xref: /openbmc/linux/net/ipv4/tcp_input.c (revision abfbd895)
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_timestamps __read_mostly = 1;
80 int sysctl_tcp_window_scaling __read_mostly = 1;
81 int sysctl_tcp_sack __read_mostly = 1;
82 int sysctl_tcp_fack __read_mostly = 1;
83 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
84 int sysctl_tcp_max_reordering __read_mostly = 300;
85 EXPORT_SYMBOL(sysctl_tcp_reordering);
86 int sysctl_tcp_dsack __read_mostly = 1;
87 int sysctl_tcp_app_win __read_mostly = 31;
88 int sysctl_tcp_adv_win_scale __read_mostly = 1;
89 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
90 
91 /* rfc5961 challenge ack rate limiting */
92 int sysctl_tcp_challenge_ack_limit = 100;
93 
94 int sysctl_tcp_stdurg __read_mostly;
95 int sysctl_tcp_rfc1337 __read_mostly;
96 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
97 int sysctl_tcp_frto __read_mostly = 2;
98 int sysctl_tcp_min_rtt_wlen __read_mostly = 300;
99 
100 int sysctl_tcp_thin_dupack __read_mostly;
101 
102 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
103 int sysctl_tcp_early_retrans __read_mostly = 3;
104 int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
105 
106 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
107 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
108 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
109 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
110 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
111 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
112 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
113 #define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
114 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
115 #define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
116 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
117 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
118 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
119 #define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
120 
121 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
122 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
123 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
124 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
125 
126 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
127 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
128 
129 /* Adapt the MSS value used to make delayed ack decision to the
130  * real world.
131  */
132 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
133 {
134 	struct inet_connection_sock *icsk = inet_csk(sk);
135 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
136 	unsigned int len;
137 
138 	icsk->icsk_ack.last_seg_size = 0;
139 
140 	/* skb->len may jitter because of SACKs, even if peer
141 	 * sends good full-sized frames.
142 	 */
143 	len = skb_shinfo(skb)->gso_size ? : skb->len;
144 	if (len >= icsk->icsk_ack.rcv_mss) {
145 		icsk->icsk_ack.rcv_mss = len;
146 	} else {
147 		/* Otherwise, we make more careful check taking into account,
148 		 * that SACKs block is variable.
149 		 *
150 		 * "len" is invariant segment length, including TCP header.
151 		 */
152 		len += skb->data - skb_transport_header(skb);
153 		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
154 		    /* If PSH is not set, packet should be
155 		     * full sized, provided peer TCP is not badly broken.
156 		     * This observation (if it is correct 8)) allows
157 		     * to handle super-low mtu links fairly.
158 		     */
159 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
160 		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
161 			/* Subtract also invariant (if peer is RFC compliant),
162 			 * tcp header plus fixed timestamp option length.
163 			 * Resulting "len" is MSS free of SACK jitter.
164 			 */
165 			len -= tcp_sk(sk)->tcp_header_len;
166 			icsk->icsk_ack.last_seg_size = len;
167 			if (len == lss) {
168 				icsk->icsk_ack.rcv_mss = len;
169 				return;
170 			}
171 		}
172 		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
173 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
174 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
175 	}
176 }
177 
178 static void tcp_incr_quickack(struct sock *sk)
179 {
180 	struct inet_connection_sock *icsk = inet_csk(sk);
181 	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
182 
183 	if (quickacks == 0)
184 		quickacks = 2;
185 	if (quickacks > icsk->icsk_ack.quick)
186 		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
187 }
188 
189 static void tcp_enter_quickack_mode(struct sock *sk)
190 {
191 	struct inet_connection_sock *icsk = inet_csk(sk);
192 	tcp_incr_quickack(sk);
193 	icsk->icsk_ack.pingpong = 0;
194 	icsk->icsk_ack.ato = TCP_ATO_MIN;
195 }
196 
197 /* Send ACKs quickly, if "quick" count is not exhausted
198  * and the session is not interactive.
199  */
200 
201 static bool tcp_in_quickack_mode(struct sock *sk)
202 {
203 	const struct inet_connection_sock *icsk = inet_csk(sk);
204 	const struct dst_entry *dst = __sk_dst_get(sk);
205 
206 	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
207 		(icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
208 }
209 
210 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
211 {
212 	if (tp->ecn_flags & TCP_ECN_OK)
213 		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
214 }
215 
216 static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
217 {
218 	if (tcp_hdr(skb)->cwr)
219 		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
220 }
221 
222 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
223 {
224 	tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
225 }
226 
227 static void __tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
228 {
229 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
230 	case INET_ECN_NOT_ECT:
231 		/* Funny extension: if ECT is not set on a segment,
232 		 * and we already seen ECT on a previous segment,
233 		 * it is probably a retransmit.
234 		 */
235 		if (tp->ecn_flags & TCP_ECN_SEEN)
236 			tcp_enter_quickack_mode((struct sock *)tp);
237 		break;
238 	case INET_ECN_CE:
239 		if (tcp_ca_needs_ecn((struct sock *)tp))
240 			tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);
241 
242 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
243 			/* Better not delay acks, sender can have a very low cwnd */
244 			tcp_enter_quickack_mode((struct sock *)tp);
245 			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
246 		}
247 		tp->ecn_flags |= TCP_ECN_SEEN;
248 		break;
249 	default:
250 		if (tcp_ca_needs_ecn((struct sock *)tp))
251 			tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
252 		tp->ecn_flags |= TCP_ECN_SEEN;
253 		break;
254 	}
255 }
256 
257 static void tcp_ecn_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
258 {
259 	if (tp->ecn_flags & TCP_ECN_OK)
260 		__tcp_ecn_check_ce(tp, skb);
261 }
262 
263 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
264 {
265 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
266 		tp->ecn_flags &= ~TCP_ECN_OK;
267 }
268 
269 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
270 {
271 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
272 		tp->ecn_flags &= ~TCP_ECN_OK;
273 }
274 
275 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
276 {
277 	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
278 		return true;
279 	return false;
280 }
281 
282 /* Buffer size and advertised window tuning.
283  *
284  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
285  */
286 
287 static void tcp_sndbuf_expand(struct sock *sk)
288 {
289 	const struct tcp_sock *tp = tcp_sk(sk);
290 	int sndmem, per_mss;
291 	u32 nr_segs;
292 
293 	/* Worst case is non GSO/TSO : each frame consumes one skb
294 	 * and skb->head is kmalloced using power of two area of memory
295 	 */
296 	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
297 		  MAX_TCP_HEADER +
298 		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
299 
300 	per_mss = roundup_pow_of_two(per_mss) +
301 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
302 
303 	nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
304 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
305 
306 	/* Fast Recovery (RFC 5681 3.2) :
307 	 * Cubic needs 1.7 factor, rounded to 2 to include
308 	 * extra cushion (application might react slowly to POLLOUT)
309 	 */
310 	sndmem = 2 * nr_segs * per_mss;
311 
312 	if (sk->sk_sndbuf < sndmem)
313 		sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
314 }
315 
316 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
317  *
318  * All tcp_full_space() is split to two parts: "network" buffer, allocated
319  * forward and advertised in receiver window (tp->rcv_wnd) and
320  * "application buffer", required to isolate scheduling/application
321  * latencies from network.
322  * window_clamp is maximal advertised window. It can be less than
323  * tcp_full_space(), in this case tcp_full_space() - window_clamp
324  * is reserved for "application" buffer. The less window_clamp is
325  * the smoother our behaviour from viewpoint of network, but the lower
326  * throughput and the higher sensitivity of the connection to losses. 8)
327  *
328  * rcv_ssthresh is more strict window_clamp used at "slow start"
329  * phase to predict further behaviour of this connection.
330  * It is used for two goals:
331  * - to enforce header prediction at sender, even when application
332  *   requires some significant "application buffer". It is check #1.
333  * - to prevent pruning of receive queue because of misprediction
334  *   of receiver window. Check #2.
335  *
336  * The scheme does not work when sender sends good segments opening
337  * window and then starts to feed us spaghetti. But it should work
338  * in common situations. Otherwise, we have to rely on queue collapsing.
339  */
340 
341 /* Slow part of check#2. */
342 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
343 {
344 	struct tcp_sock *tp = tcp_sk(sk);
345 	/* Optimize this! */
346 	int truesize = tcp_win_from_space(skb->truesize) >> 1;
347 	int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
348 
349 	while (tp->rcv_ssthresh <= window) {
350 		if (truesize <= skb->len)
351 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
352 
353 		truesize >>= 1;
354 		window >>= 1;
355 	}
356 	return 0;
357 }
358 
359 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
360 {
361 	struct tcp_sock *tp = tcp_sk(sk);
362 
363 	/* Check #1 */
364 	if (tp->rcv_ssthresh < tp->window_clamp &&
365 	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
366 	    !tcp_under_memory_pressure(sk)) {
367 		int incr;
368 
369 		/* Check #2. Increase window, if skb with such overhead
370 		 * will fit to rcvbuf in future.
371 		 */
372 		if (tcp_win_from_space(skb->truesize) <= skb->len)
373 			incr = 2 * tp->advmss;
374 		else
375 			incr = __tcp_grow_window(sk, skb);
376 
377 		if (incr) {
378 			incr = max_t(int, incr, 2 * skb->len);
379 			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
380 					       tp->window_clamp);
381 			inet_csk(sk)->icsk_ack.quick |= 1;
382 		}
383 	}
384 }
385 
386 /* 3. Tuning rcvbuf, when connection enters established state. */
387 static void tcp_fixup_rcvbuf(struct sock *sk)
388 {
389 	u32 mss = tcp_sk(sk)->advmss;
390 	int rcvmem;
391 
392 	rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
393 		 tcp_default_init_rwnd(mss);
394 
395 	/* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
396 	 * Allow enough cushion so that sender is not limited by our window
397 	 */
398 	if (sysctl_tcp_moderate_rcvbuf)
399 		rcvmem <<= 2;
400 
401 	if (sk->sk_rcvbuf < rcvmem)
402 		sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
403 }
404 
405 /* 4. Try to fixup all. It is made immediately after connection enters
406  *    established state.
407  */
408 void tcp_init_buffer_space(struct sock *sk)
409 {
410 	struct tcp_sock *tp = tcp_sk(sk);
411 	int maxwin;
412 
413 	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
414 		tcp_fixup_rcvbuf(sk);
415 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
416 		tcp_sndbuf_expand(sk);
417 
418 	tp->rcvq_space.space = tp->rcv_wnd;
419 	tp->rcvq_space.time = tcp_time_stamp;
420 	tp->rcvq_space.seq = tp->copied_seq;
421 
422 	maxwin = tcp_full_space(sk);
423 
424 	if (tp->window_clamp >= maxwin) {
425 		tp->window_clamp = maxwin;
426 
427 		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
428 			tp->window_clamp = max(maxwin -
429 					       (maxwin >> sysctl_tcp_app_win),
430 					       4 * tp->advmss);
431 	}
432 
433 	/* Force reservation of one segment. */
434 	if (sysctl_tcp_app_win &&
435 	    tp->window_clamp > 2 * tp->advmss &&
436 	    tp->window_clamp + tp->advmss > maxwin)
437 		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
438 
439 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
440 	tp->snd_cwnd_stamp = tcp_time_stamp;
441 }
442 
443 /* 5. Recalculate window clamp after socket hit its memory bounds. */
444 static void tcp_clamp_window(struct sock *sk)
445 {
446 	struct tcp_sock *tp = tcp_sk(sk);
447 	struct inet_connection_sock *icsk = inet_csk(sk);
448 
449 	icsk->icsk_ack.quick = 0;
450 
451 	if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
452 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
453 	    !tcp_under_memory_pressure(sk) &&
454 	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
455 		sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
456 				    sysctl_tcp_rmem[2]);
457 	}
458 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
459 		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
460 }
461 
462 /* Initialize RCV_MSS value.
463  * RCV_MSS is an our guess about MSS used by the peer.
464  * We haven't any direct information about the MSS.
465  * It's better to underestimate the RCV_MSS rather than overestimate.
466  * Overestimations make us ACKing less frequently than needed.
467  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
468  */
469 void tcp_initialize_rcv_mss(struct sock *sk)
470 {
471 	const struct tcp_sock *tp = tcp_sk(sk);
472 	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
473 
474 	hint = min(hint, tp->rcv_wnd / 2);
475 	hint = min(hint, TCP_MSS_DEFAULT);
476 	hint = max(hint, TCP_MIN_MSS);
477 
478 	inet_csk(sk)->icsk_ack.rcv_mss = hint;
479 }
480 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
481 
482 /* Receiver "autotuning" code.
483  *
484  * The algorithm for RTT estimation w/o timestamps is based on
485  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
486  * <http://public.lanl.gov/radiant/pubs.html#DRS>
487  *
488  * More detail on this code can be found at
489  * <http://staff.psc.edu/jheffner/>,
490  * though this reference is out of date.  A new paper
491  * is pending.
492  */
493 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
494 {
495 	u32 new_sample = tp->rcv_rtt_est.rtt;
496 	long m = sample;
497 
498 	if (m == 0)
499 		m = 1;
500 
501 	if (new_sample != 0) {
502 		/* If we sample in larger samples in the non-timestamp
503 		 * case, we could grossly overestimate the RTT especially
504 		 * with chatty applications or bulk transfer apps which
505 		 * are stalled on filesystem I/O.
506 		 *
507 		 * Also, since we are only going for a minimum in the
508 		 * non-timestamp case, we do not smooth things out
509 		 * else with timestamps disabled convergence takes too
510 		 * long.
511 		 */
512 		if (!win_dep) {
513 			m -= (new_sample >> 3);
514 			new_sample += m;
515 		} else {
516 			m <<= 3;
517 			if (m < new_sample)
518 				new_sample = m;
519 		}
520 	} else {
521 		/* No previous measure. */
522 		new_sample = m << 3;
523 	}
524 
525 	if (tp->rcv_rtt_est.rtt != new_sample)
526 		tp->rcv_rtt_est.rtt = new_sample;
527 }
528 
529 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
530 {
531 	if (tp->rcv_rtt_est.time == 0)
532 		goto new_measure;
533 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
534 		return;
535 	tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
536 
537 new_measure:
538 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
539 	tp->rcv_rtt_est.time = tcp_time_stamp;
540 }
541 
542 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
543 					  const struct sk_buff *skb)
544 {
545 	struct tcp_sock *tp = tcp_sk(sk);
546 	if (tp->rx_opt.rcv_tsecr &&
547 	    (TCP_SKB_CB(skb)->end_seq -
548 	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
549 		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
550 }
551 
552 /*
553  * This function should be called every time data is copied to user space.
554  * It calculates the appropriate TCP receive buffer space.
555  */
556 void tcp_rcv_space_adjust(struct sock *sk)
557 {
558 	struct tcp_sock *tp = tcp_sk(sk);
559 	int time;
560 	int copied;
561 
562 	time = tcp_time_stamp - tp->rcvq_space.time;
563 	if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
564 		return;
565 
566 	/* Number of bytes copied to user in last RTT */
567 	copied = tp->copied_seq - tp->rcvq_space.seq;
568 	if (copied <= tp->rcvq_space.space)
569 		goto new_measure;
570 
571 	/* A bit of theory :
572 	 * copied = bytes received in previous RTT, our base window
573 	 * To cope with packet losses, we need a 2x factor
574 	 * To cope with slow start, and sender growing its cwin by 100 %
575 	 * every RTT, we need a 4x factor, because the ACK we are sending
576 	 * now is for the next RTT, not the current one :
577 	 * <prev RTT . ><current RTT .. ><next RTT .... >
578 	 */
579 
580 	if (sysctl_tcp_moderate_rcvbuf &&
581 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
582 		int rcvwin, rcvmem, rcvbuf;
583 
584 		/* minimal window to cope with packet losses, assuming
585 		 * steady state. Add some cushion because of small variations.
586 		 */
587 		rcvwin = (copied << 1) + 16 * tp->advmss;
588 
589 		/* If rate increased by 25%,
590 		 *	assume slow start, rcvwin = 3 * copied
591 		 * If rate increased by 50%,
592 		 *	assume sender can use 2x growth, rcvwin = 4 * copied
593 		 */
594 		if (copied >=
595 		    tp->rcvq_space.space + (tp->rcvq_space.space >> 2)) {
596 			if (copied >=
597 			    tp->rcvq_space.space + (tp->rcvq_space.space >> 1))
598 				rcvwin <<= 1;
599 			else
600 				rcvwin += (rcvwin >> 1);
601 		}
602 
603 		rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
604 		while (tcp_win_from_space(rcvmem) < tp->advmss)
605 			rcvmem += 128;
606 
607 		rcvbuf = min(rcvwin / tp->advmss * rcvmem, sysctl_tcp_rmem[2]);
608 		if (rcvbuf > sk->sk_rcvbuf) {
609 			sk->sk_rcvbuf = rcvbuf;
610 
611 			/* Make the window clamp follow along.  */
612 			tp->window_clamp = rcvwin;
613 		}
614 	}
615 	tp->rcvq_space.space = copied;
616 
617 new_measure:
618 	tp->rcvq_space.seq = tp->copied_seq;
619 	tp->rcvq_space.time = tcp_time_stamp;
620 }
621 
622 /* There is something which you must keep in mind when you analyze the
623  * behavior of the tp->ato delayed ack timeout interval.  When a
624  * connection starts up, we want to ack as quickly as possible.  The
625  * problem is that "good" TCP's do slow start at the beginning of data
626  * transmission.  The means that until we send the first few ACK's the
627  * sender will sit on his end and only queue most of his data, because
628  * he can only send snd_cwnd unacked packets at any given time.  For
629  * each ACK we send, he increments snd_cwnd and transmits more of his
630  * queue.  -DaveM
631  */
632 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
633 {
634 	struct tcp_sock *tp = tcp_sk(sk);
635 	struct inet_connection_sock *icsk = inet_csk(sk);
636 	u32 now;
637 
638 	inet_csk_schedule_ack(sk);
639 
640 	tcp_measure_rcv_mss(sk, skb);
641 
642 	tcp_rcv_rtt_measure(tp);
643 
644 	now = tcp_time_stamp;
645 
646 	if (!icsk->icsk_ack.ato) {
647 		/* The _first_ data packet received, initialize
648 		 * delayed ACK engine.
649 		 */
650 		tcp_incr_quickack(sk);
651 		icsk->icsk_ack.ato = TCP_ATO_MIN;
652 	} else {
653 		int m = now - icsk->icsk_ack.lrcvtime;
654 
655 		if (m <= TCP_ATO_MIN / 2) {
656 			/* The fastest case is the first. */
657 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
658 		} else if (m < icsk->icsk_ack.ato) {
659 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
660 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
661 				icsk->icsk_ack.ato = icsk->icsk_rto;
662 		} else if (m > icsk->icsk_rto) {
663 			/* Too long gap. Apparently sender failed to
664 			 * restart window, so that we send ACKs quickly.
665 			 */
666 			tcp_incr_quickack(sk);
667 			sk_mem_reclaim(sk);
668 		}
669 	}
670 	icsk->icsk_ack.lrcvtime = now;
671 
672 	tcp_ecn_check_ce(tp, skb);
673 
674 	if (skb->len >= 128)
675 		tcp_grow_window(sk, skb);
676 }
677 
678 /* Called to compute a smoothed rtt estimate. The data fed to this
679  * routine either comes from timestamps, or from segments that were
680  * known _not_ to have been retransmitted [see Karn/Partridge
681  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
682  * piece by Van Jacobson.
683  * NOTE: the next three routines used to be one big routine.
684  * To save cycles in the RFC 1323 implementation it was better to break
685  * it up into three procedures. -- erics
686  */
687 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
688 {
689 	struct tcp_sock *tp = tcp_sk(sk);
690 	long m = mrtt_us; /* RTT */
691 	u32 srtt = tp->srtt_us;
692 
693 	/*	The following amusing code comes from Jacobson's
694 	 *	article in SIGCOMM '88.  Note that rtt and mdev
695 	 *	are scaled versions of rtt and mean deviation.
696 	 *	This is designed to be as fast as possible
697 	 *	m stands for "measurement".
698 	 *
699 	 *	On a 1990 paper the rto value is changed to:
700 	 *	RTO = rtt + 4 * mdev
701 	 *
702 	 * Funny. This algorithm seems to be very broken.
703 	 * These formulae increase RTO, when it should be decreased, increase
704 	 * too slowly, when it should be increased quickly, decrease too quickly
705 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
706 	 * does not matter how to _calculate_ it. Seems, it was trap
707 	 * that VJ failed to avoid. 8)
708 	 */
709 	if (srtt != 0) {
710 		m -= (srtt >> 3);	/* m is now error in rtt est */
711 		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
712 		if (m < 0) {
713 			m = -m;		/* m is now abs(error) */
714 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
715 			/* This is similar to one of Eifel findings.
716 			 * Eifel blocks mdev updates when rtt decreases.
717 			 * This solution is a bit different: we use finer gain
718 			 * for mdev in this case (alpha*beta).
719 			 * Like Eifel it also prevents growth of rto,
720 			 * but also it limits too fast rto decreases,
721 			 * happening in pure Eifel.
722 			 */
723 			if (m > 0)
724 				m >>= 3;
725 		} else {
726 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
727 		}
728 		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
729 		if (tp->mdev_us > tp->mdev_max_us) {
730 			tp->mdev_max_us = tp->mdev_us;
731 			if (tp->mdev_max_us > tp->rttvar_us)
732 				tp->rttvar_us = tp->mdev_max_us;
733 		}
734 		if (after(tp->snd_una, tp->rtt_seq)) {
735 			if (tp->mdev_max_us < tp->rttvar_us)
736 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
737 			tp->rtt_seq = tp->snd_nxt;
738 			tp->mdev_max_us = tcp_rto_min_us(sk);
739 		}
740 	} else {
741 		/* no previous measure. */
742 		srtt = m << 3;		/* take the measured time to be rtt */
743 		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
744 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
745 		tp->mdev_max_us = tp->rttvar_us;
746 		tp->rtt_seq = tp->snd_nxt;
747 	}
748 	tp->srtt_us = max(1U, srtt);
749 }
750 
751 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
752  * Note: TCP stack does not yet implement pacing.
753  * FQ packet scheduler can be used to implement cheap but effective
754  * TCP pacing, to smooth the burst on large writes when packets
755  * in flight is significantly lower than cwnd (or rwin)
756  */
757 int sysctl_tcp_pacing_ss_ratio __read_mostly = 200;
758 int sysctl_tcp_pacing_ca_ratio __read_mostly = 120;
759 
760 static void tcp_update_pacing_rate(struct sock *sk)
761 {
762 	const struct tcp_sock *tp = tcp_sk(sk);
763 	u64 rate;
764 
765 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
766 	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
767 
768 	/* current rate is (cwnd * mss) / srtt
769 	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
770 	 * In Congestion Avoidance phase, set it to 120 % the current rate.
771 	 *
772 	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
773 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
774 	 *	 end of slow start and should slow down.
775 	 */
776 	if (tp->snd_cwnd < tp->snd_ssthresh / 2)
777 		rate *= sysctl_tcp_pacing_ss_ratio;
778 	else
779 		rate *= sysctl_tcp_pacing_ca_ratio;
780 
781 	rate *= max(tp->snd_cwnd, tp->packets_out);
782 
783 	if (likely(tp->srtt_us))
784 		do_div(rate, tp->srtt_us);
785 
786 	/* ACCESS_ONCE() is needed because sch_fq fetches sk_pacing_rate
787 	 * without any lock. We want to make sure compiler wont store
788 	 * intermediate values in this location.
789 	 */
790 	ACCESS_ONCE(sk->sk_pacing_rate) = min_t(u64, rate,
791 						sk->sk_max_pacing_rate);
792 }
793 
794 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
795  * routine referred to above.
796  */
797 static void tcp_set_rto(struct sock *sk)
798 {
799 	const struct tcp_sock *tp = tcp_sk(sk);
800 	/* Old crap is replaced with new one. 8)
801 	 *
802 	 * More seriously:
803 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
804 	 *    It cannot be less due to utterly erratic ACK generation made
805 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
806 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
807 	 *    is invisible. Actually, Linux-2.4 also generates erratic
808 	 *    ACKs in some circumstances.
809 	 */
810 	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
811 
812 	/* 2. Fixups made earlier cannot be right.
813 	 *    If we do not estimate RTO correctly without them,
814 	 *    all the algo is pure shit and should be replaced
815 	 *    with correct one. It is exactly, which we pretend to do.
816 	 */
817 
818 	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
819 	 * guarantees that rto is higher.
820 	 */
821 	tcp_bound_rto(sk);
822 }
823 
824 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
825 {
826 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
827 
828 	if (!cwnd)
829 		cwnd = TCP_INIT_CWND;
830 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
831 }
832 
833 /*
834  * Packet counting of FACK is based on in-order assumptions, therefore TCP
835  * disables it when reordering is detected
836  */
837 void tcp_disable_fack(struct tcp_sock *tp)
838 {
839 	/* RFC3517 uses different metric in lost marker => reset on change */
840 	if (tcp_is_fack(tp))
841 		tp->lost_skb_hint = NULL;
842 	tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
843 }
844 
845 /* Take a notice that peer is sending D-SACKs */
846 static void tcp_dsack_seen(struct tcp_sock *tp)
847 {
848 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
849 }
850 
851 static void tcp_update_reordering(struct sock *sk, const int metric,
852 				  const int ts)
853 {
854 	struct tcp_sock *tp = tcp_sk(sk);
855 	if (metric > tp->reordering) {
856 		int mib_idx;
857 
858 		tp->reordering = min(sysctl_tcp_max_reordering, metric);
859 
860 		/* This exciting event is worth to be remembered. 8) */
861 		if (ts)
862 			mib_idx = LINUX_MIB_TCPTSREORDER;
863 		else if (tcp_is_reno(tp))
864 			mib_idx = LINUX_MIB_TCPRENOREORDER;
865 		else if (tcp_is_fack(tp))
866 			mib_idx = LINUX_MIB_TCPFACKREORDER;
867 		else
868 			mib_idx = LINUX_MIB_TCPSACKREORDER;
869 
870 		NET_INC_STATS_BH(sock_net(sk), mib_idx);
871 #if FASTRETRANS_DEBUG > 1
872 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
873 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
874 			 tp->reordering,
875 			 tp->fackets_out,
876 			 tp->sacked_out,
877 			 tp->undo_marker ? tp->undo_retrans : 0);
878 #endif
879 		tcp_disable_fack(tp);
880 	}
881 
882 	if (metric > 0)
883 		tcp_disable_early_retrans(tp);
884 	tp->rack.reord = 1;
885 }
886 
887 /* This must be called before lost_out is incremented */
888 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
889 {
890 	if (!tp->retransmit_skb_hint ||
891 	    before(TCP_SKB_CB(skb)->seq,
892 		   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
893 		tp->retransmit_skb_hint = skb;
894 
895 	if (!tp->lost_out ||
896 	    after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
897 		tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
898 }
899 
900 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
901 {
902 	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
903 		tcp_verify_retransmit_hint(tp, skb);
904 
905 		tp->lost_out += tcp_skb_pcount(skb);
906 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
907 	}
908 }
909 
910 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
911 {
912 	tcp_verify_retransmit_hint(tp, skb);
913 
914 	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
915 		tp->lost_out += tcp_skb_pcount(skb);
916 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
917 	}
918 }
919 
920 /* This procedure tags the retransmission queue when SACKs arrive.
