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 #include <net/tcp_ecn.h> 26 #include <net/rstreason.h> 27 28 static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk) 29 { 30 const struct inet_connection_sock *icsk = inet_csk(sk); 31 const struct tcp_sock *tp = tcp_sk(sk); 32 u32 elapsed, user_timeout; 33 s32 remaining; 34 35 user_timeout = READ_ONCE(icsk->icsk_user_timeout); 36 if (!user_timeout) 37 return icsk->icsk_rto; 38 39 elapsed = tcp_time_stamp_ts(tp) - tp->retrans_stamp; 40 if (tp->tcp_usec_ts) 41 elapsed /= USEC_PER_MSEC; 42 43 remaining = user_timeout - elapsed; 44 if (remaining <= 0) 45 return 1; /* user timeout has passed; fire ASAP */ 46 47 return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining)); 48 } 49 50 u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when) 51 { 52 const struct inet_connection_sock *icsk = inet_csk(sk); 53 u32 user_timeout; 54 s32 remaining; 55 s32 elapsed; 56 57 user_timeout = READ_ONCE(icsk->icsk_user_timeout); 58 if (!user_timeout || !icsk->icsk_probes_tstamp) 59 return when; 60 61 elapsed = tcp_jiffies32 - icsk->icsk_probes_tstamp; 62 if (unlikely(elapsed < 0)) 63 elapsed = 0; 64 remaining = msecs_to_jiffies(user_timeout) - elapsed; 65 remaining = max_t(int, remaining, TCP_TIMEOUT_MIN); 66 67 return min_t(u32, remaining, when); 68 } 69 70 /** 71 * tcp_write_err() - close socket and save error info 72 * @sk: The socket the error has appeared on. 73 * 74 * Returns: Nothing (void) 75 */ 76 77 static void tcp_write_err(struct sock *sk) 78 { 79 tcp_done_with_error(sk, READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT); 80 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); 81 } 82 83 /** 84 * tcp_out_of_resources() - Close socket if out of resources 85 * @sk: pointer to current socket 86 * @do_reset: send a last packet with reset flag 87 * 88 * Do not allow orphaned sockets to eat all our resources. 89 * This is direct violation of TCP specs, but it is required 90 * to prevent DoS attacks. It is called when a retransmission timeout 91 * or zero probe timeout occurs on orphaned socket. 92 * 93 * Also close if our net namespace is exiting; in that case there is no 94 * hope of ever communicating again since all netns interfaces are already 95 * down (or about to be down), and we need to release our dst references, 96 * which have been moved to the netns loopback interface, so the namespace 97 * can finish exiting. This condition is only possible if we are a kernel 98 * socket, as those do not hold references to the namespace. 99 * 100 * Criteria is still not confirmed experimentally and may change. 101 * We kill the socket, if: 102 * 1. If number of orphaned sockets exceeds an administratively configured 103 * limit. 104 * 2. If we have strong memory pressure. 105 * 3. If our net namespace is exiting. 106 */ 107 static int tcp_out_of_resources(struct sock *sk, bool do_reset) 108 { 109 struct tcp_sock *tp = tcp_sk(sk); 110 int shift = 0; 111 112 /* If peer does not open window for long time, or did not transmit 113 * anything for long time, penalize it. */ 114 if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*tcp_rto_max(sk) || !do_reset) 115 shift++; 116 117 /* If some dubious ICMP arrived, penalize even more. */ 118 if (READ_ONCE(sk->sk_err_soft)) 119 shift++; 120 121 if (tcp_check_oom(sk, shift)) { 122 /* Catch exceptional cases, when connection requires reset. 