
4899 		skb = NULL;
4900 		goto add_sack;
4901 	}
4902 	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4903 	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4904 		parent = &tp->ooo_last_skb->rbnode;
4905 		p = &parent->rb_right;
4906 		goto insert;
4907 	}
4908 
4909 	/* Find place to insert this segment. Handle overlaps on the way. */
4910 	parent = NULL;
4911 	while (*p) {
4912 		parent = *p;
4913 		skb1 = rb_to_skb(parent);
4914 		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4915 			p = &parent->rb_left;
4916 			continue;
4917 		}
4918 		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4919 			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4920 				/* All the bits are present. Drop. */
4921 				NET_INC_STATS(sock_net(sk),
4922 					      LINUX_MIB_TCPOFOMERGE);
4923 				tcp_drop_reason(sk, skb,
4924 						SKB_DROP_REASON_TCP_OFOMERGE);
4925 				skb = NULL;
4926 				tcp_dsack_set(sk, seq, end_seq);
4927 				goto add_sack;
4928 			}
4929 			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4930 				/* Partial overlap. */
4931 				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4932 			} else {
4933 				/* skb's seq == skb1's seq and skb covers skb1.
4934 				 * Replace skb1 with skb.
4935 				 */
4936 				rb_replace_node(&skb1->rbnode, &skb->rbnode,
4937 						&tp->out_of_order_queue);
4938 				tcp_dsack_extend(sk,
4939 						 TCP_SKB_CB(skb1)->seq,
4940 						 TCP_SKB_CB(skb1)->end_seq);
4941 				NET_INC_STATS(sock_net(sk),
4942 					      LINUX_MIB_TCPOFOMERGE);
4943 				tcp_drop_reason(sk, skb1,
4944 						SKB_DROP_REASON_TCP_OFOMERGE);
4945 				goto merge_right;
4946 			}
4947 		} else if (tcp_ooo_try_coalesce(sk, skb1,
4948 						skb, &fragstolen)) {
4949 			goto coalesce_done;
4950 		}
4951 		p = &parent->rb_right;
4952 	}
4953 insert:
4954 	/* Insert segment into RB tree. */
4955 	rb_link_node(&skb->rbnode, parent, p);
4956 	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4957 
4958 merge_right:
4959 	/* Remove other segments covered by skb. */
4960 	while ((skb1 = skb_rb_next(skb)) != NULL) {
4961 		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4962 			break;
4963 		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4964 			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4965 					 end_seq);
4966 			break;
4967 		}
4968 		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4969 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4970 				 TCP_SKB_CB(skb1)->end_seq);
4971 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4972 		tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE);
4973 	}
4974 	/* If there is no skb after us, we are the last_skb ! */
4975 	if (!skb1)
4976 		tp->ooo_last_skb = skb;
4977 
4978 add_sack:
4979 	if (tcp_is_sack(tp))
4980 		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4981 end:
4982 	if (skb) {
4983 		/* For non sack flows, do not grow window to force DUPACK
4984 		 * and trigger fast retransmit.
4985 		 */
4986 		if (tcp_is_sack(tp))
4987 			tcp_grow_window(sk, skb, false);
4988 		skb_condense(skb);
4989 		skb_set_owner_r(skb, sk);
4990 	}
4991 }
4992 
4993 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
4994 				      bool *fragstolen)
4995 {
4996 	int eaten;
4997 	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4998 
4999 	eaten = (tail &&
5000 		 tcp_try_coalesce(sk, tail,
5001 				  skb, fragstolen)) ? 1 : 0;
5002 	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
5003 	if (!eaten) {
5004 		__skb_queue_tail(&sk->sk_receive_queue, skb);
5005 		skb_set_owner_r(skb, sk);
5006 	}
5007 	return eaten;
5008 }
5009 
5010 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
5011 {
5012 	struct sk_buff *skb;
5013 	int err = -ENOMEM;
5014 	int data_len = 0;
5015 	bool fragstolen;
5016 
5017 	if (size == 0)
5018 		return 0;
5019 
5020 	if (size > PAGE_SIZE) {
5021 		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
5022 
5023 		data_len = npages << PAGE_SHIFT;
5024 		size = data_len + (size & ~PAGE_MASK);
5025 	}
5026 	skb = alloc_skb_with_frags(size - data_len, data_len,
5027 				   PAGE_ALLOC_COSTLY_ORDER,
5028 				   &err, sk->sk_allocation);
5029 	if (!skb)
5030 		goto err;
5031 
5032 	skb_put(skb, size - data_len);
5033 	skb->data_len = data_len;
5034 	skb->len = size;
5035 
5036 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5037 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5038 		goto err_free;
5039 	}
5040 
5041 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
5042 	if (err)
5043 		goto err_free;
5044 
5045 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
5046 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
5047 	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
5048 
5049 	if (tcp_queue_rcv(sk, skb, &fragstolen)) {
5050 		WARN_ON_ONCE(fragstolen); /* should not happen */
5051 		__kfree_skb(skb);
5052 	}
5053 	return size;
5054 
5055 err_free:
5056 	kfree_skb(skb);
5057 err:
5058 	return err;
5059 
5060 }
5061 
5062 void tcp_data_ready(struct sock *sk)
5063 {
5064 	if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
5065 		sk->sk_data_ready(sk);
5066 }
5067 
5068 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
5069 {
5070 	struct tcp_sock *tp = tcp_sk(sk);
5071 	enum skb_drop_reason reason;
5072 	bool fragstolen;
5073 	int eaten;
5074 
5075 	/* If a subflow has been reset, the packet should not continue
5076 	 * to be processed, drop the packet.
5077 	 */
5078 	if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
5079 		__kfree_skb(skb);
5080 		return;
5081 	}
5082 
5083 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
5084 		__kfree_skb(skb);
5085 		return;
5086 	}
5087 	skb_dst_drop(skb);
5088 	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
5089 
5090 	reason = SKB_DROP_REASON_NOT_SPECIFIED;
5091 	tp->rx_opt.dsack = 0;
5092 
5093 	/*  Queue data for delivery to the user.
5094 	 *  Packets in sequence go to the receive queue.
5095 	 *  Out of sequence packets to the out_of_order_queue.
5096 	 */
5097 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5098 		if (tcp_receive_window(tp) == 0) {
5099 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5100 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5101 			goto out_of_window;
5102 		}
5103 
5104 		/* Ok. In sequence. In window. */
5105 queue_and_out:
5106 		if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5107 			/* TODO: maybe ratelimit these WIN 0 ACK ? */
5108 			inet_csk(sk)->icsk_ack.pending |=
5109 					(ICSK_ACK_NOMEM | ICSK_ACK_NOW);
5110 			inet_csk_schedule_ack(sk);
5111 			sk->sk_data_ready(sk);
5112 
5113 			if (skb_queue_len(&sk->sk_receive_queue)) {
5114 				reason = SKB_DROP_REASON_PROTO_MEM;
5115 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5116 				goto drop;
5117 			}
5118 			sk_forced_mem_schedule(sk, skb->truesize);
5119 		}
5120 
5121 		eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5122 		if (skb->len)
5123 			tcp_event_data_recv(sk, skb);
5124 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
5125 			tcp_fin(sk);
5126 
5127 		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5128 			tcp_ofo_queue(sk);
5129 
5130 			/* RFC5681. 4.2. SHOULD send immediate ACK, when
5131 			 * gap in queue is filled.
5132 			 */
5133 			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5134 				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
5135 		}
5136 
5137 		if (tp->rx_opt.num_sacks)
5138 			tcp_sack_remove(tp);
5139 
5140 		tcp_fast_path_check(sk);
5141 
5142 		if (eaten > 0)
5143 			kfree_skb_partial(skb, fragstolen);
5144 		if (!sock_flag(sk, SOCK_DEAD))
5145 			tcp_data_ready(sk);
5146 		return;
5147 	}
5148 
5149 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
5150 		tcp_rcv_spurious_retrans(sk, skb);
5151 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
5152 		reason = SKB_DROP_REASON_TCP_OLD_DATA;
5153 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
5154 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5155 
5156 out_of_window:
5157 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5158 		inet_csk_schedule_ack(sk);
5159 drop:
5160 		tcp_drop_reason(sk, skb, reason);
5161 		return;
5162 	}
5163 
5164 	/* Out of window. F.e. zero window probe. */
5165 	if (!before(TCP_SKB_CB(skb)->seq,
5166 		    tp->rcv_nxt + tcp_receive_window(tp))) {
5167 		reason = SKB_DROP_REASON_TCP_OVERWINDOW;
5168 		goto out_of_window;
5169 	}
5170 
5171 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5172 		/* Partial packet, seq < rcv_next < end_seq */
5173 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
5174 
5175 		/* If window is closed, drop tail of packet. But after
5176 		 * remembering D-SACK for its head made in previous line.
5177 		 */
5178 		if (!tcp_receive_window(tp)) {
5179 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5180 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5181 			goto out_of_window;
5182 		}
5183 		goto queue_and_out;
5184 	}
5185 
5186 	tcp_data_queue_ofo(sk, skb);
5187 }
5188 
5189 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
5190 {
5191 	if (list)
5192 		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
5193 
5194 	return skb_rb_next(skb);
5195 }
5196 
5197 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
5198 					struct sk_buff_head *list,
5199 					struct rb_root *root)
5200 {
5201 	struct sk_buff *next = tcp_skb_next(skb, list);
5202 
5203 	if (list)
5204 		__skb_unlink(skb, list);
5205 	else
5206 		rb_erase(&skb->rbnode, root);
5207 
5208 	__kfree_skb(skb);
5209 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
5210 
5211 	return next;
5212 }
5213 
5214 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
5215 void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
5216 {
5217 	struct rb_node **p = &root->rb_node;
5218 	struct rb_node *parent = NULL;
5219 	struct sk_buff *skb1;
5220 
5221 	while (*p) {
5222 		parent = *p;
5223 		skb1 = rb_to_skb(parent);
5224 		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
5225 			p = &parent->rb_left;
5226 		else
5227 			p = &parent->rb_right;
5228 	}
5229 	rb_link_node(&skb->rbnode, parent, p);
5230 	rb_insert_color(&skb->rbnode, root);
5231 }
5232 
5233 /* Collapse contiguous sequence of skbs head..tail with
5234  * sequence numbers start..end.
