1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * INET An implementation of the TCP/IP protocol suite for the LINUX
4 * operating system. INET is implemented using the BSD Socket
5 * interface as the means of communication with the user level.
6 *
7 * Implementation of the Transmission Control Protocol(TCP).
8 *
9 * Authors: Ross Biro
10 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11 * Mark Evans, <evansmp@uhura.aston.ac.uk>
12 * Corey Minyard <wf-rch!minyard@relay.EU.net>
13 * Florian La Roche, <flla@stud.uni-sb.de>
14 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15 * Linus Torvalds, <torvalds@cs.helsinki.fi>
16 * Alan Cox, <gw4pts@gw4pts.ampr.org>
17 * Matthew Dillon, <dillon@apollo.west.oic.com>
18 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19 * Jorge Cwik, <jorge@laser.satlink.net>
20 */
21
22 #include <linux/module.h>
23 #include <linux/gfp.h>
24 #include <net/tcp.h>
25
tcp_clamp_rto_to_user_timeout(const struct sock * sk)26 static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
27 {
28 struct inet_connection_sock *icsk = inet_csk(sk);
29 u32 elapsed, start_ts;
30 s32 remaining;
31
32 start_ts = tcp_sk(sk)->retrans_stamp;
33 if (!icsk->icsk_user_timeout)
34 return icsk->icsk_rto;
35 elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;
36 remaining = icsk->icsk_user_timeout - elapsed;
37 if (remaining <= 0)
38 return 1; /* user timeout has passed; fire ASAP */
39
40 return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining));
41 }
42
tcp_clamp_probe0_to_user_timeout(const struct sock * sk,u32 when)43 u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
44 {
45 struct inet_connection_sock *icsk = inet_csk(sk);
46 u32 remaining;
47 s32 elapsed;
48
49 if (!icsk->icsk_user_timeout || !icsk->icsk_probes_tstamp)
50 return when;
51
52 elapsed = tcp_jiffies32 - icsk->icsk_probes_tstamp;
53 if (unlikely(elapsed < 0))
54 elapsed = 0;
55 remaining = msecs_to_jiffies(icsk->icsk_user_timeout) - elapsed;
56 remaining = max_t(u32, remaining, TCP_TIMEOUT_MIN);
57
58 return min_t(u32, remaining, when);
59 }
60
61 /**
62 * tcp_write_err() - close socket and save error info
63 * @sk: The socket the error has appeared on.
64 *
65 * Returns: Nothing (void)
66 */
67
tcp_write_err(struct sock * sk)68 static void tcp_write_err(struct sock *sk)
69 {
70 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
71 sk->sk_error_report(sk);
72
73 tcp_write_queue_purge(sk);
74 tcp_done(sk);
75 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
76 }
77
78 /**
79 * tcp_out_of_resources() - Close socket if out of resources
80 * @sk: pointer to current socket
81 * @do_reset: send a last packet with reset flag
82 *
83 * Do not allow orphaned sockets to eat all our resources.
84 * This is direct violation of TCP specs, but it is required
85 * to prevent DoS attacks. It is called when a retransmission timeout
86 * or zero probe timeout occurs on orphaned socket.
87 *
88 * Also close if our net namespace is exiting; in that case there is no
89 * hope of ever communicating again since all netns interfaces are already
90 * down (or about to be down), and we need to release our dst references,
91 * which have been moved to the netns loopback interface, so the namespace
92 * can finish exiting. This condition is only possible if we are a kernel
93 * socket, as those do not hold references to the namespace.
94 *
95 * Criteria is still not confirmed experimentally and may change.
96 * We kill the socket, if:
97 * 1. If number of orphaned sockets exceeds an administratively configured
98 * limit.
99 * 2. If we have strong memory pressure.
100 * 3. If our net namespace is exiting.
