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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#include <linux/module.h>
22#include <linux/gfp.h>
23#include <net/tcp.h>
24
25int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
26int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
27int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
28int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
29int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
30int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
31int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
32int sysctl_tcp_orphan_retries __read_mostly;
33int sysctl_tcp_thin_linear_timeouts __read_mostly;
34
35static void tcp_write_err(struct sock *sk)
36{
37 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
38 sk->sk_error_report(sk);
39
40 tcp_done(sk);
41 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
42}
43
44/* Do not allow orphaned sockets to eat all our resources.
45 * This is direct violation of TCP specs, but it is required
46 * to prevent DoS attacks. It is called when a retransmission timeout
47 * or zero probe timeout occurs on orphaned socket.
48 *
49 * Criteria is still not confirmed experimentally and may change.
50 * We kill the socket, if:
51 * 1. If number of orphaned sockets exceeds an administratively configured
52 * limit.
53 * 2. If we have strong memory pressure.
54 */
55static int tcp_out_of_resources(struct sock *sk, int do_reset)
56{
57 struct tcp_sock *tp = tcp_sk(sk);
58 int shift = 0;
59
60 /* If peer does not open window for long time, or did not transmit
61 * anything for long time, penalize it. */
62 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
63 shift++;
64
65 /* If some dubious ICMP arrived, penalize even more. */
66 if (sk->sk_err_soft)
67 shift++;
68
69 if (tcp_check_oom(sk, shift)) {
70 /* Catch exceptional cases, when connection requires reset.
71 * 1. Last segment was sent recently. */
72 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
73 /* 2. Window is closed. */
74 (!tp->snd_wnd && !tp->packets_out))
75 do_reset = 1;
76 if (do_reset)
77 tcp_send_active_reset(sk, GFP_ATOMIC);
78 tcp_done(sk);
79 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
80 return 1;
81 }
82 return 0;
83}
84
85/* Calculate maximal number or retries on an orphaned socket. */
86static int tcp_orphan_retries(struct sock *sk, int alive)
87{
88 int retries = sysctl_tcp_orphan_retries; /* May be zero. */
89
90 /* We know from an ICMP that something is wrong. */
91 if (sk->sk_err_soft && !alive)
92 retries = 0;
93
94 /* However, if socket sent something recently, select some safe
95 * number of retries. 8 corresponds to >100 seconds with minimal
96 * RTO of 200msec. */
97 if (retries == 0 && alive)
98 retries = 8;
99 return retries;
100}
101
102static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
103{
104 /* Black hole detection */
105 if (sysctl_tcp_mtu_probing) {
106 if (!icsk->icsk_mtup.enabled) {
107 icsk->icsk_mtup.enabled = 1;
108 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
109 } else {
110 struct tcp_sock *tp = tcp_sk(sk);
111 int mss;
112
113 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
114 mss = min(sysctl_tcp_base_mss, mss);
115 mss = max(mss, 68 - tp->tcp_header_len);
116 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
117 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
118 }
119 }
120}
121
122/* This function calculates a "timeout" which is equivalent to the timeout of a
123 * TCP connection after "boundary" unsuccessful, exponentially backed-off
124 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
125 * syn_set flag is set.