5235  *
5236  * If tail is NULL, this means until the end of the queue.
5237  *
5238  * Segments with FIN/SYN are not collapsed (only because this
5239  * simplifies code)
5240  */
5241 static void
5242 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
5243 	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
5244 {
5245 	struct sk_buff *skb = head, *n;
5246 	struct sk_buff_head tmp;
5247 	bool end_of_skbs;
5248 
5249 	/* First, check that queue is collapsible and find
5250 	 * the point where collapsing can be useful.
5251 	 */
5252 restart:
5253 	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
5254 		n = tcp_skb_next(skb, list);
5255 
5256 		/* No new bits? It is possible on ofo queue. */
5257 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5258 			skb = tcp_collapse_one(sk, skb, list, root);
5259 			if (!skb)
5260 				break;
5261 			goto restart;
5262 		}
5263 
5264 		/* The first skb to collapse is:
5265 		 * - not SYN/FIN and
5266 		 * - bloated or contains data before "start" or
5267 		 *   overlaps to the next one and mptcp allow collapsing.
5268 		 */
5269 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
5270 		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
5271 		     before(TCP_SKB_CB(skb)->seq, start))) {
5272 			end_of_skbs = false;
5273 			break;
5274 		}
5275 
5276 		if (n && n != tail && mptcp_skb_can_collapse(skb, n) &&
5277 		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
5278 			end_of_skbs = false;
5279 			break;
5280 		}
5281 
5282 		/* Decided to skip this, advance start seq. */
5283 		start = TCP_SKB_CB(skb)->end_seq;
5284 	}
5285 	if (end_of_skbs ||
5286 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5287 		return;
5288 
5289 	__skb_queue_head_init(&tmp);
5290 
5291 	while (before(start, end)) {
5292 		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
5293 		struct sk_buff *nskb;
5294 
5295 		nskb = alloc_skb(copy, GFP_ATOMIC);
5296 		if (!nskb)
5297 			break;
5298 
5299 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
5300 #ifdef CONFIG_TLS_DEVICE
5301 		nskb->decrypted = skb->decrypted;
5302 #endif
5303 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
5304 		if (list)
5305 			__skb_queue_before(list, skb, nskb);
5306 		else
5307 			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
5308 		skb_set_owner_r(nskb, sk);
5309 		mptcp_skb_ext_move(nskb, skb);
5310 
5311 		/* Copy data, releasing collapsed skbs. */
5312 		while (copy > 0) {
5313 			int offset = start - TCP_SKB_CB(skb)->seq;
5314 			int size = TCP_SKB_CB(skb)->end_seq - start;
5315 
5316 			BUG_ON(offset < 0);
5317 			if (size > 0) {
5318 				size = min(copy, size);
5319 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
5320 					BUG();
5321 				TCP_SKB_CB(nskb)->end_seq += size;
5322 				copy -= size;
5323 				start += size;
5324 			}
5325 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5326 				skb = tcp_collapse_one(sk, skb, list, root);
5327 				if (!skb ||
5328 				    skb == tail ||
5329 				    !mptcp_skb_can_collapse(nskb, skb) ||
5330 				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5331 					goto end;
5332 #ifdef CONFIG_TLS_DEVICE
5333 				if (skb->decrypted != nskb->decrypted)
5334 					goto end;
5335 #endif
5336 			}
5337 		}
5338 	}
5339 end:
5340 	skb_queue_walk_safe(&tmp, skb, n)
5341 		tcp_rbtree_insert(root, skb);
5342 }
5343 
5344 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5345  * and tcp_collapse() them until all the queue is collapsed.
5346  */
5347 static void tcp_collapse_ofo_queue(struct sock *sk)
5348 {
5349 	struct tcp_sock *tp = tcp_sk(sk);
5350 	u32 range_truesize, sum_tiny = 0;
5351 	struct sk_buff *skb, *head;
5352 	u32 start, end;
5353 
5354 	skb = skb_rb_first(&tp->out_of_order_queue);
5355 new_range:
5356 	if (!skb) {
5357 		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5358 		return;
5359 	}
5360 	start = TCP_SKB_CB(skb)->seq;
5361 	end = TCP_SKB_CB(skb)->end_seq;
5362 	range_truesize = skb->truesize;
5363 
5364 	for (head = skb;;) {
5365 		skb = skb_rb_next(skb);
5366 
5367 		/* Range is terminated when we see a gap or when
5368 		 * we are at the queue end.
5369 		 */
5370 		if (!skb ||
5371 		    after(TCP_SKB_CB(skb)->seq, end) ||
5372 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5373 			/* Do not attempt collapsing tiny skbs */
5374 			if (range_truesize != head->truesize ||
5375 			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
5376 				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5377 					     head, skb, start, end);
5378 			} else {
5379 				sum_tiny += range_truesize;
5380 				if (sum_tiny > sk->sk_rcvbuf >> 3)
5381 					return;
5382 			}
5383 			goto new_range;
5384 		}
5385 
5386 		range_truesize += skb->truesize;
5387 		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5388 			start = TCP_SKB_CB(skb)->seq;
5389 		if (after(TCP_SKB_CB(skb)->end_seq, end))
5390 			end = TCP_SKB_CB(skb)->end_seq;
5391 	}
5392 }
5393 
5394 /*
5395  * Clean the out-of-order queue to make room.
5396  * We drop high sequences packets to :
5397  * 1) Let a chance for holes to be filled.
5398  *    This means we do not drop packets from ooo queue if their sequence
5399  *    is before incoming packet sequence.
5400  * 2) not add too big latencies if thousands of packets sit there.
5401  *    (But if application shrinks SO_RCVBUF, we could still end up
5402  *     freeing whole queue here)
5403  * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5404  *
5405  * Return true if queue has shrunk.
5406  */
5407 static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb)
5408 {
5409 	struct tcp_sock *tp = tcp_sk(sk);
5410 	struct rb_node *node, *prev;
5411 	bool pruned = false;
5412 	int goal;
5413 
5414 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5415 		return false;
5416 
5417 	goal = sk->sk_rcvbuf >> 3;
5418 	node = &tp->ooo_last_skb->rbnode;
5419 
5420 	do {
5421 		struct sk_buff *skb = rb_to_skb(node);
5422 
5423 		/* If incoming skb would land last in ofo queue, stop pruning. */
5424 		if (after(TCP_SKB_CB(in_skb)->seq, TCP_SKB_CB(skb)->seq))
5425 			break;
5426 		pruned = true;
5427 		prev = rb_prev(node);
5428 		rb_erase(node, &tp->out_of_order_queue);
5429 		goal -= skb->truesize;
5430 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
5431 		tp->ooo_last_skb = rb_to_skb(prev);
5432 		if (!prev || goal <= 0) {
5433 			if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5434 			    !tcp_under_memory_pressure(sk))
5435 				break;
5436 			goal = sk->sk_rcvbuf >> 3;
5437 		}
5438 		node = prev;
5439 	} while (node);
5440 
5441 	if (pruned) {
5442 		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5443 		/* Reset SACK state.  A conforming SACK implementation will
5444 		 * do the same at a timeout based retransmit.  When a connection
5445 		 * is in a sad state like this, we care only about integrity
5446 		 * of the connection not performance.
5447 		 */
5448 		if (tp->rx_opt.sack_ok)
5449 			tcp_sack_reset(&tp->rx_opt);
5450 	}
5451 	return pruned;
5452 }
5453 
5454 /* Reduce allocated memory if we can, trying to get
5455  * the socket within its memory limits again.
5456  *
5457  * Return less than zero if we should start dropping frames
5458  * until the socket owning process reads some of the data
5459  * to stabilize the situation.
5460  */
5461 static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
5462 {
5463 	struct tcp_sock *tp = tcp_sk(sk);
5464 
5465 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5466 
5467 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5468 		tcp_clamp_window(sk);
5469 	else if (tcp_under_memory_pressure(sk))
5470 		tcp_adjust_rcv_ssthresh(sk);
5471 
5472 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5473 		return 0;
5474 
5475 	tcp_collapse_ofo_queue(sk);
5476 	if (!skb_queue_empty(&sk->sk_receive_queue))
5477 		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5478 			     skb_peek(&sk->sk_receive_queue),
5479 			     NULL,
5480 			     tp->copied_seq, tp->rcv_nxt);
5481 
5482 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5483 		return 0;
5484 
5485 	/* Collapsing did not help, destructive actions follow.
5486 	 * This must not ever occur. */
5487 
5488 	tcp_prune_ofo_queue(sk, in_skb);
5489 
5490 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5491 		return 0;
5492 
5493 	/* If we are really being abused, tell the caller to silently
5494 	 * drop receive data on the floor.  It will get retransmitted
5495 	 * and hopefully then we'll have sufficient space.
