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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_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}
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_too_many_orphans(sk, shift)) {
81 if (net_ratelimit())
82 printk(KERN_INFO "Out of socket memory\n");
83
84 /* Catch exceptional cases, when connection requires reset.
85 * 1. Last segment was sent recently. */
86 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
87 /* 2. Window is closed. */
88 (!tp->snd_wnd && !tp->packets_out))
89 do_reset = 1;
90 if (do_reset)
91 tcp_send_active_reset(sk, GFP_ATOMIC);
92 tcp_done(sk);
93 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
94 return 1;
95 }
96 return 0;
97}
98
99/* Calculate maximal number or retries on an orphaned socket. */
100static int tcp_orphan_retries(struct sock *sk, int alive)
101{
102 int retries = sysctl_tcp_orphan_retries; /* May be zero. */
103
104 /* We know from an ICMP that something is wrong. */
105 if (sk->sk_err_soft && !alive)
106 retries = 0;
107
108 /* However, if socket sent something recently, select some safe
109 * number of retries. 8 corresponds to >100 seconds with minimal
110 * RTO of 200msec. */
111 if (retries == 0 && alive)
112 retries = 8;
113 return retries;
114}
115
116static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
117{
118 /* Black hole detection */
119 if (sysctl_tcp_mtu_probing) {
120 if (!icsk->icsk_mtup.enabled) {
121 icsk->icsk_mtup.enabled = 1;
122 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
123 } else {
124 struct tcp_sock *tp = tcp_sk(sk);
125 int mss;
126
127 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
128 mss = min(sysctl_tcp_base_mss, mss);
129 mss = max(mss, 68 - tp->tcp_header_len);
130 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
131 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
132 }
133 }
134}
135
136/* This function calculates a "timeout" which is equivalent to the timeout of a
137 * TCP connection after "boundary" unsuccessful, exponentially backed-off
138 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
139 * syn_set flag is set.
140 */
141static bool retransmits_timed_out(struct sock *sk,
142 unsigned int boundary,
143 unsigned int timeout,
144 bool syn_set)
145{
146 unsigned int linear_backoff_thresh, start_ts;
147 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
148
149 if (!inet_csk(sk)->icsk_retransmits)
150 return false;
151
152 if (unlikely(!tcp_sk(sk)->retrans_stamp))
153 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
154 else
155 start_ts = tcp_sk(sk)->retrans_stamp;
156
157 if (likely(timeout == 0)) {
158 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
159
160 if (boundary <= linear_backoff_thresh)
161 timeout = ((2 << boundary) - 1) * rto_base;
162 else
163 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
164 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
165 }
166 return (tcp_time_stamp - start_ts) >= timeout;
167}
168
169/* A write timeout has occurred. Process the after effects. */
170static int tcp_write_timeout(struct sock *sk)
171{
172 struct inet_connection_sock *icsk = inet_csk(sk);
173 int retry_until;
174 bool do_reset, syn_set = 0;
175
176 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
177 if (icsk->icsk_retransmits)
178 dst_negative_advice(sk);
179 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
180 syn_set = 1;
181 } else {
182 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
183 /* Black hole detection */
184 tcp_mtu_probing(icsk, sk);
185
186 dst_negative_advice(sk);
187 }
188
189 retry_until = sysctl_tcp_retries2;
190 if (sock_flag(sk, SOCK_DEAD)) {
191 const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
192
193 retry_until = tcp_orphan_retries(sk, alive);
194 do_reset = alive ||
195 !retransmits_timed_out(sk, retry_until, 0, 0);
196
197 if (tcp_out_of_resources(sk, do_reset))
198 return 1;
199 }
200 }
201
202 if (retransmits_timed_out(sk, retry_until,
203 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
204 /* Has it gone just too far? */
205 tcp_write_err(sk);
206 return 1;
207 }
208 return 0;
209}
210
211static void tcp_delack_timer(unsigned long data)
212{
213 struct sock *sk = (struct sock *)data;
214 struct tcp_sock *tp = tcp_sk(sk);
215 struct inet_connection_sock *icsk = inet_csk(sk);
216
217 bh_lock_sock(sk);
218 if (sock_owned_by_user(sk)) {
219 /* Try again later. */
220 icsk->icsk_ack.blocked = 1;
221 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
222 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
223 goto out_unlock;
224 }
225
226 sk_mem_reclaim_partial(sk);
227
228 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
229 goto out;
230
231 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
232 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
233 goto out;
234 }
235 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
236
237 if (!skb_queue_empty(&tp->ucopy.prequeue)) {
238 struct sk_buff *skb;
239
240 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
241
242 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
243 sk_backlog_rcv(sk, skb);
244
245 tp->ucopy.memory = 0;
246 }
247
248 if (inet_csk_ack_scheduled(sk)) {
249 if (!icsk->icsk_ack.pingpong) {
250 /* Delayed ACK missed: inflate ATO. */
251 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
252 } else {
253 /* Delayed ACK missed: leave pingpong mode and
254 * deflate ATO.
