xref: /openbmc/linux/net/ipv4/tcp_input.c (revision 4da722ca)
1 /*
2  * INET		An implementation of the TCP/IP protocol suite for the LINUX
3  *		operating system.  INET is implemented using the  BSD Socket
4  *		interface as the means of communication with the user level.
5  *
6  *		Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Authors:	Ross Biro
9  *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10  *		Mark Evans, <evansmp@uhura.aston.ac.uk>
11  *		Corey Minyard <wf-rch!minyard@relay.EU.net>
12  *		Florian La Roche, <flla@stud.uni-sb.de>
13  *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14  *		Linus Torvalds, <torvalds@cs.helsinki.fi>
15  *		Alan Cox, <gw4pts@gw4pts.ampr.org>
16  *		Matthew Dillon, <dillon@apollo.west.oic.com>
17  *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18  *		Jorge Cwik, <jorge@laser.satlink.net>
19  */
20 
21 /*
22  * Changes:
23  *		Pedro Roque	:	Fast Retransmit/Recovery.
24  *					Two receive queues.
25  *					Retransmit queue handled by TCP.
26  *					Better retransmit timer handling.
27  *					New congestion avoidance.
28  *					Header prediction.
29  *					Variable renaming.
30  *
31  *		Eric		:	Fast Retransmit.
32  *		Randy Scott	:	MSS option defines.
33  *		Eric Schenk	:	Fixes to slow start algorithm.
34  *		Eric Schenk	:	Yet another double ACK bug.
35  *		Eric Schenk	:	Delayed ACK bug fixes.
36  *		Eric Schenk	:	Floyd style fast retrans war avoidance.
37  *		David S. Miller	:	Don't allow zero congestion window.
38  *		Eric Schenk	:	Fix retransmitter so that it sends
39  *					next packet on ack of previous packet.
40  *		Andi Kleen	:	Moved open_request checking here
41  *					and process RSTs for open_requests.
42  *		Andi Kleen	:	Better prune_queue, and other fixes.
43  *		Andrey Savochkin:	Fix RTT measurements in the presence of
44  *					timestamps.
45  *		Andrey Savochkin:	Check sequence numbers correctly when
46  *					removing SACKs due to in sequence incoming
47  *					data segments.
48  *		Andi Kleen:		Make sure we never ack data there is not
49  *					enough room for. Also make this condition
50  *					a fatal error if it might still happen.
51  *		Andi Kleen:		Add tcp_measure_rcv_mss to make
52  *					connections with MSS<min(MTU,ann. MSS)
53  *					work without delayed acks.
54  *		Andi Kleen:		Process packets with PSH set in the
55  *					fast path.
56  *		J Hadi Salim:		ECN support
57  *	 	Andrei Gurtov,
58  *		Pasi Sarolahti,
59  *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
60  *					engine. Lots of bugs are found.
61  *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
62  */
63 
64 #define pr_fmt(fmt) "TCP: " fmt
65 
66 #include <linux/mm.h>
67 #include <linux/slab.h>
68 #include <linux/module.h>
69 #include <linux/sysctl.h>
70 #include <linux/kernel.h>
71 #include <linux/prefetch.h>
72 #include <net/dst.h>
73 #include <net/tcp.h>
74 #include <net/inet_common.h>
75 #include <linux/ipsec.h>
76 #include <asm/unaligned.h>
77 #include <linux/errqueue.h>
78 
79 int sysctl_tcp_fack __read_mostly;
80 int sysctl_tcp_max_reordering __read_mostly = 300;
81 int sysctl_tcp_dsack __read_mostly = 1;
82 int sysctl_tcp_app_win __read_mostly = 31;
83 int sysctl_tcp_adv_win_scale __read_mostly = 1;
84 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
85 
86 /* rfc5961 challenge ack rate limiting */
87 int sysctl_tcp_challenge_ack_limit = 1000;
88 
89 int sysctl_tcp_stdurg __read_mostly;
90 int sysctl_tcp_rfc1337 __read_mostly;
91 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
92 int sysctl_tcp_frto __read_mostly = 2;
93 int sysctl_tcp_min_rtt_wlen __read_mostly = 300;
94 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
95 int sysctl_tcp_early_retrans __read_mostly = 3;
96 int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
97 
98 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
99 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
100 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
101 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
102 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
103 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
104 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
105 #define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
106 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
107 #define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
108 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
109 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
110 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
111 #define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
112 #define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
113 
114 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
115 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
116 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
117 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
118 
119 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
120 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
121 
122 #define REXMIT_NONE	0 /* no loss recovery to do */
123 #define REXMIT_LOST	1 /* retransmit packets marked lost */
124 #define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
125 
126 static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
127 			     unsigned int len)
128 {
129 	static bool __once __read_mostly;
130 
131 	if (!__once) {
132 		struct net_device *dev;
133 
134 		__once = true;
135 
136 		rcu_read_lock();
137 		dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
138 		if (!dev || len >= dev->mtu)
139 			pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
140 				dev ? dev->name : "Unknown driver");
141 		rcu_read_unlock();
142 	}
143 }
144 
145 /* Adapt the MSS value used to make delayed ack decision to the
146  * real world.
147  */
148 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
149 {
150 	struct inet_connection_sock *icsk = inet_csk(sk);
151 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
152 	unsigned int len;
153 
154 	icsk->icsk_ack.last_seg_size = 0;
155 
156 	/* skb->len may jitter because of SACKs, even if peer
157 	 * sends good full-sized frames.
158 	 */
159 	len = skb_shinfo(skb)->gso_size ? : skb->len;
160 	if (len >= icsk->icsk_ack.rcv_mss) {
161 		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
162 					       tcp_sk(sk)->advmss);
163 		/* Account for possibly-removed options */
164 		if (unlikely(len > icsk->icsk_ack.rcv_mss +
165 				   MAX_TCP_OPTION_SPACE))
166 			tcp_gro_dev_warn(sk, skb, len);
167 	} else {
168 		/* Otherwise, we make more careful check taking into account,
169 		 * that SACKs block is variable.
170 		 *
171 		 * "len" is invariant segment length, including TCP header.
172 		 */
173 		len += skb->data - skb_transport_header(skb);
174 		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
175 		    /* If PSH is not set, packet should be
176 		     * full sized, provided peer TCP is not badly broken.
177 		     * This observation (if it is correct 8)) allows
178 		     * to handle super-low mtu links fairly.
179 		     */
180 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
181 		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
182 			/* Subtract also invariant (if peer is RFC compliant),
183 			 * tcp header plus fixed timestamp option length.
184 			 * Resulting "len" is MSS free of SACK jitter.
185 			 */
186 			len -= tcp_sk(sk)->tcp_header_len;
187 			icsk->icsk_ack.last_seg_size = len;
188 			if (len == lss) {
189 				icsk->icsk_ack.rcv_mss = len;
190 				return;
191 			}
192 		}
193 		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
194 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
195 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
196 	}
197 }
198 
199 static void tcp_incr_quickack(struct sock *sk)
200 {
201 	struct inet_connection_sock *icsk = inet_csk(sk);
202 	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
203 
204 	if (quickacks == 0)
205 		quickacks = 2;
206 	if (quickacks > icsk->icsk_ack.quick)
207 		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
208 }
209 
210 static void tcp_enter_quickack_mode(struct sock *sk)
211 {
212 	struct inet_connection_sock *icsk = inet_csk(sk);
213 	tcp_incr_quickack(sk);
214 	icsk->icsk_ack.pingpong = 0;
215 	icsk->icsk_ack.ato = TCP_ATO_MIN;
216 }
217 
218 /* Send ACKs quickly, if "quick" count is not exhausted
219  * and the session is not interactive.
220  */
221 
222 static bool tcp_in_quickack_mode(struct sock *sk)
223 {
224 	const struct inet_connection_sock *icsk = inet_csk(sk);
225 	const struct dst_entry *dst = __sk_dst_get(sk);
226 
227 	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
228 		(icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
229 }
230 
231 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
232 {
233 	if (tp->ecn_flags & TCP_ECN_OK)
234 		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
235 }
236 
237 static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
238 {
239 	if (tcp_hdr(skb)->cwr)
240 		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
241 }
242 
243 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
244 {
245 	tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
246 }
247 
248 static void __tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
249 {
250 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
251 	case INET_ECN_NOT_ECT:
252 		/* Funny extension: if ECT is not set on a segment,
253 		 * and we already seen ECT on a previous segment,
254 		 * it is probably a retransmit.
255 		 */
256 		if (tp->ecn_flags & TCP_ECN_SEEN)
257 			tcp_enter_quickack_mode((struct sock *)tp);
258 		break;
259 	case INET_ECN_CE:
260 		if (tcp_ca_needs_ecn((struct sock *)tp))
261 			tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);
262 
263 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
264 			/* Better not delay acks, sender can have a very low cwnd */
265 			tcp_enter_quickack_mode((struct sock *)tp);
266 			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
267 		}
268 		tp->ecn_flags |= TCP_ECN_SEEN;
269 		break;
270 	default:
271 		if (tcp_ca_needs_ecn((struct sock *)tp))
272 			tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
273 		tp->ecn_flags |= TCP_ECN_SEEN;
274 		break;
275 	}
276 }
277 
278 static void tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
279 {
280 	if (tp->ecn_flags & TCP_ECN_OK)
281 		__tcp_ecn_check_ce(tp, skb);
282 }
283 
284 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
285 {
286 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
287 		tp->ecn_flags &= ~TCP_ECN_OK;
288 }
289 
290 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
291 {
292 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
293 		tp->ecn_flags &= ~TCP_ECN_OK;
294 }
295 
296 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
297 {
298 	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
299 		return true;
300 	return false;
301 }
302 
303 /* Buffer size and advertised window tuning.
304  *
305  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
306  */
307 
308 static void tcp_sndbuf_expand(struct sock *sk)
309 {
310 	const struct tcp_sock *tp = tcp_sk(sk);
311 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
312 	int sndmem, per_mss;
313 	u32 nr_segs;
314 
315 	/* Worst case is non GSO/TSO : each frame consumes one skb
316 	 * and skb->head is kmalloced using power of two area of memory
317 	 */
318 	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
319 		  MAX_TCP_HEADER +
320 		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
321 
322 	per_mss = roundup_pow_of_two(per_mss) +
323 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
324 
325 	nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
326 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
327 
328 	/* Fast Recovery (RFC 5681 3.2) :
329 	 * Cubic needs 1.7 factor, rounded to 2 to include
330 	 * extra cushion (application might react slowly to POLLOUT)
331 	 */
332 	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
333 	sndmem *= nr_segs * per_mss;
334 
335 	if (sk->sk_sndbuf < sndmem)
336 		sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
337 }
338 
339 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
340  *
341  * All tcp_full_space() is split to two parts: "network" buffer, allocated
342  * forward and advertised in receiver window (tp->rcv_wnd) and
343  * "application buffer", required to isolate scheduling/application
344  * latencies from network.
345  * window_clamp is maximal advertised window. It can be less than
346  * tcp_full_space(), in this case tcp_full_space() - window_clamp
347  * is reserved for "application" buffer. The less window_clamp is
348  * the smoother our behaviour from viewpoint of network, but the lower
349  * throughput and the higher sensitivity of the connection to losses. 8)
350  *
351  * rcv_ssthresh is more strict window_clamp used at "slow start"
352  * phase to predict further behaviour of this connection.
353  * It is used for two goals:
354  * - to enforce header prediction at sender, even when application
355  *   requires some significant "application buffer". It is check #1.
356  * - to prevent pruning of receive queue because of misprediction
357  *   of receiver window. Check #2.
358  *
359  * The scheme does not work when sender sends good segments opening
360  * window and then starts to feed us spaghetti. But it should work
361  * in common situations. Otherwise, we have to rely on queue collapsing.
362  */
363 
364 /* Slow part of check#2. */
365 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
366 {
367 	struct tcp_sock *tp = tcp_sk(sk);
368 	/* Optimize this! */
369 	int truesize = tcp_win_from_space(skb->truesize) >> 1;
370 	int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
371 
372 	while (tp->rcv_ssthresh <= window) {
373 		if (truesize <= skb->len)
374 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
375 
376 		truesize >>= 1;
377 		window >>= 1;
378 	}
379 	return 0;
380 }
381 
382 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
383 {
384 	struct tcp_sock *tp = tcp_sk(sk);
385 
386 	/* Check #1 */
387 	if (tp->rcv_ssthresh < tp->window_clamp &&
388 	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
389 	    !tcp_under_memory_pressure(sk)) {
390 		int incr;
391 
392 		/* Check #2. Increase window, if skb with such overhead
393 		 * will fit to rcvbuf in future.
394 		 */
395 		if (tcp_win_from_space(skb->truesize) <= skb->len)
396 			incr = 2 * tp->advmss;
397 		else
398 			incr = __tcp_grow_window(sk, skb);
399 
400 		if (incr) {
401 			incr = max_t(int, incr, 2 * skb->len);
402 			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
403 					       tp->window_clamp);
404 			inet_csk(sk)->icsk_ack.quick |= 1;
405 		}
406 	}
407 }
408 
409 /* 3. Tuning rcvbuf, when connection enters established state. */
410 static void tcp_fixup_rcvbuf(struct sock *sk)
411 {
412 	u32 mss = tcp_sk(sk)->advmss;
413 	int rcvmem;
414 
415 	rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
416 		 tcp_default_init_rwnd(mss);
417 
418 	/* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
419 	 * Allow enough cushion so that sender is not limited by our window
420 	 */
421 	if (sysctl_tcp_moderate_rcvbuf)
422 		rcvmem <<= 2;
423 
424 	if (sk->sk_rcvbuf < rcvmem)
425 		sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
426 }
427 
428 /* 4. Try to fixup all. It is made immediately after connection enters
429  *    established state.
430  */
431 void tcp_init_buffer_space(struct sock *sk)
432 {
433 	struct tcp_sock *tp = tcp_sk(sk);
434 	int maxwin;
435 
436 	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
437 		tcp_fixup_rcvbuf(sk);
438 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
439 		tcp_sndbuf_expand(sk);
440 
441 	tp->rcvq_space.space = tp->rcv_wnd;
442 	tcp_mstamp_refresh(tp);
443 	tp->rcvq_space.time = tp->tcp_mstamp;
444 	tp->rcvq_space.seq = tp->copied_seq;
445 
446 	maxwin = tcp_full_space(sk);
447 
448 	if (tp->window_clamp >= maxwin) {
449 		tp->window_clamp = maxwin;
450 
451 		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
452 			tp->window_clamp = max(maxwin -
453 					       (maxwin >> sysctl_tcp_app_win),
454 					       4 * tp->advmss);
455 	}
456 
457 	/* Force reservation of one segment. */
458 	if (sysctl_tcp_app_win &&
459 	    tp->window_clamp > 2 * tp->advmss &&
460 	    tp->window_clamp + tp->advmss > maxwin)
461 		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
462 
463 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
464 	tp->snd_cwnd_stamp = tcp_jiffies32;
465 }
466 
467 /* 5. Recalculate window clamp after socket hit its memory bounds. */
468 static void tcp_clamp_window(struct sock *sk)
469 {
470 	struct tcp_sock *tp = tcp_sk(sk);
471 	struct inet_connection_sock *icsk = inet_csk(sk);
472 
473 	icsk->icsk_ack.quick = 0;
474 
475 	if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
476 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
477 	    !tcp_under_memory_pressure(sk) &&
478 	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
479 		sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
480 				    sysctl_tcp_rmem[2]);
481 	}
482 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
483 		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
484 }
485 
486 /* Initialize RCV_MSS value.
487  * RCV_MSS is an our guess about MSS used by the peer.
488  * We haven't any direct information about the MSS.
489  * It's better to underestimate the RCV_MSS rather than overestimate.
490  * Overestimations make us ACKing less frequently than needed.
491  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
492  */
493 void tcp_initialize_rcv_mss(struct sock *sk)
494 {
495 	const struct tcp_sock *tp = tcp_sk(sk);
496 	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
497 
498 	hint = min(hint, tp->rcv_wnd / 2);
499 	hint = min(hint, TCP_MSS_DEFAULT);
500 	hint = max(hint, TCP_MIN_MSS);
501 
502 	inet_csk(sk)->icsk_ack.rcv_mss = hint;
503 }
504 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
505 
506 /* Receiver "autotuning" code.
507  *
508  * The algorithm for RTT estimation w/o timestamps is based on
509  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
510  * <http://public.lanl.gov/radiant/pubs.html#DRS>
511  *
512  * More detail on this code can be found at
513  * <http://staff.psc.edu/jheffner/>,
514  * though this reference is out of date.  A new paper
515  * is pending.
516  */
517 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
518 {
519 	u32 new_sample = tp->rcv_rtt_est.rtt_us;
520 	long m = sample;
521 
522 	if (m == 0)
523 		m = 1;
524 
525 	if (new_sample != 0) {
526 		/* If we sample in larger samples in the non-timestamp
527 		 * case, we could grossly overestimate the RTT especially
528 		 * with chatty applications or bulk transfer apps which
529 		 * are stalled on filesystem I/O.
530 		 *
531 		 * Also, since we are only going for a minimum in the
532 		 * non-timestamp case, we do not smooth things out
533 		 * else with timestamps disabled convergence takes too
534 		 * long.
535 		 */
536 		if (!win_dep) {
537 			m -= (new_sample >> 3);
538 			new_sample += m;
539 		} else {
540 			m <<= 3;
541 			if (m < new_sample)
542 				new_sample = m;
543 		}
544 	} else {
545 		/* No previous measure. */
546 		new_sample = m << 3;
547 	}
548 
549 	tp->rcv_rtt_est.rtt_us = new_sample;
550 }
551 
552 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
553 {
554 	u32 delta_us;
555 
556 	if (tp->rcv_rtt_est.time == 0)
557 		goto new_measure;
558 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
559 		return;
560 	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
561 	tcp_rcv_rtt_update(tp, delta_us, 1);
562 
563 new_measure:
564 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
565 	tp->rcv_rtt_est.time = tp->tcp_mstamp;
566 }
567 
568 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
569 					  const struct sk_buff *skb)
570 {
571 	struct tcp_sock *tp = tcp_sk(sk);
572 
573 	if (tp->rx_opt.rcv_tsecr &&
574 	    (TCP_SKB_CB(skb)->end_seq -
575 	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss)) {
576 		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
577 		u32 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
578 
579 		tcp_rcv_rtt_update(tp, delta_us, 0);
580 	}
581 }
582 
583 /*
584  * This function should be called every time data is copied to user space.
585  * It calculates the appropriate TCP receive buffer space.
586  */
587 void tcp_rcv_space_adjust(struct sock *sk)
588 {
589 	struct tcp_sock *tp = tcp_sk(sk);
590 	int time;
591 	int copied;
592 
593 	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
594 	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
595 		return;
596 
597 	/* Number of bytes copied to user in last RTT */
598 	copied = tp->copied_seq - tp->rcvq_space.seq;
599 	if (copied <= tp->rcvq_space.space)
600 		goto new_measure;
601 
602 	/* A bit of theory :
603 	 * copied = bytes received in previous RTT, our base window
604 	 * To cope with packet losses, we need a 2x factor
605 	 * To cope with slow start, and sender growing its cwin by 100 %
606 	 * every RTT, we need a 4x factor, because the ACK we are sending
607 	 * now is for the next RTT, not the current one :
608 	 * <prev RTT . ><current RTT .. ><next RTT .... >
609 	 */
610 
611 	if (sysctl_tcp_moderate_rcvbuf &&
612 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
613 		int rcvwin, rcvmem, rcvbuf;
614 
615 		/* minimal window to cope with packet losses, assuming
616 		 * steady state. Add some cushion because of small variations.
617 		 */
618 		rcvwin = (copied << 1) + 16 * tp->advmss;
619 
620 		/* If rate increased by 25%,
621 		 *	assume slow start, rcvwin = 3 * copied
622 		 * If rate increased by 50%,
623 		 *	assume sender can use 2x growth, rcvwin = 4 * copied
624 		 */
625 		if (copied >=
626 		    tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
627 			if (copied >=
628 			    tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
629 				rcvwin <<= 1;
630 			else
631 				rcvwin += (rcvwin >> 1);
632 		}
633 
634 		rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
635 		while (tcp_win_from_space(rcvmem) < tp->advmss)
636 			rcvmem += 128;
637 
638 		rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
639 		if (rcvbuf > sk->sk_rcvbuf) {
640 			sk->sk_rcvbuf = rcvbuf;
641 
642 			/* Make the window clamp follow along.  */
643 			tp->window_clamp = rcvwin;
644 		}
645 	}
646 	tp->rcvq_space.space = copied;
647 
648 new_measure:
649 	tp->rcvq_space.seq = tp->copied_seq;
650 	tp->rcvq_space.time = tp->tcp_mstamp;
651 }
652 
653 /* There is something which you must keep in mind when you analyze the
654  * behavior of the tp->ato delayed ack timeout interval.  When a
655  * connection starts up, we want to ack as quickly as possible.  The
656  * problem is that "good" TCP's do slow start at the beginning of data
657  * transmission.  The means that until we send the first few ACK's the
658  * sender will sit on his end and only queue most of his data, because
659  * he can only send snd_cwnd unacked packets at any given time.  For
660  * each ACK we send, he increments snd_cwnd and transmits more of his
661  * queue.  -DaveM
662  */
663 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
664 {
665 	struct tcp_sock *tp = tcp_sk(sk);
666 	struct inet_connection_sock *icsk = inet_csk(sk);
667 	u32 now;
668 
669 	inet_csk_schedule_ack(sk);
670 
671 	tcp_measure_rcv_mss(sk, skb);
672 
673 	tcp_rcv_rtt_measure(tp);
674 
675 	now = tcp_jiffies32;
676 
677 	if (!icsk->icsk_ack.ato) {
678 		/* The _first_ data packet received, initialize
679 		 * delayed ACK engine.
680 		 */
681 		tcp_incr_quickack(sk);
682 		icsk->icsk_ack.ato = TCP_ATO_MIN;
683 	} else {
684 		int m = now - icsk->icsk_ack.lrcvtime;
685 
686 		if (m <= TCP_ATO_MIN / 2) {
687 			/* The fastest case is the first. */
688 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
689 		} else if (m < icsk->icsk_ack.ato) {
690 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
691 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
692 				icsk->icsk_ack.ato = icsk->icsk_rto;
693 		} else if (m > icsk->icsk_rto) {
694 			/* Too long gap. Apparently sender failed to
695 			 * restart window, so that we send ACKs quickly.
696 			 */
697 			tcp_incr_quickack(sk);
698 			sk_mem_reclaim(sk);
699 		}
700 	}
701 	icsk->icsk_ack.lrcvtime = now;
702 
703 	tcp_ecn_check_ce(tp, skb);
704 
705 	if (skb->len >= 128)
706 		tcp_grow_window(sk, skb);
707 }
708 
709 /* Called to compute a smoothed rtt estimate. The data fed to this
710  * routine either comes from timestamps, or from segments that were
711  * known _not_ to have been retransmitted [see Karn/Partridge
712  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
713  * piece by Van Jacobson.
714  * NOTE: the next three routines used to be one big routine.
715  * To save cycles in the RFC 1323 implementation it was better to break
716  * it up into three procedures. -- erics
717  */
718 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
719 {
720 	struct tcp_sock *tp = tcp_sk(sk);
721 	long m = mrtt_us; /* RTT */
722 	u32 srtt = tp->srtt_us;
723 
724 	/*	The following amusing code comes from Jacobson's
725 	 *	article in SIGCOMM '88.  Note that rtt and mdev
726 	 *	are scaled versions of rtt and mean deviation.
727 	 *	This is designed to be as fast as possible
728 	 *	m stands for "measurement".
729 	 *
730 	 *	On a 1990 paper the rto value is changed to:
731 	 *	RTO = rtt + 4 * mdev
732 	 *
733 	 * Funny. This algorithm seems to be very broken.
734 	 * These formulae increase RTO, when it should be decreased, increase
735 	 * too slowly, when it should be increased quickly, decrease too quickly
736 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
737 	 * does not matter how to _calculate_ it. Seems, it was trap
738 	 * that VJ failed to avoid. 8)
739 	 */
740 	if (srtt != 0) {
741 		m -= (srtt >> 3);	/* m is now error in rtt est */
742 		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
743 		if (m < 0) {
744 			m = -m;		/* m is now abs(error) */
745 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
746 			/* This is similar to one of Eifel findings.
747 			 * Eifel blocks mdev updates when rtt decreases.
748 			 * This solution is a bit different: we use finer gain
749 			 * for mdev in this case (alpha*beta).
750 			 * Like Eifel it also prevents growth of rto,
751 			 * but also it limits too fast rto decreases,
752 			 * happening in pure Eifel.
753 			 */
754 			if (m > 0)
755 				m >>= 3;
756 		} else {
757 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
758 		}
759 		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
760 		if (tp->mdev_us > tp->mdev_max_us) {
761 			tp->mdev_max_us = tp->mdev_us;
762 			if (tp->mdev_max_us > tp->rttvar_us)
763 				tp->rttvar_us = tp->mdev_max_us;
764 		}
765 		if (after(tp->snd_una, tp->rtt_seq)) {
766 			if (tp->mdev_max_us < tp->rttvar_us)
767 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
768 			tp->rtt_seq = tp->snd_nxt;
769 			tp->mdev_max_us = tcp_rto_min_us(sk);
770 		}
771 	} else {
772 		/* no previous measure. */
773 		srtt = m << 3;		/* take the measured time to be rtt */
774 		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
775 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
776 		tp->mdev_max_us = tp->rttvar_us;
777 		tp->rtt_seq = tp->snd_nxt;
778 	}
779 	tp->srtt_us = max(1U, srtt);
780 }
781 
782 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
783  * Note: TCP stack does not yet implement pacing.
784  * FQ packet scheduler can be used to implement cheap but effective
785  * TCP pacing, to smooth the burst on large writes when packets
786  * in flight is significantly lower than cwnd (or rwin)
787  */
788 int sysctl_tcp_pacing_ss_ratio __read_mostly = 200;
789 int sysctl_tcp_pacing_ca_ratio __read_mostly = 120;
790 
791 static void tcp_update_pacing_rate(struct sock *sk)
792 {
793 	const struct tcp_sock *tp = tcp_sk(sk);
794 	u64 rate;
795 
796 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
797 	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
798 
799 	/* current rate is (cwnd * mss) / srtt
800 	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
801 	 * In Congestion Avoidance phase, set it to 120 % the current rate.
802 	 *
803 	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
804 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
805 	 *	 end of slow start and should slow down.
806 	 */
807 	if (tp->snd_cwnd < tp->snd_ssthresh / 2)
808 		rate *= sysctl_tcp_pacing_ss_ratio;
809 	else
810 		rate *= sysctl_tcp_pacing_ca_ratio;
811 
812 	rate *= max(tp->snd_cwnd, tp->packets_out);
813 
814 	if (likely(tp->srtt_us))
815 		do_div(rate, tp->srtt_us);
816 
817 	/* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
818 	 * without any lock. We want to make sure compiler wont store
819 	 * intermediate values in this location.