921  *
922  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
923  * Packets in queue with these bits set are counted in variables
924  * sacked_out, retrans_out and lost_out, correspondingly.
925  *
926  * Valid combinations are:
927  * Tag  InFlight	Description
928  * 0	1		- orig segment is in flight.
929  * S	0		- nothing flies, orig reached receiver.
930  * L	0		- nothing flies, orig lost by net.
931  * R	2		- both orig and retransmit are in flight.
932  * L|R	1		- orig is lost, retransmit is in flight.
933  * S|R  1		- orig reached receiver, retrans is still in flight.
934  * (L|S|R is logically valid, it could occur when L|R is sacked,
935  *  but it is equivalent to plain S and code short-curcuits it to S.
936  *  L|S is logically invalid, it would mean -1 packet in flight 8))
937  *
938  * These 6 states form finite state machine, controlled by the following events:
939  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
940  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
941  * 3. Loss detection event of two flavors:
942  *	A. Scoreboard estimator decided the packet is lost.
943  *	   A'. Reno "three dupacks" marks head of queue lost.
944  *	   A''. Its FACK modification, head until snd.fack is lost.
945  *	B. SACK arrives sacking SND.NXT at the moment, when the
946  *	   segment was retransmitted.
947  * 4. D-SACK added new rule: D-SACK changes any tag to S.
948  *
949  * It is pleasant to note, that state diagram turns out to be commutative,
950  * so that we are allowed not to be bothered by order of our actions,
951  * when multiple events arrive simultaneously. (see the function below).
952  *
953  * Reordering detection.
954  * --------------------
955  * Reordering metric is maximal distance, which a packet can be displaced
956  * in packet stream. With SACKs we can estimate it:
957  *
958  * 1. SACK fills old hole and the corresponding segment was not
959  *    ever retransmitted -> reordering. Alas, we cannot use it
960  *    when segment was retransmitted.
961  * 2. The last flaw is solved with D-SACK. D-SACK arrives
962  *    for retransmitted and already SACKed segment -> reordering..
963  * Both of these heuristics are not used in Loss state, when we cannot
964  * account for retransmits accurately.
965  *
966  * SACK block validation.
967  * ----------------------
968  *
969  * SACK block range validation checks that the received SACK block fits to
970  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
971  * Note that SND.UNA is not included to the range though being valid because
972  * it means that the receiver is rather inconsistent with itself reporting
973  * SACK reneging when it should advance SND.UNA. Such SACK block this is
974  * perfectly valid, however, in light of RFC2018 which explicitly states
975  * that "SACK block MUST reflect the newest segment.  Even if the newest
976  * segment is going to be discarded ...", not that it looks very clever
977  * in case of head skb. Due to potentional receiver driven attacks, we
978  * choose to avoid immediate execution of a walk in write queue due to
979  * reneging and defer head skb's loss recovery to standard loss recovery
980  * procedure that will eventually trigger (nothing forbids us doing this).
981  *
982  * Implements also blockage to start_seq wrap-around. Problem lies in the
983  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
984  * there's no guarantee that it will be before snd_nxt (n). The problem
985  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
986  * wrap (s_w):
987  *
988  *         <- outs wnd ->                          <- wrapzone ->
989  *         u     e      n                         u_w   e_w  s n_w
990  *         |     |      |                          |     |   |  |
991  * |<------------+------+----- TCP seqno space --------------+---------->|
992  * ...-- <2^31 ->|                                           |<--------...
993  * ...---- >2^31 ------>|                                    |<--------...
994  *
995  * Current code wouldn't be vulnerable but it's better still to discard such
996  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
997  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
998  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
999  * equal to the ideal case (infinite seqno space without wrap caused issues).
1000  *
1001  * With D-SACK the lower bound is extended to cover sequence space below
1002  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1003  * again, D-SACK block must not to go across snd_una (for the same reason as
1004  * for the normal SACK blocks, explained above). But there all simplicity
1005  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1006  * fully below undo_marker they do not affect behavior in anyway and can
1007  * therefore be safely ignored. In rare cases (which are more or less
1008  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1009  * fragmentation and packet reordering past skb's retransmission. To consider
1010  * them correctly, the acceptable range must be extended even more though
1011  * the exact amount is rather hard to quantify. However, tp->max_window can
1012  * be used as an exaggerated estimate.
1013  */
1014 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1015 				   u32 start_seq, u32 end_seq)
1016 {
1017 	/* Too far in future, or reversed (interpretation is ambiguous) */
1018 	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1019 		return false;
1020 
1021 	/* Nasty start_seq wrap-around check (see comments above) */
1022 	if (!before(start_seq, tp->snd_nxt))
1023 		return false;
1024 
1025 	/* In outstanding window? ...This is valid exit for D-SACKs too.
1026 	 * start_seq == snd_una is non-sensical (see comments above)
1027 	 */
1028 	if (after(start_seq, tp->snd_una))
1029 		return true;
1030 
1031 	if (!is_dsack || !tp->undo_marker)
1032 		return false;
1033 
1034 	/* ...Then it's D-SACK, and must reside below snd_una completely */
1035 	if (after(end_seq, tp->snd_una))
1036 		return false;
1037 
1038 	if (!before(start_seq, tp->undo_marker))
1039 		return true;
1040 
1041 	/* Too old */
1042 	if (!after(end_seq, tp->undo_marker))
1043 		return false;
1044 
1045 	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1046 	 *   start_seq < undo_marker and end_seq >= undo_marker.
1047 	 */
1048 	return !before(start_seq, end_seq - tp->max_window);
1049 }
1050 
1051 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1052 			    struct tcp_sack_block_wire *sp, int num_sacks,
1053 			    u32 prior_snd_una)
1054 {
1055 	struct tcp_sock *tp = tcp_sk(sk);
1056 	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1057 	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1058 	bool dup_sack = false;
1059 
1060 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1061 		dup_sack = true;
1062 		tcp_dsack_seen(tp);
1063 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1064 	} else if (num_sacks > 1) {
1065 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1066 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1067 
1068 		if (!after(end_seq_0, end_seq_1) &&
1069 		    !before(start_seq_0, start_seq_1)) {
1070 			dup_sack = true;
1071 			tcp_dsack_seen(tp);
1072 			NET_INC_STATS_BH(sock_net(sk),
1073 					LINUX_MIB_TCPDSACKOFORECV);
1074 		}
1075 	}
1076 
1077 	/* D-SACK for already forgotten data... Do dumb counting. */
1078 	if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1079 	    !after(end_seq_0, prior_snd_una) &&
1080 	    after(end_seq_0, tp->undo_marker))
1081 		tp->undo_retrans--;
1082 
1083 	return dup_sack;
1084 }
1085 
1086 struct tcp_sacktag_state {
1087 	int	reord;
1088 	int	fack_count;
1089 	/* Timestamps for earliest and latest never-retransmitted segment
1090 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1091 	 * but congestion control should still get an accurate delay signal.
1092 	 */
1093 	struct skb_mstamp first_sackt;
1094 	struct skb_mstamp last_sackt;
1095 	int	flag;
1096 };
1097 
1098 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1099  * the incoming SACK may not exactly match but we can find smaller MSS
1100  * aligned portion of it that matches. Therefore we might need to fragment
1101  * which may fail and creates some hassle (caller must handle error case
1102  * returns).
1103  *
1104  * FIXME: this could be merged to shift decision code
1105  */
1106 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1107 				  u32 start_seq, u32 end_seq)
1108 {
1109 	int err;
1110 	bool in_sack;
1111 	unsigned int pkt_len;
1112 	unsigned int mss;
1113 
1114 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1115 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1116 
1117 	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1118 	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1119 		mss = tcp_skb_mss(skb);
1120 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1121 
1122 		if (!in_sack) {
1123 			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1124 			if (pkt_len < mss)
1125 				pkt_len = mss;
1126 		} else {
1127 			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1128 			if (pkt_len < mss)
1129 				return -EINVAL;
1130 		}
1131 
1132 		/* Round if necessary so that SACKs cover only full MSSes
1133 		 * and/or the remaining small portion (if present)
1134 		 */
1135 		if (pkt_len > mss) {
1136 			unsigned int new_len = (pkt_len / mss) * mss;
1137 			if (!in_sack && new_len < pkt_len) {
1138 				new_len += mss;
1139 				if (new_len >= skb->len)
1140 					return 0;
1141 			}
1142 			pkt_len = new_len;
1143 		}
1144 		err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
1145 		if (err < 0)
1146 			return err;
1147 	}
1148 
1149 	return in_sack;
1150 }
1151 
1152 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1153 static u8 tcp_sacktag_one(struct sock *sk,
1154 			  struct tcp_sacktag_state *state, u8 sacked,
1155 			  u32 start_seq, u32 end_seq,
1156 			  int dup_sack, int pcount,
1157 			  const struct skb_mstamp *xmit_time)
1158 {
1159 	struct tcp_sock *tp = tcp_sk(sk);
1160 	int fack_count = state->fack_count;
1161 
1162 	/* Account D-SACK for retransmitted packet. */
1163 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1164 		if (tp->undo_marker && tp->undo_retrans > 0 &&
1165 		    after(end_seq, tp->undo_marker))
1166 			tp->undo_retrans--;
1167 		if (sacked & TCPCB_SACKED_ACKED)
1168 			state->reord = min(fack_count, state->reord);
1169 	}
1170 
1171 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1172 	if (!after(end_seq, tp->snd_una))
1173 		return sacked;
1174 
1175 	if (!(sacked & TCPCB_SACKED_ACKED)) {
1176 		tcp_rack_advance(tp, xmit_time, sacked);
1177 
1178 		if (sacked & TCPCB_SACKED_RETRANS) {
1179 			/* If the segment is not tagged as lost,
1180 			 * we do not clear RETRANS, believing
1181 			 * that retransmission is still in flight.
1182 			 */
1183 			if (sacked & TCPCB_LOST) {
1184 				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1185 				tp->lost_out -= pcount;
1186 				tp->retrans_out -= pcount;
1187 			}
1188 		} else {
1189 			if (!(sacked & TCPCB_RETRANS)) {
1190 				/* New sack for not retransmitted frame,
1191 				 * which was in hole. It is reordering.
1192 				 */
1193 				if (before(start_seq,
1194 					   tcp_highest_sack_seq(tp)))
1195 					state->reord = min(fack_count,
1196 							   state->reord);
1197 				if (!after(end_seq, tp->high_seq))
1198 					state->flag |= FLAG_ORIG_SACK_ACKED;
1199 				if (state->first_sackt.v64 == 0)
1200 					state->first_sackt = *xmit_time;
1201 				state->last_sackt = *xmit_time;
1202 			}
1203 
1204 			if (sacked & TCPCB_LOST) {
1205 				sacked &= ~TCPCB_LOST;
1206 				tp->lost_out -= pcount;
1207 			}
1208 		}
1209 
1210 		sacked |= TCPCB_SACKED_ACKED;
1211 		state->flag |= FLAG_DATA_SACKED;
1212 		tp->sacked_out += pcount;
1213 
1214 		fack_count += pcount;
1215 
1216 		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1217 		if (!tcp_is_fack(tp) && tp->lost_skb_hint &&
1218 		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1219 			tp->lost_cnt_hint += pcount;
1220 
1221 		if (fack_count > tp->fackets_out)
1222 			tp->fackets_out = fack_count;
1223 	}
1224 
1225 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1226 	 * frames and clear it. undo_retrans is decreased above, L|R frames
1227 	 * are accounted above as well.
1228 	 */
1229 	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1230 		sacked &= ~TCPCB_SACKED_RETRANS;
1231 		tp->retrans_out -= pcount;
1232 	}
1233 
1234 	return sacked;
1235 }
1236 
1237 /* Shift newly-SACKed bytes from this skb to the immediately previous
1238  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1239  */
1240 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1241 			    struct tcp_sacktag_state *state,
1242 			    unsigned int pcount, int shifted, int mss,
1243 			    bool dup_sack)
1244 {
1245 	struct tcp_sock *tp = tcp_sk(sk);
1246 	struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1247 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1248 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1249 
1250 	BUG_ON(!pcount);
1251 
1252 	/* Adjust counters and hints for the newly sacked sequence
1253 	 * range but discard the return value since prev is already
1254 	 * marked. We must tag the range first because the seq
1255 	 * advancement below implicitly advances
1256 	 * tcp_highest_sack_seq() when skb is highest_sack.
1257 	 */
1258 	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1259 			start_seq, end_seq, dup_sack, pcount,
1260 			&skb->skb_mstamp);
1261 
1262 	if (skb == tp->lost_skb_hint)
1263 		tp->lost_cnt_hint += pcount;
1264 
1265 	TCP_SKB_CB(prev)->end_seq += shifted;
1266 	TCP_SKB_CB(skb)->seq += shifted;
1267 
1268 	tcp_skb_pcount_add(prev, pcount);
1269 	BUG_ON(tcp_skb_pcount(skb) < pcount);
1270 	tcp_skb_pcount_add(skb, -pcount);
1271 
1272 	/* When we're adding to gso_segs == 1, gso_size will be zero,
1273 	 * in theory this shouldn't be necessary but as long as DSACK
1274 	 * code can come after this skb later on it's better to keep
1275 	 * setting gso_size to something.
1276 	 */
1277 	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1278 		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1279 
1280 	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1281 	if (tcp_skb_pcount(skb) <= 1)
1282 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1283 
1284 	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1285 	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1286 
1287 	if (skb->len > 0) {
1288 		BUG_ON(!tcp_skb_pcount(skb));
1289 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1290 		return false;
1291 	}
1292 
1293 	/* Whole SKB was eaten :-) */
1294 
1295 	if (skb == tp->retransmit_skb_hint)
1296 		tp->retransmit_skb_hint = prev;
1297 	if (skb == tp->lost_skb_hint) {
1298 		tp->lost_skb_hint = prev;
1299 		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1300 	}
1301 
1302 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1303 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1304 		TCP_SKB_CB(prev)->end_seq++;
1305 
1306 	if (skb == tcp_highest_sack(sk))
1307 		tcp_advance_highest_sack(sk, skb);
1308 
1309 	tcp_unlink_write_queue(skb, sk);
1310 	sk_wmem_free_skb(sk, skb);
1311 
1312 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1313 
1314 	return true;
1315 }
1316 
1317 /* I wish gso_size would have a bit more sane initialization than
1318  * something-or-zero which complicates things
1319  */
1320 static int tcp_skb_seglen(const struct sk_buff *skb)
1321 {
1322 	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1323 }
1324 
1325 /* Shifting pages past head area doesn't work */
1326 static int skb_can_shift(const struct sk_buff *skb)
1327 {
1328 	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1329 }
1330 
1331 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1332  * skb.
1333  */
1334 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1335 					  struct tcp_sacktag_state *state,
1336 					  u32 start_seq, u32 end_seq,
1337 					  bool dup_sack)
1338 {
1339 	struct tcp_sock *tp = tcp_sk(sk);
1340 	struct sk_buff *prev;
1341 	int mss;
1342 	int pcount = 0;
1343 	int len;
1344 	int in_sack;
1345 
1346 	if (!sk_can_gso(sk))
1347 		goto fallback;
1348 
1349 	/* Normally R but no L won't result in plain S */
1350 	if (!dup_sack &&
1351 	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1352 		goto fallback;
1353 	if (!skb_can_shift(skb))
1354 		goto fallback;
1355 	/* This frame is about to be dropped (was ACKed). */
1356 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1357 		goto fallback;
1358 
1359 	/* Can only happen with delayed DSACK + discard craziness */
1360 	if (unlikely(skb == tcp_write_queue_head(sk)))
1361 		goto fallback;
1362 	prev = tcp_write_queue_prev(sk, skb);
1363 
1364 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1365 		goto fallback;
1366 
1367 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1368 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1369 
1370 	if (in_sack) {
1371 		len = skb->len;
1372 		pcount = tcp_skb_pcount(skb);
1373 		mss = tcp_skb_seglen(skb);
1374 
1375 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1376 		 * drop this restriction as unnecessary
1377 		 */
1378 		if (mss != tcp_skb_seglen(prev))
1379 			goto fallback;
1380 	} else {
1381 		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1382 			goto noop;
1383 		/* CHECKME: This is non-MSS split case only?, this will
1384 		 * cause skipped skbs due to advancing loop btw, original
1385 		 * has that feature too
1386 		 */
1387 		if (tcp_skb_pcount(skb) <= 1)
1388 			goto noop;
1389 
1390 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1391 		if (!in_sack) {
1392 			/* TODO: head merge to next could be attempted here
1393 			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1394 			 * though it might not be worth of the additional hassle
1395 			 *
1396 			 * ...we can probably just fallback to what was done
1397 			 * previously. We could try merging non-SACKed ones
1398 			 * as well but it probably isn't going to buy off
1399 			 * because later SACKs might again split them, and
1400 			 * it would make skb timestamp tracking considerably
1401 			 * harder problem.
1402 			 */
1403 			goto fallback;
1404 		}
1405 
1406 		len = end_seq - TCP_SKB_CB(skb)->seq;
1407 		BUG_ON(len < 0);
1408 		BUG_ON(len > skb->len);
1409 
1410 		/* MSS boundaries should be honoured or else pcount will
1411 		 * severely break even though it makes things bit trickier.
1412 		 * Optimize common case to avoid most of the divides
1413 		 */
1414 		mss = tcp_skb_mss(skb);
1415 
1416 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1417 		 * drop this restriction as unnecessary
1418 		 */
1419 		if (mss != tcp_skb_seglen(prev))
1420 			goto fallback;
1421 
1422 		if (len == mss) {
1423 			pcount = 1;
1424 		} else if (len < mss) {
1425 			goto noop;
1426 		} else {
1427 			pcount = len / mss;
1428 			len = pcount * mss;
1429 		}
1430 	}
1431 
1432 	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1433 	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1434 		goto fallback;
1435 
1436 	if (!skb_shift(prev, skb, len))
1437 		goto fallback;
1438 	if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1439 		goto out;
1440 
1441 	/* Hole filled allows collapsing with the next as well, this is very
1442 	 * useful when hole on every nth skb pattern happens
1443 	 */
1444 	if (prev == tcp_write_queue_tail(sk))
1445 		goto out;
1446 	skb = tcp_write_queue_next(sk, prev);
1447 
1448 	if (!skb_can_shift(skb) ||
1449 	    (skb == tcp_send_head(sk)) ||
1450 	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1451 	    (mss != tcp_skb_seglen(skb)))
1452 		goto out;
1453 
1454 	len = skb->len;
1455 	if (skb_shift(prev, skb, len)) {
1456 		pcount += tcp_skb_pcount(skb);
1457 		tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1458 	}
1459 
1460 out:
1461 	state->fack_count += pcount;
1462 	return prev;
1463 
1464 noop:
1465 	return skb;
1466 
1467 fallback:
1468 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1469 	return NULL;
1470 }
1471 
1472 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1473 					struct tcp_sack_block *next_dup,
1474 					struct tcp_sacktag_state *state,
1475 					u32 start_seq, u32 end_seq,
1476 					bool dup_sack_in)
1477 {
1478 	struct tcp_sock *tp = tcp_sk(sk);
1479 	struct sk_buff *tmp;
1480 
1481 	tcp_for_write_queue_from(skb, sk) {
1482 		int in_sack = 0;
1483 		bool dup_sack = dup_sack_in;
1484 
1485 		if (skb == tcp_send_head(sk))
1486 			break;
1487 
1488 		/* queue is in-order => we can short-circuit the walk early */
1489 		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1490 			break;
1491 
1492 		if (next_dup  &&
1493 		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1494 			in_sack = tcp_match_skb_to_sack(sk, skb,
1495 							next_dup->start_seq,
1496 							next_dup->end_seq);
1497 			if (in_sack > 0)
1498 				dup_sack = true;
1499 		}
1500 
1501 		/* skb reference here is a bit tricky to get right, since
1502 		 * shifting can eat and free both this skb and the next,
1503 		 * so not even _safe variant of the loop is enough.
1504 		 */
1505 		if (in_sack <= 0) {
1506 			tmp = tcp_shift_skb_data(sk, skb, state,
1507 						 start_seq, end_seq, dup_sack);
1508 			if (tmp) {
1509 				if (tmp != skb) {
1510 					skb = tmp;
1511 					continue;
1512 				}
1513 
1514 				in_sack = 0;
1515 			} else {
1516 				in_sack = tcp_match_skb_to_sack(sk, skb,
1517 								start_seq,
1518 								end_seq);
1519 			}
1520 		}
1521 
1522 		if (unlikely(in_sack < 0))
1523 			break;
1524 
1525 		if (in_sack) {
1526 			TCP_SKB_CB(skb)->sacked =
1527 				tcp_sacktag_one(sk,
1528 						state,
1529 						TCP_SKB_CB(skb)->sacked,
1530 						TCP_SKB_CB(skb)->seq,
1531 						TCP_SKB_CB(skb)->end_seq,
1532 						dup_sack,
1533 						tcp_skb_pcount(skb),
1534 						&skb->skb_mstamp);
1535 
1536 			if (!before(TCP_SKB_CB(skb)->seq,
1537 				    tcp_highest_sack_seq(tp)))
1538 				tcp_advance_highest_sack(sk, skb);
1539 		}
1540 
1541 		state->fack_count += tcp_skb_pcount(skb);
1542 	}
1543 	return skb;
1544 }
1545 
1546 /* Avoid all extra work that is being done by sacktag while walking in
1547  * a normal way
1548  */
1549 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1550 					struct tcp_sacktag_state *state,
1551 					u32 skip_to_seq)
1552 {
1553 	tcp_for_write_queue_from(skb, sk) {
1554 		if (skb == tcp_send_head(sk))
1555 			break;
1556 
1557 		if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1558 			break;
1559 
1560 		state->fack_count += tcp_skb_pcount(skb);
1561 	}
1562 	return skb;
1563 }
1564 
1565 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1566 						struct sock *sk,
1567 						struct tcp_sack_block *next_dup,
1568 						struct tcp_sacktag_state *state,
1569 						u32 skip_to_seq)
1570 {
1571 	if (!next_dup)
1572 		return skb;
1573 
1574 	if (before(next_dup->start_seq, skip_to_seq)) {
1575 		skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1576 		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1577 				       next_dup->start_seq, next_dup->end_seq,
1578 				       1);
1579 	}
1580 
1581 	return skb;
1582 }
1583 
1584 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1585 {
1586 	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1587 }
1588 
1589 static int
1590 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1591 			u32 prior_snd_una, struct tcp_sacktag_state *state)
1592 {
1593 	struct tcp_sock *tp = tcp_sk(sk);
1594 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1595 				    TCP_SKB_CB(ack_skb)->sacked);
1596 	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1597 	struct tcp_sack_block sp[TCP_NUM_SACKS];
1598 	struct tcp_sack_block *cache;
1599 	struct sk_buff *skb;
1600 	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1601 	int used_sacks;
1602 	bool found_dup_sack = false;
1603 	int i, j;
1604 	int first_sack_index;
1605 
1606 	state->flag = 0;
1607 	state->reord = tp->packets_out;
1608 
1609 	if (!tp->sacked_out) {
1610 		if (WARN_ON(tp->fackets_out))
1611 			tp->fackets_out = 0;
1612 		tcp_highest_sack_reset(sk);
1613 	}
1614 
1615 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1616 					 num_sacks, prior_snd_una);
1617 	if (found_dup_sack)
1618 		state->flag |= FLAG_DSACKING_ACK;
1619 
1620 	/* Eliminate too old ACKs, but take into
1621 	 * account more or less fresh ones, they can
1622 	 * contain valid SACK info.