5496 	 */
5497 	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5498 
5499 	/* Massive buffer overcommit. */
5500 	tp->pred_flags = 0;
5501 	return -1;
5502 }
5503 
5504 static bool tcp_should_expand_sndbuf(struct sock *sk)
5505 {
5506 	const struct tcp_sock *tp = tcp_sk(sk);
5507 
5508 	/* If the user specified a specific send buffer setting, do
5509 	 * not modify it.
5510 	 */
5511 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5512 		return false;
5513 
5514 	/* If we are under global TCP memory pressure, do not expand.  */
5515 	if (tcp_under_memory_pressure(sk)) {
5516 		int unused_mem = sk_unused_reserved_mem(sk);
5517 
5518 		/* Adjust sndbuf according to reserved mem. But make sure
5519 		 * it never goes below SOCK_MIN_SNDBUF.
5520 		 * See sk_stream_moderate_sndbuf() for more details.
5521 		 */
5522 		if (unused_mem > SOCK_MIN_SNDBUF)
5523 			WRITE_ONCE(sk->sk_sndbuf, unused_mem);
5524 
5525 		return false;
5526 	}
5527 
5528 	/* If we are under soft global TCP memory pressure, do not expand.  */
5529 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5530 		return false;
5531 
5532 	/* If we filled the congestion window, do not expand.  */
5533 	if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
5534 		return false;
5535 
5536 	return true;
5537 }
5538 
5539 static void tcp_new_space(struct sock *sk)
5540 {
5541 	struct tcp_sock *tp = tcp_sk(sk);
5542 
5543 	if (tcp_should_expand_sndbuf(sk)) {
5544 		tcp_sndbuf_expand(sk);
5545 		tp->snd_cwnd_stamp = tcp_jiffies32;
5546 	}
5547 
5548 	INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
5549 }
5550 
5551 /* Caller made space either from:
5552  * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced)
5553  * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt)
5554  *
5555  * We might be able to generate EPOLLOUT to the application if:
5556  * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2
5557  * 2) notsent amount (tp->write_seq - tp->snd_nxt) became
5558  *    small enough that tcp_stream_memory_free() decides it
5559  *    is time to generate EPOLLOUT.
5560  */
5561 void tcp_check_space(struct sock *sk)
5562 {
5563 	/* pairs with tcp_poll() */
5564 	smp_mb();
5565 	if (sk->sk_socket &&
5566 	    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5567 		tcp_new_space(sk);
5568 		if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5569 			tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5570 	}
5571 }
5572 
5573 static inline void tcp_data_snd_check(struct sock *sk)
5574 {
5575 	tcp_push_pending_frames(sk);
5576 	tcp_check_space(sk);
5577 }
5578 
5579 /*
5580  * Check if sending an ack is needed.
5581  */
5582 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5583 {
5584 	struct tcp_sock *tp = tcp_sk(sk);
5585 	unsigned long rtt, delay;
5586 
5587 	    /* More than one full frame received... */
5588 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5589 	     /* ... and right edge of window advances far enough.
5590 	      * (tcp_recvmsg() will send ACK otherwise).
5591 	      * If application uses SO_RCVLOWAT, we want send ack now if
5592 	      * we have not received enough bytes to satisfy the condition.
5593 	      */
5594 	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5595 	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5596 	    /* We ACK each frame or... */
5597 	    tcp_in_quickack_mode(sk) ||
5598 	    /* Protocol state mandates a one-time immediate ACK */
5599 	    inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5600 send_now:
5601 		tcp_send_ack(sk);
5602 		return;
5603 	}
5604 
5605 	if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5606 		tcp_send_delayed_ack(sk);
5607 		return;
5608 	}
5609 
5610 	if (!tcp_is_sack(tp) ||
5611 	    tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr))
5612 		goto send_now;
5613 
5614 	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5615 		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5616 		tp->dup_ack_counter = 0;
5617 	}
5618 	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
5619 		tp->dup_ack_counter++;
5620 		goto send_now;
5621 	}
5622 	tp->compressed_ack++;
5623 	if (hrtimer_is_queued(&tp->compressed_ack_timer))
5624 		return;
5625 
5626 	/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5627 
5628 	rtt = tp->rcv_rtt_est.rtt_us;
5629 	if (tp->srtt_us && tp->srtt_us < rtt)
5630 		rtt = tp->srtt_us;
5631 
5632 	delay = min_t(unsigned long,
5633 		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns),
5634 		      rtt * (NSEC_PER_USEC >> 3)/20);
5635 	sock_hold(sk);
5636 	hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
5637 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns),
5638 			       HRTIMER_MODE_REL_PINNED_SOFT);
5639 }
5640 
5641 static inline void tcp_ack_snd_check(struct sock *sk)
5642 {
5643 	if (!inet_csk_ack_scheduled(sk)) {
5644 		/* We sent a data segment already. */
5645 		return;
5646 	}
5647 	__tcp_ack_snd_check(sk, 1);
5648 }
5649 
5650 /*
5651  *	This routine is only called when we have urgent data
5652  *	signaled. Its the 'slow' part of tcp_urg. It could be
5653  *	moved inline now as tcp_urg is only called from one
5654  *	place. We handle URGent data wrong. We have to - as
5655  *	BSD still doesn't use the correction from RFC961.
5656  *	For 1003.1g we should support a new option TCP_STDURG to permit
5657  *	either form (or just set the sysctl tcp_stdurg).
5658  */
5659 
5660 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5661 {
5662 	struct tcp_sock *tp = tcp_sk(sk);
5663 	u32 ptr = ntohs(th->urg_ptr);
5664 
5665 	if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg))
5666 		ptr--;
5667 	ptr += ntohl(th->seq);
5668 
5669 	/* Ignore urgent data that we've already seen and read. */
5670 	if (after(tp->copied_seq, ptr))
5671 		return;
5672 
5673 	/* Do not replay urg ptr.
5674 	 *
5675 	 * NOTE: interesting situation not covered by specs.
5676 	 * Misbehaving sender may send urg ptr, pointing to segment,
5677 	 * which we already have in ofo queue. We are not able to fetch
5678 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5679 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5680 	 * situations. But it is worth to think about possibility of some
5681 	 * DoSes using some hypothetical application level deadlock.
5682 	 */
5683 	if (before(ptr, tp->rcv_nxt))
5684 		return;
5685 
5686 	/* Do we already have a newer (or duplicate) urgent pointer? */
5687 	if (tp->urg_data && !after(ptr, tp->urg_seq))
5688 		return;
5689 
5690 	/* Tell the world about our new urgent pointer. */
5691 	sk_send_sigurg(sk);
5692 
5693 	/* We may be adding urgent data when the last byte read was
5694 	 * urgent. To do this requires some care. We cannot just ignore
5695 	 * tp->copied_seq since we would read the last urgent byte again
5696 	 * as data, nor can we alter copied_seq until this data arrives
5697 	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5698 	 *
5699 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5700 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5701 	 * and expect that both A and B disappear from stream. This is _wrong_.
5702 	 * Though this happens in BSD with high probability, this is occasional.
5703 	 * Any application relying on this is buggy. Note also, that fix "works"
5704 	 * only in this artificial test. Insert some normal data between A and B and we will
5705 	 * decline of BSD again. Verdict: it is better to remove to trap
5706 	 * buggy users.
5707 	 */
5708 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5709 	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5710 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5711 		tp->copied_seq++;
5712 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5713 			__skb_unlink(skb, &sk->sk_receive_queue);
5714 			__kfree_skb(skb);
5715 		}
5716 	}
5717 
5718 	WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
5719 	WRITE_ONCE(tp->urg_seq, ptr);
5720 
5721 	/* Disable header prediction. */
5722 	tp->pred_flags = 0;
5723 }
5724 
5725 /* This is the 'fast' part of urgent handling. */
5726 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5727 {
5728 	struct tcp_sock *tp = tcp_sk(sk);
5729 
5730 	/* Check if we get a new urgent pointer - normally not. */
5731 	if (unlikely(th->urg))
5732 		tcp_check_urg(sk, th);
5733 
5734 	/* Do we wait for any urgent data? - normally not... */
5735 	if (unlikely(tp->urg_data == TCP_URG_NOTYET)) {
5736 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5737 			  th->syn;
5738 
5739 		/* Is the urgent pointer pointing into this packet? */
5740 		if (ptr < skb->len) {
5741 			u8 tmp;
5742 			if (skb_copy_bits(skb, ptr, &tmp, 1))
5743 				BUG();
5744 			WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
5745 			if (!sock_flag(sk, SOCK_DEAD))
5746 				sk->sk_data_ready(sk);
5747 		}
5748 	}
5749 }
5750 
5751 /* Accept RST for rcv_nxt - 1 after a FIN.
5752  * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5753  * FIN is sent followed by a RST packet. The RST is sent with the same
5754  * sequence number as the FIN, and thus according to RFC 5961 a challenge
5755  * ACK should be sent. However, Mac OSX rate limits replies to challenge
5756  * ACKs on the closed socket. In addition middleboxes can drop either the
5757  * challenge ACK or a subsequent RST.
5758  */
5759 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5760 {
5761 	const struct tcp_sock *tp = tcp_sk(sk);
5762 
5763 	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5764 			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5765 					       TCPF_CLOSING));
5766 }
5767 
5768 /* Does PAWS and seqno based validation of an incoming segment, flags will
5769  * play significant role here.