255 */
256 icsk->icsk_ack.pingpong = 0;
257 icsk->icsk_ack.ato = TCP_ATO_MIN;
258 }
259 tcp_send_ack(sk);
260 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
261 }
262
263out:
264 if (tcp_memory_pressure)
265 sk_mem_reclaim(sk);
266out_unlock:
267 bh_unlock_sock(sk);
268 sock_put(sk);
269}
270
271static void tcp_probe_timer(struct sock *sk)
272{
273 struct inet_connection_sock *icsk = inet_csk(sk);
274 struct tcp_sock *tp = tcp_sk(sk);
275 int max_probes;
276
277 if (tp->packets_out || !tcp_send_head(sk)) {
278 icsk->icsk_probes_out = 0;
279 return;
280 }
281
282 /* *WARNING* RFC 1122 forbids this
283 *
284 * It doesn't AFAIK, because we kill the retransmit timer -AK
285 *
286 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
287 * this behaviour in Solaris down as a bug fix. [AC]
288 *
289 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
290 * even if they advertise zero window. Hence, connection is killed only
291 * if we received no ACKs for normal connection timeout. It is not killed
292 * only because window stays zero for some time, window may be zero
293 * until armageddon and even later. We are in full accordance
294 * with RFCs, only probe timer combines both retransmission timeout
295 * and probe timeout in one bottle. --ANK
296 */
297 max_probes = sysctl_tcp_retries2;
298
299 if (sock_flag(sk, SOCK_DEAD)) {
300 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
301
302 max_probes = tcp_orphan_retries(sk, alive);
303
304 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
305 return;
306 }
307
308 if (icsk->icsk_probes_out > max_probes) {
309 tcp_write_err(sk);
310 } else {
311 /* Only send another probe if we didn't close things up. */
312 tcp_send_probe0(sk);
313 }
314}
315
316/*
317 * The TCP retransmit timer.
318 */
319
320void tcp_retransmit_timer(struct sock *sk)
321{
322 struct tcp_sock *tp = tcp_sk(sk);
323 struct inet_connection_sock *icsk = inet_csk(sk);
324
325 if (!tp->packets_out)
326 goto out;
327
328 WARN_ON(tcp_write_queue_empty(sk));
329
330 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
331 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
332 /* Receiver dastardly shrinks window. Our retransmits
333 * become zero probes, but we should not timeout this
334 * connection. If the socket is an orphan, time it out,
335 * we cannot allow such beasts to hang infinitely.
336 */
337#ifdef TCP_DEBUG
338 struct inet_sock *inet = inet_sk(sk);
339 if (sk->sk_family == AF_INET) {
340 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
341 &inet->inet_daddr, ntohs(inet->inet_dport),
342 inet->inet_num, tp->snd_una, tp->snd_nxt);
343 }
344#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
345 else if (sk->sk_family == AF_INET6) {
346 struct ipv6_pinfo *np = inet6_sk(sk);
347 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
348 &np->daddr, ntohs(inet->inet_dport),
349 inet->inet_num, tp->snd_una, tp->snd_nxt);
350 }
351#endif
352#endif
353 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
354 tcp_write_err(sk);
355 goto out;
356 }
357 tcp_enter_loss(sk, 0);
358 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
359 __sk_dst_reset(sk);
360 goto out_reset_timer;
361 }
362
363 if (tcp_write_timeout(sk))
364 goto out;
365
366 if (icsk->icsk_retransmits == 0) {
367 int mib_idx;
368
369 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
370 if (tcp_is_sack(tp))
371 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
372 else
373 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
374 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
375 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
376 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
377 tp->sacked_out) {
378 if (tcp_is_sack(tp))
379 mib_idx = LINUX_MIB_TCPSACKFAILURES;
380 else
381 mib_idx = LINUX_MIB_TCPRENOFAILURES;
382 } else {
383 mib_idx = LINUX_MIB_TCPTIMEOUTS;
384 }
385 NET_INC_STATS_BH(sock_net(sk), mib_idx);
386 }
387
388 if (tcp_use_frto(sk)) {
389 tcp_enter_frto(sk);
390 } else {
391 tcp_enter_loss(sk, 0);
392 }
393
394 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
395 /* Retransmission failed because of local congestion,
396 * do not backoff.
397 */
398 if (!icsk->icsk_retransmits)
399 icsk->icsk_retransmits = 1;
400 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
401 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
402 TCP_RTO_MAX);
403 goto out;
404 }
405
406 /* Increase the timeout each time we retransmit. Note that
407 * we do not increase the rtt estimate. rto is initialized
408 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
409 * that doubling rto each time is the least we can get away with.
410 * In KA9Q, Karn uses this for the first few times, and then
411 * goes to quadratic. netBSD doubles, but only goes up to *64,
412 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
413 * defined in the protocol as the maximum possible RTT. I guess
414 * we'll have to use something other than TCP to talk to the
415 * University of Mars.