1623 	 */
1624 	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1625 		return 0;
1626 
1627 	if (!tp->packets_out)
1628 		goto out;
1629 
1630 	used_sacks = 0;
1631 	first_sack_index = 0;
1632 	for (i = 0; i < num_sacks; i++) {
1633 		bool dup_sack = !i && found_dup_sack;
1634 
1635 		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1636 		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1637 
1638 		if (!tcp_is_sackblock_valid(tp, dup_sack,
1639 					    sp[used_sacks].start_seq,
1640 					    sp[used_sacks].end_seq)) {
1641 			int mib_idx;
1642 
1643 			if (dup_sack) {
1644 				if (!tp->undo_marker)
1645 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1646 				else
1647 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1648 			} else {
1649 				/* Don't count olds caused by ACK reordering */
1650 				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1651 				    !after(sp[used_sacks].end_seq, tp->snd_una))
1652 					continue;
1653 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1654 			}
1655 
1656 			NET_INC_STATS_BH(sock_net(sk), mib_idx);
1657 			if (i == 0)
1658 				first_sack_index = -1;
1659 			continue;
1660 		}
1661 
1662 		/* Ignore very old stuff early */
1663 		if (!after(sp[used_sacks].end_seq, prior_snd_una))
1664 			continue;
1665 
1666 		used_sacks++;
1667 	}
1668 
1669 	/* order SACK blocks to allow in order walk of the retrans queue */
1670 	for (i = used_sacks - 1; i > 0; i--) {
1671 		for (j = 0; j < i; j++) {
1672 			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1673 				swap(sp[j], sp[j + 1]);
1674 
1675 				/* Track where the first SACK block goes to */
1676 				if (j == first_sack_index)
1677 					first_sack_index = j + 1;
1678 			}
1679 		}
1680 	}
1681 
1682 	skb = tcp_write_queue_head(sk);
1683 	state->fack_count = 0;
1684 	i = 0;
1685 
1686 	if (!tp->sacked_out) {
1687 		/* It's already past, so skip checking against it */
1688 		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1689 	} else {
1690 		cache = tp->recv_sack_cache;
1691 		/* Skip empty blocks in at head of the cache */
1692 		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1693 		       !cache->end_seq)
1694 			cache++;
1695 	}
1696 
1697 	while (i < used_sacks) {
1698 		u32 start_seq = sp[i].start_seq;
1699 		u32 end_seq = sp[i].end_seq;
1700 		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1701 		struct tcp_sack_block *next_dup = NULL;
1702 
1703 		if (found_dup_sack && ((i + 1) == first_sack_index))
1704 			next_dup = &sp[i + 1];
1705 
1706 		/* Skip too early cached blocks */
1707 		while (tcp_sack_cache_ok(tp, cache) &&
1708 		       !before(start_seq, cache->end_seq))
1709 			cache++;
1710 
1711 		/* Can skip some work by looking recv_sack_cache? */
1712 		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1713 		    after(end_seq, cache->start_seq)) {
1714 
1715 			/* Head todo? */
1716 			if (before(start_seq, cache->start_seq)) {
1717 				skb = tcp_sacktag_skip(skb, sk, state,
1718 						       start_seq);
1719 				skb = tcp_sacktag_walk(skb, sk, next_dup,
1720 						       state,
1721 						       start_seq,
1722 						       cache->start_seq,
1723 						       dup_sack);
1724 			}
1725 
1726 			/* Rest of the block already fully processed? */
1727 			if (!after(end_seq, cache->end_seq))
1728 				goto advance_sp;
1729 
1730 			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1731 						       state,
1732 						       cache->end_seq);
1733 
1734 			/* ...tail remains todo... */
1735 			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1736 				/* ...but better entrypoint exists! */
1737 				skb = tcp_highest_sack(sk);
1738 				if (!skb)
1739 					break;
1740 				state->fack_count = tp->fackets_out;
1741 				cache++;
1742 				goto walk;
1743 			}
1744 
1745 			skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
1746 			/* Check overlap against next cached too (past this one already) */
1747 			cache++;
1748 			continue;
1749 		}
1750 
1751 		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1752 			skb = tcp_highest_sack(sk);
1753 			if (!skb)
1754 				break;
1755 			state->fack_count = tp->fackets_out;
1756 		}
1757 		skb = tcp_sacktag_skip(skb, sk, state, start_seq);
1758 
1759 walk:
1760 		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1761 				       start_seq, end_seq, dup_sack);
1762 
1763 advance_sp:
1764 		i++;
1765 	}
1766 
1767 	/* Clear the head of the cache sack blocks so we can skip it next time */
1768 	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1769 		tp->recv_sack_cache[i].start_seq = 0;
1770 		tp->recv_sack_cache[i].end_seq = 0;
1771 	}
1772 	for (j = 0; j < used_sacks; j++)
1773 		tp->recv_sack_cache[i++] = sp[j];
1774 
1775 	if ((state->reord < tp->fackets_out) &&
1776 	    ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
1777 		tcp_update_reordering(sk, tp->fackets_out - state->reord, 0);
1778 
1779 	tcp_verify_left_out(tp);
1780 out:
1781 
1782 #if FASTRETRANS_DEBUG > 0
1783 	WARN_ON((int)tp->sacked_out < 0);
1784 	WARN_ON((int)tp->lost_out < 0);
1785 	WARN_ON((int)tp->retrans_out < 0);
1786 	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1787 #endif
1788 	return state->flag;
1789 }
1790 
1791 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1792  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1793  */
1794 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1795 {
1796 	u32 holes;
1797 
1798 	holes = max(tp->lost_out, 1U);
1799 	holes = min(holes, tp->packets_out);
1800 
1801 	if ((tp->sacked_out + holes) > tp->packets_out) {
1802 		tp->sacked_out = tp->packets_out - holes;
1803 		return true;
1804 	}
1805 	return false;
1806 }
1807 
1808 /* If we receive more dupacks than we expected counting segments
1809  * in assumption of absent reordering, interpret this as reordering.
1810  * The only another reason could be bug in receiver TCP.
1811  */
1812 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1813 {
1814 	struct tcp_sock *tp = tcp_sk(sk);
1815 	if (tcp_limit_reno_sacked(tp))
1816 		tcp_update_reordering(sk, tp->packets_out + addend, 0);
1817 }
1818 
1819 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1820 
1821 static void tcp_add_reno_sack(struct sock *sk)
1822 {
1823 	struct tcp_sock *tp = tcp_sk(sk);
1824 	tp->sacked_out++;
1825 	tcp_check_reno_reordering(sk, 0);
1826 	tcp_verify_left_out(tp);
1827 }
1828 
1829 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1830 
1831 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1832 {
1833 	struct tcp_sock *tp = tcp_sk(sk);
1834 
1835 	if (acked > 0) {
1836 		/* One ACK acked hole. The rest eat duplicate ACKs. */
1837 		if (acked - 1 >= tp->sacked_out)
1838 			tp->sacked_out = 0;
1839 		else
1840 			tp->sacked_out -= acked - 1;
1841 	}
1842 	tcp_check_reno_reordering(sk, acked);
1843 	tcp_verify_left_out(tp);
1844 }
1845 
1846 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1847 {
1848 	tp->sacked_out = 0;
1849 }
1850 
1851 void tcp_clear_retrans(struct tcp_sock *tp)
1852 {
1853 	tp->retrans_out = 0;
1854 	tp->lost_out = 0;
1855 	tp->undo_marker = 0;
1856 	tp->undo_retrans = -1;
1857 	tp->fackets_out = 0;
1858 	tp->sacked_out = 0;
1859 }
1860 
1861 static inline void tcp_init_undo(struct tcp_sock *tp)
1862 {
1863 	tp->undo_marker = tp->snd_una;
1864 	/* Retransmission still in flight may cause DSACKs later. */
1865 	tp->undo_retrans = tp->retrans_out ? : -1;
1866 }
1867 
1868 /* Enter Loss state. If we detect SACK reneging, forget all SACK information
1869  * and reset tags completely, otherwise preserve SACKs. If receiver
1870  * dropped its ofo queue, we will know this due to reneging detection.
1871  */
1872 void tcp_enter_loss(struct sock *sk)
1873 {
1874 	const struct inet_connection_sock *icsk = inet_csk(sk);
1875 	struct tcp_sock *tp = tcp_sk(sk);
1876 	struct sk_buff *skb;
1877 	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
1878 	bool is_reneg;			/* is receiver reneging on SACKs? */
1879 
1880 	/* Reduce ssthresh if it has not yet been made inside this window. */
1881 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1882 	    !after(tp->high_seq, tp->snd_una) ||
1883 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1884 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
1885 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1886 		tcp_ca_event(sk, CA_EVENT_LOSS);
1887 		tcp_init_undo(tp);
1888 	}
1889 	tp->snd_cwnd	   = 1;
1890 	tp->snd_cwnd_cnt   = 0;
1891 	tp->snd_cwnd_stamp = tcp_time_stamp;
1892 
1893 	tp->retrans_out = 0;
1894 	tp->lost_out = 0;
1895 
1896 	if (tcp_is_reno(tp))
1897 		tcp_reset_reno_sack(tp);
1898 
1899 	skb = tcp_write_queue_head(sk);
1900 	is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
1901 	if (is_reneg) {
1902 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1903 		tp->sacked_out = 0;
1904 		tp->fackets_out = 0;
1905 	}
1906 	tcp_clear_all_retrans_hints(tp);
1907 
1908 	tcp_for_write_queue(skb, sk) {
1909 		if (skb == tcp_send_head(sk))
1910 			break;
1911 
1912 		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1913 		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
1914 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1915 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1916 			tp->lost_out += tcp_skb_pcount(skb);
1917 			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
1918 		}
1919 	}
1920 	tcp_verify_left_out(tp);
1921 
1922 	/* Timeout in disordered state after receiving substantial DUPACKs
1923 	 * suggests that the degree of reordering is over-estimated.
1924 	 */
1925 	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
1926 	    tp->sacked_out >= sysctl_tcp_reordering)
1927 		tp->reordering = min_t(unsigned int, tp->reordering,
1928 				       sysctl_tcp_reordering);
1929 	tcp_set_ca_state(sk, TCP_CA_Loss);
1930 	tp->high_seq = tp->snd_nxt;
1931 	tcp_ecn_queue_cwr(tp);
1932 
1933 	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
1934 	 * loss recovery is underway except recurring timeout(s) on
1935 	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
1936 	 */
1937 	tp->frto = sysctl_tcp_frto &&
1938 		   (new_recovery || icsk->icsk_retransmits) &&
1939 		   !inet_csk(sk)->icsk_mtup.probe_size;
1940 }
1941 
1942 /* If ACK arrived pointing to a remembered SACK, it means that our
1943  * remembered SACKs do not reflect real state of receiver i.e.
1944  * receiver _host_ is heavily congested (or buggy).
1945  *
1946  * To avoid big spurious retransmission bursts due to transient SACK
1947  * scoreboard oddities that look like reneging, we give the receiver a
1948  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
1949  * restore sanity to the SACK scoreboard. If the apparent reneging
1950  * persists until this RTO then we'll clear the SACK scoreboard.
1951  */
1952 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
1953 {
1954 	if (flag & FLAG_SACK_RENEGING) {
1955 		struct tcp_sock *tp = tcp_sk(sk);
1956 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
1957 					  msecs_to_jiffies(10));
1958 
1959 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1960 					  delay, TCP_RTO_MAX);
1961 		return true;
1962 	}
1963 	return false;
1964 }
1965 
1966 static inline int tcp_fackets_out(const struct tcp_sock *tp)
1967 {
1968 	return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
1969 }
1970 
1971 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
1972  * counter when SACK is enabled (without SACK, sacked_out is used for
1973  * that purpose).
1974  *
1975  * Instead, with FACK TCP uses fackets_out that includes both SACKed
1976  * segments up to the highest received SACK block so far and holes in
1977  * between them.
1978  *
1979  * With reordering, holes may still be in flight, so RFC3517 recovery
1980  * uses pure sacked_out (total number of SACKed segments) even though
1981  * it violates the RFC that uses duplicate ACKs, often these are equal
1982  * but when e.g. out-of-window ACKs or packet duplication occurs,
1983  * they differ. Since neither occurs due to loss, TCP should really
1984  * ignore them.
1985  */
1986 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
1987 {
1988 	return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
1989 }
1990 
1991 static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
1992 {
1993 	struct tcp_sock *tp = tcp_sk(sk);
1994 	unsigned long delay;
1995 
1996 	/* Delay early retransmit and entering fast recovery for
1997 	 * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
1998 	 * available, or RTO is scheduled to fire first.
1999 	 */
2000 	if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
2001 	    (flag & FLAG_ECE) || !tp->srtt_us)
2002 		return false;
2003 
2004 	delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
2005 		    msecs_to_jiffies(2));
2006 
2007 	if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2008 		return false;
2009 
2010 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
2011 				  TCP_RTO_MAX);
2012 	return true;
2013 }
2014 
2015 /* Linux NewReno/SACK/FACK/ECN state machine.
2016  * --------------------------------------
2017  *
2018  * "Open"	Normal state, no dubious events, fast path.
2019  * "Disorder"   In all the respects it is "Open",
2020  *		but requires a bit more attention. It is entered when
2021  *		we see some SACKs or dupacks. It is split of "Open"
2022  *		mainly to move some processing from fast path to slow one.
2023  * "CWR"	CWND was reduced due to some Congestion Notification event.
2024  *		It can be ECN, ICMP source quench, local device congestion.
2025  * "Recovery"	CWND was reduced, we are fast-retransmitting.
2026  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2027  *
2028  * tcp_fastretrans_alert() is entered:
2029  * - each incoming ACK, if state is not "Open"
2030  * - when arrived ACK is unusual, namely:
2031  *	* SACK
2032  *	* Duplicate ACK.
2033  *	* ECN ECE.
2034  *
2035  * Counting packets in flight is pretty simple.
2036  *
2037  *	in_flight = packets_out - left_out + retrans_out
2038  *
2039  *	packets_out is SND.NXT-SND.UNA counted in packets.
2040  *
2041  *	retrans_out is number of retransmitted segments.
2042  *
2043  *	left_out is number of segments left network, but not ACKed yet.
2044  *
2045  *		left_out = sacked_out + lost_out
2046  *
2047  *     sacked_out: Packets, which arrived to receiver out of order
2048  *		   and hence not ACKed. With SACKs this number is simply
2049  *		   amount of SACKed data. Even without SACKs
2050  *		   it is easy to give pretty reliable estimate of this number,
2051  *		   counting duplicate ACKs.
2052  *
2053  *       lost_out: Packets lost by network. TCP has no explicit
2054  *		   "loss notification" feedback from network (for now).
2055  *		   It means that this number can be only _guessed_.
2056  *		   Actually, it is the heuristics to predict lossage that
2057  *		   distinguishes different algorithms.
2058  *
2059  *	F.e. after RTO, when all the queue is considered as lost,
2060  *	lost_out = packets_out and in_flight = retrans_out.
2061  *
2062  *		Essentially, we have now two algorithms counting
2063  *		lost packets.
2064  *
2065  *		FACK: It is the simplest heuristics. As soon as we decided
2066  *		that something is lost, we decide that _all_ not SACKed
2067  *		packets until the most forward SACK are lost. I.e.
2068  *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
2069  *		It is absolutely correct estimate, if network does not reorder
2070  *		packets. And it loses any connection to reality when reordering
2071  *		takes place. We use FACK by default until reordering
2072  *		is suspected on the path to this destination.
2073  *
2074  *		NewReno: when Recovery is entered, we assume that one segment
2075  *		is lost (classic Reno). While we are in Recovery and
2076  *		a partial ACK arrives, we assume that one more packet
2077  *		is lost (NewReno). This heuristics are the same in NewReno
2078  *		and SACK.
2079  *
2080  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2081  *  deflation etc. CWND is real congestion window, never inflated, changes
2082  *  only according to classic VJ rules.
2083  *
2084  * Really tricky (and requiring careful tuning) part of algorithm
2085  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2086  * The first determines the moment _when_ we should reduce CWND and,
2087  * hence, slow down forward transmission. In fact, it determines the moment
2088  * when we decide that hole is caused by loss, rather than by a reorder.
2089  *
2090  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2091  * holes, caused by lost packets.
2092  *
2093  * And the most logically complicated part of algorithm is undo
2094  * heuristics. We detect false retransmits due to both too early
2095  * fast retransmit (reordering) and underestimated RTO, analyzing
2096  * timestamps and D-SACKs. When we detect that some segments were
2097  * retransmitted by mistake and CWND reduction was wrong, we undo
2098  * window reduction and abort recovery phase. This logic is hidden
2099  * inside several functions named tcp_try_undo_<something>.
2100  */
2101 
2102 /* This function decides, when we should leave Disordered state
2103  * and enter Recovery phase, reducing congestion window.
2104  *
2105  * Main question: may we further continue forward transmission
2106  * with the same cwnd?
2107  */
2108 static bool tcp_time_to_recover(struct sock *sk, int flag)
2109 {
2110 	struct tcp_sock *tp = tcp_sk(sk);
2111 	__u32 packets_out;
2112 
2113 	/* Trick#1: The loss is proven. */
2114 	if (tp->lost_out)
2115 		return true;
2116 
2117 	/* Not-A-Trick#2 : Classic rule... */
2118 	if (tcp_dupack_heuristics(tp) > tp->reordering)
2119 		return true;
2120 
2121 	/* Trick#4: It is still not OK... But will it be useful to delay
2122 	 * recovery more?
2123 	 */
2124 	packets_out = tp->packets_out;
2125 	if (packets_out <= tp->reordering &&
2126 	    tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2127 	    !tcp_may_send_now(sk)) {
2128 		/* We have nothing to send. This connection is limited
2129 		 * either by receiver window or by application.
2130 		 */
2131 		return true;
2132 	}
2133 
2134 	/* If a thin stream is detected, retransmit after first
2135 	 * received dupack. Employ only if SACK is supported in order
2136 	 * to avoid possible corner-case series of spurious retransmissions
2137 	 * Use only if there are no unsent data.
2138 	 */
2139 	if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2140 	    tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2141 	    tcp_is_sack(tp) && !tcp_send_head(sk))
2142 		return true;
2143 
2144 	/* Trick#6: TCP early retransmit, per RFC5827.  To avoid spurious
2145 	 * retransmissions due to small network reorderings, we implement
2146 	 * Mitigation A.3 in the RFC and delay the retransmission for a short
2147 	 * interval if appropriate.
2148 	 */
2149 	if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2150 	    (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
2151 	    !tcp_may_send_now(sk))
2152 		return !tcp_pause_early_retransmit(sk, flag);
2153 
2154 	return false;
2155 }
2156 
2157 /* Detect loss in event "A" above by marking head of queue up as lost.
2158  * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2159  * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2160  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2161  * the maximum SACKed segments to pass before reaching this limit.
2162  */
2163 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2164 {
2165 	struct tcp_sock *tp = tcp_sk(sk);
2166 	struct sk_buff *skb;
2167 	int cnt, oldcnt;
2168 	int err;
2169 	unsigned int mss;
2170 	/* Use SACK to deduce losses of new sequences sent during recovery */
2171 	const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2172 
2173 	WARN_ON(packets > tp->packets_out);
2174 	if (tp->lost_skb_hint) {
2175 		skb = tp->lost_skb_hint;
2176 		cnt = tp->lost_cnt_hint;
2177 		/* Head already handled? */
2178 		if (mark_head && skb != tcp_write_queue_head(sk))
2179 			return;
2180 	} else {
2181 		skb = tcp_write_queue_head(sk);
2182 		cnt = 0;
2183 	}
2184 
2185 	tcp_for_write_queue_from(skb, sk) {
2186 		if (skb == tcp_send_head(sk))
2187 			break;
2188 		/* TODO: do this better */
2189 		/* this is not the most efficient way to do this... */
2190 		tp->lost_skb_hint = skb;
2191 		tp->lost_cnt_hint = cnt;
2192 
2193 		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2194 			break;
2195 
2196 		oldcnt = cnt;
2197 		if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2198 		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2199 			cnt += tcp_skb_pcount(skb);
2200 
2201 		if (cnt > packets) {
2202 			if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2203 			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2204 			    (oldcnt >= packets))
2205 				break;
2206 
2207 			mss = tcp_skb_mss(skb);
2208 			err = tcp_fragment(sk, skb, (packets - oldcnt) * mss,
2209 					   mss, GFP_ATOMIC);
2210 			if (err < 0)
2211 				break;
2212 			cnt = packets;
2213 		}
2214 
2215 		tcp_skb_mark_lost(tp, skb);
2216 
2217 		if (mark_head)
2218 			break;
2219 	}
2220 	tcp_verify_left_out(tp);
2221 }
2222 
2223 /* Account newly detected lost packet(s) */
2224 
2225 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2226 {
2227 	struct tcp_sock *tp = tcp_sk(sk);
2228 
2229 	if (tcp_is_reno(tp)) {
2230 		tcp_mark_head_lost(sk, 1, 1);
2231 	} else if (tcp_is_fack(tp)) {
2232 		int lost = tp->fackets_out - tp->reordering;
2233 		if (lost <= 0)
2234 			lost = 1;
2235 		tcp_mark_head_lost(sk, lost, 0);
2236 	} else {
2237 		int sacked_upto = tp->sacked_out - tp->reordering;
2238 		if (sacked_upto >= 0)
2239 			tcp_mark_head_lost(sk, sacked_upto, 0);
2240 		else if (fast_rexmit)
2241 			tcp_mark_head_lost(sk, 1, 1);
2242 	}
2243 }
2244 
2245 /* CWND moderation, preventing bursts due to too big ACKs
2246  * in dubious situations.
2247  */
2248 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2249 {
2250 	tp->snd_cwnd = min(tp->snd_cwnd,
2251 			   tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2252 	tp->snd_cwnd_stamp = tcp_time_stamp;
2253 }
2254 
2255 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2256 {
2257 	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2258 	       before(tp->rx_opt.rcv_tsecr, when);
2259 }
2260 
2261 /* skb is spurious retransmitted if the returned timestamp echo
2262  * reply is prior to the skb transmission time
2263  */
2264 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2265 				     const struct sk_buff *skb)
2266 {
2267 	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2268 	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2269 }
2270 
2271 /* Nothing was retransmitted or returned timestamp is less
2272  * than timestamp of the first retransmission.
2273  */
2274 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2275 {
2276 	return !tp->retrans_stamp ||
2277 	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2278 }
2279 
2280 /* Undo procedures. */
2281 
2282 /* We can clear retrans_stamp when there are no retransmissions in the
2283  * window. It would seem that it is trivially available for us in
2284  * tp->retrans_out, however, that kind of assumptions doesn't consider
2285  * what will happen if errors occur when sending retransmission for the
2286  * second time. ...It could the that such segment has only
2287  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2288  * the head skb is enough except for some reneging corner cases that
2289  * are not worth the effort.
2290  *
2291  * Main reason for all this complexity is the fact that connection dying
2292  * time now depends on the validity of the retrans_stamp, in particular,
2293  * that successive retransmissions of a segment must not advance
2294  * retrans_stamp under any conditions.
2295  */
2296 static bool tcp_any_retrans_done(const struct sock *sk)
2297 {
2298 	const struct tcp_sock *tp = tcp_sk(sk);
2299 	struct sk_buff *skb;
2300 
2301 	if (tp->retrans_out)
2302 		return true;
2303 
2304 	skb = tcp_write_queue_head(sk);
2305 	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2306 		return true;
2307 
2308 	return false;
2309 }
2310 
2311 #if FASTRETRANS_DEBUG > 1
2312 static void DBGUNDO(struct sock *sk, const char *msg)
2313 {
2314 	struct tcp_sock *tp = tcp_sk(sk);
2315 	struct inet_sock *inet = inet_sk(sk);
2316 
2317 	if (sk->sk_family == AF_INET) {
2318 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2319 			 msg,
2320 			 &inet->inet_daddr, ntohs(inet->inet_dport),
2321 			 tp->snd_cwnd, tcp_left_out(tp),
2322 			 tp->snd_ssthresh, tp->prior_ssthresh,
2323 			 tp->packets_out);
2324 	}
2325 #if IS_ENABLED(CONFIG_IPV6)
2326 	else if (sk->sk_family == AF_INET6) {
2327 		struct ipv6_pinfo *np = inet6_sk(sk);
2328 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2329 			 msg,
2330 			 &np->daddr, ntohs(inet->inet_dport),
2331 			 tp->snd_cwnd, tcp_left_out(tp),
2332 			 tp->snd_ssthresh, tp->prior_ssthresh,
2333 			 tp->packets_out);
2334 	}
2335 #endif
2336 }
2337 #else
2338 #define DBGUNDO(x...) do { } while (0)
2339 #endif
2340 
2341 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2342 {
2343 	struct tcp_sock *tp = tcp_sk(sk);
2344 
2345 	if (unmark_loss) {
2346 		struct sk_buff *skb;
2347 
2348 		tcp_for_write_queue(skb, sk) {
2349 			if (skb == tcp_send_head(sk))
2350 				break;
2351 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2352 		}
2353 		tp->lost_out = 0;
2354 		tcp_clear_all_retrans_hints(tp);
2355 	}
2356 
2357 	if (tp->prior_ssthresh) {
2358 		const struct inet_connection_sock *icsk = inet_csk(sk);
2359 
2360 		if (icsk->icsk_ca_ops->undo_cwnd)
2361 			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2362 		else
2363 			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2364 
2365 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2366 			tp->snd_ssthresh = tp->prior_ssthresh;
2367 			tcp_ecn_withdraw_cwr(tp);
2368 		}
2369 	} else {
2370 		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2371 	}
2372 	tp->snd_cwnd_stamp = tcp_time_stamp;
2373 	tp->undo_marker = 0;
2374 }
2375 
2376 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2377 {
2378 	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2379 }
2380 
2381 /* People celebrate: "We love our President!" */
2382 static bool tcp_try_undo_recovery(struct sock *sk)
2383 {
2384 	struct tcp_sock *tp = tcp_sk(sk);
2385 
2386 	if (tcp_may_undo(tp)) {
2387 		int mib_idx;
2388 
2389 		/* Happy end! We did not retransmit anything
2390 		 * or our original transmission succeeded.