820 	 */
821 	ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
822 						sk->sk_max_pacing_rate);
823 }
824 
825 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
826  * routine referred to above.
827  */
828 static void tcp_set_rto(struct sock *sk)
829 {
830 	const struct tcp_sock *tp = tcp_sk(sk);
831 	/* Old crap is replaced with new one. 8)
832 	 *
833 	 * More seriously:
834 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
835 	 *    It cannot be less due to utterly erratic ACK generation made
836 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
837 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
838 	 *    is invisible. Actually, Linux-2.4 also generates erratic
839 	 *    ACKs in some circumstances.
840 	 */
841 	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
842 
843 	/* 2. Fixups made earlier cannot be right.
844 	 *    If we do not estimate RTO correctly without them,
845 	 *    all the algo is pure shit and should be replaced
846 	 *    with correct one. It is exactly, which we pretend to do.
847 	 */
848 
849 	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
850 	 * guarantees that rto is higher.
851 	 */
852 	tcp_bound_rto(sk);
853 }
854 
855 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
856 {
857 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
858 
859 	if (!cwnd)
860 		cwnd = TCP_INIT_CWND;
861 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
862 }
863 
864 /*
865  * Packet counting of FACK is based on in-order assumptions, therefore TCP
866  * disables it when reordering is detected
867  */
868 void tcp_disable_fack(struct tcp_sock *tp)
869 {
870 	/* RFC3517 uses different metric in lost marker => reset on change */
871 	if (tcp_is_fack(tp))
872 		tp->lost_skb_hint = NULL;
873 	tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
874 }
875 
876 /* Take a notice that peer is sending D-SACKs */
877 static void tcp_dsack_seen(struct tcp_sock *tp)
878 {
879 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
880 }
881 
882 static void tcp_update_reordering(struct sock *sk, const int metric,
883 				  const int ts)
884 {
885 	struct tcp_sock *tp = tcp_sk(sk);
886 	int mib_idx;
887 
888 	if (WARN_ON_ONCE(metric < 0))
889 		return;
890 
891 	if (metric > tp->reordering) {
892 		tp->reordering = min(sysctl_tcp_max_reordering, metric);
893 
894 #if FASTRETRANS_DEBUG > 1
895 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
896 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
897 			 tp->reordering,
898 			 tp->fackets_out,
899 			 tp->sacked_out,
900 			 tp->undo_marker ? tp->undo_retrans : 0);
901 #endif
902 		tcp_disable_fack(tp);
903 	}
904 
905 	tp->rack.reord = 1;
906 
907 	/* This exciting event is worth to be remembered. 8) */
908 	if (ts)
909 		mib_idx = LINUX_MIB_TCPTSREORDER;
910 	else if (tcp_is_reno(tp))
911 		mib_idx = LINUX_MIB_TCPRENOREORDER;
912 	else if (tcp_is_fack(tp))
913 		mib_idx = LINUX_MIB_TCPFACKREORDER;
914 	else
915 		mib_idx = LINUX_MIB_TCPSACKREORDER;
916 
917 	NET_INC_STATS(sock_net(sk), mib_idx);
918 }
919 
920 /* This must be called before lost_out is incremented */
921 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
922 {
923 	if (!tp->retransmit_skb_hint ||
924 	    before(TCP_SKB_CB(skb)->seq,
925 		   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
926 		tp->retransmit_skb_hint = skb;
927 }
928 
929 /* Sum the number of packets on the wire we have marked as lost.
930  * There are two cases we care about here:
931  * a) Packet hasn't been marked lost (nor retransmitted),
932  *    and this is the first loss.
933  * b) Packet has been marked both lost and retransmitted,
934  *    and this means we think it was lost again.
935  */
936 static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
937 {
938 	__u8 sacked = TCP_SKB_CB(skb)->sacked;
939 
940 	if (!(sacked & TCPCB_LOST) ||
941 	    ((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
942 		tp->lost += tcp_skb_pcount(skb);
943 }
944 
945 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
946 {
947 	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
948 		tcp_verify_retransmit_hint(tp, skb);
949 
950 		tp->lost_out += tcp_skb_pcount(skb);
951 		tcp_sum_lost(tp, skb);
952 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
953 	}
954 }
955 
956 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
957 {
958 	tcp_verify_retransmit_hint(tp, skb);
959 
960 	tcp_sum_lost(tp, skb);
961 	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
962 		tp->lost_out += tcp_skb_pcount(skb);
963 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
964 	}
965 }
966 
967 /* This procedure tags the retransmission queue when SACKs arrive.
968  *
969  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
970  * Packets in queue with these bits set are counted in variables
971  * sacked_out, retrans_out and lost_out, correspondingly.
972  *
973  * Valid combinations are:
974  * Tag  InFlight	Description
975  * 0	1		- orig segment is in flight.
976  * S	0		- nothing flies, orig reached receiver.
977  * L	0		- nothing flies, orig lost by net.
978  * R	2		- both orig and retransmit are in flight.
979  * L|R	1		- orig is lost, retransmit is in flight.
980  * S|R  1		- orig reached receiver, retrans is still in flight.
981  * (L|S|R is logically valid, it could occur when L|R is sacked,
982  *  but it is equivalent to plain S and code short-curcuits it to S.
983  *  L|S is logically invalid, it would mean -1 packet in flight 8))
984  *
985  * These 6 states form finite state machine, controlled by the following events:
986  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
987  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
988  * 3. Loss detection event of two flavors:
989  *	A. Scoreboard estimator decided the packet is lost.
990  *	   A'. Reno "three dupacks" marks head of queue lost.
991  *	   A''. Its FACK modification, head until snd.fack is lost.
992  *	B. SACK arrives sacking SND.NXT at the moment, when the
993  *	   segment was retransmitted.
994  * 4. D-SACK added new rule: D-SACK changes any tag to S.
995  *
996  * It is pleasant to note, that state diagram turns out to be commutative,
997  * so that we are allowed not to be bothered by order of our actions,
998  * when multiple events arrive simultaneously. (see the function below).
999  *
1000  * Reordering detection.
1001  * --------------------
1002  * Reordering metric is maximal distance, which a packet can be displaced
1003  * in packet stream. With SACKs we can estimate it:
1004  *
1005  * 1. SACK fills old hole and the corresponding segment was not
1006  *    ever retransmitted -> reordering. Alas, we cannot use it
1007  *    when segment was retransmitted.
1008  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1009  *    for retransmitted and already SACKed segment -> reordering..
1010  * Both of these heuristics are not used in Loss state, when we cannot
1011  * account for retransmits accurately.
1012  *
1013  * SACK block validation.
1014  * ----------------------
1015  *
1016  * SACK block range validation checks that the received SACK block fits to
1017  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1018  * Note that SND.UNA is not included to the range though being valid because
1019  * it means that the receiver is rather inconsistent with itself reporting
1020  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1021  * perfectly valid, however, in light of RFC2018 which explicitly states
1022  * that "SACK block MUST reflect the newest segment.  Even if the newest
1023  * segment is going to be discarded ...", not that it looks very clever
1024  * in case of head skb. Due to potentional receiver driven attacks, we
1025  * choose to avoid immediate execution of a walk in write queue due to
1026  * reneging and defer head skb's loss recovery to standard loss recovery
1027  * procedure that will eventually trigger (nothing forbids us doing this).
1028  *
1029  * Implements also blockage to start_seq wrap-around. Problem lies in the
1030  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1031  * there's no guarantee that it will be before snd_nxt (n). The problem
1032  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1033  * wrap (s_w):
1034  *
1035  *         <- outs wnd ->                          <- wrapzone ->
1036  *         u     e      n                         u_w   e_w  s n_w
1037  *         |     |      |                          |     |   |  |
1038  * |<------------+------+----- TCP seqno space --------------+---------->|
1039  * ...-- <2^31 ->|                                           |<--------...
1040  * ...---- >2^31 ------>|                                    |<--------...
1041  *
1042  * Current code wouldn't be vulnerable but it's better still to discard such
1043  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1044  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1045  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1046  * equal to the ideal case (infinite seqno space without wrap caused issues).
1047  *
1048  * With D-SACK the lower bound is extended to cover sequence space below
1049  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1050  * again, D-SACK block must not to go across snd_una (for the same reason as
1051  * for the normal SACK blocks, explained above). But there all simplicity
1052  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1053  * fully below undo_marker they do not affect behavior in anyway and can
1054  * therefore be safely ignored. In rare cases (which are more or less
1055  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1056  * fragmentation and packet reordering past skb's retransmission. To consider
1057  * them correctly, the acceptable range must be extended even more though
1058  * the exact amount is rather hard to quantify. However, tp->max_window can
1059  * be used as an exaggerated estimate.
1060  */
1061 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1062 				   u32 start_seq, u32 end_seq)
1063 {
1064 	/* Too far in future, or reversed (interpretation is ambiguous) */
1065 	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1066 		return false;
1067 
1068 	/* Nasty start_seq wrap-around check (see comments above) */
1069 	if (!before(start_seq, tp->snd_nxt))
1070 		return false;
1071 
1072 	/* In outstanding window? ...This is valid exit for D-SACKs too.
1073 	 * start_seq == snd_una is non-sensical (see comments above)
1074 	 */
1075 	if (after(start_seq, tp->snd_una))
1076 		return true;
1077 
1078 	if (!is_dsack || !tp->undo_marker)
1079 		return false;
1080 
1081 	/* ...Then it's D-SACK, and must reside below snd_una completely */
1082 	if (after(end_seq, tp->snd_una))
1083 		return false;
1084 
1085 	if (!before(start_seq, tp->undo_marker))
1086 		return true;
1087 
1088 	/* Too old */
1089 	if (!after(end_seq, tp->undo_marker))
1090 		return false;
1091 
1092 	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1093 	 *   start_seq < undo_marker and end_seq >= undo_marker.
1094 	 */
1095 	return !before(start_seq, end_seq - tp->max_window);
1096 }
1097 
1098 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1099 			    struct tcp_sack_block_wire *sp, int num_sacks,
1100 			    u32 prior_snd_una)
1101 {
1102 	struct tcp_sock *tp = tcp_sk(sk);
1103 	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1104 	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1105 	bool dup_sack = false;
1106 
1107 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1108 		dup_sack = true;
1109 		tcp_dsack_seen(tp);
1110 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1111 	} else if (num_sacks > 1) {
1112 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1113 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1114 
1115 		if (!after(end_seq_0, end_seq_1) &&
1116 		    !before(start_seq_0, start_seq_1)) {
1117 			dup_sack = true;
1118 			tcp_dsack_seen(tp);
1119 			NET_INC_STATS(sock_net(sk),
1120 					LINUX_MIB_TCPDSACKOFORECV);
1121 		}
1122 	}
1123 
1124 	/* D-SACK for already forgotten data... Do dumb counting. */
1125 	if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1126 	    !after(end_seq_0, prior_snd_una) &&
1127 	    after(end_seq_0, tp->undo_marker))
1128 		tp->undo_retrans--;
1129 
1130 	return dup_sack;
1131 }
1132 
1133 struct tcp_sacktag_state {
1134 	int	reord;
1135 	int	fack_count;
1136 	/* Timestamps for earliest and latest never-retransmitted segment
1137 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1138 	 * but congestion control should still get an accurate delay signal.
1139 	 */
1140 	u64	first_sackt;
1141 	u64	last_sackt;
1142 	struct rate_sample *rate;
1143 	int	flag;
1144 };
1145 
1146 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1147  * the incoming SACK may not exactly match but we can find smaller MSS
1148  * aligned portion of it that matches. Therefore we might need to fragment
1149  * which may fail and creates some hassle (caller must handle error case
1150  * returns).
1151  *
1152  * FIXME: this could be merged to shift decision code
1153  */
1154 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1155 				  u32 start_seq, u32 end_seq)
1156 {
1157 	int err;
1158 	bool in_sack;
1159 	unsigned int pkt_len;
1160 	unsigned int mss;
1161 
1162 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1163 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1164 
1165 	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1166 	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1167 		mss = tcp_skb_mss(skb);
1168 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1169 
1170 		if (!in_sack) {
1171 			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1172 			if (pkt_len < mss)
1173 				pkt_len = mss;
1174 		} else {
1175 			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1176 			if (pkt_len < mss)
1177 				return -EINVAL;
1178 		}
1179 
1180 		/* Round if necessary so that SACKs cover only full MSSes
1181 		 * and/or the remaining small portion (if present)
1182 		 */
1183 		if (pkt_len > mss) {
1184 			unsigned int new_len = (pkt_len / mss) * mss;
1185 			if (!in_sack && new_len < pkt_len)
1186 				new_len += mss;
1187 			pkt_len = new_len;
1188 		}
1189 
1190 		if (pkt_len >= skb->len && !in_sack)
1191 			return 0;
1192 
1193 		err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
1194 		if (err < 0)
1195 			return err;
1196 	}
1197 
1198 	return in_sack;
1199 }
1200 
1201 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1202 static u8 tcp_sacktag_one(struct sock *sk,
1203 			  struct tcp_sacktag_state *state, u8 sacked,
1204 			  u32 start_seq, u32 end_seq,
1205 			  int dup_sack, int pcount,
1206 			  u64 xmit_time)
1207 {
1208 	struct tcp_sock *tp = tcp_sk(sk);
1209 	int fack_count = state->fack_count;
1210 
1211 	/* Account D-SACK for retransmitted packet. */
1212 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1213 		if (tp->undo_marker && tp->undo_retrans > 0 &&
1214 		    after(end_seq, tp->undo_marker))
1215 			tp->undo_retrans--;
1216 		if (sacked & TCPCB_SACKED_ACKED)
1217 			state->reord = min(fack_count, state->reord);
1218 	}
1219 
1220 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1221 	if (!after(end_seq, tp->snd_una))
1222 		return sacked;
1223 
1224 	if (!(sacked & TCPCB_SACKED_ACKED)) {
1225 		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1226 
1227 		if (sacked & TCPCB_SACKED_RETRANS) {
1228 			/* If the segment is not tagged as lost,
1229 			 * we do not clear RETRANS, believing
1230 			 * that retransmission is still in flight.
1231 			 */
1232 			if (sacked & TCPCB_LOST) {
1233 				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1234 				tp->lost_out -= pcount;
1235 				tp->retrans_out -= pcount;
1236 			}
1237 		} else {
1238 			if (!(sacked & TCPCB_RETRANS)) {
1239 				/* New sack for not retransmitted frame,
1240 				 * which was in hole. It is reordering.
1241 				 */
1242 				if (before(start_seq,
1243 					   tcp_highest_sack_seq(tp)))
1244 					state->reord = min(fack_count,
1245 							   state->reord);
1246 				if (!after(end_seq, tp->high_seq))
1247 					state->flag |= FLAG_ORIG_SACK_ACKED;
1248 				if (state->first_sackt == 0)
1249 					state->first_sackt = xmit_time;
1250 				state->last_sackt = xmit_time;
1251 			}
1252 
1253 			if (sacked & TCPCB_LOST) {
1254 				sacked &= ~TCPCB_LOST;
1255 				tp->lost_out -= pcount;
1256 			}
1257 		}
1258 
1259 		sacked |= TCPCB_SACKED_ACKED;
1260 		state->flag |= FLAG_DATA_SACKED;
1261 		tp->sacked_out += pcount;
1262 		tp->delivered += pcount;  /* Out-of-order packets delivered */
1263 
1264 		fack_count += pcount;
1265 
1266 		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1267 		if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
1268 		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1269 			tp->lost_cnt_hint += pcount;
1270 
1271 		if (fack_count > tp->fackets_out)
1272 			tp->fackets_out = fack_count;
1273 	}
1274 
1275 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1276 	 * frames and clear it. undo_retrans is decreased above, L|R frames
1277 	 * are accounted above as well.
1278 	 */
1279 	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1280 		sacked &= ~TCPCB_SACKED_RETRANS;
1281 		tp->retrans_out -= pcount;
1282 	}
1283 
1284 	return sacked;
1285 }
1286 
1287 /* Shift newly-SACKed bytes from this skb to the immediately previous
1288  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1289  */
1290 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1291 			    struct tcp_sacktag_state *state,
1292 			    unsigned int pcount, int shifted, int mss,
1293 			    bool dup_sack)
1294 {
1295 	struct tcp_sock *tp = tcp_sk(sk);
1296 	struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1297 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1298 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1299 
1300 	BUG_ON(!pcount);
1301 
1302 	/* Adjust counters and hints for the newly sacked sequence
1303 	 * range but discard the return value since prev is already
1304 	 * marked. We must tag the range first because the seq
1305 	 * advancement below implicitly advances
1306 	 * tcp_highest_sack_seq() when skb is highest_sack.
1307 	 */
1308 	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1309 			start_seq, end_seq, dup_sack, pcount,
1310 			skb->skb_mstamp);
1311 	tcp_rate_skb_delivered(sk, skb, state->rate);
1312 
1313 	if (skb == tp->lost_skb_hint)
1314 		tp->lost_cnt_hint += pcount;
1315 
1316 	TCP_SKB_CB(prev)->end_seq += shifted;
1317 	TCP_SKB_CB(skb)->seq += shifted;
1318 
1319 	tcp_skb_pcount_add(prev, pcount);
1320 	BUG_ON(tcp_skb_pcount(skb) < pcount);
1321 	tcp_skb_pcount_add(skb, -pcount);
1322 
1323 	/* When we're adding to gso_segs == 1, gso_size will be zero,
1324 	 * in theory this shouldn't be necessary but as long as DSACK
1325 	 * code can come after this skb later on it's better to keep
1326 	 * setting gso_size to something.
1327 	 */
1328 	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1329 		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1330 
1331 	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1332 	if (tcp_skb_pcount(skb) <= 1)
1333 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1334 
1335 	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1336 	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1337 
1338 	if (skb->len > 0) {
1339 		BUG_ON(!tcp_skb_pcount(skb));
1340 		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1341 		return false;
1342 	}
1343 
1344 	/* Whole SKB was eaten :-) */
1345 
1346 	if (skb == tp->retransmit_skb_hint)
1347 		tp->retransmit_skb_hint = prev;
1348 	if (skb == tp->lost_skb_hint) {
1349 		tp->lost_skb_hint = prev;
1350 		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1351 	}
1352 
1353 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1354 	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1355 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1356 		TCP_SKB_CB(prev)->end_seq++;
1357 
1358 	if (skb == tcp_highest_sack(sk))
1359 		tcp_advance_highest_sack(sk, skb);
1360 
1361 	tcp_skb_collapse_tstamp(prev, skb);
1362 	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1363 		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1364 
1365 	tcp_unlink_write_queue(skb, sk);
1366 	sk_wmem_free_skb(sk, skb);
1367 
1368 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1369 
1370 	return true;
1371 }
1372 
1373 /* I wish gso_size would have a bit more sane initialization than
1374  * something-or-zero which complicates things
1375  */
1376 static int tcp_skb_seglen(const struct sk_buff *skb)
1377 {
1378 	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1379 }
1380 
1381 /* Shifting pages past head area doesn't work */
1382 static int skb_can_shift(const struct sk_buff *skb)
1383 {
1384 	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1385 }
1386 
1387 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1388  * skb.
1389  */
1390 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1391 					  struct tcp_sacktag_state *state,
1392 					  u32 start_seq, u32 end_seq,
1393 					  bool dup_sack)
1394 {
1395 	struct tcp_sock *tp = tcp_sk(sk);
1396 	struct sk_buff *prev;
1397 	int mss;
1398 	int pcount = 0;
1399 	int len;
1400 	int in_sack;
1401 
1402 	if (!sk_can_gso(sk))
1403 		goto fallback;
1404 
1405 	/* Normally R but no L won't result in plain S */
1406 	if (!dup_sack &&
1407 	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1408 		goto fallback;
1409 	if (!skb_can_shift(skb))
1410 		goto fallback;
1411 	/* This frame is about to be dropped (was ACKed). */
1412 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1413 		goto fallback;
1414 
1415 	/* Can only happen with delayed DSACK + discard craziness */
1416 	if (unlikely(skb == tcp_write_queue_head(sk)))
1417 		goto fallback;
1418 	prev = tcp_write_queue_prev(sk, skb);
1419 
1420 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1421 		goto fallback;
1422 
1423 	if (!tcp_skb_can_collapse_to(prev))
1424 		goto fallback;
1425 
1426 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1427 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1428 
1429 	if (in_sack) {
1430 		len = skb->len;
1431 		pcount = tcp_skb_pcount(skb);
1432 		mss = tcp_skb_seglen(skb);
1433 
1434 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1435 		 * drop this restriction as unnecessary
1436 		 */
1437 		if (mss != tcp_skb_seglen(prev))
1438 			goto fallback;
1439 	} else {
1440 		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1441 			goto noop;
1442 		/* CHECKME: This is non-MSS split case only?, this will
1443 		 * cause skipped skbs due to advancing loop btw, original
1444 		 * has that feature too
1445 		 */
1446 		if (tcp_skb_pcount(skb) <= 1)
1447 			goto noop;
1448 
1449 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1450 		if (!in_sack) {
1451 			/* TODO: head merge to next could be attempted here
1452 			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1453 			 * though it might not be worth of the additional hassle
1454 			 *
1455 			 * ...we can probably just fallback to what was done
1456 			 * previously. We could try merging non-SACKed ones
1457 			 * as well but it probably isn't going to buy off
1458 			 * because later SACKs might again split them, and
1459 			 * it would make skb timestamp tracking considerably
1460 			 * harder problem.
1461 			 */
1462 			goto fallback;
1463 		}
1464 
1465 		len = end_seq - TCP_SKB_CB(skb)->seq;
1466 		BUG_ON(len < 0);
1467 		BUG_ON(len > skb->len);
1468 
1469 		/* MSS boundaries should be honoured or else pcount will
1470 		 * severely break even though it makes things bit trickier.
1471 		 * Optimize common case to avoid most of the divides
1472 		 */
1473 		mss = tcp_skb_mss(skb);
1474 
1475 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1476 		 * drop this restriction as unnecessary
1477 		 */
1478 		if (mss != tcp_skb_seglen(prev))
1479 			goto fallback;
1480 
1481 		if (len == mss) {
1482 			pcount = 1;
1483 		} else if (len < mss) {
1484 			goto noop;
1485 		} else {
1486 			pcount = len / mss;
1487 			len = pcount * mss;
1488 		}
1489 	}
1490 
1491 	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1492 	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1493 		goto fallback;
1494 
1495 	if (!skb_shift(prev, skb, len))
1496 		goto fallback;
1497 	if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1498 		goto out;
1499 
1500 	/* Hole filled allows collapsing with the next as well, this is very
1501 	 * useful when hole on every nth skb pattern happens
1502 	 */
1503 	if (prev == tcp_write_queue_tail(sk))
1504 		goto out;
1505 	skb = tcp_write_queue_next(sk, prev);
1506 
1507 	if (!skb_can_shift(skb) ||
1508 	    (skb == tcp_send_head(sk)) ||
1509 	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1510 	    (mss != tcp_skb_seglen(skb)))
1511 		goto out;
1512 
1513 	len = skb->len;
1514 	if (skb_shift(prev, skb, len)) {
1515 		pcount += tcp_skb_pcount(skb);
1516 		tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1517 	}
1518 
1519 out:
1520 	state->fack_count += pcount;
1521 	return prev;
1522 
1523 noop:
1524 	return skb;
1525 
1526 fallback:
1527 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1528 	return NULL;
1529 }
1530 
1531 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1532 					struct tcp_sack_block *next_dup,
1533 					struct tcp_sacktag_state *state,
1534 					u32 start_seq, u32 end_seq,
1535 					bool dup_sack_in)
1536 {
1537 	struct tcp_sock *tp = tcp_sk(sk);
1538 	struct sk_buff *tmp;
1539 
1540 	tcp_for_write_queue_from(skb, sk) {
1541 		int in_sack = 0;
1542 		bool dup_sack = dup_sack_in;
1543 
1544 		if (skb == tcp_send_head(sk))
1545 			break;
1546 
1547 		/* queue is in-order => we can short-circuit the walk early */
1548 		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1549 			break;
1550 
1551 		if (next_dup  &&
1552 		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1553 			in_sack = tcp_match_skb_to_sack(sk, skb,
1554 							next_dup->start_seq,
1555 							next_dup->end_seq);
1556 			if (in_sack > 0)
1557 				dup_sack = true;
1558 		}
1559 
1560 		/* skb reference here is a bit tricky to get right, since
1561 		 * shifting can eat and free both this skb and the next,
1562 		 * so not even _safe variant of the loop is enough.
1563 		 */
1564 		if (in_sack <= 0) {
1565 			tmp = tcp_shift_skb_data(sk, skb, state,
1566 						 start_seq, end_seq, dup_sack);
1567 			if (tmp) {
1568 				if (tmp != skb) {
1569 					skb = tmp;
1570 					continue;
1571 				}
1572 
1573 				in_sack = 0;
1574 			} else {
1575 				in_sack = tcp_match_skb_to_sack(sk, skb,
1576 								start_seq,
1577 								end_seq);
1578 			}
1579 		}
1580 
1581 		if (unlikely(in_sack < 0))
1582 			break;
1583 
1584 		if (in_sack) {
1585 			TCP_SKB_CB(skb)->sacked =
1586 				tcp_sacktag_one(sk,
1587 						state,
1588 						TCP_SKB_CB(skb)->sacked,
1589 						TCP_SKB_CB(skb)->seq,
1590 						TCP_SKB_CB(skb)->end_seq,
1591 						dup_sack,
1592 						tcp_skb_pcount(skb),
1593 						skb->skb_mstamp);
1594 			tcp_rate_skb_delivered(sk, skb, state->rate);
1595 
1596 			if (!before(TCP_SKB_CB(skb)->seq,
1597 				    tcp_highest_sack_seq(tp)))
1598 				tcp_advance_highest_sack(sk, skb);
1599 		}
1600 
1601 		state->fack_count += tcp_skb_pcount(skb);
1602 	}
1603 	return skb;
1604 }
1605 
1606 /* Avoid all extra work that is being done by sacktag while walking in
1607  * a normal way
1608  */
1609 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1610 					struct tcp_sacktag_state *state,
1611 					u32 skip_to_seq)
1612 {
1613 	tcp_for_write_queue_from(skb, sk) {
1614 		if (skb == tcp_send_head(sk))
1615 			break;
1616 
1617 		if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1618 			break;
1619 
1620 		state->fack_count += tcp_skb_pcount(skb);
1621 	}
1622 	return skb;
1623 }
1624 
1625 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1626 						struct sock *sk,
1627 						struct tcp_sack_block *next_dup,
1628 						struct tcp_sacktag_state *state,
1629 						u32 skip_to_seq)
1630 {
1631 	if (!next_dup)
1632 		return skb;
1633 
1634 	if (before(next_dup->start_seq, skip_to_seq)) {
1635 		skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1636 		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1637 				       next_dup->start_seq, next_dup->end_seq,
1638 				       1);
1639 	}
1640 
1641 	return skb;
1642 }
1643 
1644 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1645 {
1646 	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1647 }
1648 
1649 static int
1650 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1651 			u32 prior_snd_una, struct tcp_sacktag_state *state)
1652 {
1653 	struct tcp_sock *tp = tcp_sk(sk);
1654 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1655 				    TCP_SKB_CB(ack_skb)->sacked);
1656 	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1657 	struct tcp_sack_block sp[TCP_NUM_SACKS];
1658 	struct tcp_sack_block *cache;
1659 	struct sk_buff *skb;
1660 	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1661 	int used_sacks;
1662 	bool found_dup_sack = false;
1663 	int i, j;
1664 	int first_sack_index;
1665 
1666 	state->flag = 0;
1667 	state->reord = tp->packets_out;
1668 
1669 	if (!tp->sacked_out) {
1670 		if (WARN_ON(tp->fackets_out))
1671 			tp->fackets_out = 0;
1672 		tcp_highest_sack_reset(sk);
1673 	}
1674 
1675 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1676 					 num_sacks, prior_snd_una);
1677 	if (found_dup_sack) {
1678 		state->flag |= FLAG_DSACKING_ACK;
1679 		tp->delivered++; /* A spurious retransmission is delivered */
1680 	}
1681 
1682 	/* Eliminate too old ACKs, but take into
1683 	 * account more or less fresh ones, they can
1684 	 * contain valid SACK info.
