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