2391 		 */
2392 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2393 		tcp_undo_cwnd_reduction(sk, false);
2394 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2395 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2396 		else
2397 			mib_idx = LINUX_MIB_TCPFULLUNDO;
2398 
2399 		NET_INC_STATS_BH(sock_net(sk), mib_idx);
2400 	}
2401 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2402 		/* Hold old state until something *above* high_seq
2403 		 * is ACKed. For Reno it is MUST to prevent false
2404 		 * fast retransmits (RFC2582). SACK TCP is safe. */
2405 		tcp_moderate_cwnd(tp);
2406 		if (!tcp_any_retrans_done(sk))
2407 			tp->retrans_stamp = 0;
2408 		return true;
2409 	}
2410 	tcp_set_ca_state(sk, TCP_CA_Open);
2411 	return false;
2412 }
2413 
2414 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2415 static bool tcp_try_undo_dsack(struct sock *sk)
2416 {
2417 	struct tcp_sock *tp = tcp_sk(sk);
2418 
2419 	if (tp->undo_marker && !tp->undo_retrans) {
2420 		DBGUNDO(sk, "D-SACK");
2421 		tcp_undo_cwnd_reduction(sk, false);
2422 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2423 		return true;
2424 	}
2425 	return false;
2426 }
2427 
2428 /* Undo during loss recovery after partial ACK or using F-RTO. */
2429 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2430 {
2431 	struct tcp_sock *tp = tcp_sk(sk);
2432 
2433 	if (frto_undo || tcp_may_undo(tp)) {
2434 		tcp_undo_cwnd_reduction(sk, true);
2435 
2436 		DBGUNDO(sk, "partial loss");
2437 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2438 		if (frto_undo)
2439 			NET_INC_STATS_BH(sock_net(sk),
2440 					 LINUX_MIB_TCPSPURIOUSRTOS);
2441 		inet_csk(sk)->icsk_retransmits = 0;
2442 		if (frto_undo || tcp_is_sack(tp))
2443 			tcp_set_ca_state(sk, TCP_CA_Open);
2444 		return true;
2445 	}
2446 	return false;
2447 }
2448 
2449 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2450  * It computes the number of packets to send (sndcnt) based on packets newly
2451  * delivered:
2452  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2453  *	cwnd reductions across a full RTT.
2454  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2455  *      But when the retransmits are acked without further losses, PRR
2456  *      slow starts cwnd up to ssthresh to speed up the recovery.
2457  */
2458 static void tcp_init_cwnd_reduction(struct sock *sk)
2459 {
2460 	struct tcp_sock *tp = tcp_sk(sk);
2461 
2462 	tp->high_seq = tp->snd_nxt;
2463 	tp->tlp_high_seq = 0;
2464 	tp->snd_cwnd_cnt = 0;
2465 	tp->prior_cwnd = tp->snd_cwnd;
2466 	tp->prr_delivered = 0;
2467 	tp->prr_out = 0;
2468 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2469 	tcp_ecn_queue_cwr(tp);
2470 }
2471 
2472 static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
2473 			       int fast_rexmit, int flag)
2474 {
2475 	struct tcp_sock *tp = tcp_sk(sk);
2476 	int sndcnt = 0;
2477 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2478 	int newly_acked_sacked = prior_unsacked -
2479 				 (tp->packets_out - tp->sacked_out);
2480 
2481 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2482 		return;
2483 
2484 	tp->prr_delivered += newly_acked_sacked;
2485 	if (delta < 0) {
2486 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2487 			       tp->prior_cwnd - 1;
2488 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2489 	} else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
2490 		   !(flag & FLAG_LOST_RETRANS)) {
2491 		sndcnt = min_t(int, delta,
2492 			       max_t(int, tp->prr_delivered - tp->prr_out,
2493 				     newly_acked_sacked) + 1);
2494 	} else {
2495 		sndcnt = min(delta, newly_acked_sacked);
2496 	}
2497 	sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
2498 	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2499 }
2500 
2501 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2502 {
2503 	struct tcp_sock *tp = tcp_sk(sk);
2504 
2505 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2506 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
2507 	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
2508 		tp->snd_cwnd = tp->snd_ssthresh;
2509 		tp->snd_cwnd_stamp = tcp_time_stamp;
2510 	}
2511 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2512 }
2513 
2514 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2515 void tcp_enter_cwr(struct sock *sk)
2516 {
2517 	struct tcp_sock *tp = tcp_sk(sk);
2518 
2519 	tp->prior_ssthresh = 0;
2520 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2521 		tp->undo_marker = 0;
2522 		tcp_init_cwnd_reduction(sk);
2523 		tcp_set_ca_state(sk, TCP_CA_CWR);
2524 	}
2525 }
2526 EXPORT_SYMBOL(tcp_enter_cwr);
2527 
2528 static void tcp_try_keep_open(struct sock *sk)
2529 {
2530 	struct tcp_sock *tp = tcp_sk(sk);
2531 	int state = TCP_CA_Open;
2532 
2533 	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2534 		state = TCP_CA_Disorder;
2535 
2536 	if (inet_csk(sk)->icsk_ca_state != state) {
2537 		tcp_set_ca_state(sk, state);
2538 		tp->high_seq = tp->snd_nxt;
2539 	}
2540 }
2541 
2542 static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
2543 {
2544 	struct tcp_sock *tp = tcp_sk(sk);
2545 
2546 	tcp_verify_left_out(tp);
2547 
2548 	if (!tcp_any_retrans_done(sk))
2549 		tp->retrans_stamp = 0;
2550 
2551 	if (flag & FLAG_ECE)
2552 		tcp_enter_cwr(sk);
2553 
2554 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2555 		tcp_try_keep_open(sk);
2556 	} else {
2557 		tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
2558 	}
2559 }
2560 
2561 static void tcp_mtup_probe_failed(struct sock *sk)
2562 {
2563 	struct inet_connection_sock *icsk = inet_csk(sk);
2564 
2565 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2566 	icsk->icsk_mtup.probe_size = 0;
2567 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2568 }
2569 
2570 static void tcp_mtup_probe_success(struct sock *sk)
2571 {
2572 	struct tcp_sock *tp = tcp_sk(sk);
2573 	struct inet_connection_sock *icsk = inet_csk(sk);
2574 
2575 	/* FIXME: breaks with very large cwnd */
2576 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2577 	tp->snd_cwnd = tp->snd_cwnd *
2578 		       tcp_mss_to_mtu(sk, tp->mss_cache) /
2579 		       icsk->icsk_mtup.probe_size;
2580 	tp->snd_cwnd_cnt = 0;
2581 	tp->snd_cwnd_stamp = tcp_time_stamp;
2582 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2583 
2584 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2585 	icsk->icsk_mtup.probe_size = 0;
2586 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2587 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2588 }
2589 
2590 /* Do a simple retransmit without using the backoff mechanisms in
2591  * tcp_timer. This is used for path mtu discovery.
2592  * The socket is already locked here.
2593  */
2594 void tcp_simple_retransmit(struct sock *sk)
2595 {
2596 	const struct inet_connection_sock *icsk = inet_csk(sk);
2597 	struct tcp_sock *tp = tcp_sk(sk);
2598 	struct sk_buff *skb;
2599 	unsigned int mss = tcp_current_mss(sk);
2600 	u32 prior_lost = tp->lost_out;
2601 
2602 	tcp_for_write_queue(skb, sk) {
2603 		if (skb == tcp_send_head(sk))
2604 			break;
2605 		if (tcp_skb_seglen(skb) > mss &&
2606 		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2607 			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2608 				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2609 				tp->retrans_out -= tcp_skb_pcount(skb);
2610 			}
2611 			tcp_skb_mark_lost_uncond_verify(tp, skb);
2612 		}
2613 	}
2614 
2615 	tcp_clear_retrans_hints_partial(tp);
2616 
2617 	if (prior_lost == tp->lost_out)
2618 		return;
2619 
2620 	if (tcp_is_reno(tp))
2621 		tcp_limit_reno_sacked(tp);
2622 
2623 	tcp_verify_left_out(tp);
2624 
2625 	/* Don't muck with the congestion window here.
2626 	 * Reason is that we do not increase amount of _data_
2627 	 * in network, but units changed and effective
2628 	 * cwnd/ssthresh really reduced now.
2629 	 */
2630 	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2631 		tp->high_seq = tp->snd_nxt;
2632 		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2633 		tp->prior_ssthresh = 0;
2634 		tp->undo_marker = 0;
2635 		tcp_set_ca_state(sk, TCP_CA_Loss);
2636 	}
2637 	tcp_xmit_retransmit_queue(sk);
2638 }
2639 EXPORT_SYMBOL(tcp_simple_retransmit);
2640 
2641 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2642 {
2643 	struct tcp_sock *tp = tcp_sk(sk);
2644 	int mib_idx;
2645 
2646 	if (tcp_is_reno(tp))
2647 		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2648 	else
2649 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2650 
2651 	NET_INC_STATS_BH(sock_net(sk), mib_idx);
2652 
2653 	tp->prior_ssthresh = 0;
2654 	tcp_init_undo(tp);
2655 
2656 	if (!tcp_in_cwnd_reduction(sk)) {
2657 		if (!ece_ack)
2658 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2659 		tcp_init_cwnd_reduction(sk);
2660 	}
2661 	tcp_set_ca_state(sk, TCP_CA_Recovery);
2662 }
2663 
2664 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2665  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2666  */
2667 static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
2668 {
2669 	struct tcp_sock *tp = tcp_sk(sk);
2670 	bool recovered = !before(tp->snd_una, tp->high_seq);
2671 
2672 	if ((flag & FLAG_SND_UNA_ADVANCED) &&
2673 	    tcp_try_undo_loss(sk, false))
2674 		return;
2675 
2676 	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2677 		/* Step 3.b. A timeout is spurious if not all data are
2678 		 * lost, i.e., never-retransmitted data are (s)acked.
2679 		 */
2680 		if ((flag & FLAG_ORIG_SACK_ACKED) &&
2681 		    tcp_try_undo_loss(sk, true))
2682 			return;
2683 
2684 		if (after(tp->snd_nxt, tp->high_seq)) {
2685 			if (flag & FLAG_DATA_SACKED || is_dupack)
2686 				tp->frto = 0; /* Step 3.a. loss was real */
2687 		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2688 			tp->high_seq = tp->snd_nxt;
2689 			__tcp_push_pending_frames(sk, tcp_current_mss(sk),
2690 						  TCP_NAGLE_OFF);
2691 			if (after(tp->snd_nxt, tp->high_seq))
2692 				return; /* Step 2.b */
2693 			tp->frto = 0;
2694 		}
2695 	}
2696 
2697 	if (recovered) {
2698 		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2699 		tcp_try_undo_recovery(sk);
2700 		return;
2701 	}
2702 	if (tcp_is_reno(tp)) {
2703 		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2704 		 * delivered. Lower inflight to clock out (re)tranmissions.
2705 		 */
2706 		if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
2707 			tcp_add_reno_sack(sk);
2708 		else if (flag & FLAG_SND_UNA_ADVANCED)
2709 			tcp_reset_reno_sack(tp);
2710 	}
2711 	tcp_xmit_retransmit_queue(sk);
2712 }
2713 
2714 /* Undo during fast recovery after partial ACK. */
2715 static bool tcp_try_undo_partial(struct sock *sk, const int acked,
2716 				 const int prior_unsacked, int flag)
2717 {
2718 	struct tcp_sock *tp = tcp_sk(sk);
2719 
2720 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
2721 		/* Plain luck! Hole if filled with delayed
2722 		 * packet, rather than with a retransmit.
2723 		 */
2724 		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2725 
2726 		/* We are getting evidence that the reordering degree is higher
2727 		 * than we realized. If there are no retransmits out then we
2728 		 * can undo. Otherwise we clock out new packets but do not
2729 		 * mark more packets lost or retransmit more.
2730 		 */
2731 		if (tp->retrans_out) {
2732 			tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
2733 			return true;
2734 		}
2735 
2736 		if (!tcp_any_retrans_done(sk))
2737 			tp->retrans_stamp = 0;
2738 
2739 		DBGUNDO(sk, "partial recovery");
2740 		tcp_undo_cwnd_reduction(sk, true);
2741 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2742 		tcp_try_keep_open(sk);
2743 		return true;
2744 	}
2745 	return false;
2746 }
2747 
2748 /* Process an event, which can update packets-in-flight not trivially.
2749  * Main goal of this function is to calculate new estimate for left_out,
2750  * taking into account both packets sitting in receiver's buffer and
2751  * packets lost by network.
2752  *
2753  * Besides that it does CWND reduction, when packet loss is detected
2754  * and changes state of machine.
2755  *
2756  * It does _not_ decide what to send, it is made in function
2757  * tcp_xmit_retransmit_queue().
2758  */
2759 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
2760 				  const int prior_unsacked,
2761 				  bool is_dupack, int flag)
2762 {
2763 	struct inet_connection_sock *icsk = inet_csk(sk);
2764 	struct tcp_sock *tp = tcp_sk(sk);
2765 	bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2766 				    (tcp_fackets_out(tp) > tp->reordering));
2767 	int fast_rexmit = 0;
2768 
2769 	if (WARN_ON(!tp->packets_out && tp->sacked_out))
2770 		tp->sacked_out = 0;
2771 	if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2772 		tp->fackets_out = 0;
2773 
2774 	/* Now state machine starts.
2775 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2776 	if (flag & FLAG_ECE)
2777 		tp->prior_ssthresh = 0;
2778 
2779 	/* B. In all the states check for reneging SACKs. */
2780 	if (tcp_check_sack_reneging(sk, flag))
2781 		return;
2782 
2783 	/* C. Check consistency of the current state. */
2784 	tcp_verify_left_out(tp);
2785 
2786 	/* D. Check state exit conditions. State can be terminated
2787 	 *    when high_seq is ACKed. */
2788 	if (icsk->icsk_ca_state == TCP_CA_Open) {
2789 		WARN_ON(tp->retrans_out != 0);
2790 		tp->retrans_stamp = 0;
2791 	} else if (!before(tp->snd_una, tp->high_seq)) {
2792 		switch (icsk->icsk_ca_state) {
2793 		case TCP_CA_CWR:
2794 			/* CWR is to be held something *above* high_seq
2795 			 * is ACKed for CWR bit to reach receiver. */
2796 			if (tp->snd_una != tp->high_seq) {
2797 				tcp_end_cwnd_reduction(sk);
2798 				tcp_set_ca_state(sk, TCP_CA_Open);
2799 			}
2800 			break;
2801 
2802 		case TCP_CA_Recovery:
2803 			if (tcp_is_reno(tp))
2804 				tcp_reset_reno_sack(tp);
2805 			if (tcp_try_undo_recovery(sk))
2806 				return;
2807 			tcp_end_cwnd_reduction(sk);
2808 			break;
2809 		}
2810 	}
2811 
2812 	/* Use RACK to detect loss */
2813 	if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS &&
2814 	    tcp_rack_mark_lost(sk))
2815 		flag |= FLAG_LOST_RETRANS;
2816 
2817 	/* E. Process state. */
2818 	switch (icsk->icsk_ca_state) {
2819 	case TCP_CA_Recovery:
2820 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2821 			if (tcp_is_reno(tp) && is_dupack)
2822 				tcp_add_reno_sack(sk);
2823 		} else {
2824 			if (tcp_try_undo_partial(sk, acked, prior_unsacked, flag))
2825 				return;
2826 			/* Partial ACK arrived. Force fast retransmit. */
2827 			do_lost = tcp_is_reno(tp) ||
2828 				  tcp_fackets_out(tp) > tp->reordering;
2829 		}
2830 		if (tcp_try_undo_dsack(sk)) {
2831 			tcp_try_keep_open(sk);
2832 			return;
2833 		}
2834 		break;
2835 	case TCP_CA_Loss:
2836 		tcp_process_loss(sk, flag, is_dupack);
2837 		if (icsk->icsk_ca_state != TCP_CA_Open &&
2838 		    !(flag & FLAG_LOST_RETRANS))
2839 			return;
2840 		/* Change state if cwnd is undone or retransmits are lost */
2841 	default:
2842 		if (tcp_is_reno(tp)) {
2843 			if (flag & FLAG_SND_UNA_ADVANCED)
2844 				tcp_reset_reno_sack(tp);
2845 			if (is_dupack)
2846 				tcp_add_reno_sack(sk);
2847 		}
2848 
2849 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2850 			tcp_try_undo_dsack(sk);
2851 
2852 		if (!tcp_time_to_recover(sk, flag)) {
2853 			tcp_try_to_open(sk, flag, prior_unsacked);
2854 			return;
2855 		}
2856 
2857 		/* MTU probe failure: don't reduce cwnd */
2858 		if (icsk->icsk_ca_state < TCP_CA_CWR &&
2859 		    icsk->icsk_mtup.probe_size &&
2860 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
2861 			tcp_mtup_probe_failed(sk);
2862 			/* Restores the reduction we did in tcp_mtup_probe() */
2863 			tp->snd_cwnd++;
2864 			tcp_simple_retransmit(sk);
2865 			return;
2866 		}
2867 
2868 		/* Otherwise enter Recovery state */
2869 		tcp_enter_recovery(sk, (flag & FLAG_ECE));
2870 		fast_rexmit = 1;
2871 	}
2872 
2873 	if (do_lost)
2874 		tcp_update_scoreboard(sk, fast_rexmit);
2875 	tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
2876 	tcp_xmit_retransmit_queue(sk);
2877 }
2878 
2879 /* Kathleen Nichols' algorithm for tracking the minimum value of
2880  * a data stream over some fixed time interval. (E.g., the minimum
2881  * RTT over the past five minutes.) It uses constant space and constant
2882  * time per update yet almost always delivers the same minimum as an
2883  * implementation that has to keep all the data in the window.
2884  *
2885  * The algorithm keeps track of the best, 2nd best & 3rd best min
2886  * values, maintaining an invariant that the measurement time of the
2887  * n'th best >= n-1'th best. It also makes sure that the three values
2888  * are widely separated in the time window since that bounds the worse
2889  * case error when that data is monotonically increasing over the window.
2890  *
2891  * Upon getting a new min, we can forget everything earlier because it
2892  * has no value - the new min is <= everything else in the window by
2893  * definition and it's the most recent. So we restart fresh on every new min
2894  * and overwrites 2nd & 3rd choices. The same property holds for 2nd & 3rd
2895  * best.
2896  */
2897 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
2898 {
2899 	const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ;
2900 	struct rtt_meas *m = tcp_sk(sk)->rtt_min;
2901 	struct rtt_meas rttm = { .rtt = (rtt_us ? : 1), .ts = now };
2902 	u32 elapsed;
2903 
2904 	/* Check if the new measurement updates the 1st, 2nd, or 3rd choices */
2905 	if (unlikely(rttm.rtt <= m[0].rtt))
2906 		m[0] = m[1] = m[2] = rttm;
2907 	else if (rttm.rtt <= m[1].rtt)
2908 		m[1] = m[2] = rttm;
2909 	else if (rttm.rtt <= m[2].rtt)
2910 		m[2] = rttm;
2911 
2912 	elapsed = now - m[0].ts;
2913 	if (unlikely(elapsed > wlen)) {
2914 		/* Passed entire window without a new min so make 2nd choice
2915 		 * the new min & 3rd choice the new 2nd. So forth and so on.
2916 		 */
2917 		m[0] = m[1];
2918 		m[1] = m[2];
2919 		m[2] = rttm;
2920 		if (now - m[0].ts > wlen) {
2921 			m[0] = m[1];
2922 			m[1] = rttm;
2923 			if (now - m[0].ts > wlen)
2924 				m[0] = rttm;
2925 		}
2926 	} else if (m[1].ts == m[0].ts && elapsed > wlen / 4) {
2927 		/* Passed a quarter of the window without a new min so
2928 		 * take 2nd choice from the 2nd quarter of the window.
2929 		 */
2930 		m[2] = m[1] = rttm;
2931 	} else if (m[2].ts == m[1].ts && elapsed > wlen / 2) {
2932 		/* Passed half the window without a new min so take the 3rd
2933 		 * choice from the last half of the window.
2934 		 */
2935 		m[2] = rttm;
2936 	}
2937 }
2938 
2939 static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2940 				      long seq_rtt_us, long sack_rtt_us,
2941 				      long ca_rtt_us)
2942 {
2943 	const struct tcp_sock *tp = tcp_sk(sk);
2944 
2945 	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2946 	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
2947 	 * Karn's algorithm forbids taking RTT if some retransmitted data
2948 	 * is acked (RFC6298).
2949 	 */
2950 	if (seq_rtt_us < 0)
2951 		seq_rtt_us = sack_rtt_us;
2952 
2953 	/* RTTM Rule: A TSecr value received in a segment is used to
2954 	 * update the averaged RTT measurement only if the segment
2955 	 * acknowledges some new data, i.e., only if it advances the
2956 	 * left edge of the send window.
2957 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
2958 	 */
2959 	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2960 	    flag & FLAG_ACKED)
2961 		seq_rtt_us = ca_rtt_us = jiffies_to_usecs(tcp_time_stamp -
2962 							  tp->rx_opt.rcv_tsecr);
2963 	if (seq_rtt_us < 0)
2964 		return false;
2965 
2966 	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
2967 	 * always taken together with ACK, SACK, or TS-opts. Any negative
2968 	 * values will be skipped with the seq_rtt_us < 0 check above.
2969 	 */
2970 	tcp_update_rtt_min(sk, ca_rtt_us);
2971 	tcp_rtt_estimator(sk, seq_rtt_us);
2972 	tcp_set_rto(sk);
2973 
2974 	/* RFC6298: only reset backoff on valid RTT measurement. */
2975 	inet_csk(sk)->icsk_backoff = 0;
2976 	return true;
2977 }
2978 
2979 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2980 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
2981 {
2982 	long rtt_us = -1L;
2983 
2984 	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack.v64) {
2985 		struct skb_mstamp now;
2986 
2987 		skb_mstamp_get(&now);
2988 		rtt_us = skb_mstamp_us_delta(&now, &tcp_rsk(req)->snt_synack);
2989 	}
2990 
2991 	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us);
2992 }
2993 
2994 
2995 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2996 {
2997 	const struct inet_connection_sock *icsk = inet_csk(sk);
2998 
2999 	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3000 	tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3001 }
3002 
3003 /* Restart timer after forward progress on connection.
3004  * RFC2988 recommends to restart timer to now+rto.
3005  */
3006 void tcp_rearm_rto(struct sock *sk)
3007 {
3008 	const struct inet_connection_sock *icsk = inet_csk(sk);
3009 	struct tcp_sock *tp = tcp_sk(sk);
3010 
3011 	/* If the retrans timer is currently being used by Fast Open
3012 	 * for SYN-ACK retrans purpose, stay put.
3013 	 */
3014 	if (tp->fastopen_rsk)
3015 		return;
3016 
3017 	if (!tp->packets_out) {
3018 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3019 	} else {
3020 		u32 rto = inet_csk(sk)->icsk_rto;
3021 		/* Offset the time elapsed after installing regular RTO */
3022 		if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3023 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3024 			struct sk_buff *skb = tcp_write_queue_head(sk);
3025 			const u32 rto_time_stamp =
3026 				tcp_skb_timestamp(skb) + rto;
3027 			s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
3028 			/* delta may not be positive if the socket is locked
3029 			 * when the retrans timer fires and is rescheduled.
3030 			 */
3031 			if (delta > 0)
3032 				rto = delta;
3033 		}
3034 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3035 					  TCP_RTO_MAX);
3036 	}
3037 }
3038 
3039 /* This function is called when the delayed ER timer fires. TCP enters
3040  * fast recovery and performs fast-retransmit.
3041  */
3042 void tcp_resume_early_retransmit(struct sock *sk)
3043 {
3044 	struct tcp_sock *tp = tcp_sk(sk);
3045 
3046 	tcp_rearm_rto(sk);
3047 
3048 	/* Stop if ER is disabled after the delayed ER timer is scheduled */
3049 	if (!tp->do_early_retrans)
3050 		return;
3051 
3052 	tcp_enter_recovery(sk, false);
3053 	tcp_update_scoreboard(sk, 1);
3054 	tcp_xmit_retransmit_queue(sk);
3055 }
3056 
3057 /* If we get here, the whole TSO packet has not been acked. */
3058 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3059 {
3060 	struct tcp_sock *tp = tcp_sk(sk);
3061 	u32 packets_acked;
3062 
3063 	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3064 
3065 	packets_acked = tcp_skb_pcount(skb);
3066 	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3067 		return 0;
3068 	packets_acked -= tcp_skb_pcount(skb);
3069 
3070 	if (packets_acked) {
3071 		BUG_ON(tcp_skb_pcount(skb) == 0);
3072 		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3073 	}
3074 
3075 	return packets_acked;
3076 }
3077 
3078 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3079 			   u32 prior_snd_una)
3080 {
3081 	const struct skb_shared_info *shinfo;
3082 
3083 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3084 	if (likely(!(sk->sk_tsflags & SOF_TIMESTAMPING_TX_ACK)))
3085 		return;
3086 
3087 	shinfo = skb_shinfo(skb);
3088 	if ((shinfo->tx_flags & SKBTX_ACK_TSTAMP) &&
3089 	    between(shinfo->tskey, prior_snd_una, tcp_sk(sk)->snd_una - 1))
3090 		__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3091 }
3092 
3093 /* Remove acknowledged frames from the retransmission queue. If our packet
3094  * is before the ack sequence we can discard it as it's confirmed to have
3095  * arrived at the other end.
3096  */
3097 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3098 			       u32 prior_snd_una,
3099 			       struct tcp_sacktag_state *sack)
3100 {
3101 	const struct inet_connection_sock *icsk = inet_csk(sk);
3102 	struct skb_mstamp first_ackt, last_ackt, now;
3103 	struct tcp_sock *tp = tcp_sk(sk);
3104 	u32 prior_sacked = tp->sacked_out;
3105 	u32 reord = tp->packets_out;
3106 	bool fully_acked = true;
3107 	long sack_rtt_us = -1L;
3108 	long seq_rtt_us = -1L;
3109 	long ca_rtt_us = -1L;
3110 	struct sk_buff *skb;
3111 	u32 pkts_acked = 0;
3112 	bool rtt_update;
3113 	int flag = 0;
3114 
3115 	first_ackt.v64 = 0;
3116 
3117 	while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3118 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3119 		u8 sacked = scb->sacked;
3120 		u32 acked_pcount;
3121 
3122 		tcp_ack_tstamp(sk, skb, prior_snd_una);
3123 
3124 		/* Determine how many packets and what bytes were acked, tso and else */
3125 		if (after(scb->end_seq, tp->snd_una)) {
3126 			if (tcp_skb_pcount(skb) == 1 ||
3127 			    !after(tp->snd_una, scb->seq))
3128 				break;
3129 
3130 			acked_pcount = tcp_tso_acked(sk, skb);
3131 			if (!acked_pcount)
3132 				break;
3133 
3134 			fully_acked = false;
3135 		} else {
3136 			/* Speedup tcp_unlink_write_queue() and next loop */
3137 			prefetchw(skb->next);
3138 			acked_pcount = tcp_skb_pcount(skb);
3139 		}
3140 
3141 		if (unlikely(sacked & TCPCB_RETRANS)) {
3142 			if (sacked & TCPCB_SACKED_RETRANS)
3143 				tp->retrans_out -= acked_pcount;
3144 			flag |= FLAG_RETRANS_DATA_ACKED;
3145 		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3146 			last_ackt = skb->skb_mstamp;
3147 			WARN_ON_ONCE(last_ackt.v64 == 0);
3148 			if (!first_ackt.v64)
3149 				first_ackt = last_ackt;
3150 
3151 			reord = min(pkts_acked, reord);
3152 			if (!after(scb->end_seq, tp->high_seq))
3153 				flag |= FLAG_ORIG_SACK_ACKED;
3154 		}
3155 
3156 		if (sacked & TCPCB_SACKED_ACKED)
3157 			tp->sacked_out -= acked_pcount;
3158 		else if (tcp_is_sack(tp) && !tcp_skb_spurious_retrans(tp, skb))
3159 			tcp_rack_advance(tp, &skb->skb_mstamp, sacked);
3160 		if (sacked & TCPCB_LOST)
3161 			tp->lost_out -= acked_pcount;
3162 
3163 		tp->packets_out -= acked_pcount;
3164 		pkts_acked += acked_pcount;
3165 
3166 		/* Initial outgoing SYN's get put onto the write_queue
3167 		 * just like anything else we transmit.  It is not
3168 		 * true data, and if we misinform our callers that
3169 		 * this ACK acks real data, we will erroneously exit
3170 		 * connection startup slow start one packet too
3171 		 * quickly.  This is severely frowned upon behavior.