1685 	 */
1686 	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1687 		return 0;
1688 
1689 	if (!tp->packets_out)
1690 		goto out;
1691 
1692 	used_sacks = 0;
1693 	first_sack_index = 0;
1694 	for (i = 0; i < num_sacks; i++) {
1695 		bool dup_sack = !i && found_dup_sack;
1696 
1697 		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1698 		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1699 
1700 		if (!tcp_is_sackblock_valid(tp, dup_sack,
1701 					    sp[used_sacks].start_seq,
1702 					    sp[used_sacks].end_seq)) {
1703 			int mib_idx;
1704 
1705 			if (dup_sack) {
1706 				if (!tp->undo_marker)
1707 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1708 				else
1709 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1710 			} else {
1711 				/* Don't count olds caused by ACK reordering */
1712 				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1713 				    !after(sp[used_sacks].end_seq, tp->snd_una))
1714 					continue;
1715 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1716 			}
1717 
1718 			NET_INC_STATS(sock_net(sk), mib_idx);
1719 			if (i == 0)
1720 				first_sack_index = -1;
1721 			continue;
1722 		}
1723 
1724 		/* Ignore very old stuff early */
1725 		if (!after(sp[used_sacks].end_seq, prior_snd_una))
1726 			continue;
1727 
1728 		used_sacks++;
1729 	}
1730 
1731 	/* order SACK blocks to allow in order walk of the retrans queue */
1732 	for (i = used_sacks - 1; i > 0; i--) {
1733 		for (j = 0; j < i; j++) {
1734 			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1735 				swap(sp[j], sp[j + 1]);
1736 
1737 				/* Track where the first SACK block goes to */
1738 				if (j == first_sack_index)
1739 					first_sack_index = j + 1;
1740 			}
1741 		}
1742 	}
1743 
1744 	skb = tcp_write_queue_head(sk);
1745 	state->fack_count = 0;
1746 	i = 0;
1747 
1748 	if (!tp->sacked_out) {
1749 		/* It's already past, so skip checking against it */
1750 		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1751 	} else {
1752 		cache = tp->recv_sack_cache;
1753 		/* Skip empty blocks in at head of the cache */
1754 		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1755 		       !cache->end_seq)
1756 			cache++;
1757 	}
1758 
1759 	while (i < used_sacks) {
1760 		u32 start_seq = sp[i].start_seq;
1761 		u32 end_seq = sp[i].end_seq;
1762 		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1763 		struct tcp_sack_block *next_dup = NULL;
1764 
1765 		if (found_dup_sack && ((i + 1) == first_sack_index))
1766 			next_dup = &sp[i + 1];
1767 
1768 		/* Skip too early cached blocks */
1769 		while (tcp_sack_cache_ok(tp, cache) &&
1770 		       !before(start_seq, cache->end_seq))
1771 			cache++;
1772 
1773 		/* Can skip some work by looking recv_sack_cache? */
1774 		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1775 		    after(end_seq, cache->start_seq)) {
1776 
1777 			/* Head todo? */
1778 			if (before(start_seq, cache->start_seq)) {
1779 				skb = tcp_sacktag_skip(skb, sk, state,
1780 						       start_seq);
1781 				skb = tcp_sacktag_walk(skb, sk, next_dup,
1782 						       state,
1783 						       start_seq,
1784 						       cache->start_seq,
1785 						       dup_sack);
1786 			}
1787 
1788 			/* Rest of the block already fully processed? */
1789 			if (!after(end_seq, cache->end_seq))
1790 				goto advance_sp;
1791 
1792 			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1793 						       state,
1794 						       cache->end_seq);
1795 
1796 			/* ...tail remains todo... */
1797 			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1798 				/* ...but better entrypoint exists! */
1799 				skb = tcp_highest_sack(sk);
1800 				if (!skb)
1801 					break;
1802 				state->fack_count = tp->fackets_out;
1803 				cache++;
1804 				goto walk;
1805 			}
1806 
1807 			skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
1808 			/* Check overlap against next cached too (past this one already) */
1809 			cache++;
1810 			continue;
1811 		}
1812 
1813 		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1814 			skb = tcp_highest_sack(sk);
1815 			if (!skb)
1816 				break;
1817 			state->fack_count = tp->fackets_out;
1818 		}
1819 		skb = tcp_sacktag_skip(skb, sk, state, start_seq);
1820 
1821 walk:
1822 		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1823 				       start_seq, end_seq, dup_sack);
1824 
1825 advance_sp:
1826 		i++;
1827 	}
1828 
1829 	/* Clear the head of the cache sack blocks so we can skip it next time */
1830 	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1831 		tp->recv_sack_cache[i].start_seq = 0;
1832 		tp->recv_sack_cache[i].end_seq = 0;
1833 	}
1834 	for (j = 0; j < used_sacks; j++)
1835 		tp->recv_sack_cache[i++] = sp[j];
1836 
1837 	if ((state->reord < tp->fackets_out) &&
1838 	    ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1839 		tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);
1840 
1841 	tcp_verify_left_out(tp);
1842 out:
1843 
1844 #if FASTRETRANS_DEBUG > 0
1845 	WARN_ON((int)tp->sacked_out < 0);
1846 	WARN_ON((int)tp->lost_out < 0);
1847 	WARN_ON((int)tp->retrans_out < 0);
1848 	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1849 #endif
1850 	return state->flag;
1851 }
1852 
1853 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1854  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1855  */
1856 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1857 {
1858 	u32 holes;
1859 
1860 	holes = max(tp->lost_out, 1U);
1861 	holes = min(holes, tp->packets_out);
1862 
1863 	if ((tp->sacked_out + holes) > tp->packets_out) {
1864 		tp->sacked_out = tp->packets_out - holes;
1865 		return true;
1866 	}
1867 	return false;
1868 }
1869 
1870 /* If we receive more dupacks than we expected counting segments
1871  * in assumption of absent reordering, interpret this as reordering.
1872  * The only another reason could be bug in receiver TCP.
1873  */
1874 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1875 {
1876 	struct tcp_sock *tp = tcp_sk(sk);
1877 	if (tcp_limit_reno_sacked(tp))
1878 		tcp_update_reordering(sk, tp->packets_out + addend, 0);
1879 }
1880 
1881 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1882 
1883 static void tcp_add_reno_sack(struct sock *sk)
1884 {
1885 	struct tcp_sock *tp = tcp_sk(sk);
1886 	u32 prior_sacked = tp->sacked_out;
1887 
1888 	tp->sacked_out++;
1889 	tcp_check_reno_reordering(sk, 0);
1890 	if (tp->sacked_out > prior_sacked)
1891 		tp->delivered++; /* Some out-of-order packet is delivered */
1892 	tcp_verify_left_out(tp);
1893 }
1894 
1895 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1896 
1897 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1898 {
1899 	struct tcp_sock *tp = tcp_sk(sk);
1900 
1901 	if (acked > 0) {
1902 		/* One ACK acked hole. The rest eat duplicate ACKs. */
1903 		tp->delivered += max_t(int, acked - tp->sacked_out, 1);
1904 		if (acked - 1 >= tp->sacked_out)
1905 			tp->sacked_out = 0;
1906 		else
1907 			tp->sacked_out -= acked - 1;
1908 	}
1909 	tcp_check_reno_reordering(sk, acked);
1910 	tcp_verify_left_out(tp);
1911 }
1912 
1913 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1914 {
1915 	tp->sacked_out = 0;
1916 }
1917 
1918 void tcp_clear_retrans(struct tcp_sock *tp)
1919 {
1920 	tp->retrans_out = 0;
1921 	tp->lost_out = 0;
1922 	tp->undo_marker = 0;
1923 	tp->undo_retrans = -1;
1924 	tp->fackets_out = 0;
1925 	tp->sacked_out = 0;
1926 }
1927 
1928 static inline void tcp_init_undo(struct tcp_sock *tp)
1929 {
1930 	tp->undo_marker = tp->snd_una;
1931 	/* Retransmission still in flight may cause DSACKs later. */
1932 	tp->undo_retrans = tp->retrans_out ? : -1;
1933 }
1934 
1935 /* Enter Loss state. If we detect SACK reneging, forget all SACK information
1936  * and reset tags completely, otherwise preserve SACKs. If receiver
1937  * dropped its ofo queue, we will know this due to reneging detection.
1938  */
1939 void tcp_enter_loss(struct sock *sk)
1940 {
1941 	const struct inet_connection_sock *icsk = inet_csk(sk);
1942 	struct tcp_sock *tp = tcp_sk(sk);
1943 	struct net *net = sock_net(sk);
1944 	struct sk_buff *skb;
1945 	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
1946 	bool is_reneg;			/* is receiver reneging on SACKs? */
1947 	bool mark_lost;
1948 
1949 	/* Reduce ssthresh if it has not yet been made inside this window. */
1950 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1951 	    !after(tp->high_seq, tp->snd_una) ||
1952 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1953 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
1954 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1955 		tcp_ca_event(sk, CA_EVENT_LOSS);
1956 		tcp_init_undo(tp);
1957 	}
1958 	tp->snd_cwnd	   = 1;
1959 	tp->snd_cwnd_cnt   = 0;
1960 	tp->snd_cwnd_stamp = tcp_jiffies32;
1961 
1962 	tp->retrans_out = 0;
1963 	tp->lost_out = 0;
1964 
1965 	if (tcp_is_reno(tp))
1966 		tcp_reset_reno_sack(tp);
1967 
1968 	skb = tcp_write_queue_head(sk);
1969 	is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
1970 	if (is_reneg) {
1971 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1972 		tp->sacked_out = 0;
1973 		tp->fackets_out = 0;
1974 	}
1975 	tcp_clear_all_retrans_hints(tp);
1976 
1977 	tcp_for_write_queue(skb, sk) {
1978 		if (skb == tcp_send_head(sk))
1979 			break;
1980 
1981 		mark_lost = (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
1982 			     is_reneg);
1983 		if (mark_lost)
1984 			tcp_sum_lost(tp, skb);
1985 		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1986 		if (mark_lost) {
1987 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1988 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1989 			tp->lost_out += tcp_skb_pcount(skb);
1990 		}
1991 	}
1992 	tcp_verify_left_out(tp);
1993 
1994 	/* Timeout in disordered state after receiving substantial DUPACKs
1995 	 * suggests that the degree of reordering is over-estimated.
1996 	 */
1997 	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1998 	    tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
1999 		tp->reordering = min_t(unsigned int, tp->reordering,
2000 				       net->ipv4.sysctl_tcp_reordering);
2001 	tcp_set_ca_state(sk, TCP_CA_Loss);
2002 	tp->high_seq = tp->snd_nxt;
2003 	tcp_ecn_queue_cwr(tp);
2004 
2005 	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2006 	 * loss recovery is underway except recurring timeout(s) on
2007 	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2008 	 *
2009 	 * In theory F-RTO can be used repeatedly during loss recovery.
2010 	 * In practice this interacts badly with broken middle-boxes that
2011 	 * falsely raise the receive window, which results in repeated
2012 	 * timeouts and stop-and-go behavior.
2013 	 */
2014 	tp->frto = sysctl_tcp_frto &&
2015 		   (new_recovery || icsk->icsk_retransmits) &&
2016 		   !inet_csk(sk)->icsk_mtup.probe_size;
2017 }
2018 
2019 /* If ACK arrived pointing to a remembered SACK, it means that our
2020  * remembered SACKs do not reflect real state of receiver i.e.
2021  * receiver _host_ is heavily congested (or buggy).
2022  *
2023  * To avoid big spurious retransmission bursts due to transient SACK
2024  * scoreboard oddities that look like reneging, we give the receiver a
2025  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2026  * restore sanity to the SACK scoreboard. If the apparent reneging
2027  * persists until this RTO then we'll clear the SACK scoreboard.
2028  */
2029 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2030 {
2031 	if (flag & FLAG_SACK_RENEGING) {
2032 		struct tcp_sock *tp = tcp_sk(sk);
2033 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2034 					  msecs_to_jiffies(10));
2035 
2036 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2037 					  delay, TCP_RTO_MAX);
2038 		return true;
2039 	}
2040 	return false;
2041 }
2042 
2043 static inline int tcp_fackets_out(const struct tcp_sock *tp)
2044 {
2045 	return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2046 }
2047 
2048 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2049  * counter when SACK is enabled (without SACK, sacked_out is used for
2050  * that purpose).
2051  *
2052  * Instead, with FACK TCP uses fackets_out that includes both SACKed
2053  * segments up to the highest received SACK block so far and holes in
2054  * between them.
2055  *
2056  * With reordering, holes may still be in flight, so RFC3517 recovery
2057  * uses pure sacked_out (total number of SACKed segments) even though
2058  * it violates the RFC that uses duplicate ACKs, often these are equal
2059  * but when e.g. out-of-window ACKs or packet duplication occurs,
2060  * they differ. Since neither occurs due to loss, TCP should really
2061  * ignore them.
2062  */
2063 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2064 {
2065 	return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2066 }
2067 
2068 /* Linux NewReno/SACK/FACK/ECN state machine.
2069  * --------------------------------------
2070  *
2071  * "Open"	Normal state, no dubious events, fast path.
2072  * "Disorder"   In all the respects it is "Open",
2073  *		but requires a bit more attention. It is entered when
2074  *		we see some SACKs or dupacks. It is split of "Open"
2075  *		mainly to move some processing from fast path to slow one.
2076  * "CWR"	CWND was reduced due to some Congestion Notification event.
2077  *		It can be ECN, ICMP source quench, local device congestion.
2078  * "Recovery"	CWND was reduced, we are fast-retransmitting.
2079  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2080  *
2081  * tcp_fastretrans_alert() is entered:
2082  * - each incoming ACK, if state is not "Open"
2083  * - when arrived ACK is unusual, namely:
2084  *	* SACK
2085  *	* Duplicate ACK.
2086  *	* ECN ECE.
2087  *
2088  * Counting packets in flight is pretty simple.
2089  *
2090  *	in_flight = packets_out - left_out + retrans_out
2091  *
2092  *	packets_out is SND.NXT-SND.UNA counted in packets.
2093  *
2094  *	retrans_out is number of retransmitted segments.
2095  *
2096  *	left_out is number of segments left network, but not ACKed yet.
2097  *
2098  *		left_out = sacked_out + lost_out
2099  *
2100  *     sacked_out: Packets, which arrived to receiver out of order
2101  *		   and hence not ACKed. With SACKs this number is simply
2102  *		   amount of SACKed data. Even without SACKs
2103  *		   it is easy to give pretty reliable estimate of this number,
2104  *		   counting duplicate ACKs.
2105  *
2106  *       lost_out: Packets lost by network. TCP has no explicit
2107  *		   "loss notification" feedback from network (for now).
2108  *		   It means that this number can be only _guessed_.
2109  *		   Actually, it is the heuristics to predict lossage that
2110  *		   distinguishes different algorithms.
2111  *
2112  *	F.e. after RTO, when all the queue is considered as lost,
2113  *	lost_out = packets_out and in_flight = retrans_out.
2114  *
2115  *		Essentially, we have now a few algorithms detecting
2116  *		lost packets.
2117  *
2118  *		If the receiver supports SACK:
2119  *
2120  *		RFC6675/3517: It is the conventional algorithm. A packet is
2121  *		considered lost if the number of higher sequence packets
2122  *		SACKed is greater than or equal the DUPACK thoreshold
2123  *		(reordering). This is implemented in tcp_mark_head_lost and
2124  *		tcp_update_scoreboard.
2125  *
2126  *		RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2127  *		(2017-) that checks timing instead of counting DUPACKs.
2128  *		Essentially a packet is considered lost if it's not S/ACKed
2129  *		after RTT + reordering_window, where both metrics are
2130  *		dynamically measured and adjusted. This is implemented in
2131  *		tcp_rack_mark_lost.
2132  *
2133  *		FACK (Disabled by default. Subsumbed by RACK):
2134  *		It is the simplest heuristics. As soon as we decided
2135  *		that something is lost, we decide that _all_ not SACKed
2136  *		packets until the most forward SACK are lost. I.e.
2137  *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
2138  *		It is absolutely correct estimate, if network does not reorder
2139  *		packets. And it loses any connection to reality when reordering
2140  *		takes place. We use FACK by default until reordering
2141  *		is suspected on the path to this destination.
2142  *
2143  *		If the receiver does not support SACK:
2144  *
2145  *		NewReno (RFC6582): in Recovery we assume that one segment
2146  *		is lost (classic Reno). While we are in Recovery and
2147  *		a partial ACK arrives, we assume that one more packet
2148  *		is lost (NewReno). This heuristics are the same in NewReno
2149  *		and SACK.
2150  *
2151  * Really tricky (and requiring careful tuning) part of algorithm
2152  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2153  * The first determines the moment _when_ we should reduce CWND and,
2154  * hence, slow down forward transmission. In fact, it determines the moment
2155  * when we decide that hole is caused by loss, rather than by a reorder.
2156  *
2157  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2158  * holes, caused by lost packets.
2159  *
2160  * And the most logically complicated part of algorithm is undo
2161  * heuristics. We detect false retransmits due to both too early
2162  * fast retransmit (reordering) and underestimated RTO, analyzing
2163  * timestamps and D-SACKs. When we detect that some segments were
2164  * retransmitted by mistake and CWND reduction was wrong, we undo
2165  * window reduction and abort recovery phase. This logic is hidden
2166  * inside several functions named tcp_try_undo_<something>.
2167  */
2168 
2169 /* This function decides, when we should leave Disordered state
2170  * and enter Recovery phase, reducing congestion window.
2171  *
2172  * Main question: may we further continue forward transmission
2173  * with the same cwnd?
2174  */
2175 static bool tcp_time_to_recover(struct sock *sk, int flag)
2176 {
2177 	struct tcp_sock *tp = tcp_sk(sk);
2178 
2179 	/* Trick#1: The loss is proven. */
2180 	if (tp->lost_out)
2181 		return true;
2182 
2183 	/* Not-A-Trick#2 : Classic rule... */
2184 	if (tcp_dupack_heuristics(tp) > tp->reordering)
2185 		return true;
2186 
2187 	return false;
2188 }
2189 
2190 /* Detect loss in event "A" above by marking head of queue up as lost.
2191  * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2192  * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2193  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2194  * the maximum SACKed segments to pass before reaching this limit.
2195  */
2196 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2197 {
2198 	struct tcp_sock *tp = tcp_sk(sk);
2199 	struct sk_buff *skb;
2200 	int cnt, oldcnt, lost;
2201 	unsigned int mss;
2202 	/* Use SACK to deduce losses of new sequences sent during recovery */
2203 	const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2204 
2205 	WARN_ON(packets > tp->packets_out);
2206 	if (tp->lost_skb_hint) {
2207 		skb = tp->lost_skb_hint;
2208 		cnt = tp->lost_cnt_hint;
2209 		/* Head already handled? */
2210 		if (mark_head && skb != tcp_write_queue_head(sk))
2211 			return;
2212 	} else {
2213 		skb = tcp_write_queue_head(sk);
2214 		cnt = 0;
2215 	}
2216 
2217 	tcp_for_write_queue_from(skb, sk) {
2218 		if (skb == tcp_send_head(sk))
2219 			break;
2220 		/* TODO: do this better */
2221 		/* this is not the most efficient way to do this... */
2222 		tp->lost_skb_hint = skb;
2223 		tp->lost_cnt_hint = cnt;
2224 
2225 		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2226 			break;
2227 
2228 		oldcnt = cnt;
2229 		if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2230 		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2231 			cnt += tcp_skb_pcount(skb);
2232 
2233 		if (cnt > packets) {
2234 			if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2235 			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2236 			    (oldcnt >= packets))
2237 				break;
2238 
2239 			mss = tcp_skb_mss(skb);
2240 			/* If needed, chop off the prefix to mark as lost. */
2241 			lost = (packets - oldcnt) * mss;
2242 			if (lost < skb->len &&
2243 			    tcp_fragment(sk, skb, lost, mss, GFP_ATOMIC) < 0)
2244 				break;
2245 			cnt = packets;
2246 		}
2247 
2248 		tcp_skb_mark_lost(tp, skb);
2249 
2250 		if (mark_head)
2251 			break;
2252 	}
2253 	tcp_verify_left_out(tp);
2254 }
2255 
2256 /* Account newly detected lost packet(s) */
2257 
2258 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2259 {
2260 	struct tcp_sock *tp = tcp_sk(sk);
2261 
2262 	if (tcp_is_reno(tp)) {
2263 		tcp_mark_head_lost(sk, 1, 1);
2264 	} else if (tcp_is_fack(tp)) {
2265 		int lost = tp->fackets_out - tp->reordering;
2266 		if (lost <= 0)
2267 			lost = 1;
2268 		tcp_mark_head_lost(sk, lost, 0);
2269 	} else {
2270 		int sacked_upto = tp->sacked_out - tp->reordering;
2271 		if (sacked_upto >= 0)
2272 			tcp_mark_head_lost(sk, sacked_upto, 0);
2273 		else if (fast_rexmit)
2274 			tcp_mark_head_lost(sk, 1, 1);
2275 	}
2276 }
2277 
2278 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2279 {
2280 	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2281 	       before(tp->rx_opt.rcv_tsecr, when);
2282 }
2283 
2284 /* skb is spurious retransmitted if the returned timestamp echo
2285  * reply is prior to the skb transmission time
2286  */
2287 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2288 				     const struct sk_buff *skb)
2289 {
2290 	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2291 	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2292 }
2293 
2294 /* Nothing was retransmitted or returned timestamp is less
2295  * than timestamp of the first retransmission.
2296  */
2297 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2298 {
2299 	return !tp->retrans_stamp ||
2300 	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2301 }
2302 
2303 /* Undo procedures. */
2304 
2305 /* We can clear retrans_stamp when there are no retransmissions in the
2306  * window. It would seem that it is trivially available for us in
2307  * tp->retrans_out, however, that kind of assumptions doesn't consider
2308  * what will happen if errors occur when sending retransmission for the
2309  * second time. ...It could the that such segment has only
2310  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2311  * the head skb is enough except for some reneging corner cases that
2312  * are not worth the effort.
2313  *
2314  * Main reason for all this complexity is the fact that connection dying
2315  * time now depends on the validity of the retrans_stamp, in particular,
2316  * that successive retransmissions of a segment must not advance
2317  * retrans_stamp under any conditions.
2318  */
2319 static bool tcp_any_retrans_done(const struct sock *sk)
2320 {
2321 	const struct tcp_sock *tp = tcp_sk(sk);
2322 	struct sk_buff *skb;
2323 
2324 	if (tp->retrans_out)
2325 		return true;
2326 
2327 	skb = tcp_write_queue_head(sk);
2328 	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2329 		return true;
2330 
2331 	return false;
2332 }
2333 
2334 #if FASTRETRANS_DEBUG > 1
2335 static void DBGUNDO(struct sock *sk, const char *msg)
2336 {
2337 	struct tcp_sock *tp = tcp_sk(sk);
2338 	struct inet_sock *inet = inet_sk(sk);
2339 
2340 	if (sk->sk_family == AF_INET) {
2341 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2342 			 msg,
2343 			 &inet->inet_daddr, ntohs(inet->inet_dport),
2344 			 tp->snd_cwnd, tcp_left_out(tp),
2345 			 tp->snd_ssthresh, tp->prior_ssthresh,
2346 			 tp->packets_out);
2347 	}
2348 #if IS_ENABLED(CONFIG_IPV6)
2349 	else if (sk->sk_family == AF_INET6) {
2350 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2351 			 msg,
2352 			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2353 			 tp->snd_cwnd, tcp_left_out(tp),
2354 			 tp->snd_ssthresh, tp->prior_ssthresh,
2355 			 tp->packets_out);
2356 	}
2357 #endif
2358 }
2359 #else
2360 #define DBGUNDO(x...) do { } while (0)
2361 #endif
2362 
2363 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2364 {
2365 	struct tcp_sock *tp = tcp_sk(sk);
2366 
2367 	if (unmark_loss) {
2368 		struct sk_buff *skb;
2369 
2370 		tcp_for_write_queue(skb, sk) {
2371 			if (skb == tcp_send_head(sk))
2372 				break;
2373 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2374 		}
2375 		tp->lost_out = 0;
2376 		tcp_clear_all_retrans_hints(tp);
2377 	}
2378 
2379 	if (tp->prior_ssthresh) {
2380 		const struct inet_connection_sock *icsk = inet_csk(sk);
2381 
2382 		tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2383 
2384 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2385 			tp->snd_ssthresh = tp->prior_ssthresh;
2386 			tcp_ecn_withdraw_cwr(tp);
2387 		}
2388 	}
2389 	tp->snd_cwnd_stamp = tcp_jiffies32;
2390 	tp->undo_marker = 0;
2391 }
2392 
2393 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2394 {
2395 	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2396 }
2397 
2398 /* People celebrate: "We love our President!" */
2399 static bool tcp_try_undo_recovery(struct sock *sk)
2400 {
2401 	struct tcp_sock *tp = tcp_sk(sk);
2402 
2403 	if (tcp_may_undo(tp)) {
2404 		int mib_idx;
2405 
2406 		/* Happy end! We did not retransmit anything
2407 		 * or our original transmission succeeded.
