1/* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * Implementation of the Transmission Control Protocol(TCP). 7 * 8 * Authors: Ross Biro 9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 10 * Mark Evans, <evansmp@uhura.aston.ac.uk> 11 * Corey Minyard <wf-rch!minyard@relay.EU.net> 12 * Florian La Roche, <flla@stud.uni-sb.de> 13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 14 * Linus Torvalds, <torvalds@cs.helsinki.fi> 15 * Alan Cox, <gw4pts@gw4pts.ampr.org> 16 * Matthew Dillon, <dillon@apollo.west.oic.com> 17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 18 * Jorge Cwik, <jorge@laser.satlink.net> 19 */ 20 21#include <linux/module.h> 22#include <linux/gfp.h> 23#include <net/tcp.h> 24 25int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES; 26int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; 27int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; 28int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; 29int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; 30int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; 31int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; 32int sysctl_tcp_orphan_retries __read_mostly; 33int sysctl_tcp_thin_linear_timeouts __read_mostly; 34 35static void tcp_write_err(struct sock *sk) 36{ 37 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 38 sk->sk_error_report(sk); 39 40 tcp_done(sk); 41 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); 42} 43 44/* Do not allow orphaned sockets to eat all our resources. 45 * This is direct violation of TCP specs, but it is required 46 * to prevent DoS attacks. It is called when a retransmission timeout 47 * or zero probe timeout occurs on orphaned socket. 48 * 49 * Criteria is still not confirmed experimentally and may change. 50 * We kill the socket, if: 51 * 1. If number of orphaned sockets exceeds an administratively configured 52 * limit. 53 * 2. If we have strong memory pressure. 54 */ 55static int tcp_out_of_resources(struct sock *sk, bool do_reset) 56{ 57 struct tcp_sock *tp = tcp_sk(sk); 58 int shift = 0; 59 60 /* If peer does not open window for long time, or did not transmit 61 * anything for long time, penalize it. */ 62 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 63 shift++; 64 65 /* If some dubious ICMP arrived, penalize even more. */ 66 if (sk->sk_err_soft) 67 shift++; 68 69 if (tcp_check_oom(sk, shift)) { 70 /* Catch exceptional cases, when connection requires reset. 71 * 1. Last segment was sent recently. */ 72 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 73 /* 2. Window is closed. */ 74 (!tp->snd_wnd && !tp->packets_out)) 75 do_reset = true; 76 if (do_reset) 77 tcp_send_active_reset(sk, GFP_ATOMIC); 78 tcp_done(sk); 79 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 80 return 1; 81 } 82 return 0; 83} 84 85/* Calculate maximal number or retries on an orphaned socket. */ 86static int tcp_orphan_retries(struct sock *sk, bool alive) 87{ 88 int retries = sysctl_tcp_orphan_retries; /* May be zero. */ 89 90 /* We know from an ICMP that something is wrong. */ 91 if (sk->sk_err_soft && !alive) 92 retries = 0; 93 94 /* However, if socket sent something recently, select some safe 95 * number of retries. 8 corresponds to >100 seconds with minimal 96 * RTO of 200msec. */ 97 if (retries == 0 && alive) 98 retries = 8; 99 return retries; 100} 101 102static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 103{ 104 struct net *net = sock_net(sk); 105 106 /* Black hole detection */ 107 if (net->ipv4.sysctl_tcp_mtu_probing) { 108 if (!icsk->icsk_mtup.enabled) { 109 icsk->icsk_mtup.enabled = 1; 110 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 111 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 112 } else { 113 struct net *net = sock_net(sk); 114 struct tcp_sock *tp = tcp_sk(sk); 115 int mss; 116 117 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 118 mss = min(net->ipv4.sysctl_tcp_base_mss, mss); 119 mss = max(mss, 68 - tp->tcp_header_len); 120 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 121 