123 * 1. Last segment was sent recently. */ 124 if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 125 /* 2. Window is closed. */ 126 (!tp->snd_wnd && !tp->packets_out)) 127 do_reset = true; 128 if (do_reset) 129 tcp_send_active_reset(sk, GFP_ATOMIC, 130 SK_RST_REASON_TCP_ABORT_ON_MEMORY); 131 tcp_done(sk); 132 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 133 return 1; 134 } 135 136 if (!check_net(sock_net(sk))) { 137 /* Not possible to send reset; just close */ 138 tcp_done(sk); 139 return 1; 140 } 141 142 return 0; 143 } 144 145 /** 146 * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket 147 * @sk: Pointer to the current socket. 148 * @alive: bool, socket alive state 149 */ 150 static int tcp_orphan_retries(struct sock *sk, bool alive) 151 { 152 int retries = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_orphan_retries); /* May be zero. */ 153 154 /* We know from an ICMP that something is wrong. */ 155 if (READ_ONCE(sk->sk_err_soft) && !alive) 156 retries = 0; 157 158 /* However, if socket sent something recently, select some safe 159 * number of retries. 8 corresponds to >100 seconds with minimal 160 * RTO of 200msec. */ 161 if (retries == 0 && alive) 162 retries = 8; 163 return retries; 164 } 165 166 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 167 { 168 const struct net *net = sock_net(sk); 169 int mss; 170 171 /* Black hole detection */ 172 if (!READ_ONCE(net->ipv4.sysctl_tcp_mtu_probing)) 173 return; 174 175 if (!icsk->icsk_mtup.enabled) { 176 icsk->icsk_mtup.enabled = 1; 177 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32; 178 } else { 179 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 180 mss = min(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss); 181 mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_mtu_probe_floor)); 182 mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_min_snd_mss)); 183 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 184 } 185 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 186 } 187 188 static unsigned int tcp_model_timeout(struct sock *sk, 189 unsigned int boundary, 190 unsigned int rto_base) 191 { 192 unsigned int linear_backoff_thresh, timeout; 193 194 linear_backoff_thresh = ilog2(tcp_rto_max(sk) / rto_base); 195 if (boundary <= linear_backoff_thresh) 196 timeout = ((2 << boundary) - 1) * rto_base; 197 else 198 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 199 (boundary - linear_backoff_thresh) * tcp_rto_max(sk); 200 return jiffies_to_msecs(timeout); 201 } 202 /** 203 * retransmits_timed_out() - returns true if this connection has timed out 204 * @sk: The current socket 205 * @boundary: max number of retransmissions 206 * @timeout: A custom timeout value. 207 * If set to 0 the default timeout is calculated and used. 208 * Using TCP_RTO_MIN and the number of unsuccessful retransmits. 209 * 210 * The default "timeout" value this function can calculate and use 211 * is equivalent to the timeout of a TCP Connection 212 * after "boundary" unsuccessful, exponentially backed-off 213 * retransmissions with an initial RTO of TCP_RTO_MIN. 214 */ 215 static bool retransmits_timed_out(struct sock *sk, 216 unsigned int boundary, 217 unsigned int timeout) 218 { 219 struct tcp_sock *tp = tcp_sk(sk); 220 unsigned int start_ts, delta; 221 222 if (!inet_csk(sk)->icsk_retransmits) 223 return false; 224 225 start_ts = tp->retrans_stamp; 226 if (likely(timeout == 0)) { 227 unsigned int rto_base = TCP_RTO_MIN; 228 229 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) 230 rto_base = tcp_timeout_init(sk); 231 timeout = tcp_model_timeout(sk, boundary, rto_base); 232 } 233 234 if (tp->tcp_usec_ts) { 235 /* delta maybe off up to a jiffy due to timer granularity. */ 236 delta = tp->tcp_mstamp - start_ts + jiffies_to_usecs(1); 237 return (s32)(delta - timeout * USEC_PER_MSEC) >= 0; 238 } 239 return (s32)(tcp_time_stamp_ts(tp) - start_ts - timeout) >= 0; 240 } 241 242 /* A write timeout has occurred. Process the after effects. */ 243 static int tcp_write_timeout(struct sock *sk) 244 { 245 struct inet_connection_sock *icsk = inet_csk(sk); 246 struct tcp_sock *tp = tcp_sk(sk); 247 struct net *net = sock_net(sk); 248 bool expired = false, do_reset; 249 int retry_until, max_retransmits; 250 251 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 252 if (icsk->icsk_retransmits) 253 __dst_negative_advice(sk); 254 /* Paired with WRITE_ONCE() in tcp_sock_set_syncnt() */ 255 retry_until = READ_ONCE(icsk->icsk_syn_retries) ? : 256 READ_ONCE(net->ipv4.sysctl_tcp_syn_retries); 257 258 max_retransmits = retry_until; 259 if (sk->sk_state == TCP_SYN_SENT) 260 max_retransmits += READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts); 261 262 expired = icsk->icsk_retransmits >= max_retransmits; 263 } else { 264 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1), 0)) { 265 /* Black hole detection */ 266 tcp_mtu_probing(icsk, sk); 267 268 __dst_negative_advice(sk); 269 } 270 271 retry_until = READ_ONCE(net->ipv4.sysctl_tcp_retries2); 272 if (sock_flag(sk, SOCK_DEAD)) { 273 const bool alive = icsk->icsk_rto < tcp_rto_max(sk); 274 275 retry_until = tcp_orphan_retries(sk, alive); 276 do_reset = alive || 277 !retransmits_timed_out(sk, retry_until, 0); 278 279 if (tcp_out_of_resources(sk, do_reset)) 280 return 1; 281 } 282 } 283 if (!expired) 284 expired = retransmits_timed_out(sk, retry_until, 285 READ_ONCE(icsk->icsk_user_timeout)); 286 tcp_fastopen_active_detect_blackhole(sk, expired); 287 mptcp_active_detect_blackhole(sk, expired); 288 289 if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG)) 290 tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB, 291 icsk->icsk_retransmits, 292 icsk->icsk_rto, (int)expired); 293 294 if (expired) { 295 /* Has it gone just too far? */ 296 tcp_write_err(sk); 297 return 1; 298 } 299 300 if (sk_rethink_txhash(sk)) { 301 WRITE_ONCE(tp->timeout_rehash, tp->timeout_rehash + 1); 302 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH); 303 } 304 305 return 0; 306 } 307 308 /* Called with BH disabled */ 309 void tcp_delack_timer_handler(struct sock *sk) 310 { 311 struct inet_connection_sock *icsk = inet_csk(sk); 312 struct tcp_sock *tp = tcp_sk(sk); 313 314 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 315 return; 316 317 /* Handling the sack compression case */ 318 if (tp->compressed_ack) { 319 tcp_mstamp_refresh(tp); 320 tcp_sack_compress_send_ack(sk); 321 return; 322 } 323 324 if (!(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 325 return; 326 327 if (time_after(icsk_delack_timeout(icsk), jiffies)) { 328 sk_reset_timer(sk, &icsk->icsk_delack_timer, 329 icsk_delack_timeout(icsk)); 330 return; 331 } 332 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 333 334 if (inet_csk_ack_scheduled(sk)) { 335 if (!inet_csk_in_pingpong_mode(sk)) { 336 /* Delayed ACK missed: inflate ATO. */ 337 icsk->icsk_ack.ato = min_t(u32, icsk->icsk_ack.ato << 1, icsk->icsk_rto); 338 } else { 339 /* Delayed ACK missed: leave pingpong mode and 340 * deflate ATO. 341 */ 342 inet_csk_exit_pingpong_mode(sk); 343 icsk->icsk_ack.ato = TCP_ATO_MIN; 344 } 345 tcp_mstamp_refresh(tp); 346 tcp_send_ack(sk); 347 