2408 		 */
2409 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2410 		tcp_undo_cwnd_reduction(sk, false);
2411 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2412 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2413 		else
2414 			mib_idx = LINUX_MIB_TCPFULLUNDO;
2415 
2416 		NET_INC_STATS(sock_net(sk), mib_idx);
2417 	}
2418 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2419 		/* Hold old state until something *above* high_seq
2420 		 * is ACKed. For Reno it is MUST to prevent false
2421 		 * fast retransmits (RFC2582). SACK TCP is safe. */
2422 		if (!tcp_any_retrans_done(sk))
2423 			tp->retrans_stamp = 0;
2424 		return true;
2425 	}
2426 	tcp_set_ca_state(sk, TCP_CA_Open);
2427 	return false;
2428 }
2429 
2430 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2431 static bool tcp_try_undo_dsack(struct sock *sk)
2432 {
2433 	struct tcp_sock *tp = tcp_sk(sk);
2434 
2435 	if (tp->undo_marker && !tp->undo_retrans) {
2436 		DBGUNDO(sk, "D-SACK");
2437 		tcp_undo_cwnd_reduction(sk, false);
2438 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2439 		return true;
2440 	}
2441 	return false;
2442 }
2443 
2444 /* Undo during loss recovery after partial ACK or using F-RTO. */
2445 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2446 {
2447 	struct tcp_sock *tp = tcp_sk(sk);
2448 
2449 	if (frto_undo || tcp_may_undo(tp)) {
2450 		tcp_undo_cwnd_reduction(sk, true);
2451 
2452 		DBGUNDO(sk, "partial loss");
2453 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2454 		if (frto_undo)
2455 			NET_INC_STATS(sock_net(sk),
2456 					LINUX_MIB_TCPSPURIOUSRTOS);
2457 		inet_csk(sk)->icsk_retransmits = 0;
2458 		if (frto_undo || tcp_is_sack(tp))
2459 			tcp_set_ca_state(sk, TCP_CA_Open);
2460 		return true;
2461 	}
2462 	return false;
2463 }
2464 
2465 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2466  * It computes the number of packets to send (sndcnt) based on packets newly
2467  * delivered:
2468  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2469  *	cwnd reductions across a full RTT.
2470  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2471  *      But when the retransmits are acked without further losses, PRR
2472  *      slow starts cwnd up to ssthresh to speed up the recovery.
2473  */
2474 static void tcp_init_cwnd_reduction(struct sock *sk)
2475 {
2476 	struct tcp_sock *tp = tcp_sk(sk);
2477 
2478 	tp->high_seq = tp->snd_nxt;
2479 	tp->tlp_high_seq = 0;
2480 	tp->snd_cwnd_cnt = 0;
2481 	tp->prior_cwnd = tp->snd_cwnd;
2482 	tp->prr_delivered = 0;
2483 	tp->prr_out = 0;
2484 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2485 	tcp_ecn_queue_cwr(tp);
2486 }
2487 
2488 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
2489 {
2490 	struct tcp_sock *tp = tcp_sk(sk);
2491 	int sndcnt = 0;
2492 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2493 
2494 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2495 		return;
2496 
2497 	tp->prr_delivered += newly_acked_sacked;
2498 	if (delta < 0) {
2499 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2500 			       tp->prior_cwnd - 1;
2501 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2502 	} else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
2503 		   !(flag & FLAG_LOST_RETRANS)) {
2504 		sndcnt = min_t(int, delta,
2505 			       max_t(int, tp->prr_delivered - tp->prr_out,
2506 				     newly_acked_sacked) + 1);
2507 	} else {
2508 		sndcnt = min(delta, newly_acked_sacked);
2509 	}
2510 	/* Force a fast retransmit upon entering fast recovery */
2511 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2512 	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2513 }
2514 
2515 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2516 {
2517 	struct tcp_sock *tp = tcp_sk(sk);
2518 
2519 	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2520 		return;
2521 
2522 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2523 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2524 	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2525 		tp->snd_cwnd = tp->snd_ssthresh;
2526 		tp->snd_cwnd_stamp = tcp_jiffies32;
2527 	}
2528 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2529 }
2530 
2531 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2532 void tcp_enter_cwr(struct sock *sk)
2533 {
2534 	struct tcp_sock *tp = tcp_sk(sk);
2535 
2536 	tp->prior_ssthresh = 0;
2537 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2538 		tp->undo_marker = 0;
2539 		tcp_init_cwnd_reduction(sk);
2540 		tcp_set_ca_state(sk, TCP_CA_CWR);
2541 	}
2542 }
2543 EXPORT_SYMBOL(tcp_enter_cwr);
2544 
2545 static void tcp_try_keep_open(struct sock *sk)
2546 {
2547 	struct tcp_sock *tp = tcp_sk(sk);
2548 	int state = TCP_CA_Open;
2549 
2550 	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2551 		state = TCP_CA_Disorder;
2552 
2553 	if (inet_csk(sk)->icsk_ca_state != state) {
2554 		tcp_set_ca_state(sk, state);
2555 		tp->high_seq = tp->snd_nxt;
2556 	}
2557 }
2558 
2559 static void tcp_try_to_open(struct sock *sk, int flag)
2560 {
2561 	struct tcp_sock *tp = tcp_sk(sk);
2562 
2563 	tcp_verify_left_out(tp);
2564 
2565 	if (!tcp_any_retrans_done(sk))
2566 		tp->retrans_stamp = 0;
2567 
2568 	if (flag & FLAG_ECE)
2569 		tcp_enter_cwr(sk);
2570 
2571 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2572 		tcp_try_keep_open(sk);
2573 	}
2574 }
2575 
2576 static void tcp_mtup_probe_failed(struct sock *sk)
2577 {
2578 	struct inet_connection_sock *icsk = inet_csk(sk);
2579 
2580 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2581 	icsk->icsk_mtup.probe_size = 0;
2582 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2583 }
2584 
2585 static void tcp_mtup_probe_success(struct sock *sk)
2586 {
2587 	struct tcp_sock *tp = tcp_sk(sk);
2588 	struct inet_connection_sock *icsk = inet_csk(sk);
2589 
2590 	/* FIXME: breaks with very large cwnd */
2591 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2592 	tp->snd_cwnd = tp->snd_cwnd *
2593 		       tcp_mss_to_mtu(sk, tp->mss_cache) /
2594 		       icsk->icsk_mtup.probe_size;
2595 	tp->snd_cwnd_cnt = 0;
2596 	tp->snd_cwnd_stamp = tcp_jiffies32;
2597 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2598 
2599 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2600 	icsk->icsk_mtup.probe_size = 0;
2601 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2602 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2603 }
2604 
2605 /* Do a simple retransmit without using the backoff mechanisms in
2606  * tcp_timer. This is used for path mtu discovery.
2607  * The socket is already locked here.
2608  */
2609 void tcp_simple_retransmit(struct sock *sk)
2610 {
2611 	const struct inet_connection_sock *icsk = inet_csk(sk);
2612 	struct tcp_sock *tp = tcp_sk(sk);
2613 	struct sk_buff *skb;
2614 	unsigned int mss = tcp_current_mss(sk);
2615 	u32 prior_lost = tp->lost_out;
2616 
2617 	tcp_for_write_queue(skb, sk) {
2618 		if (skb == tcp_send_head(sk))
2619 			break;
2620 		if (tcp_skb_seglen(skb) > mss &&
2621 		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2622 			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2623 				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2624 				tp->retrans_out -= tcp_skb_pcount(skb);
2625 			}
2626 			tcp_skb_mark_lost_uncond_verify(tp, skb);
2627 		}
2628 	}
2629 
2630 	tcp_clear_retrans_hints_partial(tp);
2631 
2632 	if (prior_lost == tp->lost_out)
2633 		return;
2634 
2635 	if (tcp_is_reno(tp))
2636 		tcp_limit_reno_sacked(tp);
2637 
2638 	tcp_verify_left_out(tp);
2639 
2640 	/* Don't muck with the congestion window here.
2641 	 * Reason is that we do not increase amount of _data_
2642 	 * in network, but units changed and effective
2643 	 * cwnd/ssthresh really reduced now.
2644 	 */
2645 	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2646 		tp->high_seq = tp->snd_nxt;
2647 		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2648 		tp->prior_ssthresh = 0;
2649 		tp->undo_marker = 0;
2650 		tcp_set_ca_state(sk, TCP_CA_Loss);
2651 	}
2652 	tcp_xmit_retransmit_queue(sk);
2653 }
2654 EXPORT_SYMBOL(tcp_simple_retransmit);
2655 
2656 void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2657 {
2658 	struct tcp_sock *tp = tcp_sk(sk);
2659 	int mib_idx;
2660 
2661 	if (tcp_is_reno(tp))
2662 		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2663 	else
2664 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2665 
2666 	NET_INC_STATS(sock_net(sk), mib_idx);
2667 
2668 	tp->prior_ssthresh = 0;
2669 	tcp_init_undo(tp);
2670 
2671 	if (!tcp_in_cwnd_reduction(sk)) {
2672 		if (!ece_ack)
2673 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2674 		tcp_init_cwnd_reduction(sk);
2675 	}
2676 	tcp_set_ca_state(sk, TCP_CA_Recovery);
2677 }
2678 
2679 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2680  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2681  */
2682 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
2683 			     int *rexmit)
2684 {
2685 	struct tcp_sock *tp = tcp_sk(sk);
2686 	bool recovered = !before(tp->snd_una, tp->high_seq);
2687 
2688 	if ((flag & FLAG_SND_UNA_ADVANCED) &&
2689 	    tcp_try_undo_loss(sk, false))
2690 		return;
2691 
2692 	/* The ACK (s)acks some never-retransmitted data meaning not all
2693 	 * the data packets before the timeout were lost. Therefore we
2694 	 * undo the congestion window and state. This is essentially
2695 	 * the operation in F-RTO (RFC5682 section 3.1 step 3.b). Since
2696 	 * a retransmitted skb is permantly marked, we can apply such an
2697 	 * operation even if F-RTO was not used.
2698 	 */
2699 	if ((flag & FLAG_ORIG_SACK_ACKED) &&
2700 	    tcp_try_undo_loss(sk, tp->undo_marker))
2701 		return;
2702 
2703 	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2704 		if (after(tp->snd_nxt, tp->high_seq)) {
2705 			if (flag & FLAG_DATA_SACKED || is_dupack)
2706 				tp->frto = 0; /* Step 3.a. loss was real */
2707 		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2708 			tp->high_seq = tp->snd_nxt;
2709 			/* Step 2.b. Try send new data (but deferred until cwnd
2710 			 * is updated in tcp_ack()). Otherwise fall back to
2711 			 * the conventional recovery.
2712 			 */
2713 			if (tcp_send_head(sk) &&
2714 			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
2715 				*rexmit = REXMIT_NEW;
2716 				return;
2717 			}
2718 			tp->frto = 0;
2719 		}
2720 	}
2721 
2722 	if (recovered) {
2723 		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2724 		tcp_try_undo_recovery(sk);
2725 		return;
2726 	}
2727 	if (tcp_is_reno(tp)) {
2728 		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2729 		 * delivered. Lower inflight to clock out (re)tranmissions.
2730 		 */
2731 		if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2732 			tcp_add_reno_sack(sk);
2733 		else if (flag & FLAG_SND_UNA_ADVANCED)
2734 			tcp_reset_reno_sack(tp);
2735 	}
2736 	*rexmit = REXMIT_LOST;
2737 }
2738 
2739 /* Undo during fast recovery after partial ACK. */
2740 static bool tcp_try_undo_partial(struct sock *sk, const int acked)
2741 {
2742 	struct tcp_sock *tp = tcp_sk(sk);
2743 
2744 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
2745 		/* Plain luck! Hole if filled with delayed
2746 		 * packet, rather than with a retransmit.
2747 		 */
2748 		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2749 
2750 		/* We are getting evidence that the reordering degree is higher
2751 		 * than we realized. If there are no retransmits out then we
2752 		 * can undo. Otherwise we clock out new packets but do not
2753 		 * mark more packets lost or retransmit more.
2754 		 */
2755 		if (tp->retrans_out)
2756 			return true;
2757 
2758 		if (!tcp_any_retrans_done(sk))
2759 			tp->retrans_stamp = 0;
2760 
2761 		DBGUNDO(sk, "partial recovery");
2762 		tcp_undo_cwnd_reduction(sk, true);
2763 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2764 		tcp_try_keep_open(sk);
2765 		return true;
2766 	}
2767 	return false;
2768 }
2769 
2770 static void tcp_rack_identify_loss(struct sock *sk, int *ack_flag)
2771 {
2772 	struct tcp_sock *tp = tcp_sk(sk);
2773 
2774 	/* Use RACK to detect loss */
2775 	if (sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION) {
2776 		u32 prior_retrans = tp->retrans_out;
2777 
2778 		tcp_rack_mark_lost(sk);
2779 		if (prior_retrans > tp->retrans_out)
2780 			*ack_flag |= FLAG_LOST_RETRANS;
2781 	}
2782 }
2783 
2784 /* Process an event, which can update packets-in-flight not trivially.
2785  * Main goal of this function is to calculate new estimate for left_out,
2786  * taking into account both packets sitting in receiver's buffer and
2787  * packets lost by network.
2788  *
2789  * Besides that it updates the congestion state when packet loss or ECN
2790  * is detected. But it does not reduce the cwnd, it is done by the
2791  * congestion control later.
2792  *
2793  * It does _not_ decide what to send, it is made in function
2794  * tcp_xmit_retransmit_queue().
2795  */
2796 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2797 				  bool is_dupack, int *ack_flag, int *rexmit)
2798 {
2799 	struct inet_connection_sock *icsk = inet_csk(sk);
2800 	struct tcp_sock *tp = tcp_sk(sk);
2801 	int fast_rexmit = 0, flag = *ack_flag;
2802 	bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2803 				    (tcp_fackets_out(tp) > tp->reordering));
2804 
2805 	if (WARN_ON(!tp->packets_out && tp->sacked_out))
2806 		tp->sacked_out = 0;
2807 	if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2808 		tp->fackets_out = 0;
2809 
2810 	/* Now state machine starts.
2811 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2812 	if (flag & FLAG_ECE)
2813 		tp->prior_ssthresh = 0;
2814 
2815 	/* B. In all the states check for reneging SACKs. */
2816 	if (tcp_check_sack_reneging(sk, flag))
2817 		return;
2818 
2819 	/* C. Check consistency of the current state. */
2820 	tcp_verify_left_out(tp);
2821 
2822 	/* D. Check state exit conditions. State can be terminated
2823 	 *    when high_seq is ACKed. */
2824 	if (icsk->icsk_ca_state == TCP_CA_Open) {
2825 		WARN_ON(tp->retrans_out != 0);
2826 		tp->retrans_stamp = 0;
2827 	} else if (!before(tp->snd_una, tp->high_seq)) {
2828 		switch (icsk->icsk_ca_state) {
2829 		case TCP_CA_CWR:
2830 			/* CWR is to be held something *above* high_seq
2831 			 * is ACKed for CWR bit to reach receiver. */
2832 			if (tp->snd_una != tp->high_seq) {
2833 				tcp_end_cwnd_reduction(sk);
2834 				tcp_set_ca_state(sk, TCP_CA_Open);
2835 			}
2836 			break;
2837 
2838 		case TCP_CA_Recovery:
2839 			if (tcp_is_reno(tp))
2840 				tcp_reset_reno_sack(tp);
2841 			if (tcp_try_undo_recovery(sk))
2842 				return;
2843 			tcp_end_cwnd_reduction(sk);
2844 			break;
2845 		}
2846 	}
2847 
2848 	/* E. Process state. */
2849 	switch (icsk->icsk_ca_state) {
2850 	case TCP_CA_Recovery:
2851 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2852 			if (tcp_is_reno(tp) && is_dupack)
2853 				tcp_add_reno_sack(sk);
2854 		} else {
2855 			if (tcp_try_undo_partial(sk, acked))
2856 				return;
2857 			/* Partial ACK arrived. Force fast retransmit. */
2858 			do_lost = tcp_is_reno(tp) ||
2859 				  tcp_fackets_out(tp) > tp->reordering;
2860 		}
2861 		if (tcp_try_undo_dsack(sk)) {
2862 			tcp_try_keep_open(sk);
2863 			return;
2864 		}
2865 		tcp_rack_identify_loss(sk, ack_flag);
2866 		break;
2867 	case TCP_CA_Loss:
2868 		tcp_process_loss(sk, flag, is_dupack, rexmit);
2869 		tcp_rack_identify_loss(sk, ack_flag);
2870 		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
2871 		      (*ack_flag & FLAG_LOST_RETRANS)))
2872 			return;
2873 		/* Change state if cwnd is undone or retransmits are lost */
2874 	default:
2875 		if (tcp_is_reno(tp)) {
2876 			if (flag & FLAG_SND_UNA_ADVANCED)
2877 				tcp_reset_reno_sack(tp);
2878 			if (is_dupack)
2879 				tcp_add_reno_sack(sk);
2880 		}
2881 
2882 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2883 			tcp_try_undo_dsack(sk);
2884 
2885 		tcp_rack_identify_loss(sk, ack_flag);
2886 		if (!tcp_time_to_recover(sk, flag)) {
2887 			tcp_try_to_open(sk, flag);
2888 			return;
2889 		}
2890 
2891 		/* MTU probe failure: don't reduce cwnd */
2892 		if (icsk->icsk_ca_state < TCP_CA_CWR &&
2893 		    icsk->icsk_mtup.probe_size &&
2894 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
2895 			tcp_mtup_probe_failed(sk);
2896 			/* Restores the reduction we did in tcp_mtup_probe() */
2897 			tp->snd_cwnd++;
2898 			tcp_simple_retransmit(sk);
2899 			return;
2900 		}
2901 
2902 		/* Otherwise enter Recovery state */
2903 		tcp_enter_recovery(sk, (flag & FLAG_ECE));
2904 		fast_rexmit = 1;
2905 	}
2906 
2907 	if (do_lost)
2908 		tcp_update_scoreboard(sk, fast_rexmit);
2909 	*rexmit = REXMIT_LOST;
2910 }
2911 
2912 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
2913 {
2914 	struct tcp_sock *tp = tcp_sk(sk);
2915 	u32 wlen = sysctl_tcp_min_rtt_wlen * HZ;
2916 
2917 	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
2918 			   rtt_us ? : jiffies_to_usecs(1));
2919 }
2920 
2921 static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2922 			       long seq_rtt_us, long sack_rtt_us,
2923 			       long ca_rtt_us, struct rate_sample *rs)
2924 {
2925 	const struct tcp_sock *tp = tcp_sk(sk);
2926 
2927 	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2928 	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
2929 	 * Karn's algorithm forbids taking RTT if some retransmitted data
2930 	 * is acked (RFC6298).
2931 	 */
2932 	if (seq_rtt_us < 0)
2933 		seq_rtt_us = sack_rtt_us;
2934 
2935 	/* RTTM Rule: A TSecr value received in a segment is used to
2936 	 * update the averaged RTT measurement only if the segment
2937 	 * acknowledges some new data, i.e., only if it advances the
2938 	 * left edge of the send window.
2939 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
2940 	 */
2941 	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2942 	    flag & FLAG_ACKED) {
2943 		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
2944 		u32 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
2945 
2946 		seq_rtt_us = ca_rtt_us = delta_us;
2947 	}
2948 	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
2949 	if (seq_rtt_us < 0)
2950 		return false;
2951 
2952 	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
2953 	 * always taken together with ACK, SACK, or TS-opts. Any negative
2954 	 * values will be skipped with the seq_rtt_us < 0 check above.
2955 	 */
2956 	tcp_update_rtt_min(sk, ca_rtt_us);
2957 	tcp_rtt_estimator(sk, seq_rtt_us);
2958 	tcp_set_rto(sk);
2959 
2960 	/* RFC6298: only reset backoff on valid RTT measurement. */
2961 	inet_csk(sk)->icsk_backoff = 0;
2962 	return true;
2963 }
2964 
2965 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2966 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
2967 {
2968 	struct rate_sample rs;
2969 	long rtt_us = -1L;
2970 
2971 	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
2972 		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
2973 
2974 	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
2975 }
2976 
2977 
2978 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2979 {
2980 	const struct inet_connection_sock *icsk = inet_csk(sk);
2981 
2982 	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
2983 	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
2984 }
2985 
2986 /* Restart timer after forward progress on connection.
2987  * RFC2988 recommends to restart timer to now+rto.
2988  */
2989 void tcp_rearm_rto(struct sock *sk)
2990 {
2991 	const struct inet_connection_sock *icsk = inet_csk(sk);
2992 	struct tcp_sock *tp = tcp_sk(sk);
2993 
2994 	/* If the retrans timer is currently being used by Fast Open
2995 	 * for SYN-ACK retrans purpose, stay put.
2996 	 */
2997 	if (tp->fastopen_rsk)
2998 		return;
2999 
3000 	if (!tp->packets_out) {
3001 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3002 	} else {
3003 		u32 rto = inet_csk(sk)->icsk_rto;
3004 		/* Offset the time elapsed after installing regular RTO */
3005 		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3006 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3007 			struct sk_buff *skb = tcp_write_queue_head(sk);
3008 			u64 rto_time_stamp = skb->skb_mstamp +
3009 					     jiffies_to_usecs(rto);
3010 			s64 delta_us = rto_time_stamp - tp->tcp_mstamp;
3011 			/* delta_us may not be positive if the socket is locked
3012 			 * when the retrans timer fires and is rescheduled.
3013 			 */
3014 			if (delta_us > 0)
3015 				rto = usecs_to_jiffies(delta_us);
3016 		}
3017 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3018 					  TCP_RTO_MAX);
3019 	}
3020 }
3021 
3022 /* If we get here, the whole TSO packet has not been acked. */
3023 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3024 {
3025 	struct tcp_sock *tp = tcp_sk(sk);
3026 	u32 packets_acked;
3027 
3028 	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3029 
3030 	packets_acked = tcp_skb_pcount(skb);
3031 	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3032 		return 0;
3033 	packets_acked -= tcp_skb_pcount(skb);
3034 
3035 	if (packets_acked) {
3036 		BUG_ON(tcp_skb_pcount(skb) == 0);
3037 		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3038 	}
3039 
3040 	return packets_acked;
3041 }
3042 
3043 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3044 			   u32 prior_snd_una)
3045 {
3046 	const struct skb_shared_info *shinfo;
3047 
3048 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3049 	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3050 		return;
3051 
3052 	shinfo = skb_shinfo(skb);
3053 	if (!before(shinfo->tskey, prior_snd_una) &&
3054 	    before(shinfo->tskey, tcp_sk(sk)->snd_una))
3055 		__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3056 }
3057 
3058 /* Remove acknowledged frames from the retransmission queue. If our packet
3059  * is before the ack sequence we can discard it as it's confirmed to have
3060  * arrived at the other end.
3061  */
3062 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3063 			       u32 prior_snd_una, int *acked,
3064 			       struct tcp_sacktag_state *sack)
3065 {
3066 	const struct inet_connection_sock *icsk = inet_csk(sk);
3067 	u64 first_ackt, last_ackt;
3068 	struct tcp_sock *tp = tcp_sk(sk);
3069 	u32 prior_sacked = tp->sacked_out;
3070 	u32 reord = tp->packets_out;
3071 	bool fully_acked = true;
3072 	long sack_rtt_us = -1L;
3073 	long seq_rtt_us = -1L;
3074 	long ca_rtt_us = -1L;
3075 	struct sk_buff *skb;
3076 	u32 pkts_acked = 0;
3077 	u32 last_in_flight = 0;
3078 	bool rtt_update;
3079 	int flag = 0;
3080 
3081 	first_ackt = 0;
3082 
3083 	while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3084 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3085 		u8 sacked = scb->sacked;
3086 		u32 acked_pcount;
3087 
3088 		tcp_ack_tstamp(sk, skb, prior_snd_una);
3089 
3090 		/* Determine how many packets and what bytes were acked, tso and else */
3091 		if (after(scb->end_seq, tp->snd_una)) {
3092 			if (tcp_skb_pcount(skb) == 1 ||
3093 			    !after(tp->snd_una, scb->seq))
3094 				break;
3095 
3096 			acked_pcount = tcp_tso_acked(sk, skb);
3097 			if (!acked_pcount)
3098 				break;
3099 			fully_acked = false;
3100 		} else {
3101 			/* Speedup tcp_unlink_write_queue() and next loop */
3102 			prefetchw(skb->next);
3103 			acked_pcount = tcp_skb_pcount(skb);
3104 		}
3105 
3106 		if (unlikely(sacked & TCPCB_RETRANS)) {
3107 			if (sacked & TCPCB_SACKED_RETRANS)
3108 				tp->retrans_out -= acked_pcount;
3109 			flag |= FLAG_RETRANS_DATA_ACKED;
3110 		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3111 			last_ackt = skb->skb_mstamp;
3112 			WARN_ON_ONCE(last_ackt == 0);
3113 			if (!first_ackt)
3114 				first_ackt = last_ackt;
3115 
3116 			last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
3117 			reord = min(pkts_acked, reord);
3118 			if (!after(scb->end_seq, tp->high_seq))
3119 				flag |= FLAG_ORIG_SACK_ACKED;
3120 		}
3121 
3122 		if (sacked & TCPCB_SACKED_ACKED) {
3123 			tp->sacked_out -= acked_pcount;
3124 		} else if (tcp_is_sack(tp)) {
3125 			tp->delivered += acked_pcount;
3126 			if (!tcp_skb_spurious_retrans(tp, skb))
3127 				tcp_rack_advance(tp, sacked, scb->end_seq,
3128 						 skb->skb_mstamp);
3129 		}
3130 		if (sacked & TCPCB_LOST)
3131 			tp->lost_out -= acked_pcount;
3132 
3133 		tp->packets_out -= acked_pcount;
3134 		pkts_acked += acked_pcount;
3135 		tcp_rate_skb_delivered(sk, skb, sack->rate);
3136 
3137 		/* Initial outgoing SYN's get put onto the write_queue
3138 		 * just like anything else we transmit.  It is not
3139 		 * true data, and if we misinform our callers that
3140 		 * this ACK acks real data, we will erroneously exit
3141 		 * connection startup slow start one packet too
3142 		 * quickly.  This is severely frowned upon behavior.