126 */
127static bool retransmits_timed_out(struct sock *sk,
128 unsigned int boundary,
129 unsigned int timeout,
130 bool syn_set)
131{
132 unsigned int linear_backoff_thresh, start_ts;
133 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
134
135 if (!inet_csk(sk)->icsk_retransmits)
136 return false;
137
138 if (unlikely(!tcp_sk(sk)->retrans_stamp))
139 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
140 else
141 start_ts = tcp_sk(sk)->retrans_stamp;
142
143 if (likely(timeout == 0)) {
144 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
145
146 if (boundary <= linear_backoff_thresh)
147 timeout = ((2 << boundary) - 1) * rto_base;
148 else
149 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
150 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
151 }
152 return (tcp_time_stamp - start_ts) >= timeout;
153}
154
155/* A write timeout has occurred. Process the after effects. */
156static int tcp_write_timeout(struct sock *sk)
157{
158 struct inet_connection_sock *icsk = inet_csk(sk);
159 struct tcp_sock *tp = tcp_sk(sk);
160 int retry_until;
161 bool do_reset, syn_set = false;
162
163 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
164 if (icsk->icsk_retransmits) {
165 dst_negative_advice(sk);
166 if (tp->syn_fastopen || tp->syn_data)
167 tcp_fastopen_cache_set(sk, 0, NULL, true);
168 if (tp->syn_data)
169 NET_INC_STATS_BH(sock_net(sk),
170 LINUX_MIB_TCPFASTOPENACTIVEFAIL);
171 }
172 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
173 syn_set = true;
174 } else {
175 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
176 /* Black hole detection */
177 tcp_mtu_probing(icsk, sk);
178
179 dst_negative_advice(sk);
180 }
181
182 retry_until = sysctl_tcp_retries2;
183 if (sock_flag(sk, SOCK_DEAD)) {
184 const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
185
186 retry_until = tcp_orphan_retries(sk, alive);
187 do_reset = alive ||
188 !retransmits_timed_out(sk, retry_until, 0, 0);
189
190 if (tcp_out_of_resources(sk, do_reset))
191 return 1;
192 }
193 }
194
195 if (retransmits_timed_out(sk, retry_until,
196 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
197 /* Has it gone just too far? */
198 tcp_write_err(sk);
199 return 1;
200 }
201 return 0;
202}
203
204void tcp_delack_timer_handler(struct sock *sk)
205{
206 struct tcp_sock *tp = tcp_sk(sk);
207 struct inet_connection_sock *icsk = inet_csk(sk);
208
209 sk_mem_reclaim_partial(sk);
210
211 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
212 goto out;
213
214 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
215 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
216 goto out;
217 }
218 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
219
220 if (!skb_queue_empty(&tp->ucopy.prequeue)) {
221 struct sk_buff *skb;
222
223 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
224
225 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
226 sk_backlog_rcv(sk, skb);
227
228 tp->ucopy.memory = 0;
229 }
230
231 if (inet_csk_ack_scheduled(sk)) {
232 if (!icsk->icsk_ack.pingpong) {
233 /* Delayed ACK missed: inflate ATO. */
234 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
235 } else {
236 /* Delayed ACK missed: leave pingpong mode and
237 * deflate ATO.
238 */
239 icsk->icsk_ack.pingpong = 0;
240 icsk->icsk_ack.ato = TCP_ATO_MIN;
241 }
242 tcp_send_ack(sk);
243 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
244 }
245
246out:
247 if (sk_under_memory_pressure(sk))
248 sk_mem_reclaim(sk);
249}
250
251static void tcp_delack_timer(unsigned long data)
252{
253 struct sock *sk = (struct sock *)data;
254
255 bh_lock_sock(sk);
256 if (!sock_owned_by_user(sk)) {
257 tcp_delack_timer_handler(sk);
258 } else {
259 inet_csk(sk)->icsk_ack.blocked = 1;
260 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
261 /* deleguate our work to tcp_release_cb() */
262 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
263 sock_hold(sk);
264 }
265 bh_unlock_sock(sk);
266 sock_put(sk);
267}
268
269static void tcp_probe_timer(struct sock *sk)
270{
271 struct inet_connection_sock *icsk = inet_csk(sk);
272 struct tcp_sock *tp = tcp_sk(sk);
273 int max_probes;
274
275 if (tp->packets_out || !tcp_send_head(sk)) {
276 icsk->icsk_probes_out = 0;
277 return;
278 }
279
280 /* *WARNING* RFC 1122 forbids this
281 *
282 * It doesn't AFAIK, because we kill the retransmit timer -AK
283 *
284 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
285 * this behaviour in Solaris down as a bug fix. [AC]
286 *
287 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
288 * even if they advertise zero window. Hence, connection is killed only
289 * if we received no ACKs for normal connection timeout. It is not killed
290 * only because window stays zero for some time, window may be zero
291 * until armageddon and even later. We are in full accordance
292 * with RFCs, only probe timer combines both retransmission timeout
293 * and probe timeout in one bottle. --ANK
294 */
295 max_probes = sysctl_tcp_retries2;
296
297 if (sock_flag(sk, SOCK_DEAD)) {
298 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
299
300 max_probes = tcp_orphan_retries(sk, alive);
301
302 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
303 return;
304 }
305
306 if (icsk->icsk_probes_out > max_probes) {
307 tcp_write_err(sk);
308 } else {
309 /* Only send another probe if we didn't close things up. */
310 tcp_send_probe0(sk);
311 }
312}
313
314/*
315 * Timer for Fast Open socket to retransmit SYNACK. Note that the
316 * sk here is the child socket, not the parent (listener) socket.