5770  */
5771 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5772 				  const struct tcphdr *th, int syn_inerr)
5773 {
5774 	struct tcp_sock *tp = tcp_sk(sk);
5775 	SKB_DR(reason);
5776 
5777 	/* RFC1323: H1. Apply PAWS check first. */
5778 	if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
5779 	    tp->rx_opt.saw_tstamp &&
5780 	    tcp_paws_discard(sk, skb)) {
5781 		if (!th->rst) {
5782 			if (unlikely(th->syn))
5783 				goto syn_challenge;
5784 			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5785 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5786 						  LINUX_MIB_TCPACKSKIPPEDPAWS,
5787 						  &tp->last_oow_ack_time))
5788 				tcp_send_dupack(sk, skb);
5789 			SKB_DR_SET(reason, TCP_RFC7323_PAWS);
5790 			goto discard;
5791 		}
5792 		/* Reset is accepted even if it did not pass PAWS. */
5793 	}
5794 
5795 	/* Step 1: check sequence number */
5796 	reason = tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5797 	if (reason) {
5798 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5799 		 * (RST) segments are validated by checking their SEQ-fields."
5800 		 * And page 69: "If an incoming segment is not acceptable,
5801 		 * an acknowledgment should be sent in reply (unless the RST
5802 		 * bit is set, if so drop the segment and return)".
5803 		 */
5804 		if (!th->rst) {
5805 			if (th->syn)
5806 				goto syn_challenge;
5807 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5808 						  LINUX_MIB_TCPACKSKIPPEDSEQ,
5809 						  &tp->last_oow_ack_time))
5810 				tcp_send_dupack(sk, skb);
5811 		} else if (tcp_reset_check(sk, skb)) {
5812 			goto reset;
5813 		}
5814 		goto discard;
5815 	}
5816 
5817 	/* Step 2: check RST bit */
5818 	if (th->rst) {
5819 		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
5820 		 * FIN and SACK too if available):
5821 		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
5822 		 * the right-most SACK block,
5823 		 * then
5824 		 *     RESET the connection
5825 		 * else
5826 		 *     Send a challenge ACK
5827 		 */
5828 		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
5829 		    tcp_reset_check(sk, skb))
5830 			goto reset;
5831 
5832 		if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
5833 			struct tcp_sack_block *sp = &tp->selective_acks[0];
5834 			int max_sack = sp[0].end_seq;
5835 			int this_sack;
5836 
5837 			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
5838 			     ++this_sack) {
5839 				max_sack = after(sp[this_sack].end_seq,
5840 						 max_sack) ?
5841 					sp[this_sack].end_seq : max_sack;
5842 			}
5843 
5844 			if (TCP_SKB_CB(skb)->seq == max_sack)
5845 				goto reset;
5846 		}
5847 
5848 		/* Disable TFO if RST is out-of-order
5849 		 * and no data has been received
5850 		 * for current active TFO socket
5851 		 */
5852 		if (tp->syn_fastopen && !tp->data_segs_in &&
5853 		    sk->sk_state == TCP_ESTABLISHED)
5854 			tcp_fastopen_active_disable(sk);
5855 		tcp_send_challenge_ack(sk);
5856 		SKB_DR_SET(reason, TCP_RESET);
5857 		goto discard;
5858 	}
5859 
5860 	/* step 3: check security and precedence [ignored] */
5861 
5862 	/* step 4: Check for a SYN
5863 	 * RFC 5961 4.2 : Send a challenge ack
5864 	 */
5865 	if (th->syn) {
5866 syn_challenge:
5867 		if (syn_inerr)
5868 			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5869 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5870 		tcp_send_challenge_ack(sk);
5871 		SKB_DR_SET(reason, TCP_INVALID_SYN);
5872 		goto discard;
5873 	}
5874 
5875 	bpf_skops_parse_hdr(sk, skb);
5876 
5877 	return true;
5878 
5879 discard:
5880 	tcp_drop_reason(sk, skb, reason);
5881 	return false;
5882 
5883 reset:
5884 	tcp_reset(sk, skb);
5885 	__kfree_skb(skb);
5886 	return false;
5887 }
5888 
5889 /*
5890  *	TCP receive function for the ESTABLISHED state.
5891  *
5892  *	It is split into a fast path and a slow path. The fast path is
5893  * 	disabled when:
5894  *	- A zero window was announced from us - zero window probing
5895  *        is only handled properly in the slow path.
5896  *	- Out of order segments arrived.
5897  *	- Urgent data is expected.
5898  *	- There is no buffer space left
5899  *	- Unexpected TCP flags/window values/header lengths are received
5900  *	  (detected by checking the TCP header against pred_flags)
5901  *	- Data is sent in both directions. Fast path only supports pure senders
5902  *	  or pure receivers (this means either the sequence number or the ack
5903  *	  value must stay constant)
5904  *	- Unexpected TCP option.
5905  *
5906  *	When these conditions are not satisfied it drops into a standard
5907  *	receive procedure patterned after RFC793 to handle all cases.
5908  *	The first three cases are guaranteed by proper pred_flags setting,
5909  *	the rest is checked inline. Fast processing is turned on in
5910  *	tcp_data_queue when everything is OK.
5911  */
5912 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
5913 {
5914 	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
5915 	const struct tcphdr *th = (const struct tcphdr *)skb->data;
5916 	struct tcp_sock *tp = tcp_sk(sk);
5917 	unsigned int len = skb->len;
5918 
5919 	/* TCP congestion window tracking */
5920 	trace_tcp_probe(sk, skb);
5921 
5922 	tcp_mstamp_refresh(tp);
5923 	if (unlikely(!rcu_access_pointer(sk->sk_rx_dst)))
5924 		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5925 	/*
5926 	 *	Header prediction.
5927 	 *	The code loosely follows the one in the famous
5928 	 *	"30 instruction TCP receive" Van Jacobson mail.
5929 	 *
5930 	 *	Van's trick is to deposit buffers into socket queue
5931 	 *	on a device interrupt, to call tcp_recv function
5932 	 *	on the receive process context and checksum and copy
5933 	 *	the buffer to user space. smart...
5934 	 *
5935 	 *	Our current scheme is not silly either but we take the
5936 	 *	extra cost of the net_bh soft interrupt processing...
5937 	 *	We do checksum and copy also but from device to kernel.
5938 	 */
5939 
5940 	tp->rx_opt.saw_tstamp = 0;
5941 
5942 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5943 	 *	if header_prediction is to be made
5944 	 *	'S' will always be tp->tcp_header_len >> 2
5945 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5946 	 *  turn it off	(when there are holes in the receive
5947 	 *	 space for instance)
5948 	 *	PSH flag is ignored.
5949 	 */
5950 
5951 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5952 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5953 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5954 		int tcp_header_len = tp->tcp_header_len;
5955 
5956 		/* Timestamp header prediction: tcp_header_len
5957 		 * is automatically equal to th->doff*4 due to pred_flags
5958 		 * match.
5959 		 */
5960 
5961 		/* Check timestamp */
5962 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5963 			/* No? Slow path! */
5964 			if (!tcp_parse_aligned_timestamp(tp, th))
5965 				goto slow_path;
5966 
5967 			/* If PAWS failed, check it more carefully in slow path */
5968 			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5969 				goto slow_path;
5970 
5971 			/* DO NOT update ts_recent here, if checksum fails
5972 			 * and timestamp was corrupted part, it will result
5973 			 * in a hung connection since we will drop all
5974 			 * future packets due to the PAWS test.
5975 			 */
5976 		}
5977 
5978 		if (len <= tcp_header_len) {
5979 			/* Bulk data transfer: sender */
5980 			if (len == tcp_header_len) {
5981 				/* Predicted packet is in window by definition.
5982 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5983 				 * Hence, check seq<=rcv_wup reduces to:
5984 				 */
5985 				if (tcp_header_len ==
5986 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5987 				    tp->rcv_nxt == tp->rcv_wup)
5988 					tcp_store_ts_recent(tp);
5989 
5990 				/* We know that such packets are checksummed
5991 				 * on entry.
5992 				 */
5993 				tcp_ack(sk, skb, 0);
5994 				__kfree_skb(skb);
5995 				tcp_data_snd_check(sk);
5996 				/* When receiving pure ack in fast path, update
5997 				 * last ts ecr directly instead of calling
5998 				 * tcp_rcv_rtt_measure_ts()
5999 				 */
6000 				tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
6001 				return;
6002 			} else { /* Header too small */
6003 				reason = SKB_DROP_REASON_PKT_TOO_SMALL;
6004 				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6005 				goto discard;
6006 			}
6007 		} else {
6008 			int eaten = 0;
6009 			bool fragstolen = false;
6010 
6011 			if (tcp_checksum_complete(skb))
6012 				goto csum_error;
6013 
6014 			if ((int)skb->truesize > sk->sk_forward_alloc)
6015 				goto step5;
6016 
6017 			/* Predicted packet is in window by definition.
6018 			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
6019 			 * Hence, check seq<=rcv_wup reduces to:
6020 			 */
6021 			if (tcp_header_len ==
6022 			    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
6023 			    tp->rcv_nxt == tp->rcv_wup)
6024 				tcp_store_ts_recent(tp);
6025 
6026 			tcp_rcv_rtt_measure_ts(sk, skb);
6027 
6028 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
6029 
6030 			/* Bulk data transfer: receiver */
6031 			skb_dst_drop(skb);
6032 			__skb_pull(skb, tcp_header_len);
6033 			eaten = tcp_queue_rcv(sk, skb, &fragstolen);
6034 
6035 			tcp_event_data_recv(sk, skb);
6036 
6037 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
6038 				/* Well, only one small jumplet in fast path... */
6039 				tcp_ack(sk, skb, FLAG_DATA);
6040 				tcp_data_snd_check(sk);
6041 				if (!inet_csk_ack_scheduled(sk))
6042 					goto no_ack;
6043 			} else {
6044 				tcp_update_wl(tp, TCP_SKB_CB(skb)->seq);
6045 			}
6046 
6047 			__tcp_ack_snd_check(sk, 0);
6048 no_ack:
6049 			if (eaten)
6050 				kfree_skb_partial(skb, fragstolen);
6051 			tcp_data_ready(sk);
6052 			return;
6053 		}
6054 	}
6055 
6056 slow_path:
6057 	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
6058 		goto csum_error;
6059 
6060 	if (!th->ack && !th->rst && !th->syn) {
6061 		reason = SKB_DROP_REASON_TCP_FLAGS;
6062 		goto discard;
6063 	}
6064 
6065 	/*
6066 	 *	Standard slow path.