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 122 } 123 } 124} 125 126/* This function calculates a "timeout" which is equivalent to the timeout of a 127 * TCP connection after "boundary" unsuccessful, exponentially backed-off 128 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if 129 * syn_set flag is set. 130 */ 131static bool retransmits_timed_out(struct sock *sk, 132 unsigned int boundary, 133 unsigned int timeout, 134 bool syn_set) 135{ 136 unsigned int linear_backoff_thresh, start_ts; 137 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; 138 139 if (!inet_csk(sk)->icsk_retransmits) 140 return false; 141 142 start_ts = tcp_sk(sk)->retrans_stamp; 143 if (unlikely(!start_ts)) 144 start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk)); 145 146 if (likely(timeout == 0)) { 147 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 148 149 if (boundary <= linear_backoff_thresh) 150 timeout = ((2 << boundary) - 1) * rto_base; 151 else 152 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 153 (boundary - linear_backoff_thresh) * TCP_RTO_MAX; 154 } 155 return (tcp_time_stamp - start_ts) >= timeout; 156} 157 158/* A write timeout has occurred. Process the after effects. */ 159static int tcp_write_timeout(struct sock *sk) 160{ 161 struct inet_connection_sock *icsk = inet_csk(sk); 162 struct tcp_sock *tp = tcp_sk(sk); 163 int retry_until; 164 bool do_reset, syn_set = false; 165 166 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 167 if (icsk->icsk_retransmits) { 168 dst_negative_advice(sk); 169 if (tp->syn_fastopen || tp->syn_data) 170 tcp_fastopen_cache_set(sk, 0, NULL, true, 0); 171 if (tp->syn_data && icsk->icsk_retransmits == 1) 172 NET_INC_STATS_BH(sock_net(sk), 173 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 174 } 175 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 176 syn_set = true; 177 } else { 178 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) { 179 /* Some middle-boxes may black-hole Fast Open _after_ 180 * the handshake. Therefore we conservatively disable 181 * Fast Open on this path on recurring timeouts with 182 * few or zero bytes acked after Fast Open. 183 */ 184 if (tp->syn_data_acked && 185 tp->bytes_acked <= tp->rx_opt.mss_clamp) { 186 tcp_fastopen_cache_set(sk, 0, NULL, true, 0); 187 if (icsk->icsk_retransmits == sysctl_tcp_retries1) 188 NET_INC_STATS_BH(sock_net(sk), 189 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 190 } 191 /* Black hole detection */ 192 tcp_mtu_probing(icsk, sk); 193 194 dst_negative_advice(sk); 195 } 196 197 retry_until = sysctl_tcp_retries2; 198 if (sock_flag(sk, SOCK_DEAD)) { 199 const bool alive = icsk->icsk_rto < TCP_RTO_MAX; 200 201 retry_until = tcp_orphan_retries(sk, alive); 202 do_reset = alive || 203 !retransmits_timed_out(sk, retry_until, 0, 0); 204 205 if (tcp_out_of_resources(sk, do_reset)) 206 return 1; 207 } 208 } 209 210 if (retransmits_timed_out(sk, retry_until, 211 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 212 /* Has it gone just too far? */ 213 tcp_write_err(sk); 214 return 1; 215 } 216 return 0; 217} 218 219void tcp_delack_timer_handler(struct sock *sk) 220{ 221 struct tcp_sock *tp = tcp_sk(sk); 222 struct inet_connection_sock *icsk = inet_csk(sk); 223 224 sk_mem_reclaim_partial(sk); 225 226 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 227 goto out; 228 229 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 230 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 231 goto out; 232 } 233 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 234 235 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 236 struct sk_buff *skb; 237 238 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 239 240 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 241 sk_backlog_rcv(sk, skb); 242 243 tp->ucopy.memory = 0; 244 } 245 246 if (inet_csk_ack_scheduled(sk)) { 247 if (!icsk->icsk_ack.pingpong) { 248 /* Delayed ACK missed: inflate ATO. */ 249 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 250 } else { 251 /* Delayed ACK missed: leave