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 * Version: $Id: tcp_timer.c,v 1.88 2002/02/01 22:01:04 davem Exp $ 9 * 10 * Authors: Ross Biro 11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 12 * Mark Evans, <evansmp@uhura.aston.ac.uk> 13 * Corey Minyard <wf-rch!minyard@relay.EU.net> 14 * Florian La Roche, <flla@stud.uni-sb.de> 15 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 16 * Linus Torvalds, <torvalds@cs.helsinki.fi> 17 * Alan Cox, <gw4pts@gw4pts.ampr.org> 18 * Matthew Dillon, <dillon@apollo.west.oic.com> 19 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 20 * Jorge Cwik, <jorge@laser.satlink.net> 21 */ 22 23 #include <linux/module.h> 24 #include <net/tcp.h> 25 26 int sysctl_tcp_syn_retries = TCP_SYN_RETRIES; 27 int sysctl_tcp_synack_retries = TCP_SYNACK_RETRIES; 28 int sysctl_tcp_keepalive_time = TCP_KEEPALIVE_TIME; 29 int sysctl_tcp_keepalive_probes = TCP_KEEPALIVE_PROBES; 30 int sysctl_tcp_keepalive_intvl = TCP_KEEPALIVE_INTVL; 31 int sysctl_tcp_retries1 = TCP_RETR1; 32 int sysctl_tcp_retries2 = TCP_RETR2; 33 int sysctl_tcp_orphan_retries; 34 35 static void tcp_write_timer(unsigned long); 36 static void tcp_delack_timer(unsigned long); 37 static void tcp_keepalive_timer (unsigned long data); 38 39 void tcp_init_xmit_timers(struct sock *sk) 40 { 41 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 42 &tcp_keepalive_timer); 43 } 44 45 EXPORT_SYMBOL(tcp_init_xmit_timers); 46 47 static void tcp_write_err(struct sock *sk) 48 { 49 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 50 sk->sk_error_report(sk); 51 52 tcp_done(sk); 53 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONTIMEOUT); 54 } 55 56 /* Do not allow orphaned sockets to eat all our resources. 57 * This is direct violation of TCP specs, but it is required 58 * to prevent DoS attacks. It is called when a retransmission timeout 59 * or zero probe timeout occurs on orphaned socket. 60 * 61 * Criteria is still not confirmed experimentally and may change. 62 * We kill the socket, if: 63 * 1. If number of orphaned sockets exceeds an administratively configured 64 * limit. 65 * 2. If we have strong memory pressure. 66 */ 67 static int tcp_out_of_resources(struct sock *sk, int do_reset) 68 { 69 struct tcp_sock *tp = tcp_sk(sk); 70 int orphans = atomic_read(&tcp_orphan_count); 71 72 /* If peer does not open window for long time, or did not transmit 73 * anything for long time, penalize it. */ 74 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 75 orphans <<= 1; 76 77 /* If some dubious ICMP arrived, penalize even more. */ 78 if (sk->sk_err_soft) 79 orphans <<= 1; 80 81 if (orphans >= sysctl_tcp_max_orphans || 82 (sk->sk_wmem_queued > SOCK_MIN_SNDBUF && 83 atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2])) { 84 if (net_ratelimit()) 85 printk(KERN_INFO "Out of socket memory\n"); 86 87 /* Catch exceptional cases, when connection requires reset. 88 * 1. Last segment was sent recently. */ 89 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 90 /* 2. Window is closed. */ 91 (!tp->snd_wnd && !tp->packets_out)) 92 do_reset = 1; 93 if (do_reset) 94 tcp_send_active_reset(sk, GFP_ATOMIC); 95 tcp_done(sk); 96 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONMEMORY); 97 return 1; 98 } 99 return 0; 100 } 101 102 /* Calculate maximal number or retries on an orphaned socket. */ 103 static int tcp_orphan_retries(struct sock *sk, int alive) 104 { 105 int retries = sysctl_tcp_orphan_retries; /* May be zero. */ 106 107 /* We know from an ICMP that something is wrong. */ 108 if (sk->sk_err_soft && !alive) 109 retries = 0; 110 111 /* However, if socket sent something recently, select some safe 112 * number of retries. 