6067 	 */
6068 
6069 	if (!tcp_validate_incoming(sk, skb, th, 1))
6070 		return;
6071 
6072 step5:
6073 	reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
6074 	if ((int)reason < 0) {
6075 		reason = -reason;
6076 		goto discard;
6077 	}
6078 	tcp_rcv_rtt_measure_ts(sk, skb);
6079 
6080 	/* Process urgent data. */
6081 	tcp_urg(sk, skb, th);
6082 
6083 	/* step 7: process the segment text */
6084 	tcp_data_queue(sk, skb);
6085 
6086 	tcp_data_snd_check(sk);
6087 	tcp_ack_snd_check(sk);
6088 	return;
6089 
6090 csum_error:
6091 	reason = SKB_DROP_REASON_TCP_CSUM;
6092 	trace_tcp_bad_csum(skb);
6093 	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
6094 	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6095 
6096 discard:
6097 	tcp_drop_reason(sk, skb, reason);
6098 }
6099 EXPORT_SYMBOL(tcp_rcv_established);
6100 
6101 void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
6102 {
6103 	struct inet_connection_sock *icsk = inet_csk(sk);
6104 	struct tcp_sock *tp = tcp_sk(sk);
6105 
6106 	tcp_mtup_init(sk);
6107 	icsk->icsk_af_ops->rebuild_header(sk);
6108 	tcp_init_metrics(sk);
6109 
6110 	/* Initialize the congestion window to start the transfer.
6111 	 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
6112 	 * retransmitted. In light of RFC6298 more aggressive 1sec
6113 	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
6114 	 * retransmission has occurred.
6115 	 */
6116 	if (tp->total_retrans > 1 && tp->undo_marker)
6117 		tcp_snd_cwnd_set(tp, 1);
6118 	else
6119 		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
6120 	tp->snd_cwnd_stamp = tcp_jiffies32;
6121 
6122 	bpf_skops_established(sk, bpf_op, skb);
6123 	/* Initialize congestion control unless BPF initialized it already: */
6124 	if (!icsk->icsk_ca_initialized)
6125 		tcp_init_congestion_control(sk);
6126 	tcp_init_buffer_space(sk);
6127 }
6128 
6129 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
6130 {
6131 	struct tcp_sock *tp = tcp_sk(sk);
6132 	struct inet_connection_sock *icsk = inet_csk(sk);
6133 
6134 	tcp_set_state(sk, TCP_ESTABLISHED);
6135 	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
6136 
6137 	if (skb) {
6138 		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
6139 		security_inet_conn_established(sk, skb);
6140 		sk_mark_napi_id(sk, skb);
6141 	}
6142 
6143 	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
6144 
6145 	/* Prevent spurious tcp_cwnd_restart() on first data
6146 	 * packet.
6147 	 */
6148 	tp->lsndtime = tcp_jiffies32;
6149 
6150 	if (sock_flag(sk, SOCK_KEEPOPEN))
6151 		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
6152 
6153 	if (!tp->rx_opt.snd_wscale)
6154 		__tcp_fast_path_on(tp, tp->snd_wnd);
6155 	else
6156 		tp->pred_flags = 0;
6157 }
6158 
6159 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
6160 				    struct tcp_fastopen_cookie *cookie)
6161 {
6162 	struct tcp_sock *tp = tcp_sk(sk);
6163 	struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
6164 	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
6165 	bool syn_drop = false;
6166 
6167 	if (mss == tp->rx_opt.user_mss) {
6168 		struct tcp_options_received opt;
6169 
6170 		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
6171 		tcp_clear_options(&opt);
6172 		opt.user_mss = opt.mss_clamp = 0;
6173 		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
6174 		mss = opt.mss_clamp;
6175 	}
6176 
6177 	if (!tp->syn_fastopen) {
6178 		/* Ignore an unsolicited cookie */
6179 		cookie->len = -1;
6180 	} else if (tp->total_retrans) {
6181 		/* SYN timed out and the SYN-ACK neither has a cookie nor
6182 		 * acknowledges data. Presumably the remote received only
6183 		 * the retransmitted (regular) SYNs: either the original
6184 		 * SYN-data or the corresponding SYN-ACK was dropped.
6185 		 */
6186 		syn_drop = (cookie->len < 0 && data);
6187 	} else if (cookie->len < 0 && !tp->syn_data) {
6188 		/* We requested a cookie but didn't get it. If we did not use
6189 		 * the (old) exp opt format then try so next time (try_exp=1).
6190 		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
6191 		 */
6192 		try_exp = tp->syn_fastopen_exp ? 2 : 1;
6193 	}
6194 
6195 	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
6196 
6197 	if (data) { /* Retransmit unacked data in SYN */
6198 		if (tp->total_retrans)
6199 			tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
6200 		else
6201 			tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
6202 		skb_rbtree_walk_from(data)
6203 			 tcp_mark_skb_lost(sk, data);
6204 		tcp_non_congestion_loss_retransmit(sk);
6205 		NET_INC_STATS(sock_net(sk),
6206 				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
6207 		return true;
6208 	}
6209 	tp->syn_data_acked = tp->syn_data;
6210 	if (tp->syn_data_acked) {
6211 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
6212 		/* SYN-data is counted as two separate packets in tcp_ack() */
6213 		if (tp->delivered > 1)
6214 			--tp->delivered;
6215 	}
6216 
6217 	tcp_fastopen_add_skb(sk, synack);
6218 
6219 	return false;
6220 }
6221 
6222 static void smc_check_reset_syn(struct tcp_sock *tp)
6223 {
6224 #if IS_ENABLED(CONFIG_SMC)
6225 	if (static_branch_unlikely(&tcp_have_smc)) {
6226 		if (tp->syn_smc && !tp->rx_opt.smc_ok)
6227 			tp->syn_smc = 0;
6228 	}
6229 #endif
6230 }
6231 
6232 static void tcp_try_undo_spurious_syn(struct sock *sk)
6233 {
6234 	struct tcp_sock *tp = tcp_sk(sk);
6235 	u32 syn_stamp;
6236 
6237 	/* undo_marker is set when SYN or SYNACK times out. The timeout is
6238 	 * spurious if the ACK's timestamp option echo value matches the
6239 	 * original SYN timestamp.
6240 	 */
6241 	syn_stamp = tp->retrans_stamp;
6242 	if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
6243 	    syn_stamp == tp->rx_opt.rcv_tsecr)
6244 		tp->undo_marker = 0;
6245 }
6246 
6247 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
6248 					 const struct tcphdr *th)
6249 {
6250 	struct inet_connection_sock *icsk = inet_csk(sk);
6251 	struct tcp_sock *tp = tcp_sk(sk);
6252 	struct tcp_fastopen_cookie foc = { .len = -1 };
6253 	int saved_clamp = tp->rx_opt.mss_clamp;
6254 	bool fastopen_fail;
6255 	SKB_DR(reason);
6256 
6257 	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
6258 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
6259 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
6260 
6261 	if (th->ack) {
6262 		/* rfc793:
6263 		 * "If the state is SYN-SENT then
6264 		 *    first check the ACK bit
6265 		 *      If the ACK bit is set
6266 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
6267 		 *        a reset (unless the RST bit is set, if so drop
6268 		 *        the segment and return)"
6269 		 */
6270 		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
6271 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6272 			/* Previous FIN/ACK or RST/ACK might be ignored. */
6273 			if (icsk->icsk_retransmits == 0)
6274 				inet_csk_reset_xmit_timer(sk,
6275 						ICSK_TIME_RETRANS,
6276 						TCP_TIMEOUT_MIN, TCP_RTO_MAX);
6277 			goto reset_and_undo;
6278 		}
6279 
6280 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
6281 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
6282 			     tcp_time_stamp(tp))) {
6283 			NET_INC_STATS(sock_net(sk),
6284 					LINUX_MIB_PAWSACTIVEREJECTED);
6285 			goto reset_and_undo;
6286 		}
6287 
6288 		/* Now ACK is acceptable.
6289 		 *
6290 		 * "If the RST bit is set
6291 		 *    If the ACK was acceptable then signal the user "error:
6292 		 *    connection reset", drop the segment, enter CLOSED state,
6293 		 *    delete TCB, and return."
6294 		 */
6295 
6296 		if (th->rst) {
6297 			tcp_reset(sk, skb);
6298 consume:
6299 			__kfree_skb(skb);
6300 			return 0;
6301 		}
6302 
6303 		/* rfc793:
6304 		 *   "fifth, if neither of the SYN or RST bits is set then
6305 		 *    drop the segment and return."
6306 		 *
6307 		 *    See note below!
6308 		 *                                        --ANK(990513)
6309 		 */
6310 		if (!th->syn) {
6311 			SKB_DR_SET(reason, TCP_FLAGS);
6312 			goto discard_and_undo;
6313 		}
6314 		/* rfc793:
6315 		 *   "If the SYN bit is on ...
6316 		 *    are acceptable then ...