101 */
tcp_out_of_resources(struct sock * sk,bool do_reset)102 static int tcp_out_of_resources(struct sock *sk, bool do_reset)
103 {
104 struct tcp_sock *tp = tcp_sk(sk);
105 int shift = 0;
106
107 /* If peer does not open window for long time, or did not transmit
108 * anything for long time, penalize it. */
109 if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
110 shift++;
111
112 /* If some dubious ICMP arrived, penalize even more. */
113 if (sk->sk_err_soft)
114 shift++;
115
116 if (tcp_check_oom(sk, shift)) {
117 /* Catch exceptional cases, when connection requires reset.
118 * 1. Last segment was sent recently. */
119 if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
120 /* 2. Window is closed. */
121 (!tp->snd_wnd && !tp->packets_out))
122 do_reset = true;
123 if (do_reset)
124 tcp_send_active_reset(sk, GFP_ATOMIC);
125 tcp_done(sk);
126 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
127 return 1;
128 }
129
130 if (!check_net(sock_net(sk))) {
131 /* Not possible to send reset; just close */
132 tcp_done(sk);
133 return 1;
134 }
135
136 return 0;
137 }
138
139 /**
140 * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
141 * @sk: Pointer to the current socket.
142 * @alive: bool, socket alive state
143 */
tcp_orphan_retries(struct sock * sk,bool alive)144 static int tcp_orphan_retries(struct sock *sk, bool alive)
145 {
146 int retries = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_orphan_retries); /* May be zero. */
147
148 /* We know from an ICMP that something is wrong. */
149 if (sk->sk_err_soft && !alive)
150 retries = 0;
151
152 /* However, if socket sent something recently, select some safe
153 * number of retries. 8 corresponds to >100 seconds with minimal
154 * RTO of 200msec. */
155 if (retries == 0 && alive)
156 retries = 8;
157 return retries;
158 }
159
tcp_mtu_probing(struct inet_connection_sock * icsk,struct sock * sk)160 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
161 {
162 const struct net *net = sock_net(sk);
163 int mss;
164
165 /* Black hole detection */
166 if (!READ_ONCE(net->ipv4.sysctl_tcp_mtu_probing))
167 return;
168
169 if (!icsk->icsk_mtup.enabled) {
170 icsk->icsk_mtup.enabled = 1;
171 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
172 } else {
173 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
174 mss = min(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss);
175 mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_mtu_probe_floor));
176 mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_min_snd_mss));
177 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
178 }
179 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
180 }
181
tcp_model_timeout(struct sock * sk,unsigned int boundary,unsigned int rto_base)182 static unsigned int tcp_model_timeout(struct sock *sk,
183 unsigned int boundary,
184 unsigned int rto_base)
185 {
186 unsigned int linear_backoff_thresh, timeout;
187
188 linear_backoff_thresh = ilog2(TCP_RTO_MAX / rto_base);
189 if (boundary <= linear_backoff_thresh)
190 timeout = ((2 << boundary) - 1) * rto_base;
191 else
192 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
193 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
194 return jiffies_to_msecs(timeout);
195 }
196 /**
197 * retransmits_timed_out() - returns true if this connection has timed out
198 * @sk: The current socket
199 * @boundary: max number of retransmissions
200 * @timeout: A custom timeout value.
201 * If set to 0 the default timeout is calculated and used.
202 * Using TCP_RTO_MIN and the number of unsuccessful retransmits.
203 *
204 * The default "timeout" value this function can calculate and use
205 * is equivalent to the timeout of a TCP Connection
206 * after "boundary" unsuccessful, exponentially backed-off
207 * retransmissions with an initial RTO of TCP_RTO_MIN.