317 */
318static void tcp_fastopen_synack_timer(struct sock *sk)
319{
320 struct inet_connection_sock *icsk = inet_csk(sk);
321 int max_retries = icsk->icsk_syn_retries ? :
322 sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
323 struct request_sock *req;
324
325 req = tcp_sk(sk)->fastopen_rsk;
326 req->rsk_ops->syn_ack_timeout(sk, req);
327
328 if (req->num_timeout >= max_retries) {
329 tcp_write_err(sk);
330 return;
331 }
332 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
333 * returned from rtx_syn_ack() to make it more persistent like
334 * regular retransmit because if the child socket has been accepted
335 * it's not good to give up too easily.
336 */
337 inet_rtx_syn_ack(sk, req);
338 req->num_timeout++;
339 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
340 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
341}
342
343/*
344 * The TCP retransmit timer.
345 */
346
347void tcp_retransmit_timer(struct sock *sk)
348{
349 struct tcp_sock *tp = tcp_sk(sk);
350 struct inet_connection_sock *icsk = inet_csk(sk);
351
352 if (tp->fastopen_rsk) {
353 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
354 sk->sk_state != TCP_FIN_WAIT1);
355 tcp_fastopen_synack_timer(sk);
356 /* Before we receive ACK to our SYN-ACK don't retransmit
357 * anything else (e.g., data or FIN segments).
358 */
359 return;
360 }
361 if (!tp->packets_out)
362 goto out;
363
364 WARN_ON(tcp_write_queue_empty(sk));
365
366 tp->tlp_high_seq = 0;
367
368 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
369 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
370 /* Receiver dastardly shrinks window. Our retransmits
371 * become zero probes, but we should not timeout this
372 * connection. If the socket is an orphan, time it out,
373 * we cannot allow such beasts to hang infinitely.
374 */
375 struct inet_sock *inet = inet_sk(sk);
376 if (sk->sk_family == AF_INET) {
377 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
378 &inet->inet_daddr,
379 ntohs(inet->inet_dport), inet->inet_num,
380 tp->snd_una, tp->snd_nxt);
381 }
382#if IS_ENABLED(CONFIG_IPV6)
383 else if (sk->sk_family == AF_INET6) {
384 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
385 &sk->sk_v6_daddr,
386 ntohs(inet->inet_dport), inet->inet_num,
387 tp->snd_una, tp->snd_nxt);
388 }
389#endif
390 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
391 tcp_write_err(sk);
392 goto out;
393 }
394 tcp_enter_loss(sk, 0);
395 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
396 __sk_dst_reset(sk);
397 goto out_reset_timer;
398 }
399
400 if (tcp_write_timeout(sk))
401 goto out;
402
403 if (icsk->icsk_retransmits == 0) {
404 int mib_idx;
405
406 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
407 if (tcp_is_sack(tp))
408 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
409 else
410 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
411 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
412 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
413 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
414 tp->sacked_out) {
415 if (tcp_is_sack(tp))
416 mib_idx = LINUX_MIB_TCPSACKFAILURES;
417 else
418 mib_idx = LINUX_MIB_TCPRENOFAILURES;
419 } else {
420 mib_idx = LINUX_MIB_TCPTIMEOUTS;
421 }
422 NET_INC_STATS_BH(sock_net(sk), mib_idx);
423 }
424
425 tcp_enter_loss(sk, 0);
426
427 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
428 /* Retransmission failed because of local congestion,
429 * do not backoff.
430 */
431 if (!icsk->icsk_retransmits)
432 icsk->icsk_retransmits = 1;
433 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
434 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
435 TCP_RTO_MAX);
436 goto out;
437 }
438
439 /* Increase the timeout each time we retransmit. Note that
440 * we do not increase the rtt estimate. rto is initialized
441 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
442 * that doubling rto each time is the least we can get away with.
443 * In KA9Q, Karn uses this for the first few times, and then
444 * goes to quadratic. netBSD doubles, but only goes up to *64,
445 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
446 * defined in the protocol as the maximum possible RTT. I guess
447 * we'll have to use something other than TCP to talk to the
448 * University of Mars.
449 *
450 * PAWS allows us longer timeouts and large windows, so once
451 * implemented ftp to mars will work nicely. We will have to fix
452 * the 120 second clamps though!