6317 		 *    (our SYN has been ACKed), change the connection
6318 		 *    state to ESTABLISHED..."
6319 		 */
6320 
6321 		tcp_ecn_rcv_synack(tp, th);
6322 
6323 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6324 		tcp_try_undo_spurious_syn(sk);
6325 		tcp_ack(sk, skb, FLAG_SLOWPATH);
6326 
6327 		/* Ok.. it's good. Set up sequence numbers and
6328 		 * move to established.
6329 		 */
6330 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6331 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6332 
6333 		/* RFC1323: The window in SYN & SYN/ACK segments is
6334 		 * never scaled.
6335 		 */
6336 		tp->snd_wnd = ntohs(th->window);
6337 
6338 		if (!tp->rx_opt.wscale_ok) {
6339 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
6340 			tp->window_clamp = min(tp->window_clamp, 65535U);
6341 		}
6342 
6343 		if (tp->rx_opt.saw_tstamp) {
6344 			tp->rx_opt.tstamp_ok	   = 1;
6345 			tp->tcp_header_len =
6346 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6347 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
6348 			tcp_store_ts_recent(tp);
6349 		} else {
6350 			tp->tcp_header_len = sizeof(struct tcphdr);
6351 		}
6352 
6353 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6354 		tcp_initialize_rcv_mss(sk);
6355 
6356 		/* Remember, tcp_poll() does not lock socket!
6357 		 * Change state from SYN-SENT only after copied_seq
6358 		 * is initialized. */
6359 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6360 
6361 		smc_check_reset_syn(tp);
6362 
6363 		smp_mb();
6364 
6365 		tcp_finish_connect(sk, skb);
6366 
6367 		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
6368 				tcp_rcv_fastopen_synack(sk, skb, &foc);
6369 
6370 		if (!sock_flag(sk, SOCK_DEAD)) {
6371 			sk->sk_state_change(sk);
6372 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6373 		}
6374 		if (fastopen_fail)
6375 			return -1;
6376 		if (sk->sk_write_pending ||
6377 		    READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept) ||
6378 		    inet_csk_in_pingpong_mode(sk)) {
6379 			/* Save one ACK. Data will be ready after
6380 			 * several ticks, if write_pending is set.
6381 			 *
6382 			 * It may be deleted, but with this feature tcpdumps
6383 			 * look so _wonderfully_ clever, that I was not able
6384 			 * to stand against the temptation 8)     --ANK
6385 			 */
6386 			inet_csk_schedule_ack(sk);
6387 			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
6388 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
6389 						  TCP_DELACK_MAX, TCP_RTO_MAX);
6390 			goto consume;
6391 		}
6392 		tcp_send_ack(sk);
6393 		return -1;
6394 	}
6395 
6396 	/* No ACK in the segment */
6397 
6398 	if (th->rst) {
6399 		/* rfc793:
6400 		 * "If the RST bit is set
6401 		 *
6402 		 *      Otherwise (no ACK) drop the segment and return."
6403 		 */
6404 		SKB_DR_SET(reason, TCP_RESET);
6405 		goto discard_and_undo;
6406 	}
6407 
6408 	/* PAWS check. */
6409 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6410 	    tcp_paws_reject(&tp->rx_opt, 0)) {
6411 		SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6412 		goto discard_and_undo;
6413 	}
6414 	if (th->syn) {
6415 		/* We see SYN without ACK. It is attempt of
6416 		 * simultaneous connect with crossed SYNs.
6417 		 * Particularly, it can be connect to self.
6418 		 */
6419 		tcp_set_state(sk, TCP_SYN_RECV);
6420 
6421 		if (tp->rx_opt.saw_tstamp) {
6422 			tp->rx_opt.tstamp_ok = 1;
6423 			tcp_store_ts_recent(tp);
6424 			tp->tcp_header_len =
6425 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6426 		} else {
6427 			tp->tcp_header_len = sizeof(struct tcphdr);
6428 		}
6429 
6430 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6431 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6432 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6433 
6434 		/* RFC1323: The window in SYN & SYN/ACK segments is
6435 		 * never scaled.
6436 		 */
6437 		tp->snd_wnd    = ntohs(th->window);
6438 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
6439 		tp->max_window = tp->snd_wnd;
6440 
6441 		tcp_ecn_rcv_syn(tp, th);
6442 
6443 		tcp_mtup_init(sk);
6444 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6445 		tcp_initialize_rcv_mss(sk);
6446 
6447 		tcp_send_synack(sk);
6448 #if 0
6449 		/* Note, we could accept data and URG from this segment.
6450 		 * There are no obstacles to make this (except that we must
6451 		 * either change tcp_recvmsg() to prevent it from returning data
6452 		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6453 		 *
6454 		 * However, if we ignore data in ACKless segments sometimes,
6455 		 * we have no reasons to accept it sometimes.
6456 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6457 		 * is not flawless. So, discard packet for sanity.
6458 		 * Uncomment this return to process the data.
6459 		 */
6460 		return -1;
6461 #else
6462 		goto consume;
6463 #endif
6464 	}
6465 	/* "fifth, if neither of the SYN or RST bits is set then
6466 	 * drop the segment and return."
6467 	 */
6468 
6469 discard_and_undo:
6470 	tcp_clear_options(&tp->rx_opt);
6471 	tp->rx_opt.mss_clamp = saved_clamp;
6472 	tcp_drop_reason(sk, skb, reason);
6473 	return 0;
6474 
6475 reset_and_undo:
6476 	tcp_clear_options(&tp->rx_opt);
6477 	tp->rx_opt.mss_clamp = saved_clamp;
6478 	return 1;
6479 }
6480 
6481 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6482 {
6483 	struct tcp_sock *tp = tcp_sk(sk);
6484 	struct request_sock *req;
6485 
6486 	/* If we are still handling the SYNACK RTO, see if timestamp ECR allows
6487 	 * undo. If peer SACKs triggered fast recovery, we can't undo here.
6488 	 */
6489 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss && !tp->packets_out)
6490 		tcp_try_undo_recovery(sk);
6491 
6492 	/* Reset rtx states to prevent spurious retransmits_timed_out() */
6493 	tp->retrans_stamp = 0;
6494 	inet_csk(sk)->icsk_retransmits = 0;
6495 
6496 	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6497 	 * we no longer need req so release it.
6498 	 */
6499 	req = rcu_dereference_protected(tp->fastopen_rsk,
6500 					lockdep_sock_is_held(sk));
6501 	reqsk_fastopen_remove(sk, req, false);
6502 
6503 	/* Re-arm the timer because data may have been sent out.
6504 	 * This is similar to the regular data transmission case
6505 	 * when new data has just been ack'ed.
6506 	 *
6507 	 * (TFO) - we could try to be more aggressive and
6508 	 * retransmitting any data sooner based on when they
6509 	 * are sent out.
6510 	 */
6511 	tcp_rearm_rto(sk);
6512 }
6513 
6514 /*
6515  *	This function implements the receiving procedure of RFC 793 for
6516  *	all states except ESTABLISHED and TIME_WAIT.
6517  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6518  *	address independent.
6519  */
6520 
6521 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6522 {
6523 	struct tcp_sock *tp = tcp_sk(sk);
6524 	struct inet_connection_sock *icsk = inet_csk(sk);
6525 	const struct tcphdr *th = tcp_hdr(skb);
6526 	struct request_sock *req;
6527 	int queued = 0;
6528 	bool acceptable;
6529 	SKB_DR(reason);
6530 
6531 	switch (sk->sk_state) {
6532 	case TCP_CLOSE:
6533 		SKB_DR_SET(reason, TCP_CLOSE);
6534 		goto discard;
6535 
6536 	case TCP_LISTEN:
6537 		if (th->ack)
6538 			return 1;
6539 
6540 		if (th->rst) {
6541 			SKB_DR_SET(reason, TCP_RESET);
6542 			goto discard;
6543 		}
6544 		if (th->syn) {
6545 			if (th->fin) {
6546 				SKB_DR_SET(reason, TCP_FLAGS);
6547 				goto discard;
6548 			}
6549 			/* It is possible that we process SYN packets from backlog,
6550 			 * so we need to make sure to disable BH and RCU right there.