208 */
retransmits_timed_out(struct sock * sk,unsigned int boundary,unsigned int timeout)209 static bool retransmits_timed_out(struct sock *sk,
210 unsigned int boundary,
211 unsigned int timeout)
212 {
213 unsigned int start_ts;
214
215 if (!inet_csk(sk)->icsk_retransmits)
216 return false;
217
218 start_ts = tcp_sk(sk)->retrans_stamp;
219 if (likely(timeout == 0)) {
220 unsigned int rto_base = TCP_RTO_MIN;
221
222 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
223 rto_base = tcp_timeout_init(sk);
224 timeout = tcp_model_timeout(sk, boundary, rto_base);
225 }
226
227 return (s32)(tcp_time_stamp(tcp_sk(sk)) - start_ts - timeout) >= 0;
228 }
229
230 /* A write timeout has occurred. Process the after effects. */
tcp_write_timeout(struct sock * sk)231 static int tcp_write_timeout(struct sock *sk)
232 {
233 struct inet_connection_sock *icsk = inet_csk(sk);
234 struct tcp_sock *tp = tcp_sk(sk);
235 struct net *net = sock_net(sk);
236 bool expired = false, do_reset;
237 int retry_until;
238
239 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
240 if (icsk->icsk_retransmits)
241 __dst_negative_advice(sk);
242 retry_until = icsk->icsk_syn_retries ? :
243 READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
244 expired = icsk->icsk_retransmits >= retry_until;
245 } else {
246 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1), 0)) {
247 /* Black hole detection */
248 tcp_mtu_probing(icsk, sk);
249
250 __dst_negative_advice(sk);
251 }
252
253 #ifdef CONFIG_TCP_NB_URC
254 retry_until = tcp_get_retries_limit(sk);
255 #else
256 retry_until = READ_ONCE(net->ipv4.sysctl_tcp_retries2);
257 #endif /* CONFIG_TCP_NB_URC */
258 if (sock_flag(sk, SOCK_DEAD)) {
259 const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
260
261 retry_until = tcp_orphan_retries(sk, alive);
262 do_reset = alive ||
263 !retransmits_timed_out(sk, retry_until, 0);
264
265 if (tcp_out_of_resources(sk, do_reset))
266 return 1;
267 }
268 }
269 if (!expired)
270 expired = retransmits_timed_out(sk, retry_until,
271 icsk->icsk_user_timeout);
272 tcp_fastopen_active_detect_blackhole(sk, expired);
273
274 if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG))
275 tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB,
276 icsk->icsk_retransmits,
277 icsk->icsk_rto, (int)expired);
278
279 if (expired) {
280 /* Has it gone just too far? */
281 tcp_write_err(sk);
282 return 1;
283 }
284
285 if (sk_rethink_txhash(sk)) {
286 tp->timeout_rehash++;
287 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);
288 }
289
290 return 0;
291 }
292
293 /* Called with BH disabled */
tcp_delack_timer_handler(struct sock * sk)294 void tcp_delack_timer_handler(struct sock *sk)
295 {
296 struct inet_connection_sock *icsk = inet_csk(sk);
297
298 sk_mem_reclaim_partial(sk);
299
300 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
301 !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
302 goto out;
303
304 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
305 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
306 goto out;
307 }
308 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
309
310 if (inet_csk_ack_scheduled(sk)) {
311 if (!inet_csk_in_pingpong_mode(sk)) {
312 /* Delayed ACK missed: inflate ATO. */
313 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
314 } else {
315 /* Delayed ACK missed: leave pingpong mode and
316 * deflate ATO.
317 */
318 inet_csk_exit_pingpong_mode(sk);
319 icsk->icsk_ack.ato = TCP_ATO_MIN;
320 }
321 tcp_mstamp_refresh(tcp_sk(sk));
322 tcp_send_ack(sk);
323 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
324 }
325
326 out:
327 if (tcp_under_memory_pressure(sk))
328 sk_mem_reclaim(sk);
329 }
330
331
332 /**
333 * tcp_delack_timer() - The TCP delayed ACK timeout handler
334 * @t: Pointer to the timer. (gets casted to struct sock *)
335 *
336 * This function gets (indirectly) called when the kernel timer for a TCP packet
337 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
338 *
339 * Returns: Nothing (void)
340 */
tcp_delack_timer(struct timer_list * t)341 static void tcp_delack_timer(struct timer_list *t)
342 {
343 struct inet_connection_sock *icsk =
344 from_timer(icsk, t, icsk_delack_timer);
345 struct sock *sk = &icsk->icsk_inet.sk;
346
347 bh_lock_sock(sk);
348 if (!sock_owned_by_user(sk)) {
349 tcp_delack_timer_handler(sk);
350 } else {
351 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
352 /* deleguate our work to tcp_release_cb() */
353 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))
354 sock_hold(sk);
355 }
356 bh_unlock_sock(sk);
357 sock_put(sk);
358 }
359
tcp_probe_timer(struct sock * sk)360 static void tcp_probe_timer(struct sock *sk)
361 {
362 struct inet_connection_sock *icsk = inet_csk(sk);
363 struct sk_buff *skb = tcp_send_head(sk);
364 struct tcp_sock *tp = tcp_sk(sk);
365 int max_probes;
366
367 if (tp->packets_out || !skb) {
368 icsk->icsk_probes_out = 0;
369 icsk->icsk_probes_tstamp = 0;
370 return;
371 }
372
373 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
374 * long as the receiver continues to respond probes. We support this by
375 * default and reset icsk_probes_out with incoming ACKs. But if the
376 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
377 * kill the socket when the retry count and the time exceeds the
378 * corresponding system limit. We also implement similar policy when
379 * we use RTO to probe window in tcp_retransmit_timer().