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS); 348 } 349 } 350 351 352 /** 353 * tcp_delack_timer() - The TCP delayed ACK timeout handler 354 * @t: Pointer to the timer. (gets casted to struct sock *) 355 * 356 * This function gets (indirectly) called when the kernel timer for a TCP packet 357 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work. 358 * 359 * Returns: Nothing (void) 360 */ 361 static void tcp_delack_timer(struct timer_list *t) 362 { 363 struct inet_connection_sock *icsk = 364 timer_container_of(icsk, t, icsk_delack_timer); 365 struct sock *sk = &icsk->icsk_inet.sk; 366 367 /* Avoid taking socket spinlock if there is no ACK to send. 368 * The compressed_ack check is racy, but a separate hrtimer 369 * will take care of it eventually. 370 */ 371 if (!(smp_load_acquire(&icsk->icsk_ack.pending) & ICSK_ACK_TIMER) && 372 !READ_ONCE(tcp_sk(sk)->compressed_ack)) 373 goto out; 374 375 bh_lock_sock(sk); 376 if (!sock_owned_by_user(sk)) { 377 tcp_delack_timer_handler(sk); 378 } else { 379 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 380 /* deleguate our work to tcp_release_cb() */ 381 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags)) 382 sock_hold(sk); 383 } 384 bh_unlock_sock(sk); 385 out: 386 sock_put(sk); 387 } 388 389 static void tcp_probe_timer(struct sock *sk) 390 { 391 struct inet_connection_sock *icsk = inet_csk(sk); 392 struct sk_buff *skb = tcp_send_head(sk); 393 struct tcp_sock *tp = tcp_sk(sk); 394 int max_probes; 395 396 if (tp->packets_out || !skb) { 397 WRITE_ONCE(icsk->icsk_probes_out, 0); 398 icsk->icsk_probes_tstamp = 0; 399 return; 400 } 401 402 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as 403 * long as the receiver continues to respond probes. We support this by 404 * default and reset icsk_probes_out with incoming ACKs. But if the 405 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we 406 * kill the socket when the retry count and the time exceeds the 407 * corresponding system limit. We also implement similar policy when 408 * we use RTO to probe window in tcp_retransmit_timer(). 409 */ 410 if (!icsk->icsk_probes_tstamp) { 411 icsk->icsk_probes_tstamp = tcp_jiffies32; 412 } else { 413 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout); 414 415 if (user_timeout && 416 (s32)(tcp_jiffies32 - icsk->icsk_probes_tstamp) >= 417 msecs_to_jiffies(user_timeout)) 418 goto abort; 419 } 420 max_probes = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_retries2); 421 if (sock_flag(sk, SOCK_DEAD)) { 422 unsigned int rto_max = tcp_rto_max(sk); 423 const bool alive = inet_csk_rto_backoff(icsk, rto_max) < rto_max; 424 425 max_probes = tcp_orphan_retries(sk, alive); 426 if (!alive && icsk->icsk_backoff >= max_probes) 427 goto abort; 428 if (tcp_out_of_resources(sk, true)) 429 return; 430 } 431 432 if (icsk->icsk_probes_out >= max_probes) { 433 abort: tcp_write_err(sk); 434 } else { 435 /* Only send another probe if we didn't close things up. */ 436 tcp_send_probe0(sk); 437 } 438 } 439 440 static void tcp_update_rto_stats(struct sock *sk) 441 { 442 struct inet_connection_sock *icsk = inet_csk(sk); 443 struct tcp_sock *tp = tcp_sk(sk); 444 445 if (!icsk->icsk_retransmits) { 446 tp->total_rto_recoveries++; 447 tp->rto_stamp = tcp_time_stamp_ms(tp); 448 } 449 WRITE_ONCE(icsk->icsk_retransmits, icsk->icsk_retransmits + 1); 450 tp->total_rto++; 451 } 452 453 /* 454 * Timer for Fast Open socket to retransmit SYNACK. Note that the 455 * sk here is the child socket, not the parent (listener) socket. 