pingpong mode and 252 * deflate ATO. 253 */ 254 icsk->icsk_ack.pingpong = 0; 255 icsk->icsk_ack.ato = TCP_ATO_MIN; 256 } 257 tcp_send_ack(sk); 258 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); 259 } 260 261out: 262 if (tcp_under_memory_pressure(sk)) 263 sk_mem_reclaim(sk); 264} 265 266static void tcp_delack_timer(unsigned long data) 267{ 268 struct sock *sk = (struct sock *)data; 269 270 bh_lock_sock(sk); 271 if (!sock_owned_by_user(sk)) { 272 tcp_delack_timer_handler(sk); 273 } else { 274 inet_csk(sk)->icsk_ack.blocked = 1; 275 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 276 /* deleguate our work to tcp_release_cb() */ 277 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) 278 sock_hold(sk); 279 } 280 bh_unlock_sock(sk); 281 sock_put(sk); 282} 283 284static void tcp_probe_timer(struct sock *sk) 285{ 286 struct inet_connection_sock *icsk = inet_csk(sk); 287 struct tcp_sock *tp = tcp_sk(sk); 288 int max_probes; 289 u32 start_ts; 290 291 if (tp->packets_out || !tcp_send_head(sk)) { 292 icsk->icsk_probes_out = 0; 293 return; 294 } 295 296 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as 297 * long as the receiver continues to respond probes. We support this by 298 * default and reset icsk_probes_out with incoming ACKs. But if the 299 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we 300 * kill the socket when the retry count and the time exceeds the 301 * corresponding system limit. We also implement similar policy when 302 * we use RTO to probe window in tcp_retransmit_timer(). 303 */ 304 start_ts = tcp_skb_timestamp(tcp_send_head(sk)); 305 if (!start_ts) 306 skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp); 307 else if (icsk->icsk_user_timeout && 308 (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout) 309 goto abort; 310 311 max_probes = sysctl_tcp_retries2; 312 if (sock_flag(sk, SOCK_DEAD)) { 313 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX; 314 315 max_probes = tcp_orphan_retries(sk, alive); 316 if (!alive && icsk->icsk_backoff >= max_probes) 317 goto abort; 318 if (tcp_out_of_resources(sk, true)) 319 return; 320 } 321 322 if (icsk->icsk_probes_out > max_probes) { 323abort: tcp_write_err(sk); 324 } else { 325 /* Only send another probe if we didn't close things up. */ 326 tcp_send_probe0(sk); 327 } 328} 329 330/* 331 * Timer for Fast Open socket to retransmit SYNACK. Note that the 332 * sk here is the child socket, not the parent (listener) socket. 333 */ 334static void tcp_fastopen_synack_timer(struct sock *sk) 335{ 336 struct inet_connection_sock *icsk = inet_csk(sk); 337 int max_retries = icsk->icsk_syn_retries ? : 338 sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */ 339 struct request_sock *req; 340 341 req = tcp_sk(sk)->fastopen_rsk; 342 req->rsk_ops->syn_ack_timeout(req); 343 344 if (req->num_timeout >= max_retries) { 345 tcp_write_err(sk); 346 return; 347 } 348 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error 349 * returned from rtx_syn_ack() to make it more persistent like 350 * regular retransmit because if the child socket has been accepted 351 * it's not good to give up too easily. 352 */ 353 inet_rtx_syn_ack(sk, req); 354 req->num_timeout++; 355 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 356 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX); 357} 358 359/* 360 * The TCP retransmit timer. 361 */ 362 363void tcp_retransmit_timer(struct sock *sk) 364{ 365 struct tcp_sock *tp = tcp_sk(sk); 366 struct inet_connection_sock *icsk = inet_csk(sk); 367 368 if (tp->fastopen_rsk) { 369 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && 370 sk->sk_state != TCP_FIN_WAIT1); 371 tcp_fastopen_synack_timer(sk); 372 /* Before we receive ACK to our SYN-ACK don't retransmit 373 * anything else (e.g., data or FIN segments). 374 */ 375 return; 376 } 377 if (!tp->packets_out) 378 goto out; 379 380 WARN_ON(tcp_write_queue_empty(sk)); 381 382 tp->tlp_high_seq = 0; 383 384 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 385 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 386 /* Receiver dastardly shrinks window. Our retransmits 387 * become zero probes, but we should not timeout this 388 * connection. If the socket is an orphan, time it out, 389 * we cannot allow such beasts to hang infinitely. 