8 corresponds to >100 seconds with minimal 113 * RTO of 200msec. */ 114 if (retries == 0 && alive) 115 retries = 8; 116 return retries; 117 } 118 119 /* A write timeout has occurred. Process the after effects. */ 120 static int tcp_write_timeout(struct sock *sk) 121 { 122 struct inet_connection_sock *icsk = inet_csk(sk); 123 struct tcp_sock *tp = tcp_sk(sk); 124 int retry_until; 125 int mss; 126 127 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 128 if (icsk->icsk_retransmits) 129 dst_negative_advice(&sk->sk_dst_cache); 130 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 131 } else { 132 if (icsk->icsk_retransmits >= sysctl_tcp_retries1) { 133 /* Black hole detection */ 134 if (sysctl_tcp_mtu_probing) { 135 if (!icsk->icsk_mtup.enabled) { 136 icsk->icsk_mtup.enabled = 1; 137 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 138 } else { 139 mss = min(sysctl_tcp_base_mss, 140 tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)/2); 141 mss = max(mss, 68 - tp->tcp_header_len); 142 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 143 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 144 } 145 } 146 147 dst_negative_advice(&sk->sk_dst_cache); 148 } 149 150 retry_until = sysctl_tcp_retries2; 151 if (sock_flag(sk, SOCK_DEAD)) { 152 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 153 154 retry_until = tcp_orphan_retries(sk, alive); 155 156 if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until)) 157 return 1; 158 } 159 } 160 161 if (icsk->icsk_retransmits >= retry_until) { 162 /* Has it gone just too far? */ 163 tcp_write_err(sk); 164 return 1; 165 } 166 return 0; 167 } 168 169 static void tcp_delack_timer(unsigned long data) 170 { 171 struct sock *sk = (struct sock*)data; 172 struct tcp_sock *tp = tcp_sk(sk); 173 struct inet_connection_sock *icsk = inet_csk(sk); 174 175 bh_lock_sock(sk); 176 if (sock_owned_by_user(sk)) { 177 /* Try again later. */ 178 icsk->icsk_ack.blocked = 1; 179 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOCKED); 180 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); 181 goto out_unlock; 182 } 183 184 sk_stream_mem_reclaim(sk); 185 186 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 187 goto out; 188 189 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 190 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 191 goto out; 192 } 193 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 194 195 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 196 struct sk_buff *skb; 197 198 NET_INC_STATS_BH(LINUX_MIB_TCPSCHEDULERFAILED); 199 200 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 201 sk->sk_backlog_rcv(sk, skb); 202 203 tp->ucopy.memory = 0; 204 } 205 206 if (inet_csk_ack_scheduled(sk)) { 207 if (!icsk->icsk_ack.pingpong) { 208 /* Delayed ACK missed: inflate ATO. */ 209 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 210 } else { 211 /* Delayed ACK missed: leave pingpong mode and 212 * deflate ATO. 213 */ 214 icsk->icsk_ack.pingpong = 0; 215 icsk->icsk_ack.ato = TCP_ATO_MIN; 216 } 217 tcp_send_ack(sk); 218 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKS); 219 } 220 TCP_CHECK_TIMER(sk); 221 222 out: 223 if (tcp_memory_pressure) 224 sk_stream_mem_reclaim(sk); 225 out_unlock: 226 bh_unlock_sock(sk); 227 sock_put(sk); 228 } 229 230 static void tcp_probe_timer(struct sock *sk) 231 { 232 struct inet_connection_sock *icsk = inet_csk(sk); 233 struct tcp_sock *tp = tcp_sk(sk); 234 int max_probes; 235 236 if (tp->packets_out || !sk->sk_send_head) { 237 icsk->icsk_probes_out = 0; 238 return; 239 } 240 241 /* *WARNING* RFC 1122 forbids this 242 * 243 * It doesn't AFAIK, because we kill the retransmit timer -AK 244 * 245 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 246 * this behaviour in Solaris down as a bug fix. [AC] 247 * 248 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 249 * even if they advertise zero window. Hence, connection is killed only 250 * if we received no ACKs for normal connection timeout. It is not killed 251 * only because window stays zero for some time, window may be zero 252 * until armageddon and even later. We are in full accordance 253 * with RFCs, only probe timer combines both retransmission timeout 254 * and probe timeout in one bottle. --ANK 255 */ 256 max_probes = sysctl_tcp_retries2; 257 258 if (sock_flag(sk, SOCK_DEAD)) { 259 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 260 261 max_probes = tcp_orphan_retries(sk, alive); 262 263 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 264 return; 265 } 266 267 if (icsk->icsk_probes_out > max_probes) { 268 tcp_write_err(sk); 269 } else { 270 /* Only send another probe if we didn't close things up. */ 271 tcp_send_probe0(sk); 272 } 273 } 274 275 /* 276 * The TCP retransmit timer. 