453 */
454 icsk->icsk_backoff++;
455 icsk->icsk_retransmits++;
456
457out_reset_timer:
458 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
459 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
460 * might be increased if the stream oscillates between thin and thick,
461 * thus the old value might already be too high compared to the value
462 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
463 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
464 * exponential backoff behaviour to avoid continue hammering
465 * linear-timeout retransmissions into a black hole
466 */
467 if (sk->sk_state == TCP_ESTABLISHED &&
468 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
469 tcp_stream_is_thin(tp) &&
470 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
471 icsk->icsk_backoff = 0;
472 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
473 } else {
474 /* Use normal (exponential) backoff */
475 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
476 }
477 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
478 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
479 __sk_dst_reset(sk);
480
481out:;
482}
483
484void tcp_write_timer_handler(struct sock *sk)
485{
486 struct inet_connection_sock *icsk = inet_csk(sk);
487 int event;
488
489 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
490 goto out;
491
492 if (time_after(icsk->icsk_timeout, jiffies)) {
493 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
494 goto out;
495 }
496
497 event = icsk->icsk_pending;
498
499 switch (event) {
500 case ICSK_TIME_EARLY_RETRANS:
501 tcp_resume_early_retransmit(sk);
502 break;
503 case ICSK_TIME_LOSS_PROBE:
504 tcp_send_loss_probe(sk);
505 break;
506 case ICSK_TIME_RETRANS:
507 icsk->icsk_pending = 0;
508 tcp_retransmit_timer(sk);
509 break;
510 case ICSK_TIME_PROBE0:
511 icsk->icsk_pending = 0;
512 tcp_probe_timer(sk);
513 break;
514 }
515
516out:
517 sk_mem_reclaim(sk);
518}
519
520static void tcp_write_timer(unsigned long data)
521{
522 struct sock *sk = (struct sock *)data;
523
524 bh_lock_sock(sk);
525 if (!sock_owned_by_user(sk)) {
526 tcp_write_timer_handler(sk);
527 } else {
528 /* deleguate our work to tcp_release_cb() */
529 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
530 sock_hold(sk);
531 }
532 bh_unlock_sock(sk);
533 sock_put(sk);
534}
535
536/*
537 * Timer for listening sockets
538 */
539
540static void tcp_synack_timer(struct sock *sk)
541{
542 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
543 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
544}
545
546void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
547{
548 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
549}
550EXPORT_SYMBOL(tcp_syn_ack_timeout);
551
552void tcp_set_keepalive(struct sock *sk, int val)
553{
554 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
555 return;
556
557 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
558 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
559 else if (!val)
560 inet_csk_delete_keepalive_timer(sk);
561}
562
563
564static void tcp_keepalive_timer (unsigned long data)
565{
566 struct sock *sk = (struct sock *) data;
567 struct inet_connection_sock *icsk = inet_csk(sk);
568 struct tcp_sock *tp = tcp_sk(sk);
569 u32 elapsed;
570
571 /* Only process if socket is not in use. */
572 bh_lock_sock(sk);
573 if (sock_owned_by_user(sk)) {
574 /* Try again later. */
575 inet_csk_reset_keepalive_timer (sk, HZ/20);
576 goto out;
577 }
578
579 if (sk->sk_state == TCP_LISTEN) {
580 tcp_synack_timer(sk);
581 goto out;
582 }
583
584 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
585 if (tp->linger2 >= 0) {
586 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
587
588 if (tmo > 0) {
589 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
590 goto out;
591 }
592 }
593 tcp_send_active_reset(sk, GFP_ATOMIC);
594 goto death;
595 }
596
597 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
598 goto out;
599
600 elapsed = keepalive_time_when(tp);
601
602 /* It is alive without keepalive 8) */
603 if (tp->packets_out || tcp_send_head(sk))
604 goto resched;
605
606 elapsed = keepalive_time_elapsed(tp);
607
608 if (elapsed >= keepalive_time_when(tp)) {
609 /* If the TCP_USER_TIMEOUT option is enabled, use that
610 * to determine when to timeout instead.
611 */
612 if ((icsk->icsk_user_timeout != 0 &&
613 elapsed >= icsk->icsk_user_timeout &&
614 icsk->icsk_probes_out > 0) ||
615 (icsk->icsk_user_timeout == 0 &&
616 icsk->icsk_probes_out >= keepalive_probes(tp))) {
617 tcp_send_active_reset(sk, GFP_ATOMIC);
618 tcp_write_err(sk);
619 goto out;
620 }
621 if (tcp_write_wakeup(sk) <= 0) {
622 icsk->icsk_probes_out++;
623 elapsed = keepalive_intvl_when(tp);
624 } else {
625 /* If keepalive was lost due to local congestion,
626 * try harder.