456 */ 457 static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req) 458 { 459 struct inet_connection_sock *icsk = inet_csk(sk); 460 struct tcp_sock *tp = tcp_sk(sk); 461 int max_retries; 462 463 tcp_syn_ack_timeout(req); 464 465 /* Add one more retry for fastopen. 466 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt() 467 */ 468 max_retries = READ_ONCE(icsk->icsk_syn_retries) ? : 469 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1; 470 471 if (req->num_timeout >= max_retries) { 472 tcp_write_err(sk); 473 return; 474 } 475 /* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */ 476 if (icsk->icsk_retransmits == 1) 477 tcp_enter_loss(sk); 478 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error 479 * returned from rtx_syn_ack() to make it more persistent like 480 * regular retransmit because if the child socket has been accepted 481 * it's not good to give up too easily. 482 */ 483 tcp_rtx_synack(sk, req); 484 if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok) 485 tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND; 486 req->num_timeout++; 487 tcp_update_rto_stats(sk); 488 if (!tp->retrans_stamp) 489 tp->retrans_stamp = tcp_time_stamp_ts(tp); 490 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 491 req->timeout << req->num_timeout, false); 492 } 493 494 static bool tcp_rtx_probe0_timed_out(const struct sock *sk, 495 const struct sk_buff *skb, 496 u32 rtx_delta) 497 { 498 const struct inet_connection_sock *icsk = inet_csk(sk); 499 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout); 500 const struct tcp_sock *tp = tcp_sk(sk); 501 int timeout = tcp_rto_max(sk) * 2; 502 s32 rcv_delta; 503 504 if (user_timeout) { 505 /* If user application specified a TCP_USER_TIMEOUT, 506 * it does not want win 0 packets to 'reset the timer' 507 * while retransmits are not making progress. 508 */ 509 if (rtx_delta > user_timeout) 510 return true; 511 timeout = min_t(u32, timeout, msecs_to_jiffies(user_timeout)); 512 } 513 /* Note: timer interrupt might have been delayed by at least one jiffy, 514 * and tp->rcv_tstamp might very well have been written recently. 515 * rcv_delta can thus be negative. 516 */ 517 rcv_delta = tcp_timeout_expires(sk) - tp->rcv_tstamp; 518 if (rcv_delta <= timeout) 519 return false; 520 521 return msecs_to_jiffies(rtx_delta) > timeout; 522 } 523 524 /** 525 * tcp_retransmit_timer() - The TCP retransmit timeout handler 526 * @sk: Pointer to the current socket. 527 * 528 * This function gets called when the kernel timer for a TCP packet 529 * of this socket expires. 530 * 531 * It handles retransmission, timer adjustment and other necessary measures. 532 * 533 * Returns: Nothing (void) 534 */ 535 void tcp_retransmit_timer(struct sock *sk) 536 { 537 struct tcp_sock *tp = tcp_sk(sk); 538 struct net *net = sock_net(sk); 539 struct inet_connection_sock *icsk = inet_csk(sk); 540 struct request_sock *req; 541 struct sk_buff *skb; 542 543 req = rcu_dereference_protected(tp->fastopen_rsk, 544 lockdep_sock_is_held(sk)); 545 if (req) { 546 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && 547 sk->sk_state != TCP_FIN_WAIT1); 548 tcp_fastopen_synack_timer(sk, req); 549 /* Before we receive ACK to our SYN-ACK don't retransmit 550 * anything else (e.g., data or FIN segments). 551 */ 552 return; 553 } 554 555 if (!tp->packets_out) 556 return; 557 558 skb = tcp_rtx_queue_head(sk); 559 if (WARN_ON_ONCE(!skb)) 560 return; 561 562 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 563 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 564 /* Receiver dastardly shrinks window. Our retransmits 565 * become zero probes, but we should not timeout this 566 * connection. If the socket is an orphan, time it out, 567 * we cannot allow such beasts to hang infinitely. 