380 */
381 if (!icsk->icsk_probes_tstamp)
382 icsk->icsk_probes_tstamp = tcp_jiffies32;
383 else if (icsk->icsk_user_timeout &&
384 (s32)(tcp_jiffies32 - icsk->icsk_probes_tstamp) >=
385 msecs_to_jiffies(icsk->icsk_user_timeout))
386 goto abort;
387
388 #ifdef CONFIG_TCP_NB_URC
389 max_probes = tcp_get_retries_limit(sk);
390 #else
391 max_probes = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_retries2);
392 #endif /* CONFIG_TCP_NB_URC */
393 if (sock_flag(sk, SOCK_DEAD)) {
394 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
395
396 max_probes = tcp_orphan_retries(sk, alive);
397 if (!alive && icsk->icsk_backoff >= max_probes)
398 goto abort;
399 if (tcp_out_of_resources(sk, true))
400 return;
401 }
402
403 if (icsk->icsk_probes_out >= max_probes) {
404 abort: tcp_write_err(sk);
405 } else {
406 /* Only send another probe if we didn't close things up. */
407 tcp_send_probe0(sk);
408 }
409 }
410
411 /*
412 * Timer for Fast Open socket to retransmit SYNACK. Note that the
413 * sk here is the child socket, not the parent (listener) socket.
414 */
tcp_fastopen_synack_timer(struct sock * sk,struct request_sock * req)415 static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
416 {
417 struct inet_connection_sock *icsk = inet_csk(sk);
418 struct tcp_sock *tp = tcp_sk(sk);
419 int max_retries;
420
421 req->rsk_ops->syn_ack_timeout(req);
422
423 /* add one more retry for fastopen */
424 max_retries = icsk->icsk_syn_retries ? :
425 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
426
427 if (req->num_timeout >= max_retries) {
428 tcp_write_err(sk);
429 return;
430 }
431 /* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */
432 if (icsk->icsk_retransmits == 1)
433 tcp_enter_loss(sk);
434 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
435 * returned from rtx_syn_ack() to make it more persistent like
436 * regular retransmit because if the child socket has been accepted
437 * it's not good to give up too easily.
438 */
439 inet_rtx_syn_ack(sk, req);
440 req->num_timeout++;
441 icsk->icsk_retransmits++;
442 if (!tp->retrans_stamp)
443 tp->retrans_stamp = tcp_time_stamp(tp);
444 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
445 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
446 }
447
tcp_rtx_probe0_timed_out(const struct sock * sk,const struct sk_buff * skb)448 static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
449 const struct sk_buff *skb)
450 {
451 const struct tcp_sock *tp = tcp_sk(sk);
452 const int timeout = TCP_RTO_MAX * 2;
453 u32 rcv_delta, rtx_delta;
454
455 rcv_delta = inet_csk(sk)->icsk_timeout - tp->rcv_tstamp;
456 if (rcv_delta <= timeout)
457 return false;
458
459 rtx_delta = (u32)msecs_to_jiffies(tcp_time_stamp(tp) -
460 (tp->retrans_stamp ?: tcp_skb_timestamp(skb)));
461
462 return rtx_delta > timeout;
463 }
464
465 /**
466 * tcp_retransmit_timer() - The TCP retransmit timeout handler
467 * @sk: Pointer to the current socket.