3143 		 */
3144 		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3145 			flag |= FLAG_DATA_ACKED;
3146 		} else {
3147 			flag |= FLAG_SYN_ACKED;
3148 			tp->retrans_stamp = 0;
3149 		}
3150 
3151 		if (!fully_acked)
3152 			break;
3153 
3154 		tcp_unlink_write_queue(skb, sk);
3155 		sk_wmem_free_skb(sk, skb);
3156 		if (unlikely(skb == tp->retransmit_skb_hint))
3157 			tp->retransmit_skb_hint = NULL;
3158 		if (unlikely(skb == tp->lost_skb_hint))
3159 			tp->lost_skb_hint = NULL;
3160 	}
3161 
3162 	if (!skb)
3163 		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3164 
3165 	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3166 		tp->snd_up = tp->snd_una;
3167 
3168 	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3169 		flag |= FLAG_SACK_RENEGING;
3170 
3171 	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3172 		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3173 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3174 	}
3175 	if (sack->first_sackt) {
3176 		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3177 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3178 	}
3179 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3180 					ca_rtt_us, sack->rate);
3181 
3182 	if (flag & FLAG_ACKED) {
3183 		tcp_rearm_rto(sk);
3184 		if (unlikely(icsk->icsk_mtup.probe_size &&
3185 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3186 			tcp_mtup_probe_success(sk);
3187 		}
3188 
3189 		if (tcp_is_reno(tp)) {
3190 			tcp_remove_reno_sacks(sk, pkts_acked);
3191 		} else {
3192 			int delta;
3193 
3194 			/* Non-retransmitted hole got filled? That's reordering */
3195 			if (reord < prior_fackets && reord <= tp->fackets_out)
3196 				tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3197 
3198 			delta = tcp_is_fack(tp) ? pkts_acked :
3199 						  prior_sacked - tp->sacked_out;
3200 			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3201 		}
3202 
3203 		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3204 
3205 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3206 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp, skb->skb_mstamp)) {
3207 		/* Do not re-arm RTO if the sack RTT is measured from data sent
3208 		 * after when the head was last (re)transmitted. Otherwise the
3209 		 * timeout may continue to extend in loss recovery.
3210 		 */
3211 		tcp_rearm_rto(sk);
3212 	}
3213 
3214 	if (icsk->icsk_ca_ops->pkts_acked) {
3215 		struct ack_sample sample = { .pkts_acked = pkts_acked,
3216 					     .rtt_us = sack->rate->rtt_us,
3217 					     .in_flight = last_in_flight };
3218 
3219 		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3220 	}
3221 
3222 #if FASTRETRANS_DEBUG > 0
3223 	WARN_ON((int)tp->sacked_out < 0);
3224 	WARN_ON((int)tp->lost_out < 0);
3225 	WARN_ON((int)tp->retrans_out < 0);
3226 	if (!tp->packets_out && tcp_is_sack(tp)) {
3227 		icsk = inet_csk(sk);
3228 		if (tp->lost_out) {
3229 			pr_debug("Leak l=%u %d\n",
3230 				 tp->lost_out, icsk->icsk_ca_state);
3231 			tp->lost_out = 0;
3232 		}
3233 		if (tp->sacked_out) {
3234 			pr_debug("Leak s=%u %d\n",
3235 				 tp->sacked_out, icsk->icsk_ca_state);
3236 			tp->sacked_out = 0;
3237 		}
3238 		if (tp->retrans_out) {
3239 			pr_debug("Leak r=%u %d\n",
3240 				 tp->retrans_out, icsk->icsk_ca_state);
3241 			tp->retrans_out = 0;
3242 		}
3243 	}
3244 #endif
3245 	*acked = pkts_acked;
3246 	return flag;
3247 }
3248 
3249 static void tcp_ack_probe(struct sock *sk)
3250 {
3251 	const struct tcp_sock *tp = tcp_sk(sk);
3252 	struct inet_connection_sock *icsk = inet_csk(sk);
3253 
3254 	/* Was it a usable window open? */
3255 
3256 	if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3257 		icsk->icsk_backoff = 0;
3258 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3259 		/* Socket must be waked up by subsequent tcp_data_snd_check().
3260 		 * This function is not for random using!
3261 		 */
3262 	} else {
3263 		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3264 
3265 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3266 					  when, TCP_RTO_MAX);
3267 	}
3268 }
3269 
3270 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3271 {
3272 	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3273 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3274 }
3275 
3276 /* Decide wheather to run the increase function of congestion control. */
3277 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3278 {
3279 	/* If reordering is high then always grow cwnd whenever data is
3280 	 * delivered regardless of its ordering. Otherwise stay conservative
3281 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3282 	 * new SACK or ECE mark may first advance cwnd here and later reduce
3283 	 * cwnd in tcp_fastretrans_alert() based on more states.
3284 	 */
3285 	if (tcp_sk(sk)->reordering > sock_net(sk)->ipv4.sysctl_tcp_reordering)
3286 		return flag & FLAG_FORWARD_PROGRESS;
3287 
3288 	return flag & FLAG_DATA_ACKED;
3289 }
3290 
3291 /* The "ultimate" congestion control function that aims to replace the rigid
3292  * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3293  * It's called toward the end of processing an ACK with precise rate
3294  * information. All transmission or retransmission are delayed afterwards.
3295  */
3296 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3297 			     int flag, const struct rate_sample *rs)
3298 {
3299 	const struct inet_connection_sock *icsk = inet_csk(sk);
3300 
3301 	if (icsk->icsk_ca_ops->cong_control) {
3302 		icsk->icsk_ca_ops->cong_control(sk, rs);
3303 		return;
3304 	}
3305 
3306 	if (tcp_in_cwnd_reduction(sk)) {
3307 		/* Reduce cwnd if state mandates */
3308 		tcp_cwnd_reduction(sk, acked_sacked, flag);
3309 	} else if (tcp_may_raise_cwnd(sk, flag)) {
3310 		/* Advance cwnd if state allows */
3311 		tcp_cong_avoid(sk, ack, acked_sacked);
3312 	}
3313 	tcp_update_pacing_rate(sk);
3314 }
3315 
3316 /* Check that window update is acceptable.
3317  * The function assumes that snd_una<=ack<=snd_next.
3318  */
3319 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3320 					const u32 ack, const u32 ack_seq,
3321 					const u32 nwin)
3322 {
3323 	return	after(ack, tp->snd_una) ||
3324 		after(ack_seq, tp->snd_wl1) ||
3325 		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3326 }
3327 
3328 /* If we update tp->snd_una, also update tp->bytes_acked */
3329 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3330 {
3331 	u32 delta = ack - tp->snd_una;
3332 
3333 	sock_owned_by_me((struct sock *)tp);
3334 	tp->bytes_acked += delta;
3335 	tp->snd_una = ack;
3336 }
3337 
3338 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3339 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3340 {
3341 	u32 delta = seq - tp->rcv_nxt;
3342 
3343 	sock_owned_by_me((struct sock *)tp);
3344 	tp->bytes_received += delta;
3345 	tp->rcv_nxt = seq;
3346 }
3347 
3348 /* Update our send window.
3349  *
3350  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3351  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3352  */
3353 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3354 				 u32 ack_seq)
3355 {
3356 	struct tcp_sock *tp = tcp_sk(sk);
3357 	int flag = 0;
3358 	u32 nwin = ntohs(tcp_hdr(skb)->window);
3359 
3360 	if (likely(!tcp_hdr(skb)->syn))
3361 		nwin <<= tp->rx_opt.snd_wscale;
3362 
3363 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3364 		flag |= FLAG_WIN_UPDATE;
3365 		tcp_update_wl(tp, ack_seq);
3366 
3367 		if (tp->snd_wnd != nwin) {
3368 			tp->snd_wnd = nwin;
3369 
3370 			/* Note, it is the only place, where
3371 			 * fast path is recovered for sending TCP.
3372 			 */
3373 			tp->pred_flags = 0;
3374 			tcp_fast_path_check(sk);
3375 
3376 			if (tcp_send_head(sk))
3377 				tcp_slow_start_after_idle_check(sk);
3378 
3379 			if (nwin > tp->max_window) {
3380 				tp->max_window = nwin;
3381 				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3382 			}
3383 		}
3384 	}
3385 
3386 	tcp_snd_una_update(tp, ack);
3387 
3388 	return flag;
3389 }
3390 
3391 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3392 				   u32 *last_oow_ack_time)
3393 {
3394 	if (*last_oow_ack_time) {
3395 		s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
3396 
3397 		if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
3398 			NET_INC_STATS(net, mib_idx);
3399 			return true;	/* rate-limited: don't send yet! */
3400 		}
3401 	}
3402 
3403 	*last_oow_ack_time = tcp_jiffies32;
3404 
3405 	return false;	/* not rate-limited: go ahead, send dupack now! */
3406 }
3407 
3408 /* Return true if we're currently rate-limiting out-of-window ACKs and
3409  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3410  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3411  * attacks that send repeated SYNs or ACKs for the same connection. To
3412  * do this, we do not send a duplicate SYNACK or ACK if the remote
3413  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3414  */
3415 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3416 			  int mib_idx, u32 *last_oow_ack_time)
3417 {
3418 	/* Data packets without SYNs are not likely part of an ACK loop. */
3419 	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3420 	    !tcp_hdr(skb)->syn)
3421 		return false;
3422 
3423 	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3424 }
3425 
3426 /* RFC 5961 7 [ACK Throttling] */
3427 static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3428 {
3429 	/* unprotected vars, we dont care of overwrites */
3430 	static u32 challenge_timestamp;
3431 	static unsigned int challenge_count;
3432 	struct tcp_sock *tp = tcp_sk(sk);
3433 	u32 count, now;
3434 
3435 	/* First check our per-socket dupack rate limit. */
3436 	if (__tcp_oow_rate_limited(sock_net(sk),
3437 				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3438 				   &tp->last_oow_ack_time))
3439 		return;
3440 
3441 	/* Then check host-wide RFC 5961 rate limit. */
3442 	now = jiffies / HZ;
3443 	if (now != challenge_timestamp) {
3444 		u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;
3445 
3446 		challenge_timestamp = now;
3447 		WRITE_ONCE(challenge_count, half +
3448 			   prandom_u32_max(sysctl_tcp_challenge_ack_limit));
3449 	}
3450 	count = READ_ONCE(challenge_count);
3451 	if (count > 0) {
3452 		WRITE_ONCE(challenge_count, count - 1);
3453 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3454 		tcp_send_ack(sk);
3455 	}
3456 }
3457 
3458 static void tcp_store_ts_recent(struct tcp_sock *tp)
3459 {
3460 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3461 	tp->rx_opt.ts_recent_stamp = get_seconds();
3462 }
3463 
3464 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3465 {
3466 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3467 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3468 		 * extra check below makes sure this can only happen
3469 		 * for pure ACK frames.  -DaveM
3470 		 *
3471 		 * Not only, also it occurs for expired timestamps.
3472 		 */
3473 
3474 		if (tcp_paws_check(&tp->rx_opt, 0))
3475 			tcp_store_ts_recent(tp);
3476 	}
3477 }
3478 
3479 /* This routine deals with acks during a TLP episode.
3480  * We mark the end of a TLP episode on receiving TLP dupack or when
3481  * ack is after tlp_high_seq.
3482  * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3483  */
3484 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3485 {
3486 	struct tcp_sock *tp = tcp_sk(sk);
3487 
3488 	if (before(ack, tp->tlp_high_seq))
3489 		return;
3490 
3491 	if (flag & FLAG_DSACKING_ACK) {
3492 		/* This DSACK means original and TLP probe arrived; no loss */
3493 		tp->tlp_high_seq = 0;
3494 	} else if (after(ack, tp->tlp_high_seq)) {
3495 		/* ACK advances: there was a loss, so reduce cwnd. Reset
3496 		 * tlp_high_seq in tcp_init_cwnd_reduction()
3497 		 */
3498 		tcp_init_cwnd_reduction(sk);
3499 		tcp_set_ca_state(sk, TCP_CA_CWR);
3500 		tcp_end_cwnd_reduction(sk);
3501 		tcp_try_keep_open(sk);
3502 		NET_INC_STATS(sock_net(sk),
3503 				LINUX_MIB_TCPLOSSPROBERECOVERY);
3504 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3505 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3506 		/* Pure dupack: original and TLP probe arrived; no loss */
3507 		tp->tlp_high_seq = 0;
3508 	}
3509 }
3510 
3511 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3512 {
3513 	const struct inet_connection_sock *icsk = inet_csk(sk);
3514 
3515 	if (icsk->icsk_ca_ops->in_ack_event)
3516 		icsk->icsk_ca_ops->in_ack_event(sk, flags);
3517 }
3518 
3519 /* Congestion control has updated the cwnd already. So if we're in
3520  * loss recovery then now we do any new sends (for FRTO) or
3521  * retransmits (for CA_Loss or CA_recovery) that make sense.
3522  */
3523 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3524 {
3525 	struct tcp_sock *tp = tcp_sk(sk);
3526 
3527 	if (rexmit == REXMIT_NONE)
3528 		return;
3529 
3530 	if (unlikely(rexmit == 2)) {
3531 		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3532 					  TCP_NAGLE_OFF);
3533 		if (after(tp->snd_nxt, tp->high_seq))
3534 			return;
3535 		tp->frto = 0;
3536 	}
3537 	tcp_xmit_retransmit_queue(sk);
3538 }
3539 
3540 /* This routine deals with incoming acks, but not outgoing ones. */
3541 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3542 {
3543 	struct inet_connection_sock *icsk = inet_csk(sk);
3544 	struct tcp_sock *tp = tcp_sk(sk);
3545 	struct tcp_sacktag_state sack_state;
3546 	struct rate_sample rs = { .prior_delivered = 0 };
3547 	u32 prior_snd_una = tp->snd_una;
3548 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3549 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3550 	bool is_dupack = false;
3551 	u32 prior_fackets;
3552 	int prior_packets = tp->packets_out;
3553 	u32 delivered = tp->delivered;
3554 	u32 lost = tp->lost;
3555 	int acked = 0; /* Number of packets newly acked */
3556 	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3557 
3558 	sack_state.first_sackt = 0;
3559 	sack_state.rate = &rs;
3560 
3561 	/* We very likely will need to access write queue head. */
3562 	prefetchw(sk->sk_write_queue.next);
3563 
3564 	/* If the ack is older than previous acks
3565 	 * then we can probably ignore it.
3566 	 */
3567 	if (before(ack, prior_snd_una)) {
3568 		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3569 		if (before(ack, prior_snd_una - tp->max_window)) {
3570 			if (!(flag & FLAG_NO_CHALLENGE_ACK))
3571 				tcp_send_challenge_ack(sk, skb);
3572 			return -1;
3573 		}
3574 		goto old_ack;
3575 	}
3576 
3577 	/* If the ack includes data we haven't sent yet, discard
3578 	 * this segment (RFC793 Section 3.9).
3579 	 */
3580 	if (after(ack, tp->snd_nxt))
3581 		goto invalid_ack;
3582 
3583 	if (icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3584 		tcp_rearm_rto(sk);
3585 
3586 	if (after(ack, prior_snd_una)) {
3587 		flag |= FLAG_SND_UNA_ADVANCED;
3588 		icsk->icsk_retransmits = 0;
3589 	}
3590 
3591 	prior_fackets = tp->fackets_out;
3592 	rs.prior_in_flight = tcp_packets_in_flight(tp);
3593 
3594 	/* ts_recent update must be made after we are sure that the packet
3595 	 * is in window.
3596 	 */
3597 	if (flag & FLAG_UPDATE_TS_RECENT)
3598 		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3599 
3600 	if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3601 		/* Window is constant, pure forward advance.
3602 		 * No more checks are required.
3603 		 * Note, we use the fact that SND.UNA>=SND.WL2.
3604 		 */
3605 		tcp_update_wl(tp, ack_seq);
3606 		tcp_snd_una_update(tp, ack);
3607 		flag |= FLAG_WIN_UPDATE;
3608 
3609 		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3610 
3611 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3612 	} else {
3613 		u32 ack_ev_flags = CA_ACK_SLOWPATH;
3614 
3615 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3616 			flag |= FLAG_DATA;
3617 		else
3618 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3619 
3620 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3621 
3622 		if (TCP_SKB_CB(skb)->sacked)
3623 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3624 							&sack_state);
3625 
3626 		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3627 			flag |= FLAG_ECE;
3628 			ack_ev_flags |= CA_ACK_ECE;
3629 		}
3630 
3631 		if (flag & FLAG_WIN_UPDATE)
3632 			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3633 
3634 		tcp_in_ack_event(sk, ack_ev_flags);
3635 	}
3636 
3637 	/* We passed data and got it acked, remove any soft error
3638 	 * log. Something worked...
3639 	 */
3640 	sk->sk_err_soft = 0;
3641 	icsk->icsk_probes_out = 0;
3642 	tp->rcv_tstamp = tcp_jiffies32;
3643 	if (!prior_packets)
3644 		goto no_queue;
3645 
3646 	/* See if we can take anything off of the retransmit queue. */
3647 	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
3648 				    &sack_state);
3649 
3650 	if (tcp_ack_is_dubious(sk, flag)) {
3651 		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3652 		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
3653 	}
3654 	if (tp->tlp_high_seq)
3655 		tcp_process_tlp_ack(sk, ack, flag);
3656 
3657 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3658 		sk_dst_confirm(sk);
3659 
3660 	if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3661 		tcp_schedule_loss_probe(sk);
3662 	delivered = tp->delivered - delivered;	/* freshly ACKed or SACKed */
3663 	lost = tp->lost - lost;			/* freshly marked lost */
3664 	tcp_rate_gen(sk, delivered, lost, sack_state.rate);
3665 	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3666 	tcp_xmit_recovery(sk, rexmit);
3667 	return 1;
3668 
3669 no_queue:
3670 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3671 	if (flag & FLAG_DSACKING_ACK)
3672 		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
3673 	/* If this ack opens up a zero window, clear backoff.  It was
3674 	 * being used to time the probes, and is probably far higher than
3675 	 * it needs to be for normal retransmission.
3676 	 */
3677 	if (tcp_send_head(sk))
3678 		tcp_ack_probe(sk);
3679 
3680 	if (tp->tlp_high_seq)
3681 		tcp_process_tlp_ack(sk, ack, flag);
3682 	return 1;
3683 
3684 invalid_ack:
3685 	SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3686 	return -1;
3687 
3688 old_ack:
3689 	/* If data was SACKed, tag it and see if we should send more data.
3690 	 * If data was DSACKed, see if we can undo a cwnd reduction.
3691 	 */
3692 	if (TCP_SKB_CB(skb)->sacked) {
3693 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3694 						&sack_state);
3695 		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
3696 		tcp_xmit_recovery(sk, rexmit);
3697 	}
3698 
3699 	SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3700 	return 0;
3701 }
3702 
3703 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3704 				      bool syn, struct tcp_fastopen_cookie *foc,
3705 				      bool exp_opt)
3706 {
3707 	/* Valid only in SYN or SYN-ACK with an even length.  */
3708 	if (!foc || !syn || len < 0 || (len & 1))
3709 		return;
3710 
3711 	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3712 	    len <= TCP_FASTOPEN_COOKIE_MAX)
3713 		memcpy(foc->val, cookie, len);
3714 	else if (len != 0)
3715 		len = -1;
3716 	foc->len = len;
3717 	foc->exp = exp_opt;
3718 }
3719 
3720 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3721  * But, this can also be called on packets in the established flow when
3722  * the fast version below fails.
3723  */
3724 void tcp_parse_options(const struct net *net,
3725 		       const struct sk_buff *skb,
3726 		       struct tcp_options_received *opt_rx, int estab,
3727 		       struct tcp_fastopen_cookie *foc)
3728 {
3729 	const unsigned char *ptr;
3730 	const struct tcphdr *th = tcp_hdr(skb);
3731 	int length = (th->doff * 4) - sizeof(struct tcphdr);
3732 
3733 	ptr = (const unsigned char *)(th + 1);
3734 	opt_rx->saw_tstamp = 0;
3735 
3736 	while (length > 0) {
3737 		int opcode = *ptr++;
3738 		int opsize;
3739 
3740 		switch (opcode) {
3741 		case TCPOPT_EOL:
3742 			return;
3743 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
3744 			length--;
3745 			continue;
3746 		default:
3747 			opsize = *ptr++;
3748 			if (opsize < 2) /* "silly options" */
3749 				return;
3750 			if (opsize > length)
3751 				return;	/* don't parse partial options */
3752 			switch (opcode) {
3753 			case TCPOPT_MSS:
3754 				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3755 					u16 in_mss = get_unaligned_be16(ptr);
3756 					if (in_mss) {
3757 						if (opt_rx->user_mss &&
3758 						    opt_rx->user_mss < in_mss)
3759 							in_mss = opt_rx->user_mss;
3760 						opt_rx->mss_clamp = in_mss;
3761 					}
3762 				}
3763 				break;
3764 			case TCPOPT_WINDOW:
3765 				if (opsize == TCPOLEN_WINDOW && th->syn &&
3766 				    !estab && net->ipv4.sysctl_tcp_window_scaling) {
3767 					__u8 snd_wscale = *(__u8 *)ptr;
3768 					opt_rx->wscale_ok = 1;
3769 					if (snd_wscale > TCP_MAX_WSCALE) {
3770 						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
3771 								     __func__,
3772 								     snd_wscale,
3773 								     TCP_MAX_WSCALE);
3774 						snd_wscale = TCP_MAX_WSCALE;
3775 					}
3776 					opt_rx->snd_wscale = snd_wscale;
3777 				}
3778 				break;
3779 			case TCPOPT_TIMESTAMP:
3780 				if ((opsize == TCPOLEN_TIMESTAMP) &&
3781 				    ((estab && opt_rx->tstamp_ok) ||
3782 				     (!estab && net->ipv4.sysctl_tcp_timestamps))) {
3783 					opt_rx->saw_tstamp = 1;
3784 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3785 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3786 				}
3787 				break;
3788 			case TCPOPT_SACK_PERM:
3789 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3790 				    !estab && net->ipv4.sysctl_tcp_sack) {
3791 					opt_rx->sack_ok = TCP_SACK_SEEN;
3792 					tcp_sack_reset(opt_rx);
3793 				}
3794 				break;
3795 
3796 			case TCPOPT_SACK:
3797 				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3798 				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3799 				   opt_rx->sack_ok) {
3800 					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3801 				}
3802 				break;
3803 #ifdef CONFIG_TCP_MD5SIG
3804 			case TCPOPT_MD5SIG:
3805 				/*
3806 				 * The MD5 Hash has already been
3807 				 * checked (see tcp_v{4,6}_do_rcv()).
3808 				 */
3809 				break;
3810 #endif
3811 			case TCPOPT_FASTOPEN:
3812 				tcp_parse_fastopen_option(
3813 					opsize - TCPOLEN_FASTOPEN_BASE,
3814 					ptr, th->syn, foc, false);
3815 				break;
3816 
3817 			case TCPOPT_EXP:
3818 				/* Fast Open option shares code 254 using a
3819 				 * 16 bits magic number.
3820 				 */
3821 				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3822 				    get_unaligned_be16(ptr) ==
3823 				    TCPOPT_FASTOPEN_MAGIC)
3824 					tcp_parse_fastopen_option(opsize -
3825 						TCPOLEN_EXP_FASTOPEN_BASE,
3826 						ptr + 2, th->syn, foc, true);
3827 				break;
3828 
3829 			}
3830 			ptr += opsize-2;
3831 			length -= opsize;
3832 		}
3833 	}
3834 }
3835 EXPORT_SYMBOL(tcp_parse_options);
3836 
3837 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3838 {
3839 	const __be32 *ptr = (const __be32 *)(th + 1);
3840 
3841 	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3842 			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3843 		tp->rx_opt.saw_tstamp = 1;
3844 		++ptr;
3845 		tp->rx_opt.rcv_tsval = ntohl(*ptr);
3846 		++ptr;
3847 		if (*ptr)
3848 			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3849 		else
3850 			tp->rx_opt.rcv_tsecr = 0;
3851 		return true;
3852 	}
3853 	return false;
3854 }
3855 
3856 /* Fast parse options. This hopes to only see timestamps.
3857  * If it is wrong it falls back on tcp_parse_options().
3858  */
3859 static bool tcp_fast_parse_options(const struct net *net,
3860 				   const struct sk_buff *skb,
3861 				   const struct tcphdr *th, struct tcp_sock *tp)
3862 {
3863 	/* In the spirit of fast parsing, compare doff directly to constant
3864 	 * values.  Because equality is used, short doff can be ignored here.
3865 	 */
3866 	if (th->doff == (sizeof(*th) / 4)) {
3867 		tp->rx_opt.saw_tstamp = 0;
3868 		return false;
3869 	} else if (tp->rx_opt.tstamp_ok &&
3870 		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3871 		if (tcp_parse_aligned_timestamp(tp, th))
3872 			return true;
3873 	}
3874 
3875 	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
3876 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3877 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3878 
3879 	return true;
3880 }
3881 
3882 #ifdef CONFIG_TCP_MD5SIG
3883 /*
3884  * Parse MD5 Signature option
3885  */
3886 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3887 {
3888 	int length = (th->doff << 2) - sizeof(*th);
3889 	const u8 *ptr = (const u8 *)(th + 1);
3890 
3891 	/* If the TCP option is too short, we can short cut */
3892 	if (length < TCPOLEN_MD5SIG)
3893 		return NULL;
3894 
3895 	while (length > 0) {
3896 		int opcode = *ptr++;
3897 		int opsize;
3898 
3899 		switch (opcode) {
3900 		case TCPOPT_EOL:
3901 			return NULL;
3902 		case TCPOPT_NOP:
3903 			length--;
3904 			continue;
3905 		default:
3906 			opsize = *ptr++;
3907 			if (opsize < 2 || opsize > length)
3908 				return NULL;
3909 			if (opcode == TCPOPT_MD5SIG)
3910 				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3911 		}
3912 		ptr += opsize - 2;
3913 		length -= opsize;
3914 	}
3915 	return NULL;
3916 }
3917 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3918 #endif
3919 
3920 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3921  *
3922  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3923  * it can pass through stack. So, the following predicate verifies that
3924  * this segment is not used for anything but congestion avoidance or
3925  * fast retransmit. Moreover, we even are able to eliminate most of such
3926  * second order effects, if we apply some small "replay" window (~RTO)
3927  * to timestamp space.
3928  *
3929  * All these measures still do not guarantee that we reject wrapped ACKs
3930  * on networks with high bandwidth, when sequence space is recycled fastly,
3931  * but it guarantees that such events will be very rare and do not affect
3932  * connection seriously. This doesn't look nice, but alas, PAWS is really
3933  * buggy extension.
3934  *
3935  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3936  * states that events when retransmit arrives after original data are rare.
3937  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3938  * the biggest problem on large power networks even with minor reordering.
3939  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3940  * up to bandwidth of 18Gigabit/sec. 8) ]
3941  */
3942 
3943 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3944 {
3945 	const struct tcp_sock *tp = tcp_sk(sk);
3946 	const struct tcphdr *th = tcp_hdr(skb);
3947 	u32 seq = TCP_SKB_CB(skb)->seq;
3948 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3949 
3950 	return (/* 1. Pure ACK with correct sequence number. */
3951 		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3952 
3953 		/* 2. ... and duplicate ACK. */
3954 		ack == tp->snd_una &&
3955 
3956 		/* 3. ... and does not update window. */
3957 		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3958 
3959 		/* 4. ... and sits in replay window. */
3960 		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3961 }
3962 
3963 static inline bool tcp_paws_discard(const struct sock *sk,
3964 				   const struct sk_buff *skb)
3965 {
3966 	const struct tcp_sock *tp = tcp_sk(sk);
3967 
3968 	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3969 	       !tcp_disordered_ack(sk, skb);
3970 }
3971 
3972 /* Check segment sequence number for validity.