568 */ 569 struct inet_sock *inet = inet_sk(sk); 570 u32 rtx_delta; 571 572 rtx_delta = tcp_time_stamp_ts(tp) - (tp->retrans_stamp ?: 573 tcp_skb_timestamp_ts(tp->tcp_usec_ts, skb)); 574 if (tp->tcp_usec_ts) 575 rtx_delta /= USEC_PER_MSEC; 576 577 if (sk->sk_family == AF_INET) { 578 net_dbg_ratelimited("Probing zero-window on %pI4:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n", 579 &inet->inet_daddr, ntohs(inet->inet_dport), 580 inet->inet_num, tp->snd_una, tp->snd_nxt, 581 jiffies_to_msecs(jiffies - tp->rcv_tstamp), 582 rtx_delta); 583 } 584 #if IS_ENABLED(CONFIG_IPV6) 585 else if (sk->sk_family == AF_INET6) { 586 net_dbg_ratelimited("Probing zero-window on %pI6:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n", 587 &sk->sk_v6_daddr, ntohs(inet->inet_dport), 588 inet->inet_num, tp->snd_una, tp->snd_nxt, 589 jiffies_to_msecs(jiffies - tp->rcv_tstamp), 590 rtx_delta); 591 } 592 #endif 593 if (tcp_rtx_probe0_timed_out(sk, skb, rtx_delta)) { 594 tcp_write_err(sk); 595 goto out; 596 } 597 tcp_enter_loss(sk); 598 tcp_retransmit_skb(sk, skb, 1); 599 __sk_dst_reset(sk); 600 goto out_reset_timer; 601 } 602 603 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS); 604 if (tcp_write_timeout(sk)) 605 goto out; 606 607 if (icsk->icsk_retransmits == 0) { 608 int mib_idx = 0; 609 610 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 611 if (tcp_is_sack(tp)) 612 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 613 else 614 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 615 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 616 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 617 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 618 tp->sacked_out) { 619 if (tcp_is_sack(tp)) 620 mib_idx = LINUX_MIB_TCPSACKFAILURES; 621 else 622 mib_idx = LINUX_MIB_TCPRENOFAILURES; 623 } 624 if (mib_idx) 625 __NET_INC_STATS(sock_net(sk), mib_idx); 626 } 627 628 tcp_enter_loss(sk); 629 630 tcp_update_rto_stats(sk); 631 if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) { 632 /* Retransmission failed because of local congestion, 633 * Let senders fight for local resources conservatively. 634 */ 635 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 636 TCP_RESOURCE_PROBE_INTERVAL, 637 false); 638 goto out; 639 } 640 641 /* Increase the timeout each time we retransmit. Note that 642 * we do not increase the rtt estimate. rto is initialized 643 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 644 * that doubling rto each time is the least we can get away with. 645 * In KA9Q, Karn uses this for the first few times, and then 646 * goes to quadratic. netBSD doubles, but only goes up to *64, 647 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 648 * defined in the protocol as the maximum possible RTT. I guess 649 * we'll have to use something other than TCP to talk to the 650 * University of Mars. 651 * 652 * PAWS allows us longer timeouts and large windows, so once 653 * implemented ftp to mars will work nicely. We will have to fix 654 * the 120 second clamps though! 