627 */
628 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
629 }
630 } else {
631 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
632 elapsed = keepalive_time_when(tp) - elapsed;
633 }
634
635 sk_mem_reclaim(sk);
636
637resched:
638 inet_csk_reset_keepalive_timer (sk, elapsed);
639 goto out;
640
641death:
642 tcp_done(sk);
643
644out:
645 bh_unlock_sock(sk);
646 sock_put(sk);
647}
648
649void tcp_init_xmit_timers(struct sock *sk)
650{
651 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
652 &tcp_keepalive_timer);
653}
654EXPORT_SYMBOL(tcp_init_xmit_timers);
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#include <linux/module.h>
22#include <linux/gfp.h>
23#include <net/tcp.h>
24
25int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
26int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
27int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
28int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
29int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
30int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
31int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
32int sysctl_tcp_orphan_retries __read_mostly;
33int sysctl_tcp_thin_linear_timeouts __read_mostly;
34
35static void tcp_write_timer(unsigned long);
36static void tcp_delack_timer(unsigned long);
37static void tcp_keepalive_timer (unsigned long data);
38
39void tcp_init_xmit_timers(struct sock *sk)
40{
41 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
42 &tcp_keepalive_timer);
43}
44EXPORT_SYMBOL(tcp_init_xmit_timers);
45
46static void tcp_write_err(struct sock *sk)
47{
48 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
49 sk->sk_error_report(sk);
50
51 tcp_done(sk);
52 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
53}
54
55/* Do not allow orphaned sockets to eat all our resources.
56 * This is direct violation of TCP specs, but it is required
57 * to prevent DoS attacks. It is called when a retransmission timeout
58 * or zero probe timeout occurs on orphaned socket.
59 *
60 * Criteria is still not confirmed experimentally and may change.
61 * We kill the socket, if:
62 * 1. If number of orphaned sockets exceeds an administratively configured
63 * limit.
64 * 2. If we have strong memory pressure.
65 */
66static int tcp_out_of_resources(struct sock *sk, int do_reset)
67{
68 struct tcp_sock *tp = tcp_sk(sk);
69 int shift = 0;
70
71 /* If peer does not open window for long time, or did not transmit
72 * anything for long time, penalize it. */
73 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
74 shift++;
75
76 /* If some dubious ICMP arrived, penalize even more. */
77 if (sk->sk_err_soft)
78 shift++;
79
80 if (tcp_check_oom(sk, shift)) {
81 /* Catch exceptional cases, when connection requires reset.
82 * 1. Last segment was sent recently. */
83 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
84 /* 2. Window is closed. */
85 (!tp->snd_wnd && !tp->packets_out))
86 do_reset = 1;
87 if (do_reset)
88 tcp_send_active_reset(sk, GFP_ATOMIC);
89 tcp_done(sk);
90 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
91 return 1;
92 }
93 return 0;
94}
95
96/* Calculate maximal number or retries on an orphaned socket. */
97static int tcp_orphan_retries(struct sock *sk, int alive)
98{
99 int retries = sysctl_tcp_orphan_retries; /* May be zero. */
100
101 /* We know from an ICMP that something is wrong. */
102 if (sk->sk_err_soft && !alive)
103 retries = 0;
104
105 /* However, if socket sent something recently, select some safe
106 * number of retries. 8 corresponds to >100 seconds with minimal
107 * RTO of 200msec. */
108 if (retries == 0 && alive)
109 retries = 8;
110 return retries;
111}
112
113static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
114{
115 /* Black hole detection */
116 if (sysctl_tcp_mtu_probing) {
117 if (!icsk->icsk_mtup.enabled) {
118 icsk->icsk_mtup.enabled = 1;
119 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
120 } else {
121 struct tcp_sock *tp = tcp_sk(sk);
122 int mss;
123
124 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
125 mss = min(sysctl_tcp_base_mss, mss);
126 mss = max(mss, 68 - tp->tcp_header_len);
127 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
128 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
129 }
130 }
131}
132
133/* This function calculates a "timeout" which is equivalent to the timeout of a
134 * TCP connection after "boundary" unsuccessful, exponentially backed-off
135 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
136 * syn_set flag is set.