468 *
469 * This function gets called when the kernel timer for a TCP packet
470 * of this socket expires.
471 *
472 * It handles retransmission, timer adjustment and other necesarry measures.
473 *
474 * Returns: Nothing (void)
475 */
tcp_retransmit_timer(struct sock * sk)476 void tcp_retransmit_timer(struct sock *sk)
477 {
478 struct tcp_sock *tp = tcp_sk(sk);
479 struct net *net = sock_net(sk);
480 struct inet_connection_sock *icsk = inet_csk(sk);
481 struct request_sock *req;
482 struct sk_buff *skb;
483
484 req = rcu_dereference_protected(tp->fastopen_rsk,
485 lockdep_sock_is_held(sk));
486 if (req) {
487 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
488 sk->sk_state != TCP_FIN_WAIT1);
489 tcp_fastopen_synack_timer(sk, req);
490 /* Before we receive ACK to our SYN-ACK don't retransmit
491 * anything else (e.g., data or FIN segments).
492 */
493 return;
494 }
495
496 if (!tp->packets_out)
497 return;
498
499 skb = tcp_rtx_queue_head(sk);
500 if (WARN_ON_ONCE(!skb))
501 return;
502
503 tp->tlp_high_seq = 0;
504
505 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
506 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
507 /* Receiver dastardly shrinks window. Our retransmits
508 * become zero probes, but we should not timeout this
509 * connection. If the socket is an orphan, time it out,
510 * we cannot allow such beasts to hang infinitely.
511 */
512 struct inet_sock *inet = inet_sk(sk);
513 if (sk->sk_family == AF_INET) {
514 net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
515 &inet->inet_daddr,
516 ntohs(inet->inet_dport),
517 inet->inet_num,
518 tp->snd_una, tp->snd_nxt);
519 }
520 #if IS_ENABLED(CONFIG_IPV6)
521 else if (sk->sk_family == AF_INET6) {
522 net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
523 &sk->sk_v6_daddr,
524 ntohs(inet->inet_dport),
525 inet->inet_num,
526 tp->snd_una, tp->snd_nxt);
527 }
528 #endif
529 if (tcp_rtx_probe0_timed_out(sk, skb)) {
530 tcp_write_err(sk);
531 goto out;
532 }
533 tcp_enter_loss(sk);
534 tcp_retransmit_skb(sk, skb, 1);
535 __sk_dst_reset(sk);
536 goto out_reset_timer;
537 }
538
539 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
540 if (tcp_write_timeout(sk))
541 goto out;
542
543 if (icsk->icsk_retransmits == 0) {
544 int mib_idx = 0;
545
546 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
547 if (tcp_is_sack(tp))
548 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
549 else
550 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
551 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
552 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
553 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
554 tp->sacked_out) {
555 if (tcp_is_sack(tp))
556 mib_idx = LINUX_MIB_TCPSACKFAILURES;
557 else
558 mib_idx = LINUX_MIB_TCPRENOFAILURES;
559 }
560 if (mib_idx)
561 __NET_INC_STATS(sock_net(sk), mib_idx);
562 }
563
564 tcp_enter_loss(sk);
565
566 icsk->icsk_retransmits++;
567 if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) {
568 /* Retransmission failed because of local congestion,
569 * Let senders fight for local resources conservatively.
570 */
571 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
572 TCP_RESOURCE_PROBE_INTERVAL,
573 TCP_RTO_MAX);
574 goto out;
575 }
576
577 /* Increase the timeout each time we retransmit. Note that
578 * we do not increase the rtt estimate. rto is initialized
579 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
580 * that doubling rto each time is the least we can get away with.