655 */ 656 657 out_reset_timer: 658 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 659 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 660 * might be increased if the stream oscillates between thin and thick, 661 * thus the old value might already be too high compared to the value 662 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 663 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 664 * exponential backoff behaviour to avoid continue hammering 665 * linear-timeout retransmissions into a black hole 666 */ 667 if (sk->sk_state == TCP_ESTABLISHED && 668 (tp->thin_lto || READ_ONCE(net->ipv4.sysctl_tcp_thin_linear_timeouts)) && 669 tcp_stream_is_thin(tp) && 670 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 671 icsk->icsk_backoff = 0; 672 icsk->icsk_rto = clamp(__tcp_set_rto(tp), 673 tcp_rto_min(sk), 674 tcp_rto_max(sk)); 675 } else if (sk->sk_state != TCP_SYN_SENT || 676 tp->total_rto > 677 READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) { 678 /* Use normal (exponential) backoff unless linear timeouts are 679 * activated. 680 */ 681 icsk->icsk_backoff++; 682 icsk->icsk_rto = min(icsk->icsk_rto << 1, tcp_rto_max(sk)); 683 } 684 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 685 tcp_clamp_rto_to_user_timeout(sk), false); 686 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1) + 1, 0)) 687 __sk_dst_reset(sk); 688 689 out:; 690 } 691 692 /* Called with bottom-half processing disabled. 693 * Called by tcp_write_timer() and tcp_release_cb(). 694 */ 695 void tcp_write_timer_handler(struct sock *sk) 696 { 697 struct inet_connection_sock *icsk = inet_csk(sk); 698 int event; 699 700 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) || 701 !icsk->icsk_pending) 702 return; 703 704 if (time_after(tcp_timeout_expires(sk), jiffies)) { 705 sk_reset_timer(sk, &sk->tcp_retransmit_timer, 706 tcp_timeout_expires(sk)); 707 return; 708 } 709 tcp_mstamp_refresh(tcp_sk(sk)); 710 event = icsk->icsk_pending; 711 712 switch (event) { 713 case ICSK_TIME_REO_TIMEOUT: 714 tcp_rack_reo_timeout(sk); 715 break; 716 case ICSK_TIME_LOSS_PROBE: 717 tcp_send_loss_probe(sk); 718 break; 719 case ICSK_TIME_RETRANS: 720 smp_store_release(&icsk->icsk_pending, 0); 721 tcp_retransmit_timer(sk); 722 break; 723 case ICSK_TIME_PROBE0: 724 smp_store_release(&icsk->icsk_pending, 0); 725 tcp_probe_timer(sk); 726 break; 727 } 728 } 729 730 static void tcp_write_timer(struct timer_list *t) 731 { 732 struct sock *sk = timer_container_of(sk, t, tcp_retransmit_timer); 733 734 /* Avoid locking the socket when there is no pending event. */ 735 if (!smp_load_acquire(&inet_csk(sk)->icsk_pending)) 736 goto out; 737 738 bh_lock_sock(sk); 739 if (!sock_owned_by_user(sk)) { 740 tcp_write_timer_handler(sk); 741 } else { 742 /* delegate our work to tcp_release_cb() */ 743 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags)) 744 sock_hold(sk); 745 } 746 bh_unlock_sock(sk); 747 out: 748 sock_put(sk); 749 } 750 751 void tcp_syn_ack_timeout(const struct request_sock *req) 752 { 753 struct net *net = read_pnet(&inet_rsk(req)->ireq_net); 754 755 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS); 756 } 757 758 void tcp_reset_keepalive_timer(struct sock *sk, unsigned long len) 759 { 760 sk_reset_timer(sk, &inet_csk(sk)->icsk_keepalive_timer, jiffies + len); 761 } 762 763 static void tcp_delete_keepalive_timer(struct sock *sk) 764 { 765 sk_stop_timer(sk, &inet_csk(sk)->icsk_keepalive_timer); 766 } 767 768 void tcp_set_keepalive(struct sock *sk, int val) 769 { 770 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 771 return; 772 773 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 774 tcp_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 775 else if (!val) 776 tcp_delete_keepalive_timer(sk); 777 } 778 779 static void tcp_keepalive_timer(struct timer_list *t) 780 { 781 struct inet_connection_sock *icsk = 782 timer_container_of(icsk, t, icsk_keepalive_timer); 783 struct sock *sk = &icsk->icsk_inet.sk; 784 struct tcp_sock *tp = tcp_sk(sk); 785 u32 elapsed; 786 787 /* Only process if socket is not in use. */ 788 bh_lock_sock(sk); 789 if (sock_owned_by_user(sk)) { 790 /* Try again later. */ 791 tcp_reset_keepalive_timer(sk, HZ/20); 792 goto out; 793 } 794 795 if (sk->sk_state == TCP_LISTEN) { 796 pr_err("Hmm... keepalive on a LISTEN ???