6551 			 */
6552 			rcu_read_lock();
6553 			local_bh_disable();
6554 			acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
6555 			local_bh_enable();
6556 			rcu_read_unlock();
6557 
6558 			if (!acceptable)
6559 				return 1;
6560 			consume_skb(skb);
6561 			return 0;
6562 		}
6563 		SKB_DR_SET(reason, TCP_FLAGS);
6564 		goto discard;
6565 
6566 	case TCP_SYN_SENT:
6567 		tp->rx_opt.saw_tstamp = 0;
6568 		tcp_mstamp_refresh(tp);
6569 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
6570 		if (queued >= 0)
6571 			return queued;
6572 
6573 		/* Do step6 onward by hand. */
6574 		tcp_urg(sk, skb, th);
6575 		__kfree_skb(skb);
6576 		tcp_data_snd_check(sk);
6577 		return 0;
6578 	}
6579 
6580 	tcp_mstamp_refresh(tp);
6581 	tp->rx_opt.saw_tstamp = 0;
6582 	req = rcu_dereference_protected(tp->fastopen_rsk,
6583 					lockdep_sock_is_held(sk));
6584 	if (req) {
6585 		bool req_stolen;
6586 
6587 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6588 		    sk->sk_state != TCP_FIN_WAIT1);
6589 
6590 		if (!tcp_check_req(sk, skb, req, true, &req_stolen)) {
6591 			SKB_DR_SET(reason, TCP_FASTOPEN);
6592 			goto discard;
6593 		}
6594 	}
6595 
6596 	if (!th->ack && !th->rst && !th->syn) {
6597 		SKB_DR_SET(reason, TCP_FLAGS);
6598 		goto discard;
6599 	}
6600 	if (!tcp_validate_incoming(sk, skb, th, 0))
6601 		return 0;
6602 
6603 	/* step 5: check the ACK field */
6604 	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
6605 				      FLAG_UPDATE_TS_RECENT |
6606 				      FLAG_NO_CHALLENGE_ACK) > 0;
6607 
6608 	if (!acceptable) {
6609 		if (sk->sk_state == TCP_SYN_RECV)
6610 			return 1;	/* send one RST */
6611 		tcp_send_challenge_ack(sk);
6612 		SKB_DR_SET(reason, TCP_OLD_ACK);
6613 		goto discard;
6614 	}
6615 	switch (sk->sk_state) {
6616 	case TCP_SYN_RECV:
6617 		tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
6618 		if (!tp->srtt_us)
6619 			tcp_synack_rtt_meas(sk, req);
6620 
6621 		if (req) {
6622 			tcp_rcv_synrecv_state_fastopen(sk);
6623 		} else {
6624 			tcp_try_undo_spurious_syn(sk);
6625 			tp->retrans_stamp = 0;
6626 			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
6627 					  skb);
6628 			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6629 		}
6630 		smp_mb();
6631 		tcp_set_state(sk, TCP_ESTABLISHED);
6632 		sk->sk_state_change(sk);
6633 
6634 		/* Note, that this wakeup is only for marginal crossed SYN case.
6635 		 * Passively open sockets are not waked up, because
6636 		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
6637 		 */
6638 		if (sk->sk_socket)
6639 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6640 
6641 		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6642 		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6643 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6644 
6645 		if (tp->rx_opt.tstamp_ok)
6646 			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6647 
6648 		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6649 			tcp_update_pacing_rate(sk);
6650 
6651 		/* Prevent spurious tcp_cwnd_restart() on first data packet */
6652 		tp->lsndtime = tcp_jiffies32;
6653 
6654 		tcp_initialize_rcv_mss(sk);
6655 		tcp_fast_path_on(tp);
6656 		if (sk->sk_shutdown & SEND_SHUTDOWN)
6657 			tcp_shutdown(sk, SEND_SHUTDOWN);
6658 		break;
6659 
6660 	case TCP_FIN_WAIT1: {
6661 		int tmo;
6662 
6663 		if (req)
6664 			tcp_rcv_synrecv_state_fastopen(sk);
6665 
6666 		if (tp->snd_una != tp->write_seq)
6667 			break;
6668 
6669 		tcp_set_state(sk, TCP_FIN_WAIT2);
6670 		WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | SEND_SHUTDOWN);
6671 
6672 		sk_dst_confirm(sk);
6673 
6674 		if (!sock_flag(sk, SOCK_DEAD)) {
6675 			/* Wake up lingering close() */
6676 			sk->sk_state_change(sk);
6677 			break;
6678 		}
6679 
6680 		if (READ_ONCE(tp->linger2) < 0) {
6681 			tcp_done(sk);
6682 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6683 			return 1;
6684 		}
6685 		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6686 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6687 			/* Receive out of order FIN after close() */
6688 			if (tp->syn_fastopen && th->fin)
6689 				tcp_fastopen_active_disable(sk);
6690 			tcp_done(sk);
6691 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6692 			return 1;
6693 		}
6694 
6695 		tmo = tcp_fin_time(sk);
6696 		if (tmo > TCP_TIMEWAIT_LEN) {
6697 			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6698 		} else if (th->fin || sock_owned_by_user(sk)) {
6699 			/* Bad case. We could lose such FIN otherwise.
6700 			 * It is not a big problem, but it looks confusing
6701 			 * and not so rare event. We still can lose it now,
6702 			 * if it spins in bh_lock_sock(), but it is really
6703 			 * marginal case.
6704 			 */
6705 			inet_csk_reset_keepalive_timer(sk, tmo);
6706 		} else {
6707 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6708 			goto consume;
6709 		}
6710 		break;
6711 	}
6712 
6713 	case TCP_CLOSING:
6714 		if (tp->snd_una == tp->write_seq) {
6715 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6716 			goto consume;
6717 		}
6718 		break;
6719 
6720 	case TCP_LAST_ACK:
6721 		if (tp->snd_una == tp->write_seq) {
6722 			tcp_update_metrics(sk);
6723 			tcp_done(sk);
6724 			goto consume;
6725 		}
6726 		break;
6727 	}
6728 
6729 	/* step 6: check the URG bit */
6730 	tcp_urg(sk, skb, th);
6731 
6732 	/* step 7: process the segment text */
6733 	switch (sk->sk_state) {
6734 	case TCP_CLOSE_WAIT:
6735 	case TCP_CLOSING:
6736 	case TCP_LAST_ACK:
6737 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
6738 			/* If a subflow has been reset, the packet should not
6739 			 * continue to be processed, drop the packet.
6740 			 */
6741 			if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
6742 				goto discard;
6743 			break;
6744 		}
6745 		fallthrough;
6746 	case TCP_FIN_WAIT1:
6747 	case TCP_FIN_WAIT2:
6748 		/* RFC 793 says to queue data in these states,
6749 		 * RFC 1122 says we MUST send a reset.
6750 		 * BSD 4.4 also does reset.
6751 		 */
6752 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
6753 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6754 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6755 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6756 				tcp_reset(sk, skb);
6757 				return 1;
6758 			}
6759 		}
6760 		fallthrough;
6761 	case TCP_ESTABLISHED:
6762 		tcp_data_queue(sk, skb);
6763 		queued = 1;
6764 		break;
6765 	}
6766 
6767 	/* tcp_data could move socket to TIME-WAIT */
6768 	if (sk->sk_state != TCP_CLOSE) {
6769 		tcp_data_snd_check(sk);
6770 		tcp_ack_snd_check(sk);
6771 	}
6772 
6773 	if (!queued) {
6774 discard:
6775 		tcp_drop_reason(sk, skb, reason);
6776 	}
6777 	return 0;
6778 
6779 consume:
6780 	__kfree_skb(skb);
6781 	return 0;
6782 }
6783 EXPORT_SYMBOL(tcp_rcv_state_process);
6784 
6785 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6786 {
6787 	struct inet_request_sock *ireq = inet_rsk(req);
6788 
6789 	if (family == AF_INET)
6790 		net_dbg_ratelimited("drop open request from %pI4/%u\n",
6791 				    &ireq->ir_rmt_addr, port);
6792 #if IS_ENABLED(CONFIG_IPV6)
6793 	else if (family == AF_INET6)
6794 		net_dbg_ratelimited("drop open request from %pI6/%u\n",
6795 				    &ireq->ir_v6_rmt_addr, port);
6796 #endif
6797 }
6798 
6799 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6800  *
6801  * If we receive a SYN packet with these bits set, it means a
6802  * network is playing bad games with TOS bits. In order to
6803  * avoid possible false congestion notifications, we disable
6804  * TCP ECN negotiation.
6805  *
6806  * Exception: tcp_ca wants ECN. This is required for DCTCP
6807  * congestion control: Linux DCTCP asserts ECT on all packets,
6808  * including SYN, which is most optimal solution; however,
6809  * others, such as FreeBSD do not.
6810  *
6811  * Exception: At least one of the reserved bits of the TCP header (th->res1) is
6812  * set, indicating the use of a future TCP extension (such as AccECN). See
6813  * RFC8311 §4.3 which updates RFC3168 to allow the development of such
6814  * extensions.