581 * In KA9Q, Karn uses this for the first few times, and then
582 * goes to quadratic. netBSD doubles, but only goes up to *64,
583 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
584 * defined in the protocol as the maximum possible RTT. I guess
585 * we'll have to use something other than TCP to talk to the
586 * University of Mars.
587 *
588 * PAWS allows us longer timeouts and large windows, so once
589 * implemented ftp to mars will work nicely. We will have to fix
590 * the 120 second clamps though!
591 */
592 icsk->icsk_backoff++;
593
594 out_reset_timer:
595 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
596 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
597 * might be increased if the stream oscillates between thin and thick,
598 * thus the old value might already be too high compared to the value
599 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
600 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
601 * exponential backoff behaviour to avoid continue hammering
602 * linear-timeout retransmissions into a black hole
603 */
604 if (sk->sk_state == TCP_ESTABLISHED &&
605 (tp->thin_lto || READ_ONCE(net->ipv4.sysctl_tcp_thin_linear_timeouts)) &&
606 tcp_stream_is_thin(tp) &&
607 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
608 icsk->icsk_backoff = 0;
609 icsk->icsk_rto = clamp(__tcp_set_rto(tp),
610 tcp_rto_min(sk),
611 TCP_RTO_MAX);
612 } else {
613 /* Use normal (exponential) backoff */
614 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
615 }
616 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
617 tcp_clamp_rto_to_user_timeout(sk), TCP_RTO_MAX);
618 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1) + 1, 0))
619 __sk_dst_reset(sk);
620
621 out:;
622 }
623
624 /* Called with bottom-half processing disabled.
625 Called by tcp_write_timer() */
tcp_write_timer_handler(struct sock * sk)626 void tcp_write_timer_handler(struct sock *sk)
627 {
628 struct inet_connection_sock *icsk = inet_csk(sk);
629 int event;
630
631 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
632 !icsk->icsk_pending)
633 goto out;
634
635 if (time_after(icsk->icsk_timeout, jiffies)) {
636 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
637 goto out;
638 }
639
640 tcp_mstamp_refresh(tcp_sk(sk));
641 event = icsk->icsk_pending;
642
643 switch (event) {
644 case ICSK_TIME_REO_TIMEOUT:
645 tcp_rack_reo_timeout(sk);
646 break;
647 case ICSK_TIME_LOSS_PROBE:
648 tcp_send_loss_probe(sk);
649 break;
650 case ICSK_TIME_RETRANS:
651 icsk->icsk_pending = 0;
652 tcp_retransmit_timer(sk);
653 break;
654 case ICSK_TIME_PROBE0:
655 icsk->icsk_pending = 0;
656 tcp_probe_timer(sk);
657 break;
658 }
659
660 out:
661 sk_mem_reclaim(sk);
662 }
663
tcp_write_timer(struct timer_list * t)664 static void tcp_write_timer(struct timer_list *t)
665 {
666 struct inet_connection_sock *icsk =
667 from_timer(icsk, t, icsk_retransmit_timer);
668 struct sock *sk = &icsk->icsk_inet.sk;
669
670 bh_lock_sock(sk);
671 if (!sock_owned_by_user(sk)) {
672 tcp_write_timer_handler(sk);
673 } else {
674 /* delegate our work to tcp_release_cb() */
675 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags))
676 sock_hold(sk);
677 }
678 bh_unlock_sock(sk);
679 sock_put(sk);
680 }
681
tcp_syn_ack_timeout(const struct request_sock * req)682 void tcp_syn_ack_timeout(const struct request_sock *req)
683 {
684 struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
685
686 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
687 }
688 EXPORT_SYMBOL(tcp_syn_ack_timeout);
689
tcp_set_keepalive(struct sock * sk,int val)690 void tcp_set_keepalive(struct sock *sk, int val)
691 {
692 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
693 return;
694
695 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