\n"); 797 goto out; 798 } 799 800 tcp_mstamp_refresh(tp); 801 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 802 if (READ_ONCE(tp->linger2) >= 0) { 803 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 804 805 if (tmo > 0) { 806 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 807 goto out; 808 } 809 } 810 tcp_send_active_reset(sk, GFP_ATOMIC, SK_RST_REASON_TCP_STATE); 811 goto death; 812 } 813 814 if (!sock_flag(sk, SOCK_KEEPOPEN) || 815 ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT))) 816 goto out; 817 818 elapsed = keepalive_time_when(tp); 819 820 /* It is alive without keepalive 8) */ 821 if (tp->packets_out || !tcp_write_queue_empty(sk)) 822 goto resched; 823 824 elapsed = keepalive_time_elapsed(tp); 825 826 if (elapsed >= keepalive_time_when(tp)) { 827 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout); 828 829 /* If the TCP_USER_TIMEOUT option is enabled, use that 830 * to determine when to timeout instead. 831 */ 832 if ((user_timeout != 0 && 833 elapsed >= msecs_to_jiffies(user_timeout) && 834 icsk->icsk_probes_out > 0) || 835 (user_timeout == 0 && 836 icsk->icsk_probes_out >= keepalive_probes(tp))) { 837 tcp_send_active_reset(sk, GFP_ATOMIC, 838 SK_RST_REASON_TCP_KEEPALIVE_TIMEOUT); 839 tcp_write_err(sk); 840 goto out; 841 } 842 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) { 843 WRITE_ONCE(icsk->icsk_probes_out, icsk->icsk_probes_out + 1); 844 elapsed = keepalive_intvl_when(tp); 845 } else { 846 /* If keepalive was lost due to local congestion, 847 * try harder. 848 */ 849 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 850 } 851 } else { 852 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 853 elapsed = keepalive_time_when(tp) - elapsed; 854 } 855 856 resched: 857 tcp_reset_keepalive_timer(sk, elapsed); 858 goto out; 859 860 death: 861 tcp_done(sk); 862 863 out: 864 bh_unlock_sock(sk); 865 sock_put(sk); 866 } 867 868 static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer) 869 { 870 struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer); 871 struct sock *sk = (struct sock *)tp; 872 873 bh_lock_sock(sk); 874 if (!sock_owned_by_user(sk)) { 875 if (tp->compressed_ack) { 876 /* Since we have to send one ack finally, 877 * subtract one from tp->compressed_ack to keep 878 * LINUX_MIB_TCPACKCOMPRESSED accurate. 879 */ 880 tp->compressed_ack--; 881 tcp_mstamp_refresh(tp); 882 tcp_send_ack(sk); 883 } 884 } else { 885 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, 886 &sk->sk_tsq_flags)) 887 sock_hold(sk); 888 } 889 bh_unlock_sock(sk); 890 891 sock_put(sk); 892 893 return HRTIMER_NORESTART; 894 } 895 896 void tcp_init_xmit_timers(struct sock *sk) 897 { 898 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 899 &tcp_keepalive_timer); 900 hrtimer_setup(&tcp_sk(sk)->pacing_timer, tcp_pace_kick, CLOCK_MONOTONIC, 901 HRTIMER_MODE_ABS_PINNED_SOFT); 902 903 hrtimer_setup(&tcp_sk(sk)->compressed_ack_timer, tcp_compressed_ack_kick, CLOCK_MONOTONIC, 904 HRTIMER_MODE_REL_PINNED_SOFT); 905 } 906