137 */
138static bool retransmits_timed_out(struct sock *sk,
139 unsigned int boundary,
140 unsigned int timeout,
141 bool syn_set)
142{
143 unsigned int linear_backoff_thresh, start_ts;
144 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
145
146 if (!inet_csk(sk)->icsk_retransmits)
147 return false;
148
149 if (unlikely(!tcp_sk(sk)->retrans_stamp))
150 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
151 else
152 start_ts = tcp_sk(sk)->retrans_stamp;
153
154 if (likely(timeout == 0)) {
155 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
156
157 if (boundary <= linear_backoff_thresh)
158 timeout = ((2 << boundary) - 1) * rto_base;
159 else
160 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
161 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
162 }
163 return (tcp_time_stamp - start_ts) >= timeout;
164}
165
166/* A write timeout has occurred. Process the after effects. */
167static int tcp_write_timeout(struct sock *sk)
168{
169 struct inet_connection_sock *icsk = inet_csk(sk);
170 int retry_until;
171 bool do_reset, syn_set = false;
172
173 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
174 if (icsk->icsk_retransmits)
175 dst_negative_advice(sk);
176 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
177 syn_set = true;
178 } else {
179 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
180 /* Black hole detection */
181 tcp_mtu_probing(icsk, sk);
182
183 dst_negative_advice(sk);
184 }
185
186 retry_until = sysctl_tcp_retries2;
187 if (sock_flag(sk, SOCK_DEAD)) {
188 const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
189
190 retry_until = tcp_orphan_retries(sk, alive);
191 do_reset = alive ||
192 !retransmits_timed_out(sk, retry_until, 0, 0);
193
194 if (tcp_out_of_resources(sk, do_reset))
195 return 1;
196 }
197 }
198
199 if (retransmits_timed_out(sk, retry_until,
200 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
201 /* Has it gone just too far? */
202 tcp_write_err(sk);
203 return 1;
204 }
205 return 0;
206}
207
208static void tcp_delack_timer(unsigned long data)
209{
210 struct sock *sk = (struct sock *)data;
211 struct tcp_sock *tp = tcp_sk(sk);
212 struct inet_connection_sock *icsk = inet_csk(sk);
213
214 bh_lock_sock(sk);
215 if (sock_owned_by_user(sk)) {
216 /* Try again later. */
217 icsk->icsk_ack.blocked = 1;
218 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
219 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
220 goto out_unlock;
221 }
222
223 sk_mem_reclaim_partial(sk);
224
225 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
226 goto out;
227
228 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
229 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
230 goto out;
231 }
232 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
233
234 if (!skb_queue_empty(&tp->ucopy.prequeue)) {
235 struct sk_buff *skb;
236
237 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
238
239 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
240 sk_backlog_rcv(sk, skb);
241
242 tp->ucopy.memory = 0;
243 }
244
245 if (inet_csk_ack_scheduled(sk)) {
246 if (!icsk->icsk_ack.pingpong) {
247 /* Delayed ACK missed: inflate ATO. */
248 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
249 } else {
250 /* Delayed ACK missed: leave pingpong mode and
251 * deflate ATO.
252 */
253 icsk->icsk_ack.pingpong = 0;
254 icsk->icsk_ack.ato = TCP_ATO_MIN;
255 }
256 tcp_send_ack(sk);
257 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
258 }
259
260out:
261 if (sk_under_memory_pressure(sk))
262 sk_mem_reclaim(sk);
263out_unlock:
264 bh_unlock_sock(sk);
265 sock_put(sk);
266}
267
268static void tcp_probe_timer(struct sock *sk)
269{
270 struct inet_connection_sock *icsk = inet_csk(sk);
271 struct tcp_sock *tp = tcp_sk(sk);
272 int max_probes;
273
274 if (tp->packets_out || !tcp_send_head(sk)) {
275 icsk->icsk_probes_out = 0;
276 return;
277 }
278
279 /* *WARNING* RFC 1122 forbids this
280 *
281 * It doesn't AFAIK, because we kill the retransmit timer -AK
282 *
283 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
284 * this behaviour in Solaris down as a bug fix. [AC]
285 *
286 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
287 * even if they advertise zero window. Hence, connection is killed only
288 * if we received no ACKs for normal connection timeout. It is not killed
289 * only because window stays zero for some time, window may be zero
290 * until armageddon and even later. We are in full accordance
291 * with RFCs, only probe timer combines both retransmission timeout
292 * and probe timeout in one bottle. --ANK
293 */
294 max_probes = sysctl_tcp_retries2;
295
296 if (sock_flag(sk, SOCK_DEAD)) {
297 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
298
299 max_probes = tcp_orphan_retries(sk, alive);
300
301 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
302 return;
303 }
304
305 if (icsk->icsk_probes_out > max_probes) {
306 tcp_write_err(sk);
307 } else {
308 /* Only send another probe if we didn't close things up. */
309 tcp_send_probe0(sk);
310 }
311}
312
313/*
314 * The TCP retransmit timer.