696 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
697 else if (!val)
698 inet_csk_delete_keepalive_timer(sk);
699 }
700 EXPORT_SYMBOL_GPL(tcp_set_keepalive);
701
702
tcp_keepalive_timer(struct timer_list * t)703 static void tcp_keepalive_timer (struct timer_list *t)
704 {
705 struct sock *sk = from_timer(sk, t, sk_timer);
706 struct inet_connection_sock *icsk = inet_csk(sk);
707 struct tcp_sock *tp = tcp_sk(sk);
708 u32 elapsed;
709
710 /* Only process if socket is not in use. */
711 bh_lock_sock(sk);
712 if (sock_owned_by_user(sk)) {
713 /* Try again later. */
714 inet_csk_reset_keepalive_timer (sk, HZ/20);
715 goto out;
716 }
717
718 if (sk->sk_state == TCP_LISTEN) {
719 pr_err("Hmm... keepalive on a LISTEN ???\n");
720 goto out;
721 }
722
723 tcp_mstamp_refresh(tp);
724 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
725 if (tp->linger2 >= 0) {
726 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
727
728 if (tmo > 0) {
729 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
730 goto out;
731 }
732 }
733 tcp_send_active_reset(sk, GFP_ATOMIC);
734 goto death;
735 }
736
737 if (!sock_flag(sk, SOCK_KEEPOPEN) ||
738 ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
739 goto out;
740
741 elapsed = keepalive_time_when(tp);
742
743 /* It is alive without keepalive 8) */
744 if (tp->packets_out || !tcp_write_queue_empty(sk))
745 goto resched;
746
747 elapsed = keepalive_time_elapsed(tp);
748
749 if (elapsed >= keepalive_time_when(tp)) {
750 /* If the TCP_USER_TIMEOUT option is enabled, use that
751 * to determine when to timeout instead.
752 */
753 if ((icsk->icsk_user_timeout != 0 &&
754 elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout) &&
755 icsk->icsk_probes_out > 0) ||
756 (icsk->icsk_user_timeout == 0 &&
757 icsk->icsk_probes_out >= keepalive_probes(tp))) {
758 tcp_send_active_reset(sk, GFP_ATOMIC);
759 tcp_write_err(sk);
760 goto out;
761 }
762 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
763 icsk->icsk_probes_out++;
764 elapsed = keepalive_intvl_when(tp);
765 } else {
766 /* If keepalive was lost due to local congestion,
767 * try harder.
768 */
769 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
770 }
771 } else {
772 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
773 elapsed = keepalive_time_when(tp) - elapsed;
774 }
775
776 sk_mem_reclaim(sk);
777
778 resched:
779 inet_csk_reset_keepalive_timer (sk, elapsed);
780 goto out;
781
782 death:
783 tcp_done(sk);
784
785 out:
786 bh_unlock_sock(sk);
787 sock_put(sk);
788 }
789
tcp_compressed_ack_kick(struct hrtimer * timer)790 static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
791 {
792 struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer);
793 struct sock *sk = (struct sock *)tp;
794
795 bh_lock_sock(sk);
796 if (!sock_owned_by_user(sk)) {
797 if (tp->compressed_ack) {
798 /* Since we have to send one ack finally,
799 * substract one from tp->compressed_ack to keep
800 * LINUX_MIB_TCPACKCOMPRESSED accurate.
801 */
802 tp->compressed_ack--;
803 tcp_send_ack(sk);
804 }
805 } else {
806 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,
807 &sk->sk_tsq_flags))
808 sock_hold(sk);
809 }
810 bh_unlock_sock(sk);
811
812 sock_put(sk);
813
814 return HRTIMER_NORESTART;
815 }
816
tcp_init_xmit_timers(struct sock * sk)817 void tcp_init_xmit_timers(struct sock *sk)
818 {
819 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
820 &tcp_keepalive_timer);
821 hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC,
822 HRTIMER_MODE_ABS_PINNED_SOFT);
823 tcp_sk(sk)->pacing_timer.function = tcp_pace_kick;
824
825 hrtimer_init(&tcp_sk(sk)->compressed_ack_timer, CLOCK_MONOTONIC,
826 HRTIMER_MODE_REL_PINNED_SOFT);
827 tcp_sk(sk)->compressed_ack_timer.function = tcp_compressed_ack_kick;
828 }
829