390 */ 391 struct inet_sock *inet = inet_sk(sk); 392 if (sk->sk_family == AF_INET) { 393 net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 394 &inet->inet_daddr, 395 ntohs(inet->inet_dport), 396 inet->inet_num, 397 tp->snd_una, tp->snd_nxt); 398 } 399#if IS_ENABLED(CONFIG_IPV6) 400 else if (sk->sk_family == AF_INET6) { 401 net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 402 &sk->sk_v6_daddr, 403 ntohs(inet->inet_dport), 404 inet->inet_num, 405 tp->snd_una, tp->snd_nxt); 406 } 407#endif 408 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 409 tcp_write_err(sk); 410 goto out; 411 } 412 tcp_enter_loss(sk); 413 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 414 __sk_dst_reset(sk); 415 goto out_reset_timer; 416 } 417 418 if (tcp_write_timeout(sk)) 419 goto out; 420 421 if (icsk->icsk_retransmits == 0) { 422 int mib_idx; 423 424 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 425 if (tcp_is_sack(tp)) 426 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 427 else 428 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 429 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 430 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 431 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 432 tp->sacked_out) { 433 if (tcp_is_sack(tp)) 434 mib_idx = LINUX_MIB_TCPSACKFAILURES; 435 else 436 mib_idx = LINUX_MIB_TCPRENOFAILURES; 437 } else { 438 mib_idx = LINUX_MIB_TCPTIMEOUTS; 439 } 440 NET_INC_STATS_BH(sock_net(sk), mib_idx); 441 } 442 443 tcp_enter_loss(sk); 444 445 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 446 /* Retransmission failed because of local congestion, 447 * do not backoff. 448 */ 449 if (!icsk->icsk_retransmits) 450 icsk->icsk_retransmits = 1; 451 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 452 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 453 TCP_RTO_MAX); 454 goto out; 455 } 456 457 /* Increase the timeout each time we retransmit. Note that 458 * we do not increase the rtt estimate. rto is initialized 459 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 460 * that doubling rto each time is the least we can get away with. 461 * In KA9Q, Karn uses this for the first few times, and then 462 * goes to quadratic. netBSD doubles, but only goes up to *64, 463 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 464 * defined in the protocol as the maximum possible RTT. I guess 465 * we'll have to use something other than TCP to talk to the 466 * University of Mars. 467 * 468 * PAWS allows us longer timeouts and large windows, so once 469 * implemented ftp to mars will work nicely. We will have to fix 470 * the 120 second clamps though! 471 */ 472 icsk->icsk_backoff++; 473 icsk->icsk_retransmits++; 474 475out_reset_timer: 476 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 477 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 478 * might be increased if the stream oscillates between thin and thick, 479 * thus the old value might already be too high compared to the value 480 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 481 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 482 * exponential backoff behaviour to avoid continue hammering 483 * linear-timeout retransmissions into a black hole 484 */ 485 if (sk->sk_state == TCP_ESTABLISHED && 486 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 487 tcp_stream_is_thin(tp) && 488 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 489 icsk->icsk_backoff = 0; 490 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 491 } else { 492 /* Use normal (exponential) backoff */ 493 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 494 } 495 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 496 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0)) 497 __sk_dst_reset(sk); 498 499out:; 500} 501 502void