315 */
316
317void tcp_retransmit_timer(struct sock *sk)
318{
319 struct tcp_sock *tp = tcp_sk(sk);
320 struct inet_connection_sock *icsk = inet_csk(sk);
321
322 if (tp->early_retrans_delayed) {
323 tcp_resume_early_retransmit(sk);
324 return;
325 }
326
327 if (!tp->packets_out)
328 goto out;
329
330 WARN_ON(tcp_write_queue_empty(sk));
331
332 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
333 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
334 /* Receiver dastardly shrinks window. Our retransmits
335 * become zero probes, but we should not timeout this
336 * connection. If the socket is an orphan, time it out,
337 * we cannot allow such beasts to hang infinitely.
338 */
339 struct inet_sock *inet = inet_sk(sk);
340 if (sk->sk_family == AF_INET) {
341 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
342 &inet->inet_daddr,
343 ntohs(inet->inet_dport), inet->inet_num,
344 tp->snd_una, tp->snd_nxt);
345 }
346#if IS_ENABLED(CONFIG_IPV6)
347 else if (sk->sk_family == AF_INET6) {
348 struct ipv6_pinfo *np = inet6_sk(sk);
349 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
350 &np->daddr,
351 ntohs(inet->inet_dport), inet->inet_num,
352 tp->snd_una, tp->snd_nxt);
353 }
354#endif
355 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
356 tcp_write_err(sk);
357 goto out;
358 }
359 tcp_enter_loss(sk, 0);
360 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
361 __sk_dst_reset(sk);
362 goto out_reset_timer;
363 }
364
365 if (tcp_write_timeout(sk))
366 goto out;
367
368 if (icsk->icsk_retransmits == 0) {
369 int mib_idx;
370
371 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
372 if (tcp_is_sack(tp))
373 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
374 else
375 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
376 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
377 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
378 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
379 tp->sacked_out) {
380 if (tcp_is_sack(tp))
381 mib_idx = LINUX_MIB_TCPSACKFAILURES;
382 else
383 mib_idx = LINUX_MIB_TCPRENOFAILURES;
384 } else {
385 mib_idx = LINUX_MIB_TCPTIMEOUTS;
386 }
387 NET_INC_STATS_BH(sock_net(sk), mib_idx);
388 }
389
390 if (tcp_use_frto(sk)) {
391 tcp_enter_frto(sk);
392 } else {
393 tcp_enter_loss(sk, 0);
394 }
395
396 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
397 /* Retransmission failed because of local congestion,
398 * do not backoff.
399 */
400 if (!icsk->icsk_retransmits)
401 icsk->icsk_retransmits = 1;
402 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
403 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
404 TCP_RTO_MAX);
405 goto out;
406 }
407
408 /* Increase the timeout each time we retransmit. Note that
409 * we do not increase the rtt estimate. rto is initialized
410 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
411 * that doubling rto each time is the least we can get away with.
412 * In KA9Q, Karn uses this for the first few times, and then
413 * goes to quadratic. netBSD doubles, but only goes up to *64,
414 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
415 * defined in the protocol as the maximum possible RTT. I guess
416 * we'll have to use something other than TCP to talk to the
417 * University of Mars.
418 *
419 * PAWS allows us longer timeouts and large windows, so once
420 * implemented ftp to mars will work nicely. We will have to fix
421 * the 120 second clamps though!