3172 		 */
3173 		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3174 			flag |= FLAG_DATA_ACKED;
3175 		} else {
3176 			flag |= FLAG_SYN_ACKED;
3177 			tp->retrans_stamp = 0;
3178 		}
3179 
3180 		if (!fully_acked)
3181 			break;
3182 
3183 		tcp_unlink_write_queue(skb, sk);
3184 		sk_wmem_free_skb(sk, skb);
3185 		if (unlikely(skb == tp->retransmit_skb_hint))
3186 			tp->retransmit_skb_hint = NULL;
3187 		if (unlikely(skb == tp->lost_skb_hint))
3188 			tp->lost_skb_hint = NULL;
3189 	}
3190 
3191 	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3192 		tp->snd_up = tp->snd_una;
3193 
3194 	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3195 		flag |= FLAG_SACK_RENEGING;
3196 
3197 	skb_mstamp_get(&now);
3198 	if (likely(first_ackt.v64) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3199 		seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
3200 		ca_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
3201 	}
3202 	if (sack->first_sackt.v64) {
3203 		sack_rtt_us = skb_mstamp_us_delta(&now, &sack->first_sackt);
3204 		ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt);
3205 	}
3206 
3207 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3208 					ca_rtt_us);
3209 
3210 	if (flag & FLAG_ACKED) {
3211 		tcp_rearm_rto(sk);
3212 		if (unlikely(icsk->icsk_mtup.probe_size &&
3213 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3214 			tcp_mtup_probe_success(sk);
3215 		}
3216 
3217 		if (tcp_is_reno(tp)) {
3218 			tcp_remove_reno_sacks(sk, pkts_acked);
3219 		} else {
3220 			int delta;
3221 
3222 			/* Non-retransmitted hole got filled? That's reordering */
3223 			if (reord < prior_fackets)
3224 				tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3225 
3226 			delta = tcp_is_fack(tp) ? pkts_acked :
3227 						  prior_sacked - tp->sacked_out;
3228 			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3229 		}
3230 
3231 		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3232 
3233 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3234 		   sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
3235 		/* Do not re-arm RTO if the sack RTT is measured from data sent
3236 		 * after when the head was last (re)transmitted. Otherwise the
3237 		 * timeout may continue to extend in loss recovery.
3238 		 */
3239 		tcp_rearm_rto(sk);
3240 	}
3241 
3242 	if (icsk->icsk_ca_ops->pkts_acked)
3243 		icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked, ca_rtt_us);
3244 
3245 #if FASTRETRANS_DEBUG > 0
3246 	WARN_ON((int)tp->sacked_out < 0);
3247 	WARN_ON((int)tp->lost_out < 0);
3248 	WARN_ON((int)tp->retrans_out < 0);
3249 	if (!tp->packets_out && tcp_is_sack(tp)) {
3250 		icsk = inet_csk(sk);
3251 		if (tp->lost_out) {
3252 			pr_debug("Leak l=%u %d\n",
3253 				 tp->lost_out, icsk->icsk_ca_state);
3254 			tp->lost_out = 0;
3255 		}
3256 		if (tp->sacked_out) {
3257 			pr_debug("Leak s=%u %d\n",
3258 				 tp->sacked_out, icsk->icsk_ca_state);
3259 			tp->sacked_out = 0;
3260 		}
3261 		if (tp->retrans_out) {
3262 			pr_debug("Leak r=%u %d\n",
3263 				 tp->retrans_out, icsk->icsk_ca_state);
3264 			tp->retrans_out = 0;
3265 		}
3266 	}
3267 #endif
3268 	return flag;
3269 }
3270 
3271 static void tcp_ack_probe(struct sock *sk)
3272 {
3273 	const struct tcp_sock *tp = tcp_sk(sk);
3274 	struct inet_connection_sock *icsk = inet_csk(sk);
3275 
3276 	/* Was it a usable window open? */
3277 
3278 	if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3279 		icsk->icsk_backoff = 0;
3280 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3281 		/* Socket must be waked up by subsequent tcp_data_snd_check().
3282 		 * This function is not for random using!
3283 		 */
3284 	} else {
3285 		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3286 
3287 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3288 					  when, TCP_RTO_MAX);
3289 	}
3290 }
3291 
3292 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3293 {
3294 	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3295 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3296 }
3297 
3298 /* Decide wheather to run the increase function of congestion control. */
3299 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3300 {
3301 	if (tcp_in_cwnd_reduction(sk))
3302 		return false;
3303 
3304 	/* If reordering is high then always grow cwnd whenever data is
3305 	 * delivered regardless of its ordering. Otherwise stay conservative
3306 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3307 	 * new SACK or ECE mark may first advance cwnd here and later reduce
3308 	 * cwnd in tcp_fastretrans_alert() based on more states.
3309 	 */
3310 	if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
3311 		return flag & FLAG_FORWARD_PROGRESS;
3312 
3313 	return flag & FLAG_DATA_ACKED;
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 	u64_stats_update_begin(&tp->syncp);
3334 	tp->bytes_acked += delta;
3335 	u64_stats_update_end(&tp->syncp);
3336 	tp->snd_una = ack;
3337 }
3338 
3339 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3340 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3341 {
3342 	u32 delta = seq - tp->rcv_nxt;
3343 
3344 	u64_stats_update_begin(&tp->syncp);
3345 	tp->bytes_received += delta;
3346 	u64_stats_update_end(&tp->syncp);
3347 	tp->rcv_nxt = seq;
3348 }
3349 
3350 /* Update our send window.
3351  *
3352  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3353  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3354  */
3355 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3356 				 u32 ack_seq)
3357 {
3358 	struct tcp_sock *tp = tcp_sk(sk);
3359 	int flag = 0;
3360 	u32 nwin = ntohs(tcp_hdr(skb)->window);
3361 
3362 	if (likely(!tcp_hdr(skb)->syn))
3363 		nwin <<= tp->rx_opt.snd_wscale;
3364 
3365 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3366 		flag |= FLAG_WIN_UPDATE;
3367 		tcp_update_wl(tp, ack_seq);
3368 
3369 		if (tp->snd_wnd != nwin) {
3370 			tp->snd_wnd = nwin;
3371 
3372 			/* Note, it is the only place, where
3373 			 * fast path is recovered for sending TCP.
3374 			 */
3375 			tp->pred_flags = 0;
3376 			tcp_fast_path_check(sk);
3377 
3378 			if (tcp_send_head(sk))
3379 				tcp_slow_start_after_idle_check(sk);
3380 
3381 			if (nwin > tp->max_window) {
3382 				tp->max_window = nwin;
3383 				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3384 			}
3385 		}
3386 	}
3387 
3388 	tcp_snd_una_update(tp, ack);
3389 
3390 	return flag;
3391 }
3392 
3393 /* Return true if we're currently rate-limiting out-of-window ACKs and
3394  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3395  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3396  * attacks that send repeated SYNs or ACKs for the same connection. To
3397  * do this, we do not send a duplicate SYNACK or ACK if the remote
3398  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3399  */
3400 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3401 			  int mib_idx, u32 *last_oow_ack_time)
3402 {
3403 	/* Data packets without SYNs are not likely part of an ACK loop. */
3404 	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3405 	    !tcp_hdr(skb)->syn)
3406 		goto not_rate_limited;
3407 
3408 	if (*last_oow_ack_time) {
3409 		s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
3410 
3411 		if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
3412 			NET_INC_STATS_BH(net, mib_idx);
3413 			return true;	/* rate-limited: don't send yet! */
3414 		}
3415 	}
3416 
3417 	*last_oow_ack_time = tcp_time_stamp;
3418 
3419 not_rate_limited:
3420 	return false;	/* not rate-limited: go ahead, send dupack now! */
3421 }
3422 
3423 /* RFC 5961 7 [ACK Throttling] */
3424 static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3425 {
3426 	/* unprotected vars, we dont care of overwrites */
3427 	static u32 challenge_timestamp;
3428 	static unsigned int challenge_count;
3429 	struct tcp_sock *tp = tcp_sk(sk);
3430 	u32 now;
3431 
3432 	/* First check our per-socket dupack rate limit. */
3433 	if (tcp_oow_rate_limited(sock_net(sk), skb,
3434 				 LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3435 				 &tp->last_oow_ack_time))
3436 		return;
3437 
3438 	/* Then check the check host-wide RFC 5961 rate limit. */
3439 	now = jiffies / HZ;
3440 	if (now != challenge_timestamp) {
3441 		challenge_timestamp = now;
3442 		challenge_count = 0;
3443 	}
3444 	if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
3445 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
3446 		tcp_send_ack(sk);
3447 	}
3448 }
3449 
3450 static void tcp_store_ts_recent(struct tcp_sock *tp)
3451 {
3452 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3453 	tp->rx_opt.ts_recent_stamp = get_seconds();
3454 }
3455 
3456 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3457 {
3458 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3459 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3460 		 * extra check below makes sure this can only happen
3461 		 * for pure ACK frames.  -DaveM
3462 		 *
3463 		 * Not only, also it occurs for expired timestamps.
3464 		 */
3465 
3466 		if (tcp_paws_check(&tp->rx_opt, 0))
3467 			tcp_store_ts_recent(tp);
3468 	}
3469 }
3470 
3471 /* This routine deals with acks during a TLP episode.
3472  * We mark the end of a TLP episode on receiving TLP dupack or when
3473  * ack is after tlp_high_seq.
3474  * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3475  */
3476 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3477 {
3478 	struct tcp_sock *tp = tcp_sk(sk);
3479 
3480 	if (before(ack, tp->tlp_high_seq))
3481 		return;
3482 
3483 	if (flag & FLAG_DSACKING_ACK) {
3484 		/* This DSACK means original and TLP probe arrived; no loss */
3485 		tp->tlp_high_seq = 0;
3486 	} else if (after(ack, tp->tlp_high_seq)) {
3487 		/* ACK advances: there was a loss, so reduce cwnd. Reset
3488 		 * tlp_high_seq in tcp_init_cwnd_reduction()
3489 		 */
3490 		tcp_init_cwnd_reduction(sk);
3491 		tcp_set_ca_state(sk, TCP_CA_CWR);
3492 		tcp_end_cwnd_reduction(sk);
3493 		tcp_try_keep_open(sk);
3494 		NET_INC_STATS_BH(sock_net(sk),
3495 				 LINUX_MIB_TCPLOSSPROBERECOVERY);
3496 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3497 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3498 		/* Pure dupack: original and TLP probe arrived; no loss */
3499 		tp->tlp_high_seq = 0;
3500 	}
3501 }
3502 
3503 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3504 {
3505 	const struct inet_connection_sock *icsk = inet_csk(sk);
3506 
3507 	if (icsk->icsk_ca_ops->in_ack_event)
3508 		icsk->icsk_ca_ops->in_ack_event(sk, flags);
3509 }
3510 
3511 /* This routine deals with incoming acks, but not outgoing ones. */
3512 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3513 {
3514 	struct inet_connection_sock *icsk = inet_csk(sk);
3515 	struct tcp_sock *tp = tcp_sk(sk);
3516 	struct tcp_sacktag_state sack_state;
3517 	u32 prior_snd_una = tp->snd_una;
3518 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3519 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3520 	bool is_dupack = false;
3521 	u32 prior_fackets;
3522 	int prior_packets = tp->packets_out;
3523 	const int prior_unsacked = tp->packets_out - tp->sacked_out;
3524 	int acked = 0; /* Number of packets newly acked */
3525 
3526 	sack_state.first_sackt.v64 = 0;
3527 
3528 	/* We very likely will need to access write queue head. */
3529 	prefetchw(sk->sk_write_queue.next);
3530 
3531 	/* If the ack is older than previous acks
3532 	 * then we can probably ignore it.
3533 	 */
3534 	if (before(ack, prior_snd_una)) {
3535 		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3536 		if (before(ack, prior_snd_una - tp->max_window)) {
3537 			tcp_send_challenge_ack(sk, skb);
3538 			return -1;
3539 		}
3540 		goto old_ack;
3541 	}
3542 
3543 	/* If the ack includes data we haven't sent yet, discard
3544 	 * this segment (RFC793 Section 3.9).
3545 	 */
3546 	if (after(ack, tp->snd_nxt))
3547 		goto invalid_ack;
3548 
3549 	if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
3550 	    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
3551 		tcp_rearm_rto(sk);
3552 
3553 	if (after(ack, prior_snd_una)) {
3554 		flag |= FLAG_SND_UNA_ADVANCED;
3555 		icsk->icsk_retransmits = 0;
3556 	}
3557 
3558 	prior_fackets = tp->fackets_out;
3559 
3560 	/* ts_recent update must be made after we are sure that the packet
3561 	 * is in window.
3562 	 */
3563 	if (flag & FLAG_UPDATE_TS_RECENT)
3564 		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3565 
3566 	if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3567 		/* Window is constant, pure forward advance.
3568 		 * No more checks are required.
3569 		 * Note, we use the fact that SND.UNA>=SND.WL2.
3570 		 */
3571 		tcp_update_wl(tp, ack_seq);
3572 		tcp_snd_una_update(tp, ack);
3573 		flag |= FLAG_WIN_UPDATE;
3574 
3575 		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3576 
3577 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3578 	} else {
3579 		u32 ack_ev_flags = CA_ACK_SLOWPATH;
3580 
3581 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3582 			flag |= FLAG_DATA;
3583 		else
3584 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3585 
3586 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3587 
3588 		if (TCP_SKB_CB(skb)->sacked)
3589 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3590 							&sack_state);
3591 
3592 		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3593 			flag |= FLAG_ECE;
3594 			ack_ev_flags |= CA_ACK_ECE;
3595 		}
3596 
3597 		if (flag & FLAG_WIN_UPDATE)
3598 			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3599 
3600 		tcp_in_ack_event(sk, ack_ev_flags);
3601 	}
3602 
3603 	/* We passed data and got it acked, remove any soft error
3604 	 * log. Something worked...
3605 	 */
3606 	sk->sk_err_soft = 0;
3607 	icsk->icsk_probes_out = 0;
3608 	tp->rcv_tstamp = tcp_time_stamp;
3609 	if (!prior_packets)
3610 		goto no_queue;
3611 
3612 	/* See if we can take anything off of the retransmit queue. */
3613 	acked = tp->packets_out;
3614 	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una,
3615 				    &sack_state);
3616 	acked -= tp->packets_out;
3617 
3618 	if (tcp_ack_is_dubious(sk, flag)) {
3619 		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3620 		tcp_fastretrans_alert(sk, acked, prior_unsacked,
3621 				      is_dupack, flag);
3622 	}
3623 	if (tp->tlp_high_seq)
3624 		tcp_process_tlp_ack(sk, ack, flag);
3625 
3626 	/* Advance cwnd if state allows */
3627 	if (tcp_may_raise_cwnd(sk, flag))
3628 		tcp_cong_avoid(sk, ack, acked);
3629 
3630 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
3631 		struct dst_entry *dst = __sk_dst_get(sk);
3632 		if (dst)
3633 			dst_confirm(dst);
3634 	}
3635 
3636 	if (icsk->icsk_pending == ICSK_TIME_RETRANS)
3637 		tcp_schedule_loss_probe(sk);
3638 	tcp_update_pacing_rate(sk);
3639 	return 1;
3640 
3641 no_queue:
3642 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3643 	if (flag & FLAG_DSACKING_ACK)
3644 		tcp_fastretrans_alert(sk, acked, prior_unsacked,
3645 				      is_dupack, flag);
3646 	/* If this ack opens up a zero window, clear backoff.  It was
3647 	 * being used to time the probes, and is probably far higher than
3648 	 * it needs to be for normal retransmission.
3649 	 */
3650 	if (tcp_send_head(sk))
3651 		tcp_ack_probe(sk);
3652 
3653 	if (tp->tlp_high_seq)
3654 		tcp_process_tlp_ack(sk, ack, flag);
3655 	return 1;
3656 
3657 invalid_ack:
3658 	SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3659 	return -1;
3660 
3661 old_ack:
3662 	/* If data was SACKed, tag it and see if we should send more data.
3663 	 * If data was DSACKed, see if we can undo a cwnd reduction.
3664 	 */
3665 	if (TCP_SKB_CB(skb)->sacked) {
3666 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3667 						&sack_state);
3668 		tcp_fastretrans_alert(sk, acked, prior_unsacked,
3669 				      is_dupack, flag);
3670 	}
3671 
3672 	SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3673 	return 0;
3674 }
3675 
3676 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3677 				      bool syn, struct tcp_fastopen_cookie *foc,
3678 				      bool exp_opt)
3679 {
3680 	/* Valid only in SYN or SYN-ACK with an even length.  */
3681 	if (!foc || !syn || len < 0 || (len & 1))
3682 		return;
3683 
3684 	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3685 	    len <= TCP_FASTOPEN_COOKIE_MAX)
3686 		memcpy(foc->val, cookie, len);
3687 	else if (len != 0)
3688 		len = -1;
3689 	foc->len = len;
3690 	foc->exp = exp_opt;
3691 }
3692 
3693 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3694  * But, this can also be called on packets in the established flow when
3695  * the fast version below fails.
3696  */
3697 void tcp_parse_options(const struct sk_buff *skb,
3698 		       struct tcp_options_received *opt_rx, int estab,
3699 		       struct tcp_fastopen_cookie *foc)
3700 {
3701 	const unsigned char *ptr;
3702 	const struct tcphdr *th = tcp_hdr(skb);
3703 	int length = (th->doff * 4) - sizeof(struct tcphdr);
3704 
3705 	ptr = (const unsigned char *)(th + 1);
3706 	opt_rx->saw_tstamp = 0;
3707 
3708 	while (length > 0) {
3709 		int opcode = *ptr++;
3710 		int opsize;
3711 
3712 		switch (opcode) {
3713 		case TCPOPT_EOL:
3714 			return;
3715 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
3716 			length--;
3717 			continue;
3718 		default:
3719 			opsize = *ptr++;
3720 			if (opsize < 2) /* "silly options" */
3721 				return;
3722 			if (opsize > length)
3723 				return;	/* don't parse partial options */
3724 			switch (opcode) {
3725 			case TCPOPT_MSS:
3726 				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3727 					u16 in_mss = get_unaligned_be16(ptr);
3728 					if (in_mss) {
3729 						if (opt_rx->user_mss &&
3730 						    opt_rx->user_mss < in_mss)
3731 							in_mss = opt_rx->user_mss;
3732 						opt_rx->mss_clamp = in_mss;
3733 					}
3734 				}
3735 				break;
3736 			case TCPOPT_WINDOW:
3737 				if (opsize == TCPOLEN_WINDOW && th->syn &&
3738 				    !estab && sysctl_tcp_window_scaling) {
3739 					__u8 snd_wscale = *(__u8 *)ptr;
3740 					opt_rx->wscale_ok = 1;
3741 					if (snd_wscale > 14) {
3742 						net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3743 								     __func__,
3744 								     snd_wscale);
3745 						snd_wscale = 14;
3746 					}
3747 					opt_rx->snd_wscale = snd_wscale;
3748 				}
3749 				break;
3750 			case TCPOPT_TIMESTAMP:
3751 				if ((opsize == TCPOLEN_TIMESTAMP) &&
3752 				    ((estab && opt_rx->tstamp_ok) ||
3753 				     (!estab && sysctl_tcp_timestamps))) {
3754 					opt_rx->saw_tstamp = 1;
3755 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3756 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3757 				}
3758 				break;
3759 			case TCPOPT_SACK_PERM:
3760 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3761 				    !estab && sysctl_tcp_sack) {
3762 					opt_rx->sack_ok = TCP_SACK_SEEN;
3763 					tcp_sack_reset(opt_rx);
3764 				}
3765 				break;
3766 
3767 			case TCPOPT_SACK:
3768 				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3769 				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3770 				   opt_rx->sack_ok) {
3771 					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3772 				}
3773 				break;
3774 #ifdef CONFIG_TCP_MD5SIG
3775 			case TCPOPT_MD5SIG:
3776 				/*
3777 				 * The MD5 Hash has already been
3778 				 * checked (see tcp_v{4,6}_do_rcv()).
3779 				 */
3780 				break;
3781 #endif
3782 			case TCPOPT_FASTOPEN:
3783 				tcp_parse_fastopen_option(
3784 					opsize - TCPOLEN_FASTOPEN_BASE,
3785 					ptr, th->syn, foc, false);
3786 				break;
3787 
3788 			case TCPOPT_EXP:
3789 				/* Fast Open option shares code 254 using a
3790 				 * 16 bits magic number.
3791 				 */
3792 				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3793 				    get_unaligned_be16(ptr) ==
3794 				    TCPOPT_FASTOPEN_MAGIC)
3795 					tcp_parse_fastopen_option(opsize -
3796 						TCPOLEN_EXP_FASTOPEN_BASE,
3797 						ptr + 2, th->syn, foc, true);
3798 				break;
3799 
3800 			}
3801 			ptr += opsize-2;
3802 			length -= opsize;
3803 		}
3804 	}
3805 }
3806 EXPORT_SYMBOL(tcp_parse_options);
3807 
3808 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3809 {
3810 	const __be32 *ptr = (const __be32 *)(th + 1);
3811 
3812 	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3813 			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3814 		tp->rx_opt.saw_tstamp = 1;
3815 		++ptr;
3816 		tp->rx_opt.rcv_tsval = ntohl(*ptr);
3817 		++ptr;
3818 		if (*ptr)
3819 			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3820 		else
3821 			tp->rx_opt.rcv_tsecr = 0;
3822 		return true;
3823 	}
3824 	return false;
3825 }
3826 
3827 /* Fast parse options. This hopes to only see timestamps.
3828  * If it is wrong it falls back on tcp_parse_options().
3829  */
3830 static bool tcp_fast_parse_options(const struct sk_buff *skb,
3831 				   const struct tcphdr *th, struct tcp_sock *tp)
3832 {
3833 	/* In the spirit of fast parsing, compare doff directly to constant
3834 	 * values.  Because equality is used, short doff can be ignored here.
3835 	 */
3836 	if (th->doff == (sizeof(*th) / 4)) {
3837 		tp->rx_opt.saw_tstamp = 0;
3838 		return false;
3839 	} else if (tp->rx_opt.tstamp_ok &&
3840 		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3841 		if (tcp_parse_aligned_timestamp(tp, th))
3842 			return true;
3843 	}
3844 
3845 	tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
3846 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3847 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3848 
3849 	return true;
3850 }
3851 
3852 #ifdef CONFIG_TCP_MD5SIG
3853 /*
3854  * Parse MD5 Signature option
3855  */
3856 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3857 {
3858 	int length = (th->doff << 2) - sizeof(*th);
3859 	const u8 *ptr = (const u8 *)(th + 1);
3860 
3861 	/* If the TCP option is too short, we can short cut */
3862 	if (length < TCPOLEN_MD5SIG)
3863 		return NULL;
3864 
3865 	while (length > 0) {
3866 		int opcode = *ptr++;
3867 		int opsize;
3868 
3869 		switch (opcode) {
3870 		case TCPOPT_EOL:
3871 			return NULL;
3872 		case TCPOPT_NOP:
3873 			length--;
3874 			continue;
3875 		default:
3876 			opsize = *ptr++;
3877 			if (opsize < 2 || opsize > length)
3878 				return NULL;
3879 			if (opcode == TCPOPT_MD5SIG)
3880 				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3881 		}
3882 		ptr += opsize - 2;
3883 		length -= opsize;
3884 	}
3885 	return NULL;
3886 }
3887 EXPORT_SYMBOL(tcp_parse_md5sig_option);
3888 #endif
3889 
3890 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3891  *
3892  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3893  * it can pass through stack. So, the following predicate verifies that
3894  * this segment is not used for anything but congestion avoidance or
3895  * fast retransmit. Moreover, we even are able to eliminate most of such
3896  * second order effects, if we apply some small "replay" window (~RTO)
3897  * to timestamp space.
3898  *
3899  * All these measures still do not guarantee that we reject wrapped ACKs
3900  * on networks with high bandwidth, when sequence space is recycled fastly,
3901  * but it guarantees that such events will be very rare and do not affect
3902  * connection seriously. This doesn't look nice, but alas, PAWS is really
3903  * buggy extension.
3904  *
3905  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3906  * states that events when retransmit arrives after original data are rare.
3907  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3908  * the biggest problem on large power networks even with minor reordering.