3973  *
3974  * Segment controls are considered valid, if the segment
3975  * fits to the window after truncation to the window. Acceptability
3976  * of data (and SYN, FIN, of course) is checked separately.
3977  * See tcp_data_queue(), for example.
3978  *
3979  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3980  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3981  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3982  * (borrowed from freebsd)
3983  */
3984 
3985 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
3986 {
3987 	return	!before(end_seq, tp->rcv_wup) &&
3988 		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3989 }
3990 
3991 /* When we get a reset we do this. */
3992 void tcp_reset(struct sock *sk)
3993 {
3994 	/* We want the right error as BSD sees it (and indeed as we do). */
3995 	switch (sk->sk_state) {
3996 	case TCP_SYN_SENT:
3997 		sk->sk_err = ECONNREFUSED;
3998 		break;
3999 	case TCP_CLOSE_WAIT:
4000 		sk->sk_err = EPIPE;
4001 		break;
4002 	case TCP_CLOSE:
4003 		return;
4004 	default:
4005 		sk->sk_err = ECONNRESET;
4006 	}
4007 	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4008 	smp_wmb();
4009 
4010 	tcp_done(sk);
4011 
4012 	if (!sock_flag(sk, SOCK_DEAD))
4013 		sk->sk_error_report(sk);
4014 }
4015 
4016 /*
4017  * 	Process the FIN bit. This now behaves as it is supposed to work
4018  *	and the FIN takes effect when it is validly part of sequence
4019  *	space. Not before when we get holes.
4020  *
4021  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4022  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4023  *	TIME-WAIT)
4024  *
4025  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4026  *	close and we go into CLOSING (and later onto TIME-WAIT)
4027  *
4028  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4029  */
4030 void tcp_fin(struct sock *sk)
4031 {
4032 	struct tcp_sock *tp = tcp_sk(sk);
4033 
4034 	inet_csk_schedule_ack(sk);
4035 
4036 	sk->sk_shutdown |= RCV_SHUTDOWN;
4037 	sock_set_flag(sk, SOCK_DONE);
4038 
4039 	switch (sk->sk_state) {
4040 	case TCP_SYN_RECV:
4041 	case TCP_ESTABLISHED:
4042 		/* Move to CLOSE_WAIT */
4043 		tcp_set_state(sk, TCP_CLOSE_WAIT);
4044 		inet_csk(sk)->icsk_ack.pingpong = 1;
4045 		break;
4046 
4047 	case TCP_CLOSE_WAIT:
4048 	case TCP_CLOSING:
4049 		/* Received a retransmission of the FIN, do
4050 		 * nothing.
4051 		 */
4052 		break;
4053 	case TCP_LAST_ACK:
4054 		/* RFC793: Remain in the LAST-ACK state. */
4055 		break;
4056 
4057 	case TCP_FIN_WAIT1:
4058 		/* This case occurs when a simultaneous close
4059 		 * happens, we must ack the received FIN and
4060 		 * enter the CLOSING state.
4061 		 */
4062 		tcp_send_ack(sk);
4063 		tcp_set_state(sk, TCP_CLOSING);
4064 		break;
4065 	case TCP_FIN_WAIT2:
4066 		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4067 		tcp_send_ack(sk);
4068 		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4069 		break;
4070 	default:
4071 		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4072 		 * cases we should never reach this piece of code.
4073 		 */
4074 		pr_err("%s: Impossible, sk->sk_state=%d\n",
4075 		       __func__, sk->sk_state);
4076 		break;
4077 	}
4078 
4079 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4080 	 * Probably, we should reset in this case. For now drop them.
4081 	 */
4082 	skb_rbtree_purge(&tp->out_of_order_queue);
4083 	if (tcp_is_sack(tp))
4084 		tcp_sack_reset(&tp->rx_opt);
4085 	sk_mem_reclaim(sk);
4086 
4087 	if (!sock_flag(sk, SOCK_DEAD)) {
4088 		sk->sk_state_change(sk);
4089 
4090 		/* Do not send POLL_HUP for half duplex close. */
4091 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4092 		    sk->sk_state == TCP_CLOSE)
4093 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4094 		else
4095 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4096 	}
4097 }
4098 
4099 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4100 				  u32 end_seq)
4101 {
4102 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4103 		if (before(seq, sp->start_seq))
4104 			sp->start_seq = seq;
4105 		if (after(end_seq, sp->end_seq))
4106 			sp->end_seq = end_seq;
4107 		return true;
4108 	}
4109 	return false;
4110 }
4111 
4112 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4113 {
4114 	struct tcp_sock *tp = tcp_sk(sk);
4115 
4116 	if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4117 		int mib_idx;
4118 
4119 		if (before(seq, tp->rcv_nxt))
4120 			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4121 		else
4122 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4123 
4124 		NET_INC_STATS(sock_net(sk), mib_idx);
4125 
4126 		tp->rx_opt.dsack = 1;
4127 		tp->duplicate_sack[0].start_seq = seq;
4128 		tp->duplicate_sack[0].end_seq = end_seq;
4129 	}
4130 }
4131 
4132 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4133 {
4134 	struct tcp_sock *tp = tcp_sk(sk);
4135 
4136 	if (!tp->rx_opt.dsack)
4137 		tcp_dsack_set(sk, seq, end_seq);
4138 	else
4139 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4140 }
4141 
4142 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4143 {
4144 	struct tcp_sock *tp = tcp_sk(sk);
4145 
4146 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4147 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4148 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4149 		tcp_enter_quickack_mode(sk);
4150 
4151 		if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4152 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4153 
4154 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4155 				end_seq = tp->rcv_nxt;
4156 			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4157 		}
4158 	}
4159 
4160 	tcp_send_ack(sk);
4161 }
4162 
4163 /* These routines update the SACK block as out-of-order packets arrive or
4164  * in-order packets close up the sequence space.
4165  */
4166 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4167 {
4168 	int this_sack;
4169 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4170 	struct tcp_sack_block *swalk = sp + 1;
4171 
4172 	/* See if the recent change to the first SACK eats into
4173 	 * or hits the sequence space of other SACK blocks, if so coalesce.
4174 	 */
4175 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4176 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4177 			int i;
4178 
4179 			/* Zap SWALK, by moving every further SACK up by one slot.
4180 			 * Decrease num_sacks.
4181 			 */
4182 			tp->rx_opt.num_sacks--;
4183 			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4184 				sp[i] = sp[i + 1];
4185 			continue;
4186 		}
4187 		this_sack++, swalk++;
4188 	}
4189 }
4190 
4191 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4192 {
4193 	struct tcp_sock *tp = tcp_sk(sk);
4194 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4195 	int cur_sacks = tp->rx_opt.num_sacks;
4196 	int this_sack;
4197 
4198 	if (!cur_sacks)
4199 		goto new_sack;
4200 
4201 	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4202 		if (tcp_sack_extend(sp, seq, end_seq)) {
4203 			/* Rotate this_sack to the first one. */
4204 			for (; this_sack > 0; this_sack--, sp--)
4205 				swap(*sp, *(sp - 1));
4206 			if (cur_sacks > 1)
4207 				tcp_sack_maybe_coalesce(tp);
4208 			return;
4209 		}
4210 	}
4211 
4212 	/* Could not find an adjacent existing SACK, build a new one,
4213 	 * put it at the front, and shift everyone else down.  We
4214 	 * always know there is at least one SACK present already here.
4215 	 *
4216 	 * If the sack array is full, forget about the last one.
4217 	 */
4218 	if (this_sack >= TCP_NUM_SACKS) {
4219 		this_sack--;
4220 		tp->rx_opt.num_sacks--;
4221 		sp--;
4222 	}
4223 	for (; this_sack > 0; this_sack--, sp--)
4224 		*sp = *(sp - 1);
4225 
4226 new_sack:
4227 	/* Build the new head SACK, and we're done. */
4228 	sp->start_seq = seq;
4229 	sp->end_seq = end_seq;
4230 	tp->rx_opt.num_sacks++;
4231 }
4232 
4233 /* RCV.NXT advances, some SACKs should be eaten. */
4234 
4235 static void tcp_sack_remove(struct tcp_sock *tp)
4236 {
4237 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4238 	int num_sacks = tp->rx_opt.num_sacks;
4239 	int this_sack;
4240 
4241 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4242 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4243 		tp->rx_opt.num_sacks = 0;
4244 		return;
4245 	}
4246 
4247 	for (this_sack = 0; this_sack < num_sacks;) {
4248 		/* Check if the start of the sack is covered by RCV.NXT. */
4249 		if (!before(tp->rcv_nxt, sp->start_seq)) {
4250 			int i;
4251 
4252 			/* RCV.NXT must cover all the block! */
4253 			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4254 
4255 			/* Zap this SACK, by moving forward any other SACKS. */
4256 			for (i = this_sack+1; i < num_sacks; i++)
4257 				tp->selective_acks[i-1] = tp->selective_acks[i];
4258 			num_sacks--;
4259 			continue;
4260 		}
4261 		this_sack++;
4262 		sp++;
4263 	}
4264 	tp->rx_opt.num_sacks = num_sacks;
4265 }
4266 
4267 /**
4268  * tcp_try_coalesce - try to merge skb to prior one
4269  * @sk: socket
4270  * @to: prior buffer
4271  * @from: buffer to add in queue
4272  * @fragstolen: pointer to boolean
4273  *
4274  * Before queueing skb @from after @to, try to merge them
4275  * to reduce overall memory use and queue lengths, if cost is small.
4276  * Packets in ofo or receive queues can stay a long time.
4277  * Better try to coalesce them right now to avoid future collapses.
4278  * Returns true if caller should free @from instead of queueing it
4279  */
4280 static bool tcp_try_coalesce(struct sock *sk,
4281 			     struct sk_buff *to,
4282 			     struct sk_buff *from,
4283 			     bool *fragstolen)
4284 {
4285 	int delta;
4286 
4287 	*fragstolen = false;
4288 
4289 	/* Its possible this segment overlaps with prior segment in queue */
4290 	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4291 		return false;
4292 
4293 	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4294 		return false;
4295 
4296 	atomic_add(delta, &sk->sk_rmem_alloc);
4297 	sk_mem_charge(sk, delta);
4298 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4299 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4300 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4301 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4302 	return true;
4303 }
4304 
4305 static void tcp_drop(struct sock *sk, struct sk_buff *skb)
4306 {
4307 	sk_drops_add(sk, skb);
4308 	__kfree_skb(skb);
4309 }
4310 
4311 /* This one checks to see if we can put data from the
4312  * out_of_order queue into the receive_queue.
4313  */
4314 static void tcp_ofo_queue(struct sock *sk)
4315 {
4316 	struct tcp_sock *tp = tcp_sk(sk);
4317 	__u32 dsack_high = tp->rcv_nxt;
4318 	bool fin, fragstolen, eaten;
4319 	struct sk_buff *skb, *tail;
4320 	struct rb_node *p;
4321 
4322 	p = rb_first(&tp->out_of_order_queue);
4323 	while (p) {
4324 		skb = rb_entry(p, struct sk_buff, rbnode);
4325 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4326 			break;
4327 
4328 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4329 			__u32 dsack = dsack_high;
4330 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4331 				dsack_high = TCP_SKB_CB(skb)->end_seq;
4332 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4333 		}
4334 		p = rb_next(p);
4335 		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4336 
4337 		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4338 			SOCK_DEBUG(sk, "ofo packet was already received\n");
4339 			tcp_drop(sk, skb);
4340 			continue;
4341 		}
4342 		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4343 			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4344 			   TCP_SKB_CB(skb)->end_seq);
4345 
4346 		tail = skb_peek_tail(&sk->sk_receive_queue);
4347 		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4348 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4349 		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4350 		if (!eaten)
4351 			__skb_queue_tail(&sk->sk_receive_queue, skb);
4352 		else
4353 			kfree_skb_partial(skb, fragstolen);
4354 
4355 		if (unlikely(fin)) {
4356 			tcp_fin(sk);
4357 			/* tcp_fin() purges tp->out_of_order_queue,
4358 			 * so we must end this loop right now.
4359 			 */
4360 			break;
4361 		}
4362 	}
4363 }
4364 
4365 static bool tcp_prune_ofo_queue(struct sock *sk);
4366 static int tcp_prune_queue(struct sock *sk);
4367 
4368 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4369 				 unsigned int size)
4370 {
4371 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4372 	    !sk_rmem_schedule(sk, skb, size)) {
4373 
4374 		if (tcp_prune_queue(sk) < 0)
4375 			return -1;
4376 
4377 		while (!sk_rmem_schedule(sk, skb, size)) {
4378 			if (!tcp_prune_ofo_queue(sk))
4379 				return -1;
4380 		}
4381 	}
4382 	return 0;
4383 }
4384 
4385 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4386 {
4387 	struct tcp_sock *tp = tcp_sk(sk);
4388 	struct rb_node **p, *q, *parent;
4389 	struct sk_buff *skb1;
4390 	u32 seq, end_seq;
4391 	bool fragstolen;
4392 
4393 	tcp_ecn_check_ce(tp, skb);
4394 
4395 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4396 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4397 		tcp_drop(sk, skb);
4398 		return;
4399 	}
4400 
4401 	/* Disable header prediction. */
4402 	tp->pred_flags = 0;
4403 	inet_csk_schedule_ack(sk);
4404 
4405 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4406 	seq = TCP_SKB_CB(skb)->seq;
4407 	end_seq = TCP_SKB_CB(skb)->end_seq;
4408 	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4409 		   tp->rcv_nxt, seq, end_seq);
4410 
4411 	p = &tp->out_of_order_queue.rb_node;
4412 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4413 		/* Initial out of order segment, build 1 SACK. */
4414 		if (tcp_is_sack(tp)) {
4415 			tp->rx_opt.num_sacks = 1;
4416 			tp->selective_acks[0].start_seq = seq;
4417 			tp->selective_acks[0].end_seq = end_seq;
4418 		}
4419 		rb_link_node(&skb->rbnode, NULL, p);
4420 		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4421 		tp->ooo_last_skb = skb;
4422 		goto end;
4423 	}
4424 
4425 	/* In the typical case, we are adding an skb to the end of the list.
4426 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4427 	 */
4428 	if (tcp_try_coalesce(sk, tp->ooo_last_skb, skb, &fragstolen)) {
4429 coalesce_done:
4430 		tcp_grow_window(sk, skb);
4431 		kfree_skb_partial(skb, fragstolen);
4432 		skb = NULL;
4433 		goto add_sack;
4434 	}
4435 	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4436 	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4437 		parent = &tp->ooo_last_skb->rbnode;
4438 		p = &parent->rb_right;
4439 		goto insert;
4440 	}
4441 
4442 	/* Find place to insert this segment. Handle overlaps on the way. */
4443 	parent = NULL;
4444 	while (*p) {
4445 		parent = *p;
4446 		skb1 = rb_entry(parent, struct sk_buff, rbnode);
4447 		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4448 			p = &parent->rb_left;
4449 			continue;
4450 		}
4451 		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4452 			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4453 				/* All the bits are present. Drop. */
4454 				NET_INC_STATS(sock_net(sk),
4455 					      LINUX_MIB_TCPOFOMERGE);
4456 				__kfree_skb(skb);
4457 				skb = NULL;
4458 				tcp_dsack_set(sk, seq, end_seq);
4459 				goto add_sack;
4460 			}
4461 			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4462 				/* Partial overlap. */
4463 				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4464 			} else {
4465 				/* skb's seq == skb1's seq and skb covers skb1.
4466 				 * Replace skb1 with skb.
4467 				 */
4468 				rb_replace_node(&skb1->rbnode, &skb->rbnode,
4469 						&tp->out_of_order_queue);
4470 				tcp_dsack_extend(sk,
4471 						 TCP_SKB_CB(skb1)->seq,
4472 						 TCP_SKB_CB(skb1)->end_seq);
4473 				NET_INC_STATS(sock_net(sk),
4474 					      LINUX_MIB_TCPOFOMERGE);
4475 				__kfree_skb(skb1);
4476 				goto merge_right;
4477 			}
4478 		} else if (tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4479 			goto coalesce_done;
4480 		}
4481 		p = &parent->rb_right;
4482 	}
4483 insert:
4484 	/* Insert segment into RB tree. */
4485 	rb_link_node(&skb->rbnode, parent, p);
4486 	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4487 
4488 merge_right:
4489 	/* Remove other segments covered by skb. */
4490 	while ((q = rb_next(&skb->rbnode)) != NULL) {
4491 		skb1 = rb_entry(q, struct sk_buff, rbnode);
4492 
4493 		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4494 			break;
4495 		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4496 			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4497 					 end_seq);
4498 			break;
4499 		}
4500 		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4501 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4502 				 TCP_SKB_CB(skb1)->end_seq);
4503 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4504 		tcp_drop(sk, skb1);
4505 	}
4506 	/* If there is no skb after us, we are the last_skb ! */
4507 	if (!q)
4508 		tp->ooo_last_skb = skb;
4509 
4510 add_sack:
4511 	if (tcp_is_sack(tp))
4512 		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4513 end:
4514 	if (skb) {
4515 		tcp_grow_window(sk, skb);
4516 		skb_condense(skb);
4517 		skb_set_owner_r(skb, sk);
4518 	}
4519 }
4520 
4521 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4522 		  bool *fragstolen)
4523 {
4524 	int eaten;
4525 	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4526 
4527 	__skb_pull(skb, hdrlen);
4528 	eaten = (tail &&
4529 		 tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4530 	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4531 	if (!eaten) {
4532 		__skb_queue_tail(&sk->sk_receive_queue, skb);
4533 		skb_set_owner_r(skb, sk);
4534 	}
4535 	return eaten;
4536 }
4537 
4538 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4539 {
4540 	struct sk_buff *skb;
4541 	int err = -ENOMEM;
4542 	int data_len = 0;
4543 	bool fragstolen;
4544 
4545 	if (size == 0)
4546 		return 0;
4547 
4548 	if (size > PAGE_SIZE) {
4549 		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4550 
4551 		data_len = npages << PAGE_SHIFT;
4552 		size = data_len + (size & ~PAGE_MASK);
4553 	}
4554 	skb = alloc_skb_with_frags(size - data_len, data_len,
4555 				   PAGE_ALLOC_COSTLY_ORDER,
4556 				   &err, sk->sk_allocation);
4557 	if (!skb)
4558 		goto err;
4559 
4560 	skb_put(skb, size - data_len);
4561 	skb->data_len = data_len;
4562 	skb->len = size;
4563 
4564 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4565 		goto err_free;
4566 
4567 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4568 	if (err)
4569 		goto err_free;
4570 
4571 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4572 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4573 	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4574 
4575 	if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
4576 		WARN_ON_ONCE(fragstolen); /* should not happen */
4577 		__kfree_skb(skb);
4578 	}
4579 	return size;
4580 
4581 err_free:
4582 	kfree_skb(skb);
4583 err:
4584 	return err;
4585 
4586 }
4587 
4588 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4589 {
4590 	struct tcp_sock *tp = tcp_sk(sk);
4591 	bool fragstolen = false;
4592 	int eaten = -1;
4593 
4594 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
4595 		__kfree_skb(skb);
4596 		return;
4597 	}
4598 	skb_dst_drop(skb);
4599 	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
4600 
4601 	tcp_ecn_accept_cwr(tp, skb);
4602 
4603 	tp->rx_opt.dsack = 0;
4604 
4605 	/*  Queue data for delivery to the user.
4606 	 *  Packets in sequence go to the receive queue.
4607 	 *  Out of sequence packets to the out_of_order_queue.
4608 	 */
4609 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4610 		if (tcp_receive_window(tp) == 0)
4611 			goto out_of_window;
4612 
4613 		/* Ok. In sequence. In window. */
4614 		if (tp->ucopy.task == current &&
4615 		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4616 		    sock_owned_by_user(sk) && !tp->urg_data) {
4617 			int chunk = min_t(unsigned int, skb->len,
4618 					  tp->ucopy.len);
4619 
4620 			__set_current_state(TASK_RUNNING);
4621 
4622 			if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
4623 				tp->ucopy.len -= chunk;
4624 				tp->copied_seq += chunk;
4625 				eaten = (chunk == skb->len);
4626 				tcp_rcv_space_adjust(sk);
4627 			}
4628 		}
4629 
4630 		if (eaten <= 0) {
4631 queue_and_out:
4632 			if (eaten < 0) {
4633 				if (skb_queue_len(&sk->sk_receive_queue) == 0)
4634 					sk_forced_mem_schedule(sk, skb->truesize);
4635 				else if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4636 					goto drop;
4637 			}
4638 			eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4639 		}
4640 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4641 		if (skb->len)
4642 			tcp_event_data_recv(sk, skb);
4643 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4644 			tcp_fin(sk);
4645 
4646 		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4647 			tcp_ofo_queue(sk);
4648 
4649 			/* RFC2581. 4.2. SHOULD send immediate ACK, when
4650 			 * gap in queue is filled.
4651 			 */
4652 			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
4653 				inet_csk(sk)->icsk_ack.pingpong = 0;
4654 		}
4655 
4656 		if (tp->rx_opt.num_sacks)
4657 			tcp_sack_remove(tp);
4658 
4659 		tcp_fast_path_check(sk);
4660 
4661 		if (eaten > 0)
4662 			kfree_skb_partial(skb, fragstolen);
4663 		if (!sock_flag(sk, SOCK_DEAD))
4664 			sk->sk_data_ready(sk);
4665 		return;
4666 	}
4667 
4668 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4669 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
4670 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4671 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4672 
4673 out_of_window:
4674 		tcp_enter_quickack_mode(sk);
4675 		inet_csk_schedule_ack(sk);
4676 drop:
4677 		tcp_drop(sk, skb);
4678 		return;
4679 	}
4680 
4681 	/* Out of window. F.e. zero window probe. */
4682 	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4683 		goto out_of_window;
4684 
4685 	tcp_enter_quickack_mode(sk);
4686 
4687 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4688 		/* Partial packet, seq < rcv_next < end_seq */
4689 		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4690 			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4691 			   TCP_SKB_CB(skb)->end_seq);
4692 
4693 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4694 
4695 		/* If window is closed, drop tail of packet. But after
4696 		 * remembering D-SACK for its head made in previous line.
4697 		 */
4698 		if (!tcp_receive_window(tp))
4699 			goto out_of_window;
4700 		goto queue_and_out;
4701 	}
4702 
4703 	tcp_data_queue_ofo(sk, skb);
4704 }
4705 
4706 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
4707 {
4708 	if (list)
4709 		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
4710 
4711 	return rb_entry_safe(rb_next(&skb->rbnode), struct sk_buff, rbnode);
4712 }
4713 
4714 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4715 					struct sk_buff_head *list,
4716 					struct rb_root *root)
4717 {
4718 	struct sk_buff *next = tcp_skb_next(skb, list);
4719 
4720 	if (list)
4721 		__skb_unlink(skb, list);
4722 	else
4723 		rb_erase(&skb->rbnode, root);
4724 
4725 	__kfree_skb(skb);
4726 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4727 
4728 	return next;
4729 }
4730 
4731 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
4732 static void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
4733 {
4734 	struct rb_node **p = &root->rb_node;
4735 	struct rb_node *parent = NULL;
4736 	struct sk_buff *skb1;
4737 
4738 	while (*p) {
4739 		parent = *p;
4740 		skb1 = rb_entry(parent, struct sk_buff, rbnode);
4741 		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
4742 			p = &parent->rb_left;
4743 		else
4744 			p = &parent->rb_right;
4745 	}
4746 	rb_link_node(&skb->rbnode, parent, p);
4747 	rb_insert_color(&skb->rbnode, root);
4748 }
4749 
4750 /* Collapse contiguous sequence of skbs head..tail with
4751  * sequence numbers start..end.
4752  *
4753  * If tail is NULL, this means until the end of the queue.
4754  *
4755  * Segments with FIN/SYN are not collapsed (only because this
4756  * simplifies code)
4757  */
4758 static void
4759 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
4760 	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
4761 {
4762 	struct sk_buff *skb = head, *n;
4763 	struct sk_buff_head tmp;
4764 	bool end_of_skbs;
4765 
4766 	/* First, check that queue is collapsible and find
4767 	 * the point where collapsing can be useful.
4768 	 */
4769 restart:
4770 	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
4771 		n = tcp_skb_next(skb, list);
4772 
4773 		/* No new bits? It is possible on ofo queue. */
4774 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4775 			skb = tcp_collapse_one(sk, skb, list, root);
4776 			if (!skb)
4777 				break;
4778 			goto restart;
4779 		}
4780 
4781 		/* The first skb to collapse is:
4782 		 * - not SYN/FIN and
4783 		 * - bloated or contains data before "start" or
4784 		 *   overlaps to the next one.
4785 		 */
4786 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4787 		    (tcp_win_from_space(skb->truesize) > skb->len ||
4788 		     before(TCP_SKB_CB(skb)->seq, start))) {
4789 			end_of_skbs = false;
4790 			break;
4791 		}
4792 
4793 		if (n && n != tail &&
4794 		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
4795 			end_of_skbs = false;
4796 			break;
4797 		}
4798 
4799 		/* Decided to skip this, advance start seq. */
4800 		start = TCP_SKB_CB(skb)->end_seq;
4801 	}
4802 	if (end_of_skbs ||
4803 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4804 		return;
4805 
4806 	__skb_queue_head_init(&tmp);
4807 
4808 	while (before(start, end)) {
4809 		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4810 		struct sk_buff *nskb;
4811 
4812 		nskb = alloc_skb(copy, GFP_ATOMIC);
4813 		if (!nskb)
4814 			break;
4815 
4816 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4817 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4818 		if (list)
4819 			__skb_queue_before(list, skb, nskb);
4820 		else
4821 			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
4822 		skb_set_owner_r(nskb, sk);
4823 
4824 		/* Copy data, releasing collapsed skbs. */
4825 		while (copy > 0) {
4826 			int offset = start - TCP_SKB_CB(skb)->seq;
4827 			int size = TCP_SKB_CB(skb)->end_seq - start;
4828 
4829 			BUG_ON(offset < 0);
4830 			if (size > 0) {
4831 				size = min(copy, size);
4832 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4833 					BUG();
4834 				TCP_SKB_CB(nskb)->end_seq += size;
4835 				copy -= size;
4836 				start += size;
4837 			}
4838 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4839 				skb = tcp_collapse_one(sk, skb, list, root);
4840 				if (!skb ||
4841 				    skb == tail ||
4842 				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4843 					goto end;
4844 			}
4845 		}
4846 	}
4847 end:
4848 	skb_queue_walk_safe(&tmp, skb, n)
4849 		tcp_rbtree_insert(root, skb);
4850 }
4851 
4852 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4853  * and tcp_collapse() them until all the queue is collapsed.