422 */
423 icsk->icsk_backoff++;
424 icsk->icsk_retransmits++;
425
426out_reset_timer:
427 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
428 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
429 * might be increased if the stream oscillates between thin and thick,
430 * thus the old value might already be too high compared to the value
431 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
432 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
433 * exponential backoff behaviour to avoid continue hammering
434 * linear-timeout retransmissions into a black hole
435 */
436 if (sk->sk_state == TCP_ESTABLISHED &&
437 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
438 tcp_stream_is_thin(tp) &&
439 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
440 icsk->icsk_backoff = 0;
441 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
442 } else {
443 /* Use normal (exponential) backoff */
444 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
445 }
446 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
447 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
448 __sk_dst_reset(sk);
449
450out:;
451}
452
453static void tcp_write_timer(unsigned long data)
454{
455 struct sock *sk = (struct sock *)data;
456 struct inet_connection_sock *icsk = inet_csk(sk);
457 int event;
458
459 bh_lock_sock(sk);
460 if (sock_owned_by_user(sk)) {
461 /* Try again later */
462 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
463 goto out_unlock;
464 }
465
466 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
467 goto out;
468
469 if (time_after(icsk->icsk_timeout, jiffies)) {
470 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
471 goto out;
472 }
473
474 event = icsk->icsk_pending;
475 icsk->icsk_pending = 0;
476
477 switch (event) {
478 case ICSK_TIME_RETRANS:
479 tcp_retransmit_timer(sk);
480 break;
481 case ICSK_TIME_PROBE0:
482 tcp_probe_timer(sk);
483 break;
484 }
485
486out:
487 sk_mem_reclaim(sk);
488out_unlock:
489 bh_unlock_sock(sk);
490 sock_put(sk);
491}
492
493/*
494 * Timer for listening sockets
495 */
496
497static void tcp_synack_timer(struct sock *sk)
498{
499 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
500 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
501}
502
503void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
504{
505 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
506}
507EXPORT_SYMBOL(tcp_syn_ack_timeout);
508
509void tcp_set_keepalive(struct sock *sk, int val)
510{
511 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
512 return;
513
514 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
515 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
516 else if (!val)
517 inet_csk_delete_keepalive_timer(sk);
518}
519
520
521static void tcp_keepalive_timer (unsigned long data)
522{
523 struct sock *sk = (struct sock *) data;
524 struct inet_connection_sock *icsk = inet_csk(sk);
525 struct tcp_sock *tp = tcp_sk(sk);
526 u32 elapsed;
527
528 /* Only process if socket is not in use. */
529 bh_lock_sock(sk);
530 if (sock_owned_by_user(sk)) {
531 /* Try again later. */
532 inet_csk_reset_keepalive_timer (sk, HZ/20);
533 goto out;
534 }
535
536 if (sk->sk_state == TCP_LISTEN) {
537 tcp_synack_timer(sk);
538 goto out;
539 }
540
541 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
542 if (tp->linger2 >= 0) {
543 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
544
545 if (tmo > 0) {
546 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
547 goto out;
548 }
549 }
550 tcp_send_active_reset(sk, GFP_ATOMIC);
551 goto death;
552 }
553
554 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
555 goto out;
556
557 elapsed = keepalive_time_when(tp);
558
559 /* It is alive without keepalive 8) */
560 if (tp->packets_out || tcp_send_head(sk))
561 goto resched;
562
563 elapsed = keepalive_time_elapsed(tp);
564
565 if (elapsed >= keepalive_time_when(tp)) {
566 /* If the TCP_USER_TIMEOUT option is enabled, use that
567 * to determine when to timeout instead.
568 */
569 if ((icsk->icsk_user_timeout != 0 &&
570 elapsed >= icsk->icsk_user_timeout &&
571 icsk->icsk_probes_out > 0) ||
572 (icsk->icsk_user_timeout == 0 &&
573 icsk->icsk_probes_out >= keepalive_probes(tp))) {
574 tcp_send_active_reset(sk, GFP_ATOMIC);
575 tcp_write_err(sk);
576 goto out;
577 }
578 if (tcp_write_wakeup(sk) <= 0) {
579 icsk->icsk_probes_out++;
580 elapsed = keepalive_intvl_when(tp);
581 } else {
582 /* If keepalive was lost due to local congestion,
583 * try harder.
584 */
585 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
586 }
587 } else {
588 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
589 elapsed = keepalive_time_when(tp) - elapsed;
590 }
591
592 sk_mem_reclaim(sk);
593
594resched:
595 inet_csk_reset_keepalive_timer (sk, elapsed);
596 goto out;
597
598death:
599 tcp_done(sk);
600
601out:
602 bh_unlock_sock(sk);
603 sock_put(sk);
604}