3909  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3910  * up to bandwidth of 18Gigabit/sec. 8) ]
3911  */
3912 
3913 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3914 {
3915 	const struct tcp_sock *tp = tcp_sk(sk);
3916 	const struct tcphdr *th = tcp_hdr(skb);
3917 	u32 seq = TCP_SKB_CB(skb)->seq;
3918 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3919 
3920 	return (/* 1. Pure ACK with correct sequence number. */
3921 		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3922 
3923 		/* 2. ... and duplicate ACK. */
3924 		ack == tp->snd_una &&
3925 
3926 		/* 3. ... and does not update window. */
3927 		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3928 
3929 		/* 4. ... and sits in replay window. */
3930 		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3931 }
3932 
3933 static inline bool tcp_paws_discard(const struct sock *sk,
3934 				   const struct sk_buff *skb)
3935 {
3936 	const struct tcp_sock *tp = tcp_sk(sk);
3937 
3938 	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3939 	       !tcp_disordered_ack(sk, skb);
3940 }
3941 
3942 /* Check segment sequence number for validity.
3943  *
3944  * Segment controls are considered valid, if the segment
3945  * fits to the window after truncation to the window. Acceptability
3946  * of data (and SYN, FIN, of course) is checked separately.
3947  * See tcp_data_queue(), for example.
3948  *
3949  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3950  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3951  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3952  * (borrowed from freebsd)
3953  */
3954 
3955 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
3956 {
3957 	return	!before(end_seq, tp->rcv_wup) &&
3958 		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3959 }
3960 
3961 /* When we get a reset we do this. */
3962 void tcp_reset(struct sock *sk)
3963 {
3964 	/* We want the right error as BSD sees it (and indeed as we do). */
3965 	switch (sk->sk_state) {
3966 	case TCP_SYN_SENT:
3967 		sk->sk_err = ECONNREFUSED;
3968 		break;
3969 	case TCP_CLOSE_WAIT:
3970 		sk->sk_err = EPIPE;
3971 		break;
3972 	case TCP_CLOSE:
3973 		return;
3974 	default:
3975 		sk->sk_err = ECONNRESET;
3976 	}
3977 	/* This barrier is coupled with smp_rmb() in tcp_poll() */
3978 	smp_wmb();
3979 
3980 	if (!sock_flag(sk, SOCK_DEAD))
3981 		sk->sk_error_report(sk);
3982 
3983 	tcp_done(sk);
3984 }
3985 
3986 /*
3987  * 	Process the FIN bit. This now behaves as it is supposed to work
3988  *	and the FIN takes effect when it is validly part of sequence
3989  *	space. Not before when we get holes.
3990  *
3991  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3992  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
3993  *	TIME-WAIT)
3994  *
3995  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
3996  *	close and we go into CLOSING (and later onto TIME-WAIT)
3997  *
3998  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3999  */
4000 static void tcp_fin(struct sock *sk)
4001 {
4002 	struct tcp_sock *tp = tcp_sk(sk);
4003 
4004 	inet_csk_schedule_ack(sk);
4005 
4006 	sk->sk_shutdown |= RCV_SHUTDOWN;
4007 	sock_set_flag(sk, SOCK_DONE);
4008 
4009 	switch (sk->sk_state) {
4010 	case TCP_SYN_RECV:
4011 	case TCP_ESTABLISHED:
4012 		/* Move to CLOSE_WAIT */
4013 		tcp_set_state(sk, TCP_CLOSE_WAIT);
4014 		inet_csk(sk)->icsk_ack.pingpong = 1;
4015 		break;
4016 
4017 	case TCP_CLOSE_WAIT:
4018 	case TCP_CLOSING:
4019 		/* Received a retransmission of the FIN, do
4020 		 * nothing.
4021 		 */
4022 		break;
4023 	case TCP_LAST_ACK:
4024 		/* RFC793: Remain in the LAST-ACK state. */
4025 		break;
4026 
4027 	case TCP_FIN_WAIT1:
4028 		/* This case occurs when a simultaneous close
4029 		 * happens, we must ack the received FIN and
4030 		 * enter the CLOSING state.
4031 		 */
4032 		tcp_send_ack(sk);
4033 		tcp_set_state(sk, TCP_CLOSING);
4034 		break;
4035 	case TCP_FIN_WAIT2:
4036 		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4037 		tcp_send_ack(sk);
4038 		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4039 		break;
4040 	default:
4041 		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4042 		 * cases we should never reach this piece of code.
4043 		 */
4044 		pr_err("%s: Impossible, sk->sk_state=%d\n",
4045 		       __func__, sk->sk_state);
4046 		break;
4047 	}
4048 
4049 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4050 	 * Probably, we should reset in this case. For now drop them.
4051 	 */
4052 	__skb_queue_purge(&tp->out_of_order_queue);
4053 	if (tcp_is_sack(tp))
4054 		tcp_sack_reset(&tp->rx_opt);
4055 	sk_mem_reclaim(sk);
4056 
4057 	if (!sock_flag(sk, SOCK_DEAD)) {
4058 		sk->sk_state_change(sk);
4059 
4060 		/* Do not send POLL_HUP for half duplex close. */
4061 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4062 		    sk->sk_state == TCP_CLOSE)
4063 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4064 		else
4065 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4066 	}
4067 }
4068 
4069 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4070 				  u32 end_seq)
4071 {
4072 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4073 		if (before(seq, sp->start_seq))
4074 			sp->start_seq = seq;
4075 		if (after(end_seq, sp->end_seq))
4076 			sp->end_seq = end_seq;
4077 		return true;
4078 	}
4079 	return false;
4080 }
4081 
4082 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4083 {
4084 	struct tcp_sock *tp = tcp_sk(sk);
4085 
4086 	if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4087 		int mib_idx;
4088 
4089 		if (before(seq, tp->rcv_nxt))
4090 			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4091 		else
4092 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4093 
4094 		NET_INC_STATS_BH(sock_net(sk), mib_idx);
4095 
4096 		tp->rx_opt.dsack = 1;
4097 		tp->duplicate_sack[0].start_seq = seq;
4098 		tp->duplicate_sack[0].end_seq = end_seq;
4099 	}
4100 }
4101 
4102 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4103 {
4104 	struct tcp_sock *tp = tcp_sk(sk);
4105 
4106 	if (!tp->rx_opt.dsack)
4107 		tcp_dsack_set(sk, seq, end_seq);
4108 	else
4109 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4110 }
4111 
4112 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4113 {
4114 	struct tcp_sock *tp = tcp_sk(sk);
4115 
4116 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4117 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4118 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4119 		tcp_enter_quickack_mode(sk);
4120 
4121 		if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4122 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4123 
4124 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4125 				end_seq = tp->rcv_nxt;
4126 			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4127 		}
4128 	}
4129 
4130 	tcp_send_ack(sk);
4131 }
4132 
4133 /* These routines update the SACK block as out-of-order packets arrive or
4134  * in-order packets close up the sequence space.
4135  */
4136 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4137 {
4138 	int this_sack;
4139 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4140 	struct tcp_sack_block *swalk = sp + 1;
4141 
4142 	/* See if the recent change to the first SACK eats into
4143 	 * or hits the sequence space of other SACK blocks, if so coalesce.
4144 	 */
4145 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4146 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4147 			int i;
4148 
4149 			/* Zap SWALK, by moving every further SACK up by one slot.
4150 			 * Decrease num_sacks.
4151 			 */
4152 			tp->rx_opt.num_sacks--;
4153 			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4154 				sp[i] = sp[i + 1];
4155 			continue;
4156 		}
4157 		this_sack++, swalk++;
4158 	}
4159 }
4160 
4161 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4162 {
4163 	struct tcp_sock *tp = tcp_sk(sk);
4164 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4165 	int cur_sacks = tp->rx_opt.num_sacks;
4166 	int this_sack;
4167 
4168 	if (!cur_sacks)
4169 		goto new_sack;
4170 
4171 	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4172 		if (tcp_sack_extend(sp, seq, end_seq)) {
4173 			/* Rotate this_sack to the first one. */
4174 			for (; this_sack > 0; this_sack--, sp--)
4175 				swap(*sp, *(sp - 1));
4176 			if (cur_sacks > 1)
4177 				tcp_sack_maybe_coalesce(tp);
4178 			return;
4179 		}
4180 	}
4181 
4182 	/* Could not find an adjacent existing SACK, build a new one,
4183 	 * put it at the front, and shift everyone else down.  We
4184 	 * always know there is at least one SACK present already here.
4185 	 *
4186 	 * If the sack array is full, forget about the last one.
4187 	 */
4188 	if (this_sack >= TCP_NUM_SACKS) {
4189 		this_sack--;
4190 		tp->rx_opt.num_sacks--;
4191 		sp--;
4192 	}
4193 	for (; this_sack > 0; this_sack--, sp--)
4194 		*sp = *(sp - 1);
4195 
4196 new_sack:
4197 	/* Build the new head SACK, and we're done. */
4198 	sp->start_seq = seq;
4199 	sp->end_seq = end_seq;
4200 	tp->rx_opt.num_sacks++;
4201 }
4202 
4203 /* RCV.NXT advances, some SACKs should be eaten. */
4204 
4205 static void tcp_sack_remove(struct tcp_sock *tp)
4206 {
4207 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4208 	int num_sacks = tp->rx_opt.num_sacks;
4209 	int this_sack;
4210 
4211 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4212 	if (skb_queue_empty(&tp->out_of_order_queue)) {
4213 		tp->rx_opt.num_sacks = 0;
4214 		return;
4215 	}
4216 
4217 	for (this_sack = 0; this_sack < num_sacks;) {
4218 		/* Check if the start of the sack is covered by RCV.NXT. */
4219 		if (!before(tp->rcv_nxt, sp->start_seq)) {
4220 			int i;
4221 
4222 			/* RCV.NXT must cover all the block! */
4223 			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4224 
4225 			/* Zap this SACK, by moving forward any other SACKS. */
4226 			for (i = this_sack+1; i < num_sacks; i++)
4227 				tp->selective_acks[i-1] = tp->selective_acks[i];
4228 			num_sacks--;
4229 			continue;
4230 		}
4231 		this_sack++;
4232 		sp++;
4233 	}
4234 	tp->rx_opt.num_sacks = num_sacks;
4235 }
4236 
4237 /**
4238  * tcp_try_coalesce - try to merge skb to prior one
4239  * @sk: socket
4240  * @to: prior buffer
4241  * @from: buffer to add in queue
4242  * @fragstolen: pointer to boolean
4243  *
4244  * Before queueing skb @from after @to, try to merge them
4245  * to reduce overall memory use and queue lengths, if cost is small.
4246  * Packets in ofo or receive queues can stay a long time.
4247  * Better try to coalesce them right now to avoid future collapses.
4248  * Returns true if caller should free @from instead of queueing it
4249  */
4250 static bool tcp_try_coalesce(struct sock *sk,
4251 			     struct sk_buff *to,
4252 			     struct sk_buff *from,
4253 			     bool *fragstolen)
4254 {
4255 	int delta;
4256 
4257 	*fragstolen = false;
4258 
4259 	/* Its possible this segment overlaps with prior segment in queue */
4260 	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4261 		return false;
4262 
4263 	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4264 		return false;
4265 
4266 	atomic_add(delta, &sk->sk_rmem_alloc);
4267 	sk_mem_charge(sk, delta);
4268 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4269 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4270 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4271 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4272 	return true;
4273 }
4274 
4275 /* This one checks to see if we can put data from the
4276  * out_of_order queue into the receive_queue.
4277  */
4278 static void tcp_ofo_queue(struct sock *sk)
4279 {
4280 	struct tcp_sock *tp = tcp_sk(sk);
4281 	__u32 dsack_high = tp->rcv_nxt;
4282 	struct sk_buff *skb, *tail;
4283 	bool fragstolen, eaten;
4284 
4285 	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4286 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4287 			break;
4288 
4289 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4290 			__u32 dsack = dsack_high;
4291 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4292 				dsack_high = TCP_SKB_CB(skb)->end_seq;
4293 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4294 		}
4295 
4296 		__skb_unlink(skb, &tp->out_of_order_queue);
4297 		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4298 			SOCK_DEBUG(sk, "ofo packet was already received\n");
4299 			__kfree_skb(skb);
4300 			continue;
4301 		}
4302 		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4303 			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4304 			   TCP_SKB_CB(skb)->end_seq);
4305 
4306 		tail = skb_peek_tail(&sk->sk_receive_queue);
4307 		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4308 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4309 		if (!eaten)
4310 			__skb_queue_tail(&sk->sk_receive_queue, skb);
4311 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4312 			tcp_fin(sk);
4313 		if (eaten)
4314 			kfree_skb_partial(skb, fragstolen);
4315 	}
4316 }
4317 
4318 static bool tcp_prune_ofo_queue(struct sock *sk);
4319 static int tcp_prune_queue(struct sock *sk);
4320 
4321 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4322 				 unsigned int size)
4323 {
4324 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4325 	    !sk_rmem_schedule(sk, skb, size)) {
4326 
4327 		if (tcp_prune_queue(sk) < 0)
4328 			return -1;
4329 
4330 		if (!sk_rmem_schedule(sk, skb, size)) {
4331 			if (!tcp_prune_ofo_queue(sk))
4332 				return -1;
4333 
4334 			if (!sk_rmem_schedule(sk, skb, size))
4335 				return -1;
4336 		}
4337 	}
4338 	return 0;
4339 }
4340 
4341 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4342 {
4343 	struct tcp_sock *tp = tcp_sk(sk);
4344 	struct sk_buff *skb1;
4345 	u32 seq, end_seq;
4346 
4347 	tcp_ecn_check_ce(tp, skb);
4348 
4349 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4350 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFODROP);
4351 		__kfree_skb(skb);
4352 		return;
4353 	}
4354 
4355 	/* Disable header prediction. */
4356 	tp->pred_flags = 0;
4357 	inet_csk_schedule_ack(sk);
4358 
4359 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4360 	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4361 		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4362 
4363 	skb1 = skb_peek_tail(&tp->out_of_order_queue);
4364 	if (!skb1) {
4365 		/* Initial out of order segment, build 1 SACK. */
4366 		if (tcp_is_sack(tp)) {
4367 			tp->rx_opt.num_sacks = 1;
4368 			tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4369 			tp->selective_acks[0].end_seq =
4370 						TCP_SKB_CB(skb)->end_seq;
4371 		}
4372 		__skb_queue_head(&tp->out_of_order_queue, skb);
4373 		goto end;
4374 	}
4375 
4376 	seq = TCP_SKB_CB(skb)->seq;
4377 	end_seq = TCP_SKB_CB(skb)->end_seq;
4378 
4379 	if (seq == TCP_SKB_CB(skb1)->end_seq) {
4380 		bool fragstolen;
4381 
4382 		if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4383 			__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4384 		} else {
4385 			tcp_grow_window(sk, skb);
4386 			kfree_skb_partial(skb, fragstolen);
4387 			skb = NULL;
4388 		}
4389 
4390 		if (!tp->rx_opt.num_sacks ||
4391 		    tp->selective_acks[0].end_seq != seq)
4392 			goto add_sack;
4393 
4394 		/* Common case: data arrive in order after hole. */
4395 		tp->selective_acks[0].end_seq = end_seq;
4396 		goto end;
4397 	}
4398 
4399 	/* Find place to insert this segment. */
4400 	while (1) {
4401 		if (!after(TCP_SKB_CB(skb1)->seq, seq))
4402 			break;
4403 		if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4404 			skb1 = NULL;
4405 			break;
4406 		}
4407 		skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4408 	}
4409 
4410 	/* Do skb overlap to previous one? */
4411 	if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4412 		if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4413 			/* All the bits are present. Drop. */
4414 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4415 			__kfree_skb(skb);
4416 			skb = NULL;
4417 			tcp_dsack_set(sk, seq, end_seq);
4418 			goto add_sack;
4419 		}
4420 		if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4421 			/* Partial overlap. */
4422 			tcp_dsack_set(sk, seq,
4423 				      TCP_SKB_CB(skb1)->end_seq);
4424 		} else {
4425 			if (skb_queue_is_first(&tp->out_of_order_queue,
4426 					       skb1))
4427 				skb1 = NULL;
4428 			else
4429 				skb1 = skb_queue_prev(
4430 					&tp->out_of_order_queue,
4431 					skb1);
4432 		}
4433 	}
4434 	if (!skb1)
4435 		__skb_queue_head(&tp->out_of_order_queue, skb);
4436 	else
4437 		__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4438 
4439 	/* And clean segments covered by new one as whole. */
4440 	while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4441 		skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4442 
4443 		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4444 			break;
4445 		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4446 			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4447 					 end_seq);
4448 			break;
4449 		}
4450 		__skb_unlink(skb1, &tp->out_of_order_queue);
4451 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4452 				 TCP_SKB_CB(skb1)->end_seq);
4453 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4454 		__kfree_skb(skb1);
4455 	}
4456 
4457 add_sack:
4458 	if (tcp_is_sack(tp))
4459 		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4460 end:
4461 	if (skb) {
4462 		tcp_grow_window(sk, skb);
4463 		skb_set_owner_r(skb, sk);
4464 	}
4465 }
4466 
4467 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4468 		  bool *fragstolen)
4469 {
4470 	int eaten;
4471 	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4472 
4473 	__skb_pull(skb, hdrlen);
4474 	eaten = (tail &&
4475 		 tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4476 	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4477 	if (!eaten) {
4478 		__skb_queue_tail(&sk->sk_receive_queue, skb);
4479 		skb_set_owner_r(skb, sk);
4480 	}
4481 	return eaten;
4482 }
4483 
4484 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4485 {
4486 	struct sk_buff *skb;
4487 	int err = -ENOMEM;
4488 	int data_len = 0;
4489 	bool fragstolen;
4490 
4491 	if (size == 0)
4492 		return 0;
4493 
4494 	if (size > PAGE_SIZE) {
4495 		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4496 
4497 		data_len = npages << PAGE_SHIFT;
4498 		size = data_len + (size & ~PAGE_MASK);
4499 	}
4500 	skb = alloc_skb_with_frags(size - data_len, data_len,
4501 				   PAGE_ALLOC_COSTLY_ORDER,
4502 				   &err, sk->sk_allocation);
4503 	if (!skb)
4504 		goto err;
4505 
4506 	skb_put(skb, size - data_len);
4507 	skb->data_len = data_len;
4508 	skb->len = size;
4509 
4510 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4511 		goto err_free;
4512 
4513 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4514 	if (err)
4515 		goto err_free;
4516 
4517 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4518 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4519 	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4520 
4521 	if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
4522 		WARN_ON_ONCE(fragstolen); /* should not happen */
4523 		__kfree_skb(skb);
4524 	}
4525 	return size;
4526 
4527 err_free:
4528 	kfree_skb(skb);
4529 err:
4530 	return err;
4531 
4532 }
4533 
4534 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4535 {
4536 	struct tcp_sock *tp = tcp_sk(sk);
4537 	int eaten = -1;
4538 	bool fragstolen = false;
4539 
4540 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4541 		goto drop;
4542 
4543 	skb_dst_drop(skb);
4544 	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
4545 
4546 	tcp_ecn_accept_cwr(tp, skb);
4547 
4548 	tp->rx_opt.dsack = 0;
4549 
4550 	/*  Queue data for delivery to the user.
4551 	 *  Packets in sequence go to the receive queue.
4552 	 *  Out of sequence packets to the out_of_order_queue.
4553 	 */
4554 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4555 		if (tcp_receive_window(tp) == 0)
4556 			goto out_of_window;
4557 
4558 		/* Ok. In sequence. In window. */
4559 		if (tp->ucopy.task == current &&
4560 		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4561 		    sock_owned_by_user(sk) && !tp->urg_data) {
4562 			int chunk = min_t(unsigned int, skb->len,
4563 					  tp->ucopy.len);
4564 
4565 			__set_current_state(TASK_RUNNING);
4566 
4567 			local_bh_enable();
4568 			if (!skb_copy_datagram_msg(skb, 0, tp->ucopy.msg, chunk)) {
4569 				tp->ucopy.len -= chunk;
4570 				tp->copied_seq += chunk;
4571 				eaten = (chunk == skb->len);
4572 				tcp_rcv_space_adjust(sk);
4573 			}
4574 			local_bh_disable();
4575 		}
4576 
4577 		if (eaten <= 0) {
4578 queue_and_out:
4579 			if (eaten < 0) {
4580 				if (skb_queue_len(&sk->sk_receive_queue) == 0)
4581 					sk_forced_mem_schedule(sk, skb->truesize);
4582 				else if (tcp_try_rmem_schedule(sk, skb, skb->truesize))
4583 					goto drop;
4584 			}
4585 			eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
4586 		}
4587 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4588 		if (skb->len)
4589 			tcp_event_data_recv(sk, skb);
4590 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4591 			tcp_fin(sk);
4592 
4593 		if (!skb_queue_empty(&tp->out_of_order_queue)) {
4594 			tcp_ofo_queue(sk);
4595 
4596 			/* RFC2581. 4.2. SHOULD send immediate ACK, when
4597 			 * gap in queue is filled.
4598 			 */
4599 			if (skb_queue_empty(&tp->out_of_order_queue))
4600 				inet_csk(sk)->icsk_ack.pingpong = 0;
4601 		}
4602 
4603 		if (tp->rx_opt.num_sacks)
4604 			tcp_sack_remove(tp);
4605 
4606 		tcp_fast_path_check(sk);
4607 
4608 		if (eaten > 0)
4609 			kfree_skb_partial(skb, fragstolen);
4610 		if (!sock_flag(sk, SOCK_DEAD))
4611 			sk->sk_data_ready(sk);
4612 		return;
4613 	}
4614 
4615 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4616 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
4617 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4618 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4619 
4620 out_of_window:
4621 		tcp_enter_quickack_mode(sk);
4622 		inet_csk_schedule_ack(sk);
4623 drop:
4624 		__kfree_skb(skb);
4625 		return;
4626 	}
4627 
4628 	/* Out of window. F.e. zero window probe. */
4629 	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4630 		goto out_of_window;
4631 
4632 	tcp_enter_quickack_mode(sk);
4633 
4634 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4635 		/* Partial packet, seq < rcv_next < end_seq */
4636 		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4637 			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4638 			   TCP_SKB_CB(skb)->end_seq);
4639 
4640 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4641 
4642 		/* If window is closed, drop tail of packet. But after
4643 		 * remembering D-SACK for its head made in previous line.
4644 		 */
4645 		if (!tcp_receive_window(tp))
4646 			goto out_of_window;
4647 		goto queue_and_out;
4648 	}
4649 
4650 	tcp_data_queue_ofo(sk, skb);
4651 }
4652 
4653 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4654 					struct sk_buff_head *list)
4655 {
4656 	struct sk_buff *next = NULL;
4657 
4658 	if (!skb_queue_is_last(list, skb))
4659 		next = skb_queue_next(list, skb);
4660 
4661 	__skb_unlink(skb, list);
4662 	__kfree_skb(skb);
4663 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4664 
4665 	return next;
4666 }
4667 
4668 /* Collapse contiguous sequence of skbs head..tail with
4669  * sequence numbers start..end.
4670  *
4671  * If tail is NULL, this means until the end of the list.
4672  *
4673  * Segments with FIN/SYN are not collapsed (only because this
4674  * simplifies code)
4675  */
4676 static void
4677 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4678 	     struct sk_buff *head, struct sk_buff *tail,
4679 	     u32 start, u32 end)
4680 {
4681 	struct sk_buff *skb, *n;
4682 	bool end_of_skbs;
4683 
4684 	/* First, check that queue is collapsible and find
4685 	 * the point where collapsing can be useful. */
4686 	skb = head;
4687 restart:
4688 	end_of_skbs = true;
4689 	skb_queue_walk_from_safe(list, skb, n) {
4690 		if (skb == tail)
4691 			break;
4692 		/* No new bits? It is possible on ofo queue. */
4693 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4694 			skb = tcp_collapse_one(sk, skb, list);
4695 			if (!skb)
4696 				break;
4697 			goto restart;
4698 		}
4699 
4700 		/* The first skb to collapse is:
4701 		 * - not SYN/FIN and
4702 		 * - bloated or contains data before "start" or
4703 		 *   overlaps to the next one.
4704 		 */
4705 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4706 		    (tcp_win_from_space(skb->truesize) > skb->len ||
4707 		     before(TCP_SKB_CB(skb)->seq, start))) {
4708 			end_of_skbs = false;
4709 			break;
4710 		}
4711 
4712 		if (!skb_queue_is_last(list, skb)) {
4713 			struct sk_buff *next = skb_queue_next(list, skb);
4714 			if (next != tail &&
4715 			    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4716 				end_of_skbs = false;
4717 				break;
4718 			}
4719 		}
4720 
4721 		/* Decided to skip this, advance start seq. */
4722 		start = TCP_SKB_CB(skb)->end_seq;
4723 	}
4724 	if (end_of_skbs ||
4725 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4726 		return;
4727 
4728 	while (before(start, end)) {
4729 		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4730 		struct sk_buff *nskb;
4731 
4732 		nskb = alloc_skb(copy, GFP_ATOMIC);
4733 		if (!nskb)
4734 			return;
4735 
4736 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4737 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4738 		__skb_queue_before(list, skb, nskb);
4739 		skb_set_owner_r(nskb, sk);
4740 
4741 		/* Copy data, releasing collapsed skbs. */
4742 		while (copy > 0) {
4743 			int offset = start - TCP_SKB_CB(skb)->seq;
4744 			int size = TCP_SKB_CB(skb)->end_seq - start;
4745 
4746 			BUG_ON(offset < 0);
4747 			if (size > 0) {
4748 				size = min(copy, size);
4749 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4750 					BUG();
4751 				TCP_SKB_CB(nskb)->end_seq += size;
4752 				copy -= size;
4753 				start += size;
4754 			}
4755 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4756 				skb = tcp_collapse_one(sk, skb, list);
4757 				if (!skb ||
4758 				    skb == tail ||
4759 				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4760 					return;
4761 			}
4762 		}
4763 	}
4764 }
4765 
4766 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4767  * and tcp_collapse() them until all the queue is collapsed.