4854  */
4855 static void tcp_collapse_ofo_queue(struct sock *sk)
4856 {
4857 	struct tcp_sock *tp = tcp_sk(sk);
4858 	struct sk_buff *skb, *head;
4859 	struct rb_node *p;
4860 	u32 start, end;
4861 
4862 	p = rb_first(&tp->out_of_order_queue);
4863 	skb = rb_entry_safe(p, struct sk_buff, rbnode);
4864 new_range:
4865 	if (!skb) {
4866 		p = rb_last(&tp->out_of_order_queue);
4867 		/* Note: This is possible p is NULL here. We do not
4868 		 * use rb_entry_safe(), as ooo_last_skb is valid only
4869 		 * if rbtree is not empty.
4870 		 */
4871 		tp->ooo_last_skb = rb_entry(p, struct sk_buff, rbnode);
4872 		return;
4873 	}
4874 	start = TCP_SKB_CB(skb)->seq;
4875 	end = TCP_SKB_CB(skb)->end_seq;
4876 
4877 	for (head = skb;;) {
4878 		skb = tcp_skb_next(skb, NULL);
4879 
4880 		/* Range is terminated when we see a gap or when
4881 		 * we are at the queue end.
4882 		 */
4883 		if (!skb ||
4884 		    after(TCP_SKB_CB(skb)->seq, end) ||
4885 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
4886 			tcp_collapse(sk, NULL, &tp->out_of_order_queue,
4887 				     head, skb, start, end);
4888 			goto new_range;
4889 		}
4890 
4891 		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
4892 			start = TCP_SKB_CB(skb)->seq;
4893 		if (after(TCP_SKB_CB(skb)->end_seq, end))
4894 			end = TCP_SKB_CB(skb)->end_seq;
4895 	}
4896 }
4897 
4898 /*
4899  * Clean the out-of-order queue to make room.
4900  * We drop high sequences packets to :
4901  * 1) Let a chance for holes to be filled.
4902  * 2) not add too big latencies if thousands of packets sit there.
4903  *    (But if application shrinks SO_RCVBUF, we could still end up
4904  *     freeing whole queue here)
4905  *
4906  * Return true if queue has shrunk.
4907  */
4908 static bool tcp_prune_ofo_queue(struct sock *sk)
4909 {
4910 	struct tcp_sock *tp = tcp_sk(sk);
4911 	struct rb_node *node, *prev;
4912 
4913 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
4914 		return false;
4915 
4916 	NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
4917 	node = &tp->ooo_last_skb->rbnode;
4918 	do {
4919 		prev = rb_prev(node);
4920 		rb_erase(node, &tp->out_of_order_queue);
4921 		tcp_drop(sk, rb_entry(node, struct sk_buff, rbnode));
4922 		sk_mem_reclaim(sk);
4923 		if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
4924 		    !tcp_under_memory_pressure(sk))
4925 			break;
4926 		node = prev;
4927 	} while (node);
4928 	tp->ooo_last_skb = rb_entry(prev, struct sk_buff, rbnode);
4929 
4930 	/* Reset SACK state.  A conforming SACK implementation will
4931 	 * do the same at a timeout based retransmit.  When a connection
4932 	 * is in a sad state like this, we care only about integrity
4933 	 * of the connection not performance.
4934 	 */
4935 	if (tp->rx_opt.sack_ok)
4936 		tcp_sack_reset(&tp->rx_opt);
4937 	return true;
4938 }
4939 
4940 /* Reduce allocated memory if we can, trying to get
4941  * the socket within its memory limits again.
4942  *
4943  * Return less than zero if we should start dropping frames
4944  * until the socket owning process reads some of the data
4945  * to stabilize the situation.
4946  */
4947 static int tcp_prune_queue(struct sock *sk)
4948 {
4949 	struct tcp_sock *tp = tcp_sk(sk);
4950 
4951 	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4952 
4953 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
4954 
4955 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4956 		tcp_clamp_window(sk);
4957 	else if (tcp_under_memory_pressure(sk))
4958 		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4959 
4960 	tcp_collapse_ofo_queue(sk);
4961 	if (!skb_queue_empty(&sk->sk_receive_queue))
4962 		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
4963 			     skb_peek(&sk->sk_receive_queue),
4964 			     NULL,
4965 			     tp->copied_seq, tp->rcv_nxt);
4966 	sk_mem_reclaim(sk);
4967 
4968 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4969 		return 0;
4970 
4971 	/* Collapsing did not help, destructive actions follow.
4972 	 * This must not ever occur. */
4973 
4974 	tcp_prune_ofo_queue(sk);
4975 
4976 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4977 		return 0;
4978 
4979 	/* If we are really being abused, tell the caller to silently
4980 	 * drop receive data on the floor.  It will get retransmitted
4981 	 * and hopefully then we'll have sufficient space.
4982 	 */
4983 	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
4984 
4985 	/* Massive buffer overcommit. */
4986 	tp->pred_flags = 0;
4987 	return -1;
4988 }
4989 
4990 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4991 {
4992 	const struct tcp_sock *tp = tcp_sk(sk);
4993 
4994 	/* If the user specified a specific send buffer setting, do
4995 	 * not modify it.
4996 	 */
4997 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4998 		return false;
4999 
5000 	/* If we are under global TCP memory pressure, do not expand.  */
5001 	if (tcp_under_memory_pressure(sk))
5002 		return false;
5003 
5004 	/* If we are under soft global TCP memory pressure, do not expand.  */
5005 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5006 		return false;
5007 
5008 	/* If we filled the congestion window, do not expand.  */
5009 	if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
5010 		return false;
5011 
5012 	return true;
5013 }
5014 
5015 /* When incoming ACK allowed to free some skb from write_queue,
5016  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
5017  * on the exit from tcp input handler.
5018  *
5019  * PROBLEM: sndbuf expansion does not work well with largesend.
5020  */
5021 static void tcp_new_space(struct sock *sk)
5022 {
5023 	struct tcp_sock *tp = tcp_sk(sk);
5024 
5025 	if (tcp_should_expand_sndbuf(sk)) {
5026 		tcp_sndbuf_expand(sk);
5027 		tp->snd_cwnd_stamp = tcp_jiffies32;
5028 	}
5029 
5030 	sk->sk_write_space(sk);
5031 }
5032 
5033 static void tcp_check_space(struct sock *sk)
5034 {
5035 	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
5036 		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
5037 		/* pairs with tcp_poll() */
5038 		smp_mb();
5039 		if (sk->sk_socket &&
5040 		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5041 			tcp_new_space(sk);
5042 			if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5043 				tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5044 		}
5045 	}
5046 }
5047 
5048 static inline void tcp_data_snd_check(struct sock *sk)
5049 {
5050 	tcp_push_pending_frames(sk);
5051 	tcp_check_space(sk);
5052 }
5053 
5054 /*
5055  * Check if sending an ack is needed.
5056  */
5057 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5058 {
5059 	struct tcp_sock *tp = tcp_sk(sk);
5060 
5061 	    /* More than one full frame received... */
5062 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5063 	     /* ... and right edge of window advances far enough.
5064 	      * (tcp_recvmsg() will send ACK otherwise). Or...
5065 	      */
5066 	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
5067 	    /* We ACK each frame or... */
5068 	    tcp_in_quickack_mode(sk) ||
5069 	    /* We have out of order data. */
5070 	    (ofo_possible && !RB_EMPTY_ROOT(&tp->out_of_order_queue))) {
5071 		/* Then ack it now */
5072 		tcp_send_ack(sk);
5073 	} else {
5074 		/* Else, send delayed ack. */
5075 		tcp_send_delayed_ack(sk);
5076 	}
5077 }
5078 
5079 static inline void tcp_ack_snd_check(struct sock *sk)
5080 {
5081 	if (!inet_csk_ack_scheduled(sk)) {
5082 		/* We sent a data segment already. */
5083 		return;
5084 	}
5085 	__tcp_ack_snd_check(sk, 1);
5086 }
5087 
5088 /*
5089  *	This routine is only called when we have urgent data
5090  *	signaled. Its the 'slow' part of tcp_urg. It could be
5091  *	moved inline now as tcp_urg is only called from one
5092  *	place. We handle URGent data wrong. We have to - as
5093  *	BSD still doesn't use the correction from RFC961.
5094  *	For 1003.1g we should support a new option TCP_STDURG to permit
5095  *	either form (or just set the sysctl tcp_stdurg).
5096  */
5097 
5098 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5099 {
5100 	struct tcp_sock *tp = tcp_sk(sk);
5101 	u32 ptr = ntohs(th->urg_ptr);
5102 
5103 	if (ptr && !sysctl_tcp_stdurg)
5104 		ptr--;
5105 	ptr += ntohl(th->seq);
5106 
5107 	/* Ignore urgent data that we've already seen and read. */
5108 	if (after(tp->copied_seq, ptr))
5109 		return;
5110 
5111 	/* Do not replay urg ptr.
5112 	 *
5113 	 * NOTE: interesting situation not covered by specs.
5114 	 * Misbehaving sender may send urg ptr, pointing to segment,
5115 	 * which we already have in ofo queue. We are not able to fetch
5116 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5117 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5118 	 * situations. But it is worth to think about possibility of some
5119 	 * DoSes using some hypothetical application level deadlock.
5120 	 */
5121 	if (before(ptr, tp->rcv_nxt))
5122 		return;
5123 
5124 	/* Do we already have a newer (or duplicate) urgent pointer? */
5125 	if (tp->urg_data && !after(ptr, tp->urg_seq))
5126 		return;
5127 
5128 	/* Tell the world about our new urgent pointer. */
5129 	sk_send_sigurg(sk);
5130 
5131 	/* We may be adding urgent data when the last byte read was
5132 	 * urgent. To do this requires some care. We cannot just ignore
5133 	 * tp->copied_seq since we would read the last urgent byte again
5134 	 * as data, nor can we alter copied_seq until this data arrives
5135 	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5136 	 *
5137 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5138 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5139 	 * and expect that both A and B disappear from stream. This is _wrong_.
5140 	 * Though this happens in BSD with high probability, this is occasional.
5141 	 * Any application relying on this is buggy. Note also, that fix "works"
5142 	 * only in this artificial test. Insert some normal data between A and B and we will
5143 	 * decline of BSD again. Verdict: it is better to remove to trap
5144 	 * buggy users.
5145 	 */
5146 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5147 	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5148 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5149 		tp->copied_seq++;
5150 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5151 			__skb_unlink(skb, &sk->sk_receive_queue);
5152 			__kfree_skb(skb);
5153 		}
5154 	}
5155 
5156 	tp->urg_data = TCP_URG_NOTYET;
5157 	tp->urg_seq = ptr;
5158 
5159 	/* Disable header prediction. */
5160 	tp->pred_flags = 0;
5161 }
5162 
5163 /* This is the 'fast' part of urgent handling. */
5164 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5165 {
5166 	struct tcp_sock *tp = tcp_sk(sk);
5167 
5168 	/* Check if we get a new urgent pointer - normally not. */
5169 	if (th->urg)
5170 		tcp_check_urg(sk, th);
5171 
5172 	/* Do we wait for any urgent data? - normally not... */
5173 	if (tp->urg_data == TCP_URG_NOTYET) {
5174 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5175 			  th->syn;
5176 
5177 		/* Is the urgent pointer pointing into this packet? */
5178 		if (ptr < skb->len) {
5179 			u8 tmp;
5180 			if (skb_copy_bits(skb, ptr, &tmp, 1))
5181 				BUG();
5182 			tp->urg_data = TCP_URG_VALID | tmp;
5183 			if (!sock_flag(sk, SOCK_DEAD))
5184 				sk->sk_data_ready(sk);
5185 		}
5186 	}
5187 }
5188 
5189 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5190 {
5191 	struct tcp_sock *tp = tcp_sk(sk);
5192 	int chunk = skb->len - hlen;
5193 	int err;
5194 
5195 	if (skb_csum_unnecessary(skb))
5196 		err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
5197 	else
5198 		err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);
5199 
5200 	if (!err) {
5201 		tp->ucopy.len -= chunk;
5202 		tp->copied_seq += chunk;
5203 		tcp_rcv_space_adjust(sk);
5204 	}
5205 
5206 	return err;
5207 }
5208 
5209 /* Accept RST for rcv_nxt - 1 after a FIN.
5210  * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5211  * FIN is sent followed by a RST packet. The RST is sent with the same
5212  * sequence number as the FIN, and thus according to RFC 5961 a challenge
5213  * ACK should be sent. However, Mac OSX rate limits replies to challenge
5214  * ACKs on the closed socket. In addition middleboxes can drop either the
5215  * challenge ACK or a subsequent RST.
5216  */
5217 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5218 {
5219 	struct tcp_sock *tp = tcp_sk(sk);
5220 
5221 	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5222 			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5223 					       TCPF_CLOSING));
5224 }
5225 
5226 /* Does PAWS and seqno based validation of an incoming segment, flags will
5227  * play significant role here.
5228  */
5229 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5230 				  const struct tcphdr *th, int syn_inerr)
5231 {
5232 	struct tcp_sock *tp = tcp_sk(sk);
5233 	bool rst_seq_match = false;
5234 
5235 	/* RFC1323: H1. Apply PAWS check first. */
5236 	if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
5237 	    tp->rx_opt.saw_tstamp &&
5238 	    tcp_paws_discard(sk, skb)) {
5239 		if (!th->rst) {
5240 			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5241 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5242 						  LINUX_MIB_TCPACKSKIPPEDPAWS,
5243 						  &tp->last_oow_ack_time))
5244 				tcp_send_dupack(sk, skb);
5245 			goto discard;
5246 		}
5247 		/* Reset is accepted even if it did not pass PAWS. */
5248 	}
5249 
5250 	/* Step 1: check sequence number */
5251 	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5252 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5253 		 * (RST) segments are validated by checking their SEQ-fields."
5254 		 * And page 69: "If an incoming segment is not acceptable,
5255 		 * an acknowledgment should be sent in reply (unless the RST
5256 		 * bit is set, if so drop the segment and return)".
5257 		 */
5258 		if (!th->rst) {
5259 			if (th->syn)
5260 				goto syn_challenge;
5261 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5262 						  LINUX_MIB_TCPACKSKIPPEDSEQ,
5263 						  &tp->last_oow_ack_time))
5264 				tcp_send_dupack(sk, skb);
5265 		} else if (tcp_reset_check(sk, skb)) {
5266 			tcp_reset(sk);
5267 		}
5268 		goto discard;
5269 	}
5270 
5271 	/* Step 2: check RST bit */
5272 	if (th->rst) {
5273 		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
5274 		 * FIN and SACK too if available):
5275 		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
5276 		 * the right-most SACK block,
5277 		 * then
5278 		 *     RESET the connection
5279 		 * else
5280 		 *     Send a challenge ACK
5281 		 */
5282 		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
5283 		    tcp_reset_check(sk, skb)) {
5284 			rst_seq_match = true;
5285 		} else if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
5286 			struct tcp_sack_block *sp = &tp->selective_acks[0];
5287 			int max_sack = sp[0].end_seq;
5288 			int this_sack;
5289 
5290 			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
5291 			     ++this_sack) {
5292 				max_sack = after(sp[this_sack].end_seq,
5293 						 max_sack) ?
5294 					sp[this_sack].end_seq : max_sack;
5295 			}
5296 
5297 			if (TCP_SKB_CB(skb)->seq == max_sack)
5298 				rst_seq_match = true;
5299 		}
5300 
5301 		if (rst_seq_match)
5302 			tcp_reset(sk);
5303 		else {
5304 			/* Disable TFO if RST is out-of-order
5305 			 * and no data has been received
5306 			 * for current active TFO socket
5307 			 */
5308 			if (tp->syn_fastopen && !tp->data_segs_in &&
5309 			    sk->sk_state == TCP_ESTABLISHED)
5310 				tcp_fastopen_active_disable(sk);
5311 			tcp_send_challenge_ack(sk, skb);
5312 		}
5313 		goto discard;
5314 	}
5315 
5316 	/* step 3: check security and precedence [ignored] */
5317 
5318 	/* step 4: Check for a SYN
5319 	 * RFC 5961 4.2 : Send a challenge ack
5320 	 */
5321 	if (th->syn) {
5322 syn_challenge:
5323 		if (syn_inerr)
5324 			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5325 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5326 		tcp_send_challenge_ack(sk, skb);
5327 		goto discard;
5328 	}
5329 
5330 	return true;
5331 
5332 discard:
5333 	tcp_drop(sk, skb);
5334 	return false;
5335 }
5336 
5337 /*
5338  *	TCP receive function for the ESTABLISHED state.
5339  *
5340  *	It is split into a fast path and a slow path. The fast path is
5341  * 	disabled when:
5342  *	- A zero window was announced from us - zero window probing
5343  *        is only handled properly in the slow path.
5344  *	- Out of order segments arrived.
5345  *	- Urgent data is expected.
5346  *	- There is no buffer space left
5347  *	- Unexpected TCP flags/window values/header lengths are received
5348  *	  (detected by checking the TCP header against pred_flags)
5349  *	- Data is sent in both directions. Fast path only supports pure senders
5350  *	  or pure receivers (this means either the sequence number or the ack
5351  *	  value must stay constant)
5352  *	- Unexpected TCP option.
5353  *
5354  *	When these conditions are not satisfied it drops into a standard
5355  *	receive procedure patterned after RFC793 to handle all cases.
5356  *	The first three cases are guaranteed by proper pred_flags setting,
5357  *	the rest is checked inline. Fast processing is turned on in
5358  *	tcp_data_queue when everything is OK.
5359  */
5360 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5361 			 const struct tcphdr *th, unsigned int len)
5362 {
5363 	struct tcp_sock *tp = tcp_sk(sk);
5364 
5365 	tcp_mstamp_refresh(tp);
5366 	if (unlikely(!sk->sk_rx_dst))
5367 		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5368 	/*
5369 	 *	Header prediction.
5370 	 *	The code loosely follows the one in the famous
5371 	 *	"30 instruction TCP receive" Van Jacobson mail.
5372 	 *
5373 	 *	Van's trick is to deposit buffers into socket queue
5374 	 *	on a device interrupt, to call tcp_recv function
5375 	 *	on the receive process context and checksum and copy
5376 	 *	the buffer to user space. smart...
5377 	 *
5378 	 *	Our current scheme is not silly either but we take the
5379 	 *	extra cost of the net_bh soft interrupt processing...
5380 	 *	We do checksum and copy also but from device to kernel.
5381 	 */
5382 
5383 	tp->rx_opt.saw_tstamp = 0;
5384 
5385 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5386 	 *	if header_prediction is to be made
5387 	 *	'S' will always be tp->tcp_header_len >> 2
5388 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5389 	 *  turn it off	(when there are holes in the receive
5390 	 *	 space for instance)
5391 	 *	PSH flag is ignored.
5392 	 */
5393 
5394 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5395 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5396 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5397 		int tcp_header_len = tp->tcp_header_len;
5398 
5399 		/* Timestamp header prediction: tcp_header_len
5400 		 * is automatically equal to th->doff*4 due to pred_flags
5401 		 * match.
5402 		 */
5403 
5404 		/* Check timestamp */
5405 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5406 			/* No? Slow path! */
5407 			if (!tcp_parse_aligned_timestamp(tp, th))
5408 				goto slow_path;
5409 
5410 			/* If PAWS failed, check it more carefully in slow path */
5411 			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5412 				goto slow_path;
5413 
5414 			/* DO NOT update ts_recent here, if checksum fails
5415 			 * and timestamp was corrupted part, it will result
5416 			 * in a hung connection since we will drop all
5417 			 * future packets due to the PAWS test.
5418 			 */
5419 		}
5420 
5421 		if (len <= tcp_header_len) {
5422 			/* Bulk data transfer: sender */
5423 			if (len == tcp_header_len) {
5424 				/* Predicted packet is in window by definition.
5425 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5426 				 * Hence, check seq<=rcv_wup reduces to:
5427 				 */
5428 				if (tcp_header_len ==
5429 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5430 				    tp->rcv_nxt == tp->rcv_wup)
5431 					tcp_store_ts_recent(tp);
5432 
5433 				/* We know that such packets are checksummed
5434 				 * on entry.
5435 				 */
5436 				tcp_ack(sk, skb, 0);
5437 				__kfree_skb(skb);
5438 				tcp_data_snd_check(sk);
5439 				return;
5440 			} else { /* Header too small */
5441 				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5442 				goto discard;
5443 			}
5444 		} else {
5445 			int eaten = 0;
5446 			bool fragstolen = false;
5447 
5448 			if (tp->ucopy.task == current &&
5449 			    tp->copied_seq == tp->rcv_nxt &&
5450 			    len - tcp_header_len <= tp->ucopy.len &&
5451 			    sock_owned_by_user(sk)) {
5452 				__set_current_state(TASK_RUNNING);
5453 
5454 				if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
5455 					/* Predicted packet is in window by definition.
5456 					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5457 					 * Hence, check seq<=rcv_wup reduces to:
5458 					 */
5459 					if (tcp_header_len ==
5460 					    (sizeof(struct tcphdr) +
5461 					     TCPOLEN_TSTAMP_ALIGNED) &&
5462 					    tp->rcv_nxt == tp->rcv_wup)
5463 						tcp_store_ts_recent(tp);
5464 
5465 					tcp_rcv_rtt_measure_ts(sk, skb);
5466 
5467 					__skb_pull(skb, tcp_header_len);
5468 					tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
5469 					NET_INC_STATS(sock_net(sk),
5470 							LINUX_MIB_TCPHPHITSTOUSER);
5471 					eaten = 1;
5472 				}
5473 			}
5474 			if (!eaten) {
5475 				if (tcp_checksum_complete(skb))
5476 					goto csum_error;
5477 
5478 				if ((int)skb->truesize > sk->sk_forward_alloc)
5479 					goto step5;
5480 
5481 				/* Predicted packet is in window by definition.
5482 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5483 				 * Hence, check seq<=rcv_wup reduces to:
5484 				 */
5485 				if (tcp_header_len ==
5486 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5487 				    tp->rcv_nxt == tp->rcv_wup)
5488 					tcp_store_ts_recent(tp);
5489 
5490 				tcp_rcv_rtt_measure_ts(sk, skb);
5491 
5492 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
5493 
5494 				/* Bulk data transfer: receiver */
5495 				eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5496 						      &fragstolen);
5497 			}
5498 
5499 			tcp_event_data_recv(sk, skb);
5500 
5501 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5502 				/* Well, only one small jumplet in fast path... */
5503 				tcp_ack(sk, skb, FLAG_DATA);
5504 				tcp_data_snd_check(sk);
5505 				if (!inet_csk_ack_scheduled(sk))
5506 					goto no_ack;
5507 			}
5508 
5509 			__tcp_ack_snd_check(sk, 0);
5510 no_ack:
5511 			if (eaten)
5512 				kfree_skb_partial(skb, fragstolen);
5513 			sk->sk_data_ready(sk);
5514 			return;
5515 		}
5516 	}
5517 
5518 slow_path:
5519 	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
5520 		goto csum_error;
5521 
5522 	if (!th->ack && !th->rst && !th->syn)
5523 		goto discard;
5524 
5525 	/*
5526 	 *	Standard slow path.
5527 	 */
5528 
5529 	if (!tcp_validate_incoming(sk, skb, th, 1))
5530 		return;
5531 
5532 step5:
5533 	if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5534 		goto discard;
5535 
5536 	tcp_rcv_rtt_measure_ts(sk, skb);
5537 
5538 	/* Process urgent data. */
5539 	tcp_urg(sk, skb, th);
5540 
5541 	/* step 7: process the segment text */
5542 	tcp_data_queue(sk, skb);
5543 
5544 	tcp_data_snd_check(sk);
5545 	tcp_ack_snd_check(sk);
5546 	return;
5547 
5548 csum_error:
5549 	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
5550 	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5551 
5552 discard:
5553 	tcp_drop(sk, skb);
5554 }
5555 EXPORT_SYMBOL(tcp_rcv_established);
5556 
5557 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5558 {
5559 	struct tcp_sock *tp = tcp_sk(sk);
5560 	struct inet_connection_sock *icsk = inet_csk(sk);
5561 
5562 	tcp_set_state(sk, TCP_ESTABLISHED);
5563 	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
5564 
5565 	if (skb) {
5566 		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5567 		security_inet_conn_established(sk, skb);
5568 	}
5569 
5570 	/* Make sure socket is routed, for correct metrics.  */
5571 	icsk->icsk_af_ops->rebuild_header(sk);
5572 
5573 	tcp_init_metrics(sk);
5574 	tcp_call_bpf(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB);
5575 	tcp_init_congestion_control(sk);
5576 
5577 	/* Prevent spurious tcp_cwnd_restart() on first data
5578 	 * packet.
5579 	 */
5580 	tp->lsndtime = tcp_jiffies32;
5581 
5582 	tcp_init_buffer_space(sk);
5583 
5584 	if (sock_flag(sk, SOCK_KEEPOPEN))
5585 		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5586 
5587 	if (!tp->rx_opt.snd_wscale)
5588 		__tcp_fast_path_on(tp, tp->snd_wnd);
5589 	else
5590 		tp->pred_flags = 0;
5591 
5592 }
5593 
5594 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5595 				    struct tcp_fastopen_cookie *cookie)
5596 {
5597 	struct tcp_sock *tp = tcp_sk(sk);
5598 	struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5599 	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
5600 	bool syn_drop = false;
5601 
5602 	if (mss == tp->rx_opt.user_mss) {
5603 		struct tcp_options_received opt;
5604 
5605 		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
5606 		tcp_clear_options(&opt);
5607 		opt.user_mss = opt.mss_clamp = 0;
5608 		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
5609 		mss = opt.mss_clamp;
5610 	}
5611 
5612 	if (!tp->syn_fastopen) {
5613 		/* Ignore an unsolicited cookie */
5614 		cookie->len = -1;
5615 	} else if (tp->total_retrans) {
5616 		/* SYN timed out and the SYN-ACK neither has a cookie nor
5617 		 * acknowledges data. Presumably the remote received only
5618 		 * the retransmitted (regular) SYNs: either the original
5619 		 * SYN-data or the corresponding SYN-ACK was dropped.
5620 		 */
5621 		syn_drop = (cookie->len < 0 && data);
5622 	} else if (cookie->len < 0 && !tp->syn_data) {
5623 		/* We requested a cookie but didn't get it. If we did not use
5624 		 * the (old) exp opt format then try so next time (try_exp=1).