416 *
417 * PAWS allows us longer timeouts and large windows, so once
418 * implemented ftp to mars will work nicely. We will have to fix
419 * the 120 second clamps though!
420 */
421 icsk->icsk_backoff++;
422 icsk->icsk_retransmits++;
423
424out_reset_timer:
425 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
426 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
427 * might be increased if the stream oscillates between thin and thick,
428 * thus the old value might already be too high compared to the value
429 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
430 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
431 * exponential backoff behaviour to avoid continue hammering
432 * linear-timeout retransmissions into a black hole
433 */
434 if (sk->sk_state == TCP_ESTABLISHED &&
435 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
436 tcp_stream_is_thin(tp) &&
437 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
438 icsk->icsk_backoff = 0;
439 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
440 } else {
441 /* Use normal (exponential) backoff */
442 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
443 }
444 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
445 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
446 __sk_dst_reset(sk);
447
448out:;
449}
450
451static void tcp_write_timer(unsigned long data)
452{
453 struct sock *sk = (struct sock *)data;
454 struct inet_connection_sock *icsk = inet_csk(sk);
455 int event;
456
457 bh_lock_sock(sk);
458 if (sock_owned_by_user(sk)) {
459 /* Try again later */
460 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
461 goto out_unlock;
462 }
463
464 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
465 goto out;
466
467 if (time_after(icsk->icsk_timeout, jiffies)) {
468 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
469 goto out;
470 }
471
472 event = icsk->icsk_pending;
473 icsk->icsk_pending = 0;
474
475 switch (event) {
476 case ICSK_TIME_RETRANS:
477 tcp_retransmit_timer(sk);
478 break;
479 case ICSK_TIME_PROBE0:
480 tcp_probe_timer(sk);
481 break;
482 }
483
484out:
485 sk_mem_reclaim(sk);
486out_unlock:
487 bh_unlock_sock(sk);
488 sock_put(sk);
489}
490
491/*
492 * Timer for listening sockets
493 */
494
495static void tcp_synack_timer(struct sock *sk)
496{
497 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
498 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
499}
500
501void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
502{
503 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
504}
505EXPORT_SYMBOL(tcp_syn_ack_timeout);
506
507void tcp_set_keepalive(struct sock *sk, int val)
508{
509 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
510 return;
511
512 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
513 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
514 else if (!val)
515 inet_csk_delete_keepalive_timer(sk);
516}
517
518
519static void tcp_keepalive_timer (unsigned long data)
520{
521 struct sock *sk = (struct sock *) data;
522 struct inet_connection_sock *icsk = inet_csk(sk);
523 struct tcp_sock *tp = tcp_sk(sk);
524 u32 elapsed;
525
526 /* Only process if socket is not in use. */
527 bh_lock_sock(sk);
528 if (sock_owned_by_user(sk)) {
529 /* Try again later. */
530 inet_csk_reset_keepalive_timer (sk, HZ/20);
531 goto out;
532 }
533
534 if (sk->sk_state == TCP_LISTEN) {
535 tcp_synack_timer(sk);
536 goto out;
537 }
538
539 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
540 if (tp->linger2 >= 0) {
541 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
542
543 if (tmo > 0) {
544 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
545 goto out;
546 }
547 }
548 tcp_send_active_reset(sk, GFP_ATOMIC);
549 goto death;
550 }
551
552 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
553 goto out;
554
555 elapsed = keepalive_time_when(tp);
556
557 /* It is alive without keepalive 8) */
558 if (tp->packets_out || tcp_send_head(sk))
559 goto resched;
560
561 elapsed = keepalive_time_elapsed(tp);
562
563 if (elapsed >= keepalive_time_when(tp)) {
564 /* If the TCP_USER_TIMEOUT option is enabled, use that
565 * to determine when to timeout instead.
566 */
567 if ((icsk->icsk_user_timeout != 0 &&
568 elapsed >= icsk->icsk_user_timeout &&
569 icsk->icsk_probes_out > 0) ||
570 (icsk->icsk_user_timeout == 0 &&
571 icsk->icsk_probes_out >= keepalive_probes(tp))) {
572 tcp_send_active_reset(sk, GFP_ATOMIC);
573 tcp_write_err(sk);
574 goto out;
575 }
576 if (tcp_write_wakeup(sk) <= 0) {
577 icsk->icsk_probes_out++;
578 elapsed = keepalive_intvl_when(tp);
579 } else {
580 /* If keepalive was lost due to local congestion,
581 * try harder.
582 */
583 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
584 }
585 } else {
586 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
587 elapsed = keepalive_time_when(tp) - elapsed;
588 }
589
590 sk_mem_reclaim(sk);
591
592resched:
593 inet_csk_reset_keepalive_timer (sk, elapsed);
594 goto out;
595
596death:
597 tcp_done(sk);
598
599out:
600 bh_unlock_sock(sk);
601 sock_put(sk);
602}