4768  */
4769 static void tcp_collapse_ofo_queue(struct sock *sk)
4770 {
4771 	struct tcp_sock *tp = tcp_sk(sk);
4772 	struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4773 	struct sk_buff *head;
4774 	u32 start, end;
4775 
4776 	if (!skb)
4777 		return;
4778 
4779 	start = TCP_SKB_CB(skb)->seq;
4780 	end = TCP_SKB_CB(skb)->end_seq;
4781 	head = skb;
4782 
4783 	for (;;) {
4784 		struct sk_buff *next = NULL;
4785 
4786 		if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4787 			next = skb_queue_next(&tp->out_of_order_queue, skb);
4788 		skb = next;
4789 
4790 		/* Segment is terminated when we see gap or when
4791 		 * we are at the end of all the queue. */
4792 		if (!skb ||
4793 		    after(TCP_SKB_CB(skb)->seq, end) ||
4794 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
4795 			tcp_collapse(sk, &tp->out_of_order_queue,
4796 				     head, skb, start, end);
4797 			head = skb;
4798 			if (!skb)
4799 				break;
4800 			/* Start new segment */
4801 			start = TCP_SKB_CB(skb)->seq;
4802 			end = TCP_SKB_CB(skb)->end_seq;
4803 		} else {
4804 			if (before(TCP_SKB_CB(skb)->seq, start))
4805 				start = TCP_SKB_CB(skb)->seq;
4806 			if (after(TCP_SKB_CB(skb)->end_seq, end))
4807 				end = TCP_SKB_CB(skb)->end_seq;
4808 		}
4809 	}
4810 }
4811 
4812 /*
4813  * Purge the out-of-order queue.
4814  * Return true if queue was pruned.
4815  */
4816 static bool tcp_prune_ofo_queue(struct sock *sk)
4817 {
4818 	struct tcp_sock *tp = tcp_sk(sk);
4819 	bool res = false;
4820 
4821 	if (!skb_queue_empty(&tp->out_of_order_queue)) {
4822 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4823 		__skb_queue_purge(&tp->out_of_order_queue);
4824 
4825 		/* Reset SACK state.  A conforming SACK implementation will
4826 		 * do the same at a timeout based retransmit.  When a connection
4827 		 * is in a sad state like this, we care only about integrity
4828 		 * of the connection not performance.
4829 		 */
4830 		if (tp->rx_opt.sack_ok)
4831 			tcp_sack_reset(&tp->rx_opt);
4832 		sk_mem_reclaim(sk);
4833 		res = true;
4834 	}
4835 	return res;
4836 }
4837 
4838 /* Reduce allocated memory if we can, trying to get
4839  * the socket within its memory limits again.
4840  *
4841  * Return less than zero if we should start dropping frames
4842  * until the socket owning process reads some of the data
4843  * to stabilize the situation.
4844  */
4845 static int tcp_prune_queue(struct sock *sk)
4846 {
4847 	struct tcp_sock *tp = tcp_sk(sk);
4848 
4849 	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4850 
4851 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4852 
4853 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4854 		tcp_clamp_window(sk);
4855 	else if (tcp_under_memory_pressure(sk))
4856 		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4857 
4858 	tcp_collapse_ofo_queue(sk);
4859 	if (!skb_queue_empty(&sk->sk_receive_queue))
4860 		tcp_collapse(sk, &sk->sk_receive_queue,
4861 			     skb_peek(&sk->sk_receive_queue),
4862 			     NULL,
4863 			     tp->copied_seq, tp->rcv_nxt);
4864 	sk_mem_reclaim(sk);
4865 
4866 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4867 		return 0;
4868 
4869 	/* Collapsing did not help, destructive actions follow.
4870 	 * This must not ever occur. */
4871 
4872 	tcp_prune_ofo_queue(sk);
4873 
4874 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4875 		return 0;
4876 
4877 	/* If we are really being abused, tell the caller to silently
4878 	 * drop receive data on the floor.  It will get retransmitted
4879 	 * and hopefully then we'll have sufficient space.
4880 	 */
4881 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4882 
4883 	/* Massive buffer overcommit. */
4884 	tp->pred_flags = 0;
4885 	return -1;
4886 }
4887 
4888 static bool tcp_should_expand_sndbuf(const struct sock *sk)
4889 {
4890 	const struct tcp_sock *tp = tcp_sk(sk);
4891 
4892 	/* If the user specified a specific send buffer setting, do
4893 	 * not modify it.
4894 	 */
4895 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4896 		return false;
4897 
4898 	/* If we are under global TCP memory pressure, do not expand.  */
4899 	if (tcp_under_memory_pressure(sk))
4900 		return false;
4901 
4902 	/* If we are under soft global TCP memory pressure, do not expand.  */
4903 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
4904 		return false;
4905 
4906 	/* If we filled the congestion window, do not expand.  */
4907 	if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
4908 		return false;
4909 
4910 	return true;
4911 }
4912 
4913 /* When incoming ACK allowed to free some skb from write_queue,
4914  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4915  * on the exit from tcp input handler.
4916  *
4917  * PROBLEM: sndbuf expansion does not work well with largesend.
4918  */
4919 static void tcp_new_space(struct sock *sk)
4920 {
4921 	struct tcp_sock *tp = tcp_sk(sk);
4922 
4923 	if (tcp_should_expand_sndbuf(sk)) {
4924 		tcp_sndbuf_expand(sk);
4925 		tp->snd_cwnd_stamp = tcp_time_stamp;
4926 	}
4927 
4928 	sk->sk_write_space(sk);
4929 }
4930 
4931 static void tcp_check_space(struct sock *sk)
4932 {
4933 	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4934 		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4935 		/* pairs with tcp_poll() */
4936 		smp_mb__after_atomic();
4937 		if (sk->sk_socket &&
4938 		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4939 			tcp_new_space(sk);
4940 	}
4941 }
4942 
4943 static inline void tcp_data_snd_check(struct sock *sk)
4944 {
4945 	tcp_push_pending_frames(sk);
4946 	tcp_check_space(sk);
4947 }
4948 
4949 /*
4950  * Check if sending an ack is needed.
4951  */
4952 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4953 {
4954 	struct tcp_sock *tp = tcp_sk(sk);
4955 
4956 	    /* More than one full frame received... */
4957 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4958 	     /* ... and right edge of window advances far enough.
4959 	      * (tcp_recvmsg() will send ACK otherwise). Or...
4960 	      */
4961 	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
4962 	    /* We ACK each frame or... */
4963 	    tcp_in_quickack_mode(sk) ||
4964 	    /* We have out of order data. */
4965 	    (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4966 		/* Then ack it now */
4967 		tcp_send_ack(sk);
4968 	} else {
4969 		/* Else, send delayed ack. */
4970 		tcp_send_delayed_ack(sk);
4971 	}
4972 }
4973 
4974 static inline void tcp_ack_snd_check(struct sock *sk)
4975 {
4976 	if (!inet_csk_ack_scheduled(sk)) {
4977 		/* We sent a data segment already. */
4978 		return;
4979 	}
4980 	__tcp_ack_snd_check(sk, 1);
4981 }
4982 
4983 /*
4984  *	This routine is only called when we have urgent data
4985  *	signaled. Its the 'slow' part of tcp_urg. It could be
4986  *	moved inline now as tcp_urg is only called from one
4987  *	place. We handle URGent data wrong. We have to - as
4988  *	BSD still doesn't use the correction from RFC961.
4989  *	For 1003.1g we should support a new option TCP_STDURG to permit
4990  *	either form (or just set the sysctl tcp_stdurg).
4991  */
4992 
4993 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
4994 {
4995 	struct tcp_sock *tp = tcp_sk(sk);
4996 	u32 ptr = ntohs(th->urg_ptr);
4997 
4998 	if (ptr && !sysctl_tcp_stdurg)
4999 		ptr--;
5000 	ptr += ntohl(th->seq);
5001 
5002 	/* Ignore urgent data that we've already seen and read. */
5003 	if (after(tp->copied_seq, ptr))
5004 		return;
5005 
5006 	/* Do not replay urg ptr.
5007 	 *
5008 	 * NOTE: interesting situation not covered by specs.
5009 	 * Misbehaving sender may send urg ptr, pointing to segment,
5010 	 * which we already have in ofo queue. We are not able to fetch
5011 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5012 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5013 	 * situations. But it is worth to think about possibility of some
5014 	 * DoSes using some hypothetical application level deadlock.
5015 	 */
5016 	if (before(ptr, tp->rcv_nxt))
5017 		return;
5018 
5019 	/* Do we already have a newer (or duplicate) urgent pointer? */
5020 	if (tp->urg_data && !after(ptr, tp->urg_seq))
5021 		return;
5022 
5023 	/* Tell the world about our new urgent pointer. */
5024 	sk_send_sigurg(sk);
5025 
5026 	/* We may be adding urgent data when the last byte read was
5027 	 * urgent. To do this requires some care. We cannot just ignore
5028 	 * tp->copied_seq since we would read the last urgent byte again
5029 	 * as data, nor can we alter copied_seq until this data arrives
5030 	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5031 	 *
5032 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5033 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5034 	 * and expect that both A and B disappear from stream. This is _wrong_.
5035 	 * Though this happens in BSD with high probability, this is occasional.
5036 	 * Any application relying on this is buggy. Note also, that fix "works"
5037 	 * only in this artificial test. Insert some normal data between A and B and we will
5038 	 * decline of BSD again. Verdict: it is better to remove to trap
5039 	 * buggy users.
5040 	 */
5041 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5042 	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5043 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5044 		tp->copied_seq++;
5045 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5046 			__skb_unlink(skb, &sk->sk_receive_queue);
5047 			__kfree_skb(skb);
5048 		}
5049 	}
5050 
5051 	tp->urg_data = TCP_URG_NOTYET;
5052 	tp->urg_seq = ptr;
5053 
5054 	/* Disable header prediction. */
5055 	tp->pred_flags = 0;
5056 }
5057 
5058 /* This is the 'fast' part of urgent handling. */
5059 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5060 {
5061 	struct tcp_sock *tp = tcp_sk(sk);
5062 
5063 	/* Check if we get a new urgent pointer - normally not. */
5064 	if (th->urg)
5065 		tcp_check_urg(sk, th);
5066 
5067 	/* Do we wait for any urgent data? - normally not... */
5068 	if (tp->urg_data == TCP_URG_NOTYET) {
5069 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5070 			  th->syn;
5071 
5072 		/* Is the urgent pointer pointing into this packet? */
5073 		if (ptr < skb->len) {
5074 			u8 tmp;
5075 			if (skb_copy_bits(skb, ptr, &tmp, 1))
5076 				BUG();
5077 			tp->urg_data = TCP_URG_VALID | tmp;
5078 			if (!sock_flag(sk, SOCK_DEAD))
5079 				sk->sk_data_ready(sk);
5080 		}
5081 	}
5082 }
5083 
5084 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5085 {
5086 	struct tcp_sock *tp = tcp_sk(sk);
5087 	int chunk = skb->len - hlen;
5088 	int err;
5089 
5090 	local_bh_enable();
5091 	if (skb_csum_unnecessary(skb))
5092 		err = skb_copy_datagram_msg(skb, hlen, tp->ucopy.msg, chunk);
5093 	else
5094 		err = skb_copy_and_csum_datagram_msg(skb, hlen, tp->ucopy.msg);
5095 
5096 	if (!err) {
5097 		tp->ucopy.len -= chunk;
5098 		tp->copied_seq += chunk;
5099 		tcp_rcv_space_adjust(sk);
5100 	}
5101 
5102 	local_bh_disable();
5103 	return err;
5104 }
5105 
5106 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5107 					    struct sk_buff *skb)
5108 {
5109 	__sum16 result;
5110 
5111 	if (sock_owned_by_user(sk)) {
5112 		local_bh_enable();
5113 		result = __tcp_checksum_complete(skb);
5114 		local_bh_disable();
5115 	} else {
5116 		result = __tcp_checksum_complete(skb);
5117 	}
5118 	return result;
5119 }
5120 
5121 static inline bool tcp_checksum_complete_user(struct sock *sk,
5122 					     struct sk_buff *skb)
5123 {
5124 	return !skb_csum_unnecessary(skb) &&
5125 	       __tcp_checksum_complete_user(sk, skb);
5126 }
5127 
5128 /* Does PAWS and seqno based validation of an incoming segment, flags will
5129  * play significant role here.
5130  */
5131 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5132 				  const struct tcphdr *th, int syn_inerr)
5133 {
5134 	struct tcp_sock *tp = tcp_sk(sk);
5135 
5136 	/* RFC1323: H1. Apply PAWS check first. */
5137 	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5138 	    tcp_paws_discard(sk, skb)) {
5139 		if (!th->rst) {
5140 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5141 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5142 						  LINUX_MIB_TCPACKSKIPPEDPAWS,
5143 						  &tp->last_oow_ack_time))
5144 				tcp_send_dupack(sk, skb);
5145 			goto discard;
5146 		}
5147 		/* Reset is accepted even if it did not pass PAWS. */
5148 	}
5149 
5150 	/* Step 1: check sequence number */
5151 	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5152 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5153 		 * (RST) segments are validated by checking their SEQ-fields."
5154 		 * And page 69: "If an incoming segment is not acceptable,
5155 		 * an acknowledgment should be sent in reply (unless the RST
5156 		 * bit is set, if so drop the segment and return)".
5157 		 */
5158 		if (!th->rst) {
5159 			if (th->syn)
5160 				goto syn_challenge;
5161 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5162 						  LINUX_MIB_TCPACKSKIPPEDSEQ,
5163 						  &tp->last_oow_ack_time))
5164 				tcp_send_dupack(sk, skb);
5165 		}
5166 		goto discard;
5167 	}
5168 
5169 	/* Step 2: check RST bit */
5170 	if (th->rst) {
5171 		/* RFC 5961 3.2 :
5172 		 * If sequence number exactly matches RCV.NXT, then
5173 		 *     RESET the connection
5174 		 * else
5175 		 *     Send a challenge ACK
5176 		 */
5177 		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
5178 			tcp_reset(sk);
5179 		else
5180 			tcp_send_challenge_ack(sk, skb);
5181 		goto discard;
5182 	}
5183 
5184 	/* step 3: check security and precedence [ignored] */
5185 
5186 	/* step 4: Check for a SYN
5187 	 * RFC 5961 4.2 : Send a challenge ack
5188 	 */
5189 	if (th->syn) {
5190 syn_challenge:
5191 		if (syn_inerr)
5192 			TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5193 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5194 		tcp_send_challenge_ack(sk, skb);
5195 		goto discard;
5196 	}
5197 
5198 	return true;
5199 
5200 discard:
5201 	__kfree_skb(skb);
5202 	return false;
5203 }
5204 
5205 /*
5206  *	TCP receive function for the ESTABLISHED state.
5207  *
5208  *	It is split into a fast path and a slow path. The fast path is
5209  * 	disabled when:
5210  *	- A zero window was announced from us - zero window probing
5211  *        is only handled properly in the slow path.
5212  *	- Out of order segments arrived.
5213  *	- Urgent data is expected.
5214  *	- There is no buffer space left
5215  *	- Unexpected TCP flags/window values/header lengths are received
5216  *	  (detected by checking the TCP header against pred_flags)
5217  *	- Data is sent in both directions. Fast path only supports pure senders
5218  *	  or pure receivers (this means either the sequence number or the ack
5219  *	  value must stay constant)
5220  *	- Unexpected TCP option.
5221  *
5222  *	When these conditions are not satisfied it drops into a standard
5223  *	receive procedure patterned after RFC793 to handle all cases.
5224  *	The first three cases are guaranteed by proper pred_flags setting,
5225  *	the rest is checked inline. Fast processing is turned on in
5226  *	tcp_data_queue when everything is OK.
5227  */
5228 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5229 			 const struct tcphdr *th, unsigned int len)
5230 {
5231 	struct tcp_sock *tp = tcp_sk(sk);
5232 
5233 	if (unlikely(!sk->sk_rx_dst))
5234 		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5235 	/*
5236 	 *	Header prediction.
5237 	 *	The code loosely follows the one in the famous
5238 	 *	"30 instruction TCP receive" Van Jacobson mail.
5239 	 *
5240 	 *	Van's trick is to deposit buffers into socket queue
5241 	 *	on a device interrupt, to call tcp_recv function
5242 	 *	on the receive process context and checksum and copy
5243 	 *	the buffer to user space. smart...
5244 	 *
5245 	 *	Our current scheme is not silly either but we take the
5246 	 *	extra cost of the net_bh soft interrupt processing...
5247 	 *	We do checksum and copy also but from device to kernel.
5248 	 */
5249 
5250 	tp->rx_opt.saw_tstamp = 0;
5251 
5252 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5253 	 *	if header_prediction is to be made
5254 	 *	'S' will always be tp->tcp_header_len >> 2
5255 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5256 	 *  turn it off	(when there are holes in the receive
5257 	 *	 space for instance)
5258 	 *	PSH flag is ignored.
5259 	 */
5260 
5261 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5262 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5263 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5264 		int tcp_header_len = tp->tcp_header_len;
5265 
5266 		/* Timestamp header prediction: tcp_header_len
5267 		 * is automatically equal to th->doff*4 due to pred_flags
5268 		 * match.
5269 		 */
5270 
5271 		/* Check timestamp */
5272 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5273 			/* No? Slow path! */
5274 			if (!tcp_parse_aligned_timestamp(tp, th))
5275 				goto slow_path;
5276 
5277 			/* If PAWS failed, check it more carefully in slow path */
5278 			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5279 				goto slow_path;
5280 
5281 			/* DO NOT update ts_recent here, if checksum fails
5282 			 * and timestamp was corrupted part, it will result
5283 			 * in a hung connection since we will drop all
5284 			 * future packets due to the PAWS test.
5285 			 */
5286 		}
5287 
5288 		if (len <= tcp_header_len) {
5289 			/* Bulk data transfer: sender */
5290 			if (len == tcp_header_len) {
5291 				/* Predicted packet is in window by definition.
5292 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5293 				 * Hence, check seq<=rcv_wup reduces to:
5294 				 */
5295 				if (tcp_header_len ==
5296 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5297 				    tp->rcv_nxt == tp->rcv_wup)
5298 					tcp_store_ts_recent(tp);
5299 
5300 				/* We know that such packets are checksummed
5301 				 * on entry.
5302 				 */
5303 				tcp_ack(sk, skb, 0);
5304 				__kfree_skb(skb);
5305 				tcp_data_snd_check(sk);
5306 				return;
5307 			} else { /* Header too small */
5308 				TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5309 				goto discard;
5310 			}
5311 		} else {
5312 			int eaten = 0;
5313 			bool fragstolen = false;
5314 
5315 			if (tp->ucopy.task == current &&
5316 			    tp->copied_seq == tp->rcv_nxt &&
5317 			    len - tcp_header_len <= tp->ucopy.len &&
5318 			    sock_owned_by_user(sk)) {
5319 				__set_current_state(TASK_RUNNING);
5320 
5321 				if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
5322 					/* Predicted packet is in window by definition.
5323 					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5324 					 * Hence, check seq<=rcv_wup reduces to:
5325 					 */
5326 					if (tcp_header_len ==
5327 					    (sizeof(struct tcphdr) +
5328 					     TCPOLEN_TSTAMP_ALIGNED) &&
5329 					    tp->rcv_nxt == tp->rcv_wup)
5330 						tcp_store_ts_recent(tp);
5331 
5332 					tcp_rcv_rtt_measure_ts(sk, skb);
5333 
5334 					__skb_pull(skb, tcp_header_len);
5335 					tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
5336 					NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5337 					eaten = 1;
5338 				}
5339 			}
5340 			if (!eaten) {
5341 				if (tcp_checksum_complete_user(sk, skb))
5342 					goto csum_error;
5343 
5344 				if ((int)skb->truesize > sk->sk_forward_alloc)
5345 					goto step5;
5346 
5347 				/* Predicted packet is in window by definition.
5348 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5349 				 * Hence, check seq<=rcv_wup reduces to:
5350 				 */
5351 				if (tcp_header_len ==
5352 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5353 				    tp->rcv_nxt == tp->rcv_wup)
5354 					tcp_store_ts_recent(tp);
5355 
5356 				tcp_rcv_rtt_measure_ts(sk, skb);
5357 
5358 				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5359 
5360 				/* Bulk data transfer: receiver */
5361 				eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5362 						      &fragstolen);
5363 			}
5364 
5365 			tcp_event_data_recv(sk, skb);
5366 
5367 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5368 				/* Well, only one small jumplet in fast path... */
5369 				tcp_ack(sk, skb, FLAG_DATA);
5370 				tcp_data_snd_check(sk);
5371 				if (!inet_csk_ack_scheduled(sk))
5372 					goto no_ack;
5373 			}
5374 
5375 			__tcp_ack_snd_check(sk, 0);
5376 no_ack:
5377 			if (eaten)
5378 				kfree_skb_partial(skb, fragstolen);
5379 			sk->sk_data_ready(sk);
5380 			return;
5381 		}
5382 	}
5383 
5384 slow_path:
5385 	if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5386 		goto csum_error;
5387 
5388 	if (!th->ack && !th->rst && !th->syn)
5389 		goto discard;
5390 
5391 	/*
5392 	 *	Standard slow path.
5393 	 */
5394 
5395 	if (!tcp_validate_incoming(sk, skb, th, 1))
5396 		return;
5397 
5398 step5:
5399 	if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5400 		goto discard;
5401 
5402 	tcp_rcv_rtt_measure_ts(sk, skb);
5403 
5404 	/* Process urgent data. */
5405 	tcp_urg(sk, skb, th);
5406 
5407 	/* step 7: process the segment text */
5408 	tcp_data_queue(sk, skb);
5409 
5410 	tcp_data_snd_check(sk);
5411 	tcp_ack_snd_check(sk);
5412 	return;
5413 
5414 csum_error:
5415 	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_CSUMERRORS);
5416 	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5417 
5418 discard:
5419 	__kfree_skb(skb);
5420 }
5421 EXPORT_SYMBOL(tcp_rcv_established);
5422 
5423 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5424 {
5425 	struct tcp_sock *tp = tcp_sk(sk);
5426 	struct inet_connection_sock *icsk = inet_csk(sk);
5427 
5428 	tcp_set_state(sk, TCP_ESTABLISHED);
5429 
5430 	if (skb) {
5431 		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5432 		security_inet_conn_established(sk, skb);
5433 	}
5434 
5435 	/* Make sure socket is routed, for correct metrics.  */
5436 	icsk->icsk_af_ops->rebuild_header(sk);
5437 
5438 	tcp_init_metrics(sk);
5439 
5440 	tcp_init_congestion_control(sk);
5441 
5442 	/* Prevent spurious tcp_cwnd_restart() on first data
5443 	 * packet.
5444 	 */
5445 	tp->lsndtime = tcp_time_stamp;
5446 
5447 	tcp_init_buffer_space(sk);
5448 
5449 	if (sock_flag(sk, SOCK_KEEPOPEN))
5450 		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5451 
5452 	if (!tp->rx_opt.snd_wscale)
5453 		__tcp_fast_path_on(tp, tp->snd_wnd);
5454 	else
5455 		tp->pred_flags = 0;
5456 
5457 	if (!sock_flag(sk, SOCK_DEAD)) {
5458 		sk->sk_state_change(sk);
5459 		sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5460 	}
5461 }
5462 
5463 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5464 				    struct tcp_fastopen_cookie *cookie)
5465 {
5466 	struct tcp_sock *tp = tcp_sk(sk);
5467 	struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
5468 	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
5469 	bool syn_drop = false;
5470 
5471 	if (mss == tp->rx_opt.user_mss) {
5472 		struct tcp_options_received opt;
5473 
5474 		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
5475 		tcp_clear_options(&opt);
5476 		opt.user_mss = opt.mss_clamp = 0;
5477 		tcp_parse_options(synack, &opt, 0, NULL);
5478 		mss = opt.mss_clamp;
5479 	}
5480 
5481 	if (!tp->syn_fastopen) {
5482 		/* Ignore an unsolicited cookie */
5483 		cookie->len = -1;
5484 	} else if (tp->total_retrans) {
5485 		/* SYN timed out and the SYN-ACK neither has a cookie nor
5486 		 * acknowledges data. Presumably the remote received only
5487 		 * the retransmitted (regular) SYNs: either the original
5488 		 * SYN-data or the corresponding SYN-ACK was dropped.
5489 		 */
5490 		syn_drop = (cookie->len < 0 && data);
5491 	} else if (cookie->len < 0 && !tp->syn_data) {
5492 		/* We requested a cookie but didn't get it. If we did not use
5493 		 * the (old) exp opt format then try so next time (try_exp=1).
5494 		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
5495 		 */
5496 		try_exp = tp->syn_fastopen_exp ? 2 : 1;
5497 	}
5498 
5499 	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
5500 
5501 	if (data) { /* Retransmit unacked data in SYN */
5502 		tcp_for_write_queue_from(data, sk) {
5503 			if (data == tcp_send_head(sk) ||
5504 			    __tcp_retransmit_skb(sk, data))
5505 				break;
5506 		}
5507 		tcp_rearm_rto(sk);
5508 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5509 		return true;
5510 	}
5511 	tp->syn_data_acked = tp->syn_data;
5512 	if (tp->syn_data_acked)
5513 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
5514 	return false;
5515 }
5516 
5517 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5518 					 const struct tcphdr *th)
5519 {
5520 	struct inet_connection_sock *icsk = inet_csk(sk);
5521 	struct tcp_sock *tp = tcp_sk(sk);
5522 	struct tcp_fastopen_cookie foc = { .len = -1 };
5523 	int saved_clamp = tp->rx_opt.mss_clamp;
5524 
5525 	tcp_parse_options(skb, &tp->rx_opt, 0, &foc);
5526 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5527 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5528 
5529 	if (th->ack) {
5530 		/* rfc793:
5531 		 * "If the state is SYN-SENT then
5532 		 *    first check the ACK bit
5533 		 *      If the ACK bit is set
5534 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5535 		 *        a reset (unless the RST bit is set, if so drop
5536 		 *        the segment and return)"
5537 		 */
5538 		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5539 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5540 			goto reset_and_undo;
5541 
5542 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5543 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5544 			     tcp_time_stamp)) {
5545 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5546 			goto reset_and_undo;
5547 		}
5548 
5549 		/* Now ACK is acceptable.