6815  */
6816 static void tcp_ecn_create_request(struct request_sock *req,
6817 				   const struct sk_buff *skb,
6818 				   const struct sock *listen_sk,
6819 				   const struct dst_entry *dst)
6820 {
6821 	const struct tcphdr *th = tcp_hdr(skb);
6822 	const struct net *net = sock_net(listen_sk);
6823 	bool th_ecn = th->ece && th->cwr;
6824 	bool ect, ecn_ok;
6825 	u32 ecn_ok_dst;
6826 
6827 	if (!th_ecn)
6828 		return;
6829 
6830 	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6831 	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6832 	ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst;
6833 
6834 	if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6835 	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
6836 	    tcp_bpf_ca_needs_ecn((struct sock *)req))
6837 		inet_rsk(req)->ecn_ok = 1;
6838 }
6839 
6840 static void tcp_openreq_init(struct request_sock *req,
6841 			     const struct tcp_options_received *rx_opt,
6842 			     struct sk_buff *skb, const struct sock *sk)
6843 {
6844 	struct inet_request_sock *ireq = inet_rsk(req);
6845 
6846 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
6847 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6848 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6849 	tcp_rsk(req)->snt_synack = 0;
6850 	tcp_rsk(req)->last_oow_ack_time = 0;
6851 	req->mss = rx_opt->mss_clamp;
6852 	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6853 	ireq->tstamp_ok = rx_opt->tstamp_ok;
6854 	ireq->sack_ok = rx_opt->sack_ok;
6855 	ireq->snd_wscale = rx_opt->snd_wscale;
6856 	ireq->wscale_ok = rx_opt->wscale_ok;
6857 	ireq->acked = 0;
6858 	ireq->ecn_ok = 0;
6859 	ireq->ir_rmt_port = tcp_hdr(skb)->source;
6860 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6861 	ireq->ir_mark = inet_request_mark(sk, skb);
6862 #if IS_ENABLED(CONFIG_SMC)
6863 	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested &&
6864 			tcp_sk(sk)->smc_hs_congested(sk));
6865 #endif
6866 }
6867 
6868 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6869 				      struct sock *sk_listener,
6870 				      bool attach_listener)
6871 {
6872 	struct request_sock *req = reqsk_alloc(ops, sk_listener,
6873 					       attach_listener);
6874 
6875 	if (req) {
6876 		struct inet_request_sock *ireq = inet_rsk(req);
6877 
6878 		ireq->ireq_opt = NULL;
6879 #if IS_ENABLED(CONFIG_IPV6)
6880 		ireq->pktopts = NULL;
6881 #endif
6882 		atomic64_set(&ireq->ir_cookie, 0);
6883 		ireq->ireq_state = TCP_NEW_SYN_RECV;
6884 		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6885 		ireq->ireq_family = sk_listener->sk_family;
6886 		req->timeout = TCP_TIMEOUT_INIT;
6887 	}
6888 
6889 	return req;
6890 }
6891 EXPORT_SYMBOL(inet_reqsk_alloc);
6892 
6893 /*
6894  * Return true if a syncookie should be sent
6895  */
6896 static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
6897 {
6898 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6899 	const char *msg = "Dropping request";
6900 	struct net *net = sock_net(sk);
6901 	bool want_cookie = false;
6902 	u8 syncookies;
6903 
6904 	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6905 
6906 #ifdef CONFIG_SYN_COOKIES
6907 	if (syncookies) {
6908 		msg = "Sending cookies";
6909 		want_cookie = true;
6910 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6911 	} else
6912 #endif
6913 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6914 
6915 	if (!READ_ONCE(queue->synflood_warned) && syncookies != 2 &&
6916 	    xchg(&queue->synflood_warned, 1) == 0) {
6917 		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
6918 			net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
6919 					proto, inet6_rcv_saddr(sk),
6920 					sk->sk_num, msg);
6921 		} else {
6922 			net_info_ratelimited("%s: Possible SYN flooding on port %pI4:%u. %s.\n",
6923 					proto, &sk->sk_rcv_saddr,
6924 					sk->sk_num, msg);
6925 		}
6926 	}
6927 
6928 	return want_cookie;
6929 }
6930 
6931 static void tcp_reqsk_record_syn(const struct sock *sk,
6932 				 struct request_sock *req,
6933 				 const struct sk_buff *skb)
6934 {
6935 	if (tcp_sk(sk)->save_syn) {
6936 		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6937 		struct saved_syn *saved_syn;
6938 		u32 mac_hdrlen;
6939 		void *base;
6940 
6941 		if (tcp_sk(sk)->save_syn == 2) {  /* Save full header. */
6942 			base = skb_mac_header(skb);
6943 			mac_hdrlen = skb_mac_header_len(skb);
6944 			len += mac_hdrlen;
6945 		} else {
6946 			base = skb_network_header(skb);
6947 			mac_hdrlen = 0;
6948 		}
6949 
6950 		saved_syn = kmalloc(struct_size(saved_syn, data, len),
6951 				    GFP_ATOMIC);
6952 		if (saved_syn) {
6953 			saved_syn->mac_hdrlen = mac_hdrlen;
6954 			saved_syn->network_hdrlen = skb_network_header_len(skb);
6955 			saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
6956 			memcpy(saved_syn->data, base, len);
6957 			req->saved_syn = saved_syn;
6958 		}
6959 	}
6960 }
6961 
6962 /* If a SYN cookie is required and supported, returns a clamped MSS value to be
6963  * used for SYN cookie generation.
6964  */
6965 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
6966 			  const struct tcp_request_sock_ops *af_ops,
6967 			  struct sock *sk, struct tcphdr *th)
6968 {
6969 	struct tcp_sock *tp = tcp_sk(sk);
6970 	u16 mss;
6971 
6972 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
6973 	    !inet_csk_reqsk_queue_is_full(sk))
6974 		return 0;
6975 
6976 	if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
6977 		return 0;
6978 
6979 	if (sk_acceptq_is_full(sk)) {
6980 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6981 		return 0;
6982 	}
6983 
6984 	mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
6985 	if (!mss)
6986 		mss = af_ops->mss_clamp;
6987 
6988 	return mss;
6989 }
6990 EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
6991 
6992 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6993 		     const struct tcp_request_sock_ops *af_ops,
6994 		     struct sock *sk, struct sk_buff *skb)
6995 {
6996 	struct tcp_fastopen_cookie foc = { .len = -1 };
6997 	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6998 	struct tcp_options_received tmp_opt;
6999 	struct tcp_sock *tp = tcp_sk(sk);
7000 	struct net *net = sock_net(sk);
7001 	struct sock *fastopen_sk = NULL;
7002 	struct request_sock *req;
7003 	bool want_cookie = false;
7004 	struct dst_entry *dst;
7005 	struct flowi fl;
7006 	u8 syncookies;
7007 
7008 	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
7009 
7010 	/* TW buckets are converted to open requests without
7011 	 * limitations, they conserve resources and peer is
7012 	 * evidently real one.
7013 	 */
7014 	if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
7015 		want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
7016 		if (!want_cookie)
7017 			goto drop;
7018 	}
7019 
7020 	if (sk_acceptq_is_full(sk)) {
7021 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
7022 		goto drop;
7023 	}
7024 
7025 	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
7026 	if (!req)
7027 		goto drop;
7028 
7029 	req->syncookie = want_cookie;
7030 	tcp_rsk(req)->af_specific = af_ops;
7031 	tcp_rsk(req)->ts_off = 0;
7032 #if IS_ENABLED(CONFIG_MPTCP)
7033 	tcp_rsk(req)->is_mptcp = 0;
7034 #endif
7035 
7036 	tcp_clear_options(&tmp_opt);
7037 	tmp_opt.mss_clamp = af_ops->mss_clamp;
7038 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
7039 	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
7040 			  want_cookie ? NULL : &foc);
7041 
7042 	if (want_cookie && !tmp_opt.saw_tstamp)
7043 		tcp_clear_options(&tmp_opt);
7044 
7045 	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
7046 		tmp_opt.smc_ok = 0;
7047 
7048 	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
7049 	tcp_openreq_init(req, &tmp_opt, skb, sk);
7050 	inet_rsk(req)->no_srccheck = inet_test_bit(TRANSPARENT, sk);
7051 
7052 	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
7053 	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
7054 
7055 	dst = af_ops->route_req(sk, skb, &fl, req);
7056 	if (!dst)
7057 		goto drop_and_free;
7058 
7059 	if (tmp_opt.tstamp_ok)
7060 		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
7061 
7062 	if (!want_cookie && !isn) {
7063 		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
7064 
7065 		/* Kill the following clause, if you dislike this way. */
7066 		if (!syncookies &&
7067 		    (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
7068 		     (max_syn_backlog >> 2)) &&
7069 		    !tcp_peer_is_proven(req, dst)) {
7070 			/* Without syncookies last quarter of
7071 			 * backlog is filled with destinations,
7072 			 * proven to be alive.
7073 			 * It means that we continue to communicate
7074 			 * to destinations, already remembered
7075 			 * to the moment of synflood.
7076 			 */
7077 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
7078 				    rsk_ops->family);
7079 			goto drop_and_release;
7080 		}
7081 
7082 		isn = af_ops->init_seq(skb);
7083 	}
7084 
7085 	tcp_ecn_create_request(req, skb, sk, dst);
7086 
7087 	if (want_cookie) {
7088 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
7089 		if (!tmp_opt.tstamp_ok)
7090 			inet_rsk(req)->ecn_ok = 0;
7091 	}
7092 
7093 	tcp_rsk(req)->snt_isn = isn;
7094 	tcp_rsk(req)->txhash = net_tx_rndhash();
7095 	tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
7096 	tcp_openreq_init_rwin(req, sk, dst);
7097 	sk_rx_queue_set(req_to_sk(req), skb);
7098 	if (!want_cookie) {
7099 		tcp_reqsk_record_syn(sk, req, skb);
7100 		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
7101 	}
7102 	if (fastopen_sk) {
7103 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
7104 				    &foc, TCP_SYNACK_FASTOPEN, skb);
7105 		/* Add the child socket directly into the accept queue */
7106 		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
7107 			reqsk_fastopen_remove(fastopen_sk, req, false);
7108 			bh_unlock_sock(fastopen_sk);
7109 			sock_put(fastopen_sk);
7110 			goto drop_and_free;
7111 		}
7112 		sk->sk_data_ready(sk);
7113 		bh_unlock_sock(fastopen_sk);
7114 		sock_put(fastopen_sk);
7115 	} else {
7116 		tcp_rsk(req)->tfo_listener = false;
7117 		if (!want_cookie) {
7118 			req->timeout = tcp_timeout_init((struct sock *)req);
7119 			if (unlikely(!inet_csk_reqsk_queue_hash_add(sk, req,
7120 								    req->timeout))) {
7121 				reqsk_free(req);
7122 				return 0;
7123 			}
7124 
7125 		}
7126 		af_ops->send_synack(sk, dst, &fl, req, &foc,
7127 				    !want_cookie ? TCP_SYNACK_NORMAL :
7128 						   TCP_SYNACK_COOKIE,
7129 				    skb);
7130 		if (want_cookie) {
7131 			reqsk_free(req);
7132 			return 0;
7133 		}
7134 	}
7135 	reqsk_put(req);
7136 	return 0;
7137 
7138 drop_and_release:
7139 	dst_release(dst);
7140 drop_and_free:
7141 	__reqsk_free(req);
7142 drop:
7143 	tcp_listendrop(sk);
7144 	return 0;
7145 }
7146 EXPORT_SYMBOL(tcp_conn_request);
7147