tcp_write_timer_handler(struct sock *sk) 503{ 504 struct inet_connection_sock *icsk = inet_csk(sk); 505 int event; 506 507 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 508 goto out; 509 510 if (time_after(icsk->icsk_timeout, jiffies)) { 511 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 512 goto out; 513 } 514 515 event = icsk->icsk_pending; 516 517 switch (event) { 518 case ICSK_TIME_EARLY_RETRANS: 519 tcp_resume_early_retransmit(sk); 520 break; 521 case ICSK_TIME_LOSS_PROBE: 522 tcp_send_loss_probe(sk); 523 break; 524 case ICSK_TIME_RETRANS: 525 icsk->icsk_pending = 0; 526 tcp_retransmit_timer(sk); 527 break; 528 case ICSK_TIME_PROBE0: 529 icsk->icsk_pending = 0; 530 tcp_probe_timer(sk); 531 break; 532 } 533 534out: 535 sk_mem_reclaim(sk); 536} 537 538static void tcp_write_timer(unsigned long data) 539{ 540 struct sock *sk = (struct sock *)data; 541 542 bh_lock_sock(sk); 543 if (!sock_owned_by_user(sk)) { 544 tcp_write_timer_handler(sk); 545 } else { 546 /* deleguate our work to tcp_release_cb() */ 547 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) 548 sock_hold(sk); 549 } 550 bh_unlock_sock(sk); 551 sock_put(sk); 552} 553 554void tcp_syn_ack_timeout(const struct request_sock *req) 555{ 556 struct net *net = read_pnet(&inet_rsk(req)->ireq_net); 557 558 NET_INC_STATS_BH(net, LINUX_MIB_TCPTIMEOUTS); 559} 560EXPORT_SYMBOL(tcp_syn_ack_timeout); 561 562void tcp_set_keepalive(struct sock *sk, int val) 563{ 564 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 565 return; 566 567 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 568 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 569 else if (!val) 570 inet_csk_delete_keepalive_timer(sk); 571} 572 573 574static void tcp_keepalive_timer (unsigned long data) 575{ 576 struct sock *sk = (struct sock *) data; 577 struct inet_connection_sock *icsk = inet_csk(sk); 578 struct tcp_sock *tp = tcp_sk(sk); 579 u32 elapsed; 580 581 /* Only process if socket is not in use. */ 582 bh_lock_sock(sk); 583 if (sock_owned_by_user(sk)) { 584 /* Try again later. */ 585 inet_csk_reset_keepalive_timer (sk, HZ/20); 586 goto out; 587 } 588 589 if (sk->sk_state == TCP_LISTEN) { 590 pr_err("Hmm... keepalive on a LISTEN ???\n"); 591 goto out; 592 } 593 594 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 595 if (tp->linger2 >= 0) { 596 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 597 598 if (tmo > 0) { 599 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 600 goto out; 601 } 602 } 603 tcp_send_active_reset(sk, GFP_ATOMIC); 604 goto death; 605 } 606 607 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 608 goto out; 609 610 elapsed = keepalive_time_when(tp); 611 612 /* It is alive without keepalive 8) */ 613 if (tp->packets_out || tcp_send_head(sk)) 614 goto resched; 615 616 elapsed = keepalive_time_elapsed(tp); 617 618 if (elapsed >= keepalive_time_when(tp)) { 619 /* If the TCP_USER_TIMEOUT option is enabled, use that 620 * to determine when to timeout instead. 621 */ 622 if ((icsk->icsk_user_timeout != 0 && 623 elapsed >= icsk->icsk_user_timeout && 624 icsk->icsk_probes_out > 0) || 625 (icsk->icsk_user_timeout == 0 && 626 icsk->icsk_probes_out >= keepalive_probes(tp))) { 627 tcp_send_active_reset(sk, GFP_ATOMIC); 628 tcp_write_err(sk); 629 goto out; 630 } 631 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) { 632 icsk->icsk_probes_out++; 633 elapsed = keepalive_intvl_when(tp); 634 } else { 635 /* If keepalive was lost due to local congestion, 636 * try harder. 637 */ 638 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 639 } 640 } else { 641 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 642 elapsed = keepalive_time_when(tp) - elapsed; 643 } 644 645 sk_mem_reclaim(sk); 646 647resched: 648 inet_csk_reset_keepalive_timer (sk, elapsed); 649 goto out; 650 651death: 652 tcp_done(sk); 653 654out: 655 bh_unlock_sock(sk); 656 sock_put(sk); 657} 658 659void tcp_init_xmit_timers(struct sock *sk) 660{ 661 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 662 &tcp_keepalive_timer); 663} 664