5550 		 *
5551 		 * "If the RST bit is set
5552 		 *    If the ACK was acceptable then signal the user "error:
5553 		 *    connection reset", drop the segment, enter CLOSED state,
5554 		 *    delete TCB, and return."
5555 		 */
5556 
5557 		if (th->rst) {
5558 			tcp_reset(sk);
5559 			goto discard;
5560 		}
5561 
5562 		/* rfc793:
5563 		 *   "fifth, if neither of the SYN or RST bits is set then
5564 		 *    drop the segment and return."
5565 		 *
5566 		 *    See note below!
5567 		 *                                        --ANK(990513)
5568 		 */
5569 		if (!th->syn)
5570 			goto discard_and_undo;
5571 
5572 		/* rfc793:
5573 		 *   "If the SYN bit is on ...
5574 		 *    are acceptable then ...
5575 		 *    (our SYN has been ACKed), change the connection
5576 		 *    state to ESTABLISHED..."
5577 		 */
5578 
5579 		tcp_ecn_rcv_synack(tp, th);
5580 
5581 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5582 		tcp_ack(sk, skb, FLAG_SLOWPATH);
5583 
5584 		/* Ok.. it's good. Set up sequence numbers and
5585 		 * move to established.
5586 		 */
5587 		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5588 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5589 
5590 		/* RFC1323: The window in SYN & SYN/ACK segments is
5591 		 * never scaled.
5592 		 */
5593 		tp->snd_wnd = ntohs(th->window);
5594 
5595 		if (!tp->rx_opt.wscale_ok) {
5596 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5597 			tp->window_clamp = min(tp->window_clamp, 65535U);
5598 		}
5599 
5600 		if (tp->rx_opt.saw_tstamp) {
5601 			tp->rx_opt.tstamp_ok	   = 1;
5602 			tp->tcp_header_len =
5603 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5604 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
5605 			tcp_store_ts_recent(tp);
5606 		} else {
5607 			tp->tcp_header_len = sizeof(struct tcphdr);
5608 		}
5609 
5610 		if (tcp_is_sack(tp) && sysctl_tcp_fack)
5611 			tcp_enable_fack(tp);
5612 
5613 		tcp_mtup_init(sk);
5614 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5615 		tcp_initialize_rcv_mss(sk);
5616 
5617 		/* Remember, tcp_poll() does not lock socket!
5618 		 * Change state from SYN-SENT only after copied_seq
5619 		 * is initialized. */
5620 		tp->copied_seq = tp->rcv_nxt;
5621 
5622 		smp_mb();
5623 
5624 		tcp_finish_connect(sk, skb);
5625 
5626 		if ((tp->syn_fastopen || tp->syn_data) &&
5627 		    tcp_rcv_fastopen_synack(sk, skb, &foc))
5628 			return -1;
5629 
5630 		if (sk->sk_write_pending ||
5631 		    icsk->icsk_accept_queue.rskq_defer_accept ||
5632 		    icsk->icsk_ack.pingpong) {
5633 			/* Save one ACK. Data will be ready after
5634 			 * several ticks, if write_pending is set.
5635 			 *
5636 			 * It may be deleted, but with this feature tcpdumps
5637 			 * look so _wonderfully_ clever, that I was not able
5638 			 * to stand against the temptation 8)     --ANK
5639 			 */
5640 			inet_csk_schedule_ack(sk);
5641 			icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5642 			tcp_enter_quickack_mode(sk);
5643 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5644 						  TCP_DELACK_MAX, TCP_RTO_MAX);
5645 
5646 discard:
5647 			__kfree_skb(skb);
5648 			return 0;
5649 		} else {
5650 			tcp_send_ack(sk);
5651 		}
5652 		return -1;
5653 	}
5654 
5655 	/* No ACK in the segment */
5656 
5657 	if (th->rst) {
5658 		/* rfc793:
5659 		 * "If the RST bit is set
5660 		 *
5661 		 *      Otherwise (no ACK) drop the segment and return."
5662 		 */
5663 
5664 		goto discard_and_undo;
5665 	}
5666 
5667 	/* PAWS check. */
5668 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5669 	    tcp_paws_reject(&tp->rx_opt, 0))
5670 		goto discard_and_undo;
5671 
5672 	if (th->syn) {
5673 		/* We see SYN without ACK. It is attempt of
5674 		 * simultaneous connect with crossed SYNs.
5675 		 * Particularly, it can be connect to self.
5676 		 */
5677 		tcp_set_state(sk, TCP_SYN_RECV);
5678 
5679 		if (tp->rx_opt.saw_tstamp) {
5680 			tp->rx_opt.tstamp_ok = 1;
5681 			tcp_store_ts_recent(tp);
5682 			tp->tcp_header_len =
5683 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5684 		} else {
5685 			tp->tcp_header_len = sizeof(struct tcphdr);
5686 		}
5687 
5688 		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5689 		tp->copied_seq = tp->rcv_nxt;
5690 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5691 
5692 		/* RFC1323: The window in SYN & SYN/ACK segments is
5693 		 * never scaled.
5694 		 */
5695 		tp->snd_wnd    = ntohs(th->window);
5696 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5697 		tp->max_window = tp->snd_wnd;
5698 
5699 		tcp_ecn_rcv_syn(tp, th);
5700 
5701 		tcp_mtup_init(sk);
5702 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5703 		tcp_initialize_rcv_mss(sk);
5704 
5705 		tcp_send_synack(sk);
5706 #if 0
5707 		/* Note, we could accept data and URG from this segment.
5708 		 * There are no obstacles to make this (except that we must
5709 		 * either change tcp_recvmsg() to prevent it from returning data
5710 		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
5711 		 *
5712 		 * However, if we ignore data in ACKless segments sometimes,
5713 		 * we have no reasons to accept it sometimes.
5714 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
5715 		 * is not flawless. So, discard packet for sanity.
5716 		 * Uncomment this return to process the data.
5717 		 */
5718 		return -1;
5719 #else
5720 		goto discard;
5721 #endif
5722 	}
5723 	/* "fifth, if neither of the SYN or RST bits is set then
5724 	 * drop the segment and return."
5725 	 */
5726 
5727 discard_and_undo:
5728 	tcp_clear_options(&tp->rx_opt);
5729 	tp->rx_opt.mss_clamp = saved_clamp;
5730 	goto discard;
5731 
5732 reset_and_undo:
5733 	tcp_clear_options(&tp->rx_opt);
5734 	tp->rx_opt.mss_clamp = saved_clamp;
5735 	return 1;
5736 }
5737 
5738 /*
5739  *	This function implements the receiving procedure of RFC 793 for
5740  *	all states except ESTABLISHED and TIME_WAIT.
5741  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5742  *	address independent.
5743  */
5744 
5745 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
5746 {
5747 	struct tcp_sock *tp = tcp_sk(sk);
5748 	struct inet_connection_sock *icsk = inet_csk(sk);
5749 	const struct tcphdr *th = tcp_hdr(skb);
5750 	struct request_sock *req;
5751 	int queued = 0;
5752 	bool acceptable;
5753 
5754 	tp->rx_opt.saw_tstamp = 0;
5755 
5756 	switch (sk->sk_state) {
5757 	case TCP_CLOSE:
5758 		goto discard;
5759 
5760 	case TCP_LISTEN:
5761 		if (th->ack)
5762 			return 1;
5763 
5764 		if (th->rst)
5765 			goto discard;
5766 
5767 		if (th->syn) {
5768 			if (th->fin)
5769 				goto discard;
5770 			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5771 				return 1;
5772 
5773 			/* Now we have several options: In theory there is
5774 			 * nothing else in the frame. KA9Q has an option to
5775 			 * send data with the syn, BSD accepts data with the
5776 			 * syn up to the [to be] advertised window and
5777 			 * Solaris 2.1 gives you a protocol error. For now
5778 			 * we just ignore it, that fits the spec precisely
5779 			 * and avoids incompatibilities. It would be nice in
5780 			 * future to drop through and process the data.
5781 			 *
5782 			 * Now that TTCP is starting to be used we ought to
5783 			 * queue this data.
5784 			 * But, this leaves one open to an easy denial of
5785 			 * service attack, and SYN cookies can't defend
5786 			 * against this problem. So, we drop the data
5787 			 * in the interest of security over speed unless
5788 			 * it's still in use.
5789 			 */
5790 			kfree_skb(skb);
5791 			return 0;
5792 		}
5793 		goto discard;
5794 
5795 	case TCP_SYN_SENT:
5796 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
5797 		if (queued >= 0)
5798 			return queued;
5799 
5800 		/* Do step6 onward by hand. */
5801 		tcp_urg(sk, skb, th);
5802 		__kfree_skb(skb);
5803 		tcp_data_snd_check(sk);
5804 		return 0;
5805 	}
5806 
5807 	req = tp->fastopen_rsk;
5808 	if (req) {
5809 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
5810 		    sk->sk_state != TCP_FIN_WAIT1);
5811 
5812 		if (!tcp_check_req(sk, skb, req, true))
5813 			goto discard;
5814 	}
5815 
5816 	if (!th->ack && !th->rst && !th->syn)
5817 		goto discard;
5818 
5819 	if (!tcp_validate_incoming(sk, skb, th, 0))
5820 		return 0;
5821 
5822 	/* step 5: check the ACK field */
5823 	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
5824 				      FLAG_UPDATE_TS_RECENT) > 0;
5825 
5826 	switch (sk->sk_state) {
5827 	case TCP_SYN_RECV:
5828 		if (!acceptable)
5829 			return 1;
5830 
5831 		if (!tp->srtt_us)
5832 			tcp_synack_rtt_meas(sk, req);
5833 
5834 		/* Once we leave TCP_SYN_RECV, we no longer need req
5835 		 * so release it.
5836 		 */
5837 		if (req) {
5838 			tp->total_retrans = req->num_retrans;
5839 			reqsk_fastopen_remove(sk, req, false);
5840 		} else {
5841 			/* Make sure socket is routed, for correct metrics. */
5842 			icsk->icsk_af_ops->rebuild_header(sk);
5843 			tcp_init_congestion_control(sk);
5844 
5845 			tcp_mtup_init(sk);
5846 			tp->copied_seq = tp->rcv_nxt;
5847 			tcp_init_buffer_space(sk);
5848 		}
5849 		smp_mb();
5850 		tcp_set_state(sk, TCP_ESTABLISHED);
5851 		sk->sk_state_change(sk);
5852 
5853 		/* Note, that this wakeup is only for marginal crossed SYN case.
5854 		 * Passively open sockets are not waked up, because
5855 		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
5856 		 */
5857 		if (sk->sk_socket)
5858 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5859 
5860 		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5861 		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
5862 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5863 
5864 		if (tp->rx_opt.tstamp_ok)
5865 			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5866 
5867 		if (req) {
5868 			/* Re-arm the timer because data may have been sent out.
5869 			 * This is similar to the regular data transmission case
5870 			 * when new data has just been ack'ed.
5871 			 *
5872 			 * (TFO) - we could try to be more aggressive and
5873 			 * retransmitting any data sooner based on when they
5874 			 * are sent out.
5875 			 */
5876 			tcp_rearm_rto(sk);
5877 		} else
5878 			tcp_init_metrics(sk);
5879 
5880 		tcp_update_pacing_rate(sk);
5881 
5882 		/* Prevent spurious tcp_cwnd_restart() on first data packet */
5883 		tp->lsndtime = tcp_time_stamp;
5884 
5885 		tcp_initialize_rcv_mss(sk);
5886 		tcp_fast_path_on(tp);
5887 		break;
5888 
5889 	case TCP_FIN_WAIT1: {
5890 		struct dst_entry *dst;
5891 		int tmo;
5892 
5893 		/* If we enter the TCP_FIN_WAIT1 state and we are a
5894 		 * Fast Open socket and this is the first acceptable
5895 		 * ACK we have received, this would have acknowledged
5896 		 * our SYNACK so stop the SYNACK timer.
5897 		 */
5898 		if (req) {
5899 			/* Return RST if ack_seq is invalid.
5900 			 * Note that RFC793 only says to generate a
5901 			 * DUPACK for it but for TCP Fast Open it seems
5902 			 * better to treat this case like TCP_SYN_RECV
5903 			 * above.
5904 			 */
5905 			if (!acceptable)
5906 				return 1;
5907 			/* We no longer need the request sock. */
5908 			reqsk_fastopen_remove(sk, req, false);
5909 			tcp_rearm_rto(sk);
5910 		}
5911 		if (tp->snd_una != tp->write_seq)
5912 			break;
5913 
5914 		tcp_set_state(sk, TCP_FIN_WAIT2);
5915 		sk->sk_shutdown |= SEND_SHUTDOWN;
5916 
5917 		dst = __sk_dst_get(sk);
5918 		if (dst)
5919 			dst_confirm(dst);
5920 
5921 		if (!sock_flag(sk, SOCK_DEAD)) {
5922 			/* Wake up lingering close() */
5923 			sk->sk_state_change(sk);
5924 			break;
5925 		}
5926 
5927 		if (tp->linger2 < 0 ||
5928 		    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5929 		     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5930 			tcp_done(sk);
5931 			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5932 			return 1;
5933 		}
5934 
5935 		tmo = tcp_fin_time(sk);
5936 		if (tmo > TCP_TIMEWAIT_LEN) {
5937 			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5938 		} else if (th->fin || sock_owned_by_user(sk)) {
5939 			/* Bad case. We could lose such FIN otherwise.
5940 			 * It is not a big problem, but it looks confusing
5941 			 * and not so rare event. We still can lose it now,
5942 			 * if it spins in bh_lock_sock(), but it is really
5943 			 * marginal case.
5944 			 */
5945 			inet_csk_reset_keepalive_timer(sk, tmo);
5946 		} else {
5947 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5948 			goto discard;
5949 		}
5950 		break;
5951 	}
5952 
5953 	case TCP_CLOSING:
5954 		if (tp->snd_una == tp->write_seq) {
5955 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5956 			goto discard;
5957 		}
5958 		break;
5959 
5960 	case TCP_LAST_ACK:
5961 		if (tp->snd_una == tp->write_seq) {
5962 			tcp_update_metrics(sk);
5963 			tcp_done(sk);
5964 			goto discard;
5965 		}
5966 		break;
5967 	}
5968 
5969 	/* step 6: check the URG bit */
5970 	tcp_urg(sk, skb, th);
5971 
5972 	/* step 7: process the segment text */
5973 	switch (sk->sk_state) {
5974 	case TCP_CLOSE_WAIT:
5975 	case TCP_CLOSING:
5976 	case TCP_LAST_ACK:
5977 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5978 			break;
5979 	case TCP_FIN_WAIT1:
5980 	case TCP_FIN_WAIT2:
5981 		/* RFC 793 says to queue data in these states,
5982 		 * RFC 1122 says we MUST send a reset.
5983 		 * BSD 4.4 also does reset.
5984 		 */
5985 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
5986 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5987 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5988 				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5989 				tcp_reset(sk);
5990 				return 1;
5991 			}
5992 		}
5993 		/* Fall through */
5994 	case TCP_ESTABLISHED:
5995 		tcp_data_queue(sk, skb);
5996 		queued = 1;
5997 		break;
5998 	}
5999 
6000 	/* tcp_data could move socket to TIME-WAIT */
6001 	if (sk->sk_state != TCP_CLOSE) {
6002 		tcp_data_snd_check(sk);
6003 		tcp_ack_snd_check(sk);
6004 	}
6005 
6006 	if (!queued) {
6007 discard:
6008 		__kfree_skb(skb);
6009 	}
6010 	return 0;
6011 }
6012 EXPORT_SYMBOL(tcp_rcv_state_process);
6013 
6014 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6015 {
6016 	struct inet_request_sock *ireq = inet_rsk(req);
6017 
6018 	if (family == AF_INET)
6019 		net_dbg_ratelimited("drop open request from %pI4/%u\n",
6020 				    &ireq->ir_rmt_addr, port);
6021 #if IS_ENABLED(CONFIG_IPV6)
6022 	else if (family == AF_INET6)
6023 		net_dbg_ratelimited("drop open request from %pI6/%u\n",
6024 				    &ireq->ir_v6_rmt_addr, port);
6025 #endif
6026 }
6027 
6028 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6029  *
6030  * If we receive a SYN packet with these bits set, it means a
6031  * network is playing bad games with TOS bits. In order to
6032  * avoid possible false congestion notifications, we disable
6033  * TCP ECN negotiation.
6034  *
6035  * Exception: tcp_ca wants ECN. This is required for DCTCP
6036  * congestion control: Linux DCTCP asserts ECT on all packets,
6037  * including SYN, which is most optimal solution; however,
6038  * others, such as FreeBSD do not.
6039  */
6040 static void tcp_ecn_create_request(struct request_sock *req,
6041 				   const struct sk_buff *skb,
6042 				   const struct sock *listen_sk,
6043 				   const struct dst_entry *dst)
6044 {
6045 	const struct tcphdr *th = tcp_hdr(skb);
6046 	const struct net *net = sock_net(listen_sk);
6047 	bool th_ecn = th->ece && th->cwr;
6048 	bool ect, ecn_ok;
6049 	u32 ecn_ok_dst;
6050 
6051 	if (!th_ecn)
6052 		return;
6053 
6054 	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6055 	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6056 	ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
6057 
6058 	if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6059 	    (ecn_ok_dst & DST_FEATURE_ECN_CA))
6060 		inet_rsk(req)->ecn_ok = 1;
6061 }
6062 
6063 static void tcp_openreq_init(struct request_sock *req,
6064 			     const struct tcp_options_received *rx_opt,
6065 			     struct sk_buff *skb, const struct sock *sk)
6066 {
6067 	struct inet_request_sock *ireq = inet_rsk(req);
6068 
6069 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
6070 	req->cookie_ts = 0;
6071 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6072 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6073 	skb_mstamp_get(&tcp_rsk(req)->snt_synack);
6074 	tcp_rsk(req)->last_oow_ack_time = 0;
6075 	req->mss = rx_opt->mss_clamp;
6076 	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6077 	ireq->tstamp_ok = rx_opt->tstamp_ok;
6078 	ireq->sack_ok = rx_opt->sack_ok;
6079 	ireq->snd_wscale = rx_opt->snd_wscale;
6080 	ireq->wscale_ok = rx_opt->wscale_ok;
6081 	ireq->acked = 0;
6082 	ireq->ecn_ok = 0;
6083 	ireq->ir_rmt_port = tcp_hdr(skb)->source;
6084 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6085 	ireq->ir_mark = inet_request_mark(sk, skb);
6086 }
6087 
6088 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6089 				      struct sock *sk_listener,
6090 				      bool attach_listener)
6091 {
6092 	struct request_sock *req = reqsk_alloc(ops, sk_listener,
6093 					       attach_listener);
6094 
6095 	if (req) {
6096 		struct inet_request_sock *ireq = inet_rsk(req);
6097 
6098 		kmemcheck_annotate_bitfield(ireq, flags);
6099 		ireq->opt = NULL;
6100 		atomic64_set(&ireq->ir_cookie, 0);
6101 		ireq->ireq_state = TCP_NEW_SYN_RECV;
6102 		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6103 		ireq->ireq_family = sk_listener->sk_family;
6104 	}
6105 
6106 	return req;
6107 }
6108 EXPORT_SYMBOL(inet_reqsk_alloc);
6109 
6110 /*
6111  * Return true if a syncookie should be sent
6112  */
6113 static bool tcp_syn_flood_action(const struct sock *sk,
6114 				 const struct sk_buff *skb,
6115 				 const char *proto)
6116 {
6117 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6118 	const char *msg = "Dropping request";
6119 	bool want_cookie = false;
6120 
6121 #ifdef CONFIG_SYN_COOKIES
6122 	if (sysctl_tcp_syncookies) {
6123 		msg = "Sending cookies";
6124 		want_cookie = true;
6125 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6126 	} else
6127 #endif
6128 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6129 
6130 	if (!queue->synflood_warned &&
6131 	    sysctl_tcp_syncookies != 2 &&
6132 	    xchg(&queue->synflood_warned, 1) == 0)
6133 		pr_info("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
6134 			proto, ntohs(tcp_hdr(skb)->dest), msg);
6135 
6136 	return want_cookie;
6137 }
6138 
6139 static void tcp_reqsk_record_syn(const struct sock *sk,
6140 				 struct request_sock *req,
6141 				 const struct sk_buff *skb)
6142 {
6143 	if (tcp_sk(sk)->save_syn) {
6144 		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6145 		u32 *copy;
6146 
6147 		copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
6148 		if (copy) {
6149 			copy[0] = len;
6150 			memcpy(&copy[1], skb_network_header(skb), len);
6151 			req->saved_syn = copy;
6152 		}
6153 	}
6154 }
6155 
6156 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6157 		     const struct tcp_request_sock_ops *af_ops,
6158 		     struct sock *sk, struct sk_buff *skb)
6159 {
6160 	struct tcp_fastopen_cookie foc = { .len = -1 };
6161 	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6162 	struct tcp_options_received tmp_opt;
6163 	struct tcp_sock *tp = tcp_sk(sk);
6164 	struct sock *fastopen_sk = NULL;
6165 	struct dst_entry *dst = NULL;
6166 	struct request_sock *req;
6167 	bool want_cookie = false;
6168 	struct flowi fl;
6169 
6170 	/* TW buckets are converted to open requests without
6171 	 * limitations, they conserve resources and peer is
6172 	 * evidently real one.
6173 	 */
6174 	if ((sysctl_tcp_syncookies == 2 ||
6175 	     inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6176 		want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
6177 		if (!want_cookie)
6178 			goto drop;
6179 	}
6180 
6181 
6182 	/* Accept backlog is full. If we have already queued enough
6183 	 * of warm entries in syn queue, drop request. It is better than
6184 	 * clogging syn queue with openreqs with exponentially increasing
6185 	 * timeout.
6186 	 */
6187 	if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) {
6188 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6189 		goto drop;
6190 	}
6191 
6192 	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6193 	if (!req)
6194 		goto drop;
6195 
6196 	tcp_rsk(req)->af_specific = af_ops;
6197 
6198 	tcp_clear_options(&tmp_opt);
6199 	tmp_opt.mss_clamp = af_ops->mss_clamp;
6200 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
6201 	tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
6202 
6203 	if (want_cookie && !tmp_opt.saw_tstamp)
6204 		tcp_clear_options(&tmp_opt);
6205 
6206 	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6207 	tcp_openreq_init(req, &tmp_opt, skb, sk);
6208 
6209 	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
6210 	inet_rsk(req)->ir_iif = sk->sk_bound_dev_if;
6211 
6212 	af_ops->init_req(req, sk, skb);
6213 
6214 	if (security_inet_conn_request(sk, skb, req))
6215 		goto drop_and_free;
6216 
6217 	if (!want_cookie && !isn) {
6218 		/* VJ's idea. We save last timestamp seen
6219 		 * from the destination in peer table, when entering
6220 		 * state TIME-WAIT, and check against it before
6221 		 * accepting new connection request.
6222 		 *
6223 		 * If "isn" is not zero, this request hit alive
6224 		 * timewait bucket, so that all the necessary checks
6225 		 * are made in the function processing timewait state.
6226 		 */
6227 		if (tcp_death_row.sysctl_tw_recycle) {
6228 			bool strict;
6229 
6230 			dst = af_ops->route_req(sk, &fl, req, &strict);
6231 
6232 			if (dst && strict &&
6233 			    !tcp_peer_is_proven(req, dst, true,
6234 						tmp_opt.saw_tstamp)) {
6235 				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
6236 				goto drop_and_release;
6237 			}
6238 		}
6239 		/* Kill the following clause, if you dislike this way. */
6240 		else if (!sysctl_tcp_syncookies &&
6241 			 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6242 			  (sysctl_max_syn_backlog >> 2)) &&
6243 			 !tcp_peer_is_proven(req, dst, false,
6244 					     tmp_opt.saw_tstamp)) {
6245 			/* Without syncookies last quarter of
6246 			 * backlog is filled with destinations,
6247 			 * proven to be alive.
6248 			 * It means that we continue to communicate
6249 			 * to destinations, already remembered
6250 			 * to the moment of synflood.
6251 			 */
6252 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6253 				    rsk_ops->family);
6254 			goto drop_and_release;
6255 		}
6256 
6257 		isn = af_ops->init_seq(skb);
6258 	}
6259 	if (!dst) {
6260 		dst = af_ops->route_req(sk, &fl, req, NULL);
6261 		if (!dst)
6262 			goto drop_and_free;
6263 	}
6264 
6265 	tcp_ecn_create_request(req, skb, sk, dst);
6266 
6267 	if (want_cookie) {
6268 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6269 		req->cookie_ts = tmp_opt.tstamp_ok;
6270 		if (!tmp_opt.tstamp_ok)
6271 			inet_rsk(req)->ecn_ok = 0;
6272 	}
6273 
6274 	tcp_rsk(req)->snt_isn = isn;
6275 	tcp_rsk(req)->txhash = net_tx_rndhash();
6276 	tcp_openreq_init_rwin(req, sk, dst);
6277 	if (!want_cookie) {
6278 		tcp_reqsk_record_syn(sk, req, skb);
6279 		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
6280 	}
6281 	if (fastopen_sk) {
6282 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
6283 				    &foc, false);
6284 		/* Add the child socket directly into the accept queue */
6285 		inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
6286 		sk->sk_data_ready(sk);
6287 		bh_unlock_sock(fastopen_sk);
6288 		sock_put(fastopen_sk);
6289 	} else {
6290 		tcp_rsk(req)->tfo_listener = false;
6291 		if (!want_cookie)
6292 			inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
6293 		af_ops->send_synack(sk, dst, &fl, req,
6294 				    &foc, !want_cookie);
6295 		if (want_cookie)
6296 			goto drop_and_free;
6297 	}
6298 	reqsk_put(req);
6299 	return 0;
6300 
6301 drop_and_release:
6302 	dst_release(dst);
6303 drop_and_free:
6304 	reqsk_free(req);
6305 drop:
6306 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
6307 	return 0;
6308 }
6309 EXPORT_SYMBOL(tcp_conn_request);
6310