5625 		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
5626 		 */
5627 		try_exp = tp->syn_fastopen_exp ? 2 : 1;
5628 	}
5629 
5630 	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
5631 
5632 	if (data) { /* Retransmit unacked data in SYN */
5633 		tcp_for_write_queue_from(data, sk) {
5634 			if (data == tcp_send_head(sk) ||
5635 			    __tcp_retransmit_skb(sk, data, 1))
5636 				break;
5637 		}
5638 		tcp_rearm_rto(sk);
5639 		NET_INC_STATS(sock_net(sk),
5640 				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5641 		return true;
5642 	}
5643 	tp->syn_data_acked = tp->syn_data;
5644 	if (tp->syn_data_acked)
5645 		NET_INC_STATS(sock_net(sk),
5646 				LINUX_MIB_TCPFASTOPENACTIVE);
5647 
5648 	tcp_fastopen_add_skb(sk, synack);
5649 
5650 	return false;
5651 }
5652 
5653 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5654 					 const struct tcphdr *th)
5655 {
5656 	struct inet_connection_sock *icsk = inet_csk(sk);
5657 	struct tcp_sock *tp = tcp_sk(sk);
5658 	struct tcp_fastopen_cookie foc = { .len = -1 };
5659 	int saved_clamp = tp->rx_opt.mss_clamp;
5660 	bool fastopen_fail;
5661 
5662 	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
5663 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5664 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5665 
5666 	if (th->ack) {
5667 		/* rfc793:
5668 		 * "If the state is SYN-SENT then
5669 		 *    first check the ACK bit
5670 		 *      If the ACK bit is set
5671 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5672 		 *        a reset (unless the RST bit is set, if so drop
5673 		 *        the segment and return)"
5674 		 */
5675 		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5676 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5677 			goto reset_and_undo;
5678 
5679 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5680 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5681 			     tcp_time_stamp(tp))) {
5682 			NET_INC_STATS(sock_net(sk),
5683 					LINUX_MIB_PAWSACTIVEREJECTED);
5684 			goto reset_and_undo;
5685 		}
5686 
5687 		/* Now ACK is acceptable.
5688 		 *
5689 		 * "If the RST bit is set
5690 		 *    If the ACK was acceptable then signal the user "error:
5691 		 *    connection reset", drop the segment, enter CLOSED state,
5692 		 *    delete TCB, and return."
5693 		 */
5694 
5695 		if (th->rst) {
5696 			tcp_reset(sk);
5697 			goto discard;
5698 		}
5699 
5700 		/* rfc793:
5701 		 *   "fifth, if neither of the SYN or RST bits is set then
5702 		 *    drop the segment and return."
5703 		 *
5704 		 *    See note below!
5705 		 *                                        --ANK(990513)
5706 		 */
5707 		if (!th->syn)
5708 			goto discard_and_undo;
5709 
5710 		/* rfc793:
5711 		 *   "If the SYN bit is on ...
5712 		 *    are acceptable then ...
5713 		 *    (our SYN has been ACKed), change the connection
5714 		 *    state to ESTABLISHED..."
5715 		 */
5716 
5717 		tcp_ecn_rcv_synack(tp, th);
5718 
5719 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5720 		tcp_ack(sk, skb, FLAG_SLOWPATH);
5721 
5722 		/* Ok.. it's good. Set up sequence numbers and
5723 		 * move to established.
5724 		 */
5725 		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5726 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5727 
5728 		/* RFC1323: The window in SYN & SYN/ACK segments is
5729 		 * never scaled.
5730 		 */
5731 		tp->snd_wnd = ntohs(th->window);
5732 
5733 		if (!tp->rx_opt.wscale_ok) {
5734 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5735 			tp->window_clamp = min(tp->window_clamp, 65535U);
5736 		}
5737 
5738 		if (tp->rx_opt.saw_tstamp) {
5739 			tp->rx_opt.tstamp_ok	   = 1;
5740 			tp->tcp_header_len =
5741 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5742 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
5743 			tcp_store_ts_recent(tp);
5744 		} else {
5745 			tp->tcp_header_len = sizeof(struct tcphdr);
5746 		}
5747 
5748 		if (tcp_is_sack(tp) && sysctl_tcp_fack)
5749 			tcp_enable_fack(tp);
5750 
5751 		tcp_mtup_init(sk);
5752 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5753 		tcp_initialize_rcv_mss(sk);
5754 
5755 		/* Remember, tcp_poll() does not lock socket!
5756 		 * Change state from SYN-SENT only after copied_seq
5757 		 * is initialized. */
5758 		tp->copied_seq = tp->rcv_nxt;
5759 
5760 		smp_mb();
5761 
5762 		tcp_finish_connect(sk, skb);
5763 
5764 		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
5765 				tcp_rcv_fastopen_synack(sk, skb, &foc);
5766 
5767 		if (!sock_flag(sk, SOCK_DEAD)) {
5768 			sk->sk_state_change(sk);
5769 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5770 		}
5771 		if (fastopen_fail)
5772 			return -1;
5773 		if (sk->sk_write_pending ||
5774 		    icsk->icsk_accept_queue.rskq_defer_accept ||
5775 		    icsk->icsk_ack.pingpong) {
5776 			/* Save one ACK. Data will be ready after
5777 			 * several ticks, if write_pending is set.
5778 			 *
5779 			 * It may be deleted, but with this feature tcpdumps
5780 			 * look so _wonderfully_ clever, that I was not able
5781 			 * to stand against the temptation 8)     --ANK
5782 			 */
5783 			inet_csk_schedule_ack(sk);
5784 			tcp_enter_quickack_mode(sk);
5785 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5786 						  TCP_DELACK_MAX, TCP_RTO_MAX);
5787 
5788 discard:
5789 			tcp_drop(sk, skb);
5790 			return 0;
5791 		} else {
5792 			tcp_send_ack(sk);
5793 		}
5794 		return -1;
5795 	}
5796 
5797 	/* No ACK in the segment */
5798 
5799 	if (th->rst) {
5800 		/* rfc793:
5801 		 * "If the RST bit is set
5802 		 *
5803 		 *      Otherwise (no ACK) drop the segment and return."
5804 		 */
5805 
5806 		goto discard_and_undo;
5807 	}
5808 
5809 	/* PAWS check. */
5810 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5811 	    tcp_paws_reject(&tp->rx_opt, 0))
5812 		goto discard_and_undo;
5813 
5814 	if (th->syn) {
5815 		/* We see SYN without ACK. It is attempt of
5816 		 * simultaneous connect with crossed SYNs.
5817 		 * Particularly, it can be connect to self.
5818 		 */
5819 		tcp_set_state(sk, TCP_SYN_RECV);
5820 
5821 		if (tp->rx_opt.saw_tstamp) {
5822 			tp->rx_opt.tstamp_ok = 1;
5823 			tcp_store_ts_recent(tp);
5824 			tp->tcp_header_len =
5825 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5826 		} else {
5827 			tp->tcp_header_len = sizeof(struct tcphdr);
5828 		}
5829 
5830 		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5831 		tp->copied_seq = tp->rcv_nxt;
5832 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5833 
5834 		/* RFC1323: The window in SYN & SYN/ACK segments is
5835 		 * never scaled.
5836 		 */
5837 		tp->snd_wnd    = ntohs(th->window);
5838 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5839 		tp->max_window = tp->snd_wnd;
5840 
5841 		tcp_ecn_rcv_syn(tp, th);
5842 
5843 		tcp_mtup_init(sk);
5844 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5845 		tcp_initialize_rcv_mss(sk);
5846 
5847 		tcp_send_synack(sk);
5848 #if 0
5849 		/* Note, we could accept data and URG from this segment.
5850 		 * There are no obstacles to make this (except that we must
5851 		 * either change tcp_recvmsg() to prevent it from returning data
5852 		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
5853 		 *
5854 		 * However, if we ignore data in ACKless segments sometimes,
5855 		 * we have no reasons to accept it sometimes.
5856 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
5857 		 * is not flawless. So, discard packet for sanity.
5858 		 * Uncomment this return to process the data.
5859 		 */
5860 		return -1;
5861 #else
5862 		goto discard;
5863 #endif
5864 	}
5865 	/* "fifth, if neither of the SYN or RST bits is set then
5866 	 * drop the segment and return."
5867 	 */
5868 
5869 discard_and_undo:
5870 	tcp_clear_options(&tp->rx_opt);
5871 	tp->rx_opt.mss_clamp = saved_clamp;
5872 	goto discard;
5873 
5874 reset_and_undo:
5875 	tcp_clear_options(&tp->rx_opt);
5876 	tp->rx_opt.mss_clamp = saved_clamp;
5877 	return 1;
5878 }
5879 
5880 /*
5881  *	This function implements the receiving procedure of RFC 793 for
5882  *	all states except ESTABLISHED and TIME_WAIT.
5883  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5884  *	address independent.
5885  */
5886 
5887 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
5888 {
5889 	struct tcp_sock *tp = tcp_sk(sk);
5890 	struct inet_connection_sock *icsk = inet_csk(sk);
5891 	const struct tcphdr *th = tcp_hdr(skb);
5892 	struct request_sock *req;
5893 	int queued = 0;
5894 	bool acceptable;
5895 
5896 	switch (sk->sk_state) {
5897 	case TCP_CLOSE:
5898 		goto discard;
5899 
5900 	case TCP_LISTEN:
5901 		if (th->ack)
5902 			return 1;
5903 
5904 		if (th->rst)
5905 			goto discard;
5906 
5907 		if (th->syn) {
5908 			if (th->fin)
5909 				goto discard;
5910 			/* It is possible that we process SYN packets from backlog,
5911 			 * so we need to make sure to disable BH right there.
5912 			 */
5913 			local_bh_disable();
5914 			acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
5915 			local_bh_enable();
5916 
5917 			if (!acceptable)
5918 				return 1;
5919 			consume_skb(skb);
5920 			return 0;
5921 		}
5922 		goto discard;
5923 
5924 	case TCP_SYN_SENT:
5925 		tp->rx_opt.saw_tstamp = 0;
5926 		tcp_mstamp_refresh(tp);
5927 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
5928 		if (queued >= 0)
5929 			return queued;
5930 
5931 		/* Do step6 onward by hand. */
5932 		tcp_urg(sk, skb, th);
5933 		__kfree_skb(skb);
5934 		tcp_data_snd_check(sk);
5935 		return 0;
5936 	}
5937 
5938 	tcp_mstamp_refresh(tp);
5939 	tp->rx_opt.saw_tstamp = 0;
5940 	req = tp->fastopen_rsk;
5941 	if (req) {
5942 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5943 		    sk->sk_state != TCP_FIN_WAIT1);
5944 
5945 		if (!tcp_check_req(sk, skb, req, true))
5946 			goto discard;
5947 	}
5948 
5949 	if (!th->ack && !th->rst && !th->syn)
5950 		goto discard;
5951 
5952 	if (!tcp_validate_incoming(sk, skb, th, 0))
5953 		return 0;
5954 
5955 	/* step 5: check the ACK field */
5956 	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5957 				      FLAG_UPDATE_TS_RECENT |
5958 				      FLAG_NO_CHALLENGE_ACK) > 0;
5959 
5960 	if (!acceptable) {
5961 		if (sk->sk_state == TCP_SYN_RECV)
5962 			return 1;	/* send one RST */
5963 		tcp_send_challenge_ack(sk, skb);
5964 		goto discard;
5965 	}
5966 	switch (sk->sk_state) {
5967 	case TCP_SYN_RECV:
5968 		if (!tp->srtt_us)
5969 			tcp_synack_rtt_meas(sk, req);
5970 
5971 		/* Once we leave TCP_SYN_RECV, we no longer need req
5972 		 * so release it.
5973 		 */
5974 		if (req) {
5975 			inet_csk(sk)->icsk_retransmits = 0;
5976 			reqsk_fastopen_remove(sk, req, false);
5977 		} else {
5978 			/* Make sure socket is routed, for correct metrics. */
5979 			icsk->icsk_af_ops->rebuild_header(sk);
5980 			tcp_call_bpf(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
5981 			tcp_init_congestion_control(sk);
5982 
5983 			tcp_mtup_init(sk);
5984 			tp->copied_seq = tp->rcv_nxt;
5985 			tcp_init_buffer_space(sk);
5986 		}
5987 		smp_mb();
5988 		tcp_set_state(sk, TCP_ESTABLISHED);
5989 		sk->sk_state_change(sk);
5990 
5991 		/* Note, that this wakeup is only for marginal crossed SYN case.
5992 		 * Passively open sockets are not waked up, because
5993 		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5994 		 */
5995 		if (sk->sk_socket)
5996 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5997 
5998 		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5999 		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6000 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6001 
6002 		if (tp->rx_opt.tstamp_ok)
6003 			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6004 
6005 		if (req) {
6006 			/* Re-arm the timer because data may have been sent out.
6007 			 * This is similar to the regular data transmission case
6008 			 * when new data has just been ack'ed.
6009 			 *
6010 			 * (TFO) - we could try to be more aggressive and
6011 			 * retransmitting any data sooner based on when they
6012 			 * are sent out.
6013 			 */
6014 			tcp_rearm_rto(sk);
6015 		} else
6016 			tcp_init_metrics(sk);
6017 
6018 		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6019 			tcp_update_pacing_rate(sk);
6020 
6021 		/* Prevent spurious tcp_cwnd_restart() on first data packet */
6022 		tp->lsndtime = tcp_jiffies32;
6023 
6024 		tcp_initialize_rcv_mss(sk);
6025 		tcp_fast_path_on(tp);
6026 		break;
6027 
6028 	case TCP_FIN_WAIT1: {
6029 		int tmo;
6030 
6031 		/* If we enter the TCP_FIN_WAIT1 state and we are a
6032 		 * Fast Open socket and this is the first acceptable
6033 		 * ACK we have received, this would have acknowledged
6034 		 * our SYNACK so stop the SYNACK timer.
6035 		 */
6036 		if (req) {
6037 			/* We no longer need the request sock. */
6038 			reqsk_fastopen_remove(sk, req, false);
6039 			tcp_rearm_rto(sk);
6040 		}
6041 		if (tp->snd_una != tp->write_seq)
6042 			break;
6043 
6044 		tcp_set_state(sk, TCP_FIN_WAIT2);
6045 		sk->sk_shutdown |= SEND_SHUTDOWN;
6046 
6047 		sk_dst_confirm(sk);
6048 
6049 		if (!sock_flag(sk, SOCK_DEAD)) {
6050 			/* Wake up lingering close() */
6051 			sk->sk_state_change(sk);
6052 			break;
6053 		}
6054 
6055 		if (tp->linger2 < 0) {
6056 			tcp_done(sk);
6057 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6058 			return 1;
6059 		}
6060 		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6061 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6062 			/* Receive out of order FIN after close() */
6063 			if (tp->syn_fastopen && th->fin)
6064 				tcp_fastopen_active_disable(sk);
6065 			tcp_done(sk);
6066 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6067 			return 1;
6068 		}
6069 
6070 		tmo = tcp_fin_time(sk);
6071 		if (tmo > TCP_TIMEWAIT_LEN) {
6072 			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6073 		} else if (th->fin || sock_owned_by_user(sk)) {
6074 			/* Bad case. We could lose such FIN otherwise.
6075 			 * It is not a big problem, but it looks confusing
6076 			 * and not so rare event. We still can lose it now,
6077 			 * if it spins in bh_lock_sock(), but it is really
6078 			 * marginal case.
6079 			 */
6080 			inet_csk_reset_keepalive_timer(sk, tmo);
6081 		} else {
6082 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6083 			goto discard;
6084 		}
6085 		break;
6086 	}
6087 
6088 	case TCP_CLOSING:
6089 		if (tp->snd_una == tp->write_seq) {
6090 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6091 			goto discard;
6092 		}
6093 		break;
6094 
6095 	case TCP_LAST_ACK:
6096 		if (tp->snd_una == tp->write_seq) {
6097 			tcp_update_metrics(sk);
6098 			tcp_done(sk);
6099 			goto discard;
6100 		}
6101 		break;
6102 	}
6103 
6104 	/* step 6: check the URG bit */
6105 	tcp_urg(sk, skb, th);
6106 
6107 	/* step 7: process the segment text */
6108 	switch (sk->sk_state) {
6109 	case TCP_CLOSE_WAIT:
6110 	case TCP_CLOSING:
6111 	case TCP_LAST_ACK:
6112 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
6113 			break;
6114 	case TCP_FIN_WAIT1:
6115 	case TCP_FIN_WAIT2:
6116 		/* RFC 793 says to queue data in these states,
6117 		 * RFC 1122 says we MUST send a reset.
6118 		 * BSD 4.4 also does reset.
6119 		 */
6120 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
6121 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6122 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6123 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6124 				tcp_reset(sk);
6125 				return 1;
6126 			}
6127 		}
6128 		/* Fall through */
6129 	case TCP_ESTABLISHED:
6130 		tcp_data_queue(sk, skb);
6131 		queued = 1;
6132 		break;
6133 	}
6134 
6135 	/* tcp_data could move socket to TIME-WAIT */
6136 	if (sk->sk_state != TCP_CLOSE) {
6137 		tcp_data_snd_check(sk);
6138 		tcp_ack_snd_check(sk);
6139 	}
6140 
6141 	if (!queued) {
6142 discard:
6143 		tcp_drop(sk, skb);
6144 	}
6145 	return 0;
6146 }
6147 EXPORT_SYMBOL(tcp_rcv_state_process);
6148 
6149 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6150 {
6151 	struct inet_request_sock *ireq = inet_rsk(req);
6152 
6153 	if (family == AF_INET)
6154 		net_dbg_ratelimited("drop open request from %pI4/%u\n",
6155 				    &ireq->ir_rmt_addr, port);
6156 #if IS_ENABLED(CONFIG_IPV6)
6157 	else if (family == AF_INET6)
6158 		net_dbg_ratelimited("drop open request from %pI6/%u\n",
6159 				    &ireq->ir_v6_rmt_addr, port);
6160 #endif
6161 }
6162 
6163 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6164  *
6165  * If we receive a SYN packet with these bits set, it means a
6166  * network is playing bad games with TOS bits. In order to
6167  * avoid possible false congestion notifications, we disable
6168  * TCP ECN negotiation.
6169  *
6170  * Exception: tcp_ca wants ECN. This is required for DCTCP
6171  * congestion control: Linux DCTCP asserts ECT on all packets,
6172  * including SYN, which is most optimal solution; however,
6173  * others, such as FreeBSD do not.
6174  */
6175 static void tcp_ecn_create_request(struct request_sock *req,
6176 				   const struct sk_buff *skb,
6177 				   const struct sock *listen_sk,
6178 				   const struct dst_entry *dst)
6179 {
6180 	const struct tcphdr *th = tcp_hdr(skb);
6181 	const struct net *net = sock_net(listen_sk);
6182 	bool th_ecn = th->ece && th->cwr;
6183 	bool ect, ecn_ok;
6184 	u32 ecn_ok_dst;
6185 
6186 	if (!th_ecn)
6187 		return;
6188 
6189 	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6190 	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6191 	ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
6192 
6193 	if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6194 	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
6195 	    tcp_bpf_ca_needs_ecn((struct sock *)req))
6196 		inet_rsk(req)->ecn_ok = 1;
6197 }
6198 
6199 static void tcp_openreq_init(struct request_sock *req,
6200 			     const struct tcp_options_received *rx_opt,
6201 			     struct sk_buff *skb, const struct sock *sk)
6202 {
6203 	struct inet_request_sock *ireq = inet_rsk(req);
6204 
6205 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
6206 	req->cookie_ts = 0;
6207 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6208 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6209 	tcp_rsk(req)->snt_synack = tcp_clock_us();
6210 	tcp_rsk(req)->last_oow_ack_time = 0;
6211 	req->mss = rx_opt->mss_clamp;
6212 	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6213 	ireq->tstamp_ok = rx_opt->tstamp_ok;
6214 	ireq->sack_ok = rx_opt->sack_ok;
6215 	ireq->snd_wscale = rx_opt->snd_wscale;
6216 	ireq->wscale_ok = rx_opt->wscale_ok;
6217 	ireq->acked = 0;
6218 	ireq->ecn_ok = 0;
6219 	ireq->ir_rmt_port = tcp_hdr(skb)->source;
6220 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6221 	ireq->ir_mark = inet_request_mark(sk, skb);
6222 }
6223 
6224 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6225 				      struct sock *sk_listener,
6226 				      bool attach_listener)
6227 {
6228 	struct request_sock *req = reqsk_alloc(ops, sk_listener,
6229 					       attach_listener);
6230 
6231 	if (req) {
6232 		struct inet_request_sock *ireq = inet_rsk(req);
6233 
6234 		kmemcheck_annotate_bitfield(ireq, flags);
6235 		ireq->opt = NULL;
6236 #if IS_ENABLED(CONFIG_IPV6)
6237 		ireq->pktopts = NULL;
6238 #endif
6239 		atomic64_set(&ireq->ir_cookie, 0);
6240 		ireq->ireq_state = TCP_NEW_SYN_RECV;
6241 		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6242 		ireq->ireq_family = sk_listener->sk_family;
6243 	}
6244 
6245 	return req;
6246 }
6247 EXPORT_SYMBOL(inet_reqsk_alloc);
6248 
6249 /*
6250  * Return true if a syncookie should be sent
6251  */
6252 static bool tcp_syn_flood_action(const struct sock *sk,
6253 				 const struct sk_buff *skb,
6254 				 const char *proto)
6255 {
6256 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6257 	const char *msg = "Dropping request";
6258 	bool want_cookie = false;
6259 	struct net *net = sock_net(sk);
6260 
6261 #ifdef CONFIG_SYN_COOKIES
6262 	if (net->ipv4.sysctl_tcp_syncookies) {
6263 		msg = "Sending cookies";
6264 		want_cookie = true;
6265 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6266 	} else
6267 #endif
6268 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6269 
6270 	if (!queue->synflood_warned &&
6271 	    net->ipv4.sysctl_tcp_syncookies != 2 &&
6272 	    xchg(&queue->synflood_warned, 1) == 0)
6273 		pr_info("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
6274 			proto, ntohs(tcp_hdr(skb)->dest), msg);
6275 
6276 	return want_cookie;
6277 }
6278 
6279 static void tcp_reqsk_record_syn(const struct sock *sk,
6280 				 struct request_sock *req,
6281 				 const struct sk_buff *skb)
6282 {
6283 	if (tcp_sk(sk)->save_syn) {
6284 		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6285 		u32 *copy;
6286 
6287 		copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
6288 		if (copy) {
6289 			copy[0] = len;
6290 			memcpy(&copy[1], skb_network_header(skb), len);
6291 			req->saved_syn = copy;
6292 		}
6293 	}
6294 }
6295 
6296 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6297 		     const struct tcp_request_sock_ops *af_ops,
6298 		     struct sock *sk, struct sk_buff *skb)
6299 {
6300 	struct tcp_fastopen_cookie foc = { .len = -1 };
6301 	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6302 	struct tcp_options_received tmp_opt;
6303 	struct tcp_sock *tp = tcp_sk(sk);
6304 	struct net *net = sock_net(sk);
6305 	struct sock *fastopen_sk = NULL;
6306 	struct dst_entry *dst = NULL;
6307 	struct request_sock *req;
6308 	bool want_cookie = false;
6309 	struct flowi fl;
6310 
6311 	/* TW buckets are converted to open requests without
6312 	 * limitations, they conserve resources and peer is
6313 	 * evidently real one.
6314 	 */
6315 	if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
6316 	     inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6317 		want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
6318 		if (!want_cookie)
6319 			goto drop;
6320 	}
6321 
6322 	if (sk_acceptq_is_full(sk)) {
6323 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6324 		goto drop;
6325 	}
6326 
6327 	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6328 	if (!req)
6329 		goto drop;
6330 
6331 	tcp_rsk(req)->af_specific = af_ops;
6332 	tcp_rsk(req)->ts_off = 0;
6333 
6334 	tcp_clear_options(&tmp_opt);
6335 	tmp_opt.mss_clamp = af_ops->mss_clamp;
6336 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
6337 	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
6338 			  want_cookie ? NULL : &foc);
6339 
6340 	if (want_cookie && !tmp_opt.saw_tstamp)
6341 		tcp_clear_options(&tmp_opt);
6342 
6343 	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6344 	tcp_openreq_init(req, &tmp_opt, skb, sk);
6345 	inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
6346 
6347 	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
6348 	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
6349 
6350 	af_ops->init_req(req, sk, skb);
6351 
6352 	if (security_inet_conn_request(sk, skb, req))
6353 		goto drop_and_free;
6354 
6355 	if (tmp_opt.tstamp_ok)
6356 		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
6357 
6358 	if (!want_cookie && !isn) {
6359 		/* Kill the following clause, if you dislike this way. */
6360 		if (!net->ipv4.sysctl_tcp_syncookies &&
6361 		    (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6362 		     (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
6363 		    !tcp_peer_is_proven(req, dst)) {
6364 			/* Without syncookies last quarter of
6365 			 * backlog is filled with destinations,
6366 			 * proven to be alive.
6367 			 * It means that we continue to communicate
6368 			 * to destinations, already remembered
6369 			 * to the moment of synflood.
6370 			 */
6371 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6372 				    rsk_ops->family);
6373 			goto drop_and_release;
6374 		}
6375 
6376 		isn = af_ops->init_seq(skb);
6377 	}
6378 	if (!dst) {
6379 		dst = af_ops->route_req(sk, &fl, req);
6380 		if (!dst)
6381 			goto drop_and_free;
6382 	}
6383 
6384 	tcp_ecn_create_request(req, skb, sk, dst);
6385 
6386 	if (want_cookie) {
6387 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6388 		req->cookie_ts = tmp_opt.tstamp_ok;
6389 		if (!tmp_opt.tstamp_ok)
6390 			inet_rsk(req)->ecn_ok = 0;
6391 	}
6392 
6393 	tcp_rsk(req)->snt_isn = isn;
6394 	tcp_rsk(req)->txhash = net_tx_rndhash();
6395 	tcp_openreq_init_rwin(req, sk, dst);
6396 	if (!want_cookie) {
6397 		tcp_reqsk_record_syn(sk, req, skb);
6398 		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
6399 	}
6400 	if (fastopen_sk) {
6401 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
6402 				    &foc, TCP_SYNACK_FASTOPEN);
6403 		/* Add the child socket directly into the accept queue */
6404 		inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
6405 		sk->sk_data_ready(sk);
6406 		bh_unlock_sock(fastopen_sk);
6407 		sock_put(fastopen_sk);
6408 	} else {
6409 		tcp_rsk(req)->tfo_listener = false;
6410 		if (!want_cookie)
6411 			inet_csk_reqsk_queue_hash_add(sk, req,
6412 				tcp_timeout_init((struct sock *)req));
6413 		af_ops->send_synack(sk, dst, &fl, req, &foc,
6414 				    !want_cookie ? TCP_SYNACK_NORMAL :
6415 						   TCP_SYNACK_COOKIE);
6416 		if (want_cookie) {
6417 			reqsk_free(req);
6418 			return 0;
6419 		}
6420 	}
6421 	reqsk_put(req);
6422 	return 0;
6423 
6424 drop_and_release:
6425 	dst_release(dst);
6426 drop_and_free:
6427 	reqsk_free(req);
6428 drop:
6429 	tcp_listendrop(sk);
6430 	return 0;
6431 }
6432 EXPORT_SYMBOL(tcp_conn_request);
6433