277 */ 278 279 static void tcp_retransmit_timer(struct sock *sk) 280 { 281 struct tcp_sock *tp = tcp_sk(sk); 282 struct inet_connection_sock *icsk = inet_csk(sk); 283 284 if (!tp->packets_out) 285 goto out; 286 287 BUG_TRAP(!skb_queue_empty(&sk->sk_write_queue)); 288 289 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 290 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 291 /* Receiver dastardly shrinks window. Our retransmits 292 * become zero probes, but we should not timeout this 293 * connection. If the socket is an orphan, time it out, 294 * we cannot allow such beasts to hang infinitely. 295 */ 296 #ifdef TCP_DEBUG 297 if (net_ratelimit()) { 298 struct inet_sock *inet = inet_sk(sk); 299 printk(KERN_DEBUG "TCP: Treason uncloaked! Peer %u.%u.%u.%u:%u/%u shrinks window %u:%u. Repaired.\n", 300 NIPQUAD(inet->daddr), htons(inet->dport), 301 inet->num, tp->snd_una, tp->snd_nxt); 302 } 303 #endif 304 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 305 tcp_write_err(sk); 306 goto out; 307 } 308 tcp_enter_loss(sk, 0); 309 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue)); 310 __sk_dst_reset(sk); 311 goto out_reset_timer; 312 } 313 314 if (tcp_write_timeout(sk)) 315 goto out; 316 317 if (icsk->icsk_retransmits == 0) { 318 if (icsk->icsk_ca_state == TCP_CA_Disorder || 319 icsk->icsk_ca_state == TCP_CA_Recovery) { 320 if (tp->rx_opt.sack_ok) { 321 if (icsk->icsk_ca_state == TCP_CA_Recovery) 322 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERYFAIL); 323 else 324 NET_INC_STATS_BH(LINUX_MIB_TCPSACKFAILURES); 325 } else { 326 if (icsk->icsk_ca_state == TCP_CA_Recovery) 327 NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERYFAIL); 328 else 329 NET_INC_STATS_BH(LINUX_MIB_TCPRENOFAILURES); 330 } 331 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 332 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSFAILURES); 333 } else { 334 NET_INC_STATS_BH(LINUX_MIB_TCPTIMEOUTS); 335 } 336 } 337 338 if (tcp_use_frto(sk)) { 339 tcp_enter_frto(sk); 340 } else { 341 tcp_enter_loss(sk, 0); 342 } 343 344 if (tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue)) > 0) { 345 /* Retransmission failed because of local congestion, 346 * do not backoff. 347 */ 348 if (!icsk->icsk_retransmits) 349 icsk->icsk_retransmits = 1; 350 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 351 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 352 TCP_RTO_MAX); 353 goto out; 354 } 355 356 /* Increase the timeout each time we retransmit. Note that 357 * we do not increase the rtt estimate. rto is initialized 358 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 359 * that doubling rto each time is the least we can get away with. 360 * In KA9Q, Karn uses this for the first few times, and then 361 * goes to quadratic. netBSD doubles, but only goes up to *64, 362 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 363 * defined in the protocol as the maximum possible RTT. I guess 364 * we'll have to use something other than TCP to talk to the 365 * University of Mars. 366 * 367 * PAWS allows us longer timeouts and large windows, so once 368 * implemented ftp to mars will work nicely. We will have to fix 369 * the 120 second clamps though! 370 */ 371 icsk->icsk_backoff++; 372 icsk->icsk_retransmits++; 373 374 out_reset_timer: 375 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 376 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 377 if (icsk->icsk_retransmits > sysctl_tcp_retries1) 378 __sk_dst_reset(sk); 379 380 out:; 381 } 382 383 static void tcp_write_timer(unsigned long data) 384 { 385 struct sock *sk = (struct sock*)data; 386 struct inet_connection_sock *icsk = inet_csk(sk); 387 int event; 388 389 bh_lock_sock(sk); 390 if (sock_owned_by_user(sk)) { 391 /* Try again later */ 392 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); 393 goto out_unlock; 394 } 395 396 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 397 goto out; 398 399 if (time_after(icsk->icsk_timeout, jiffies)) { 400 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 401 goto out; 402 } 403 404 event = icsk->icsk_pending; 405 icsk->icsk_pending = 0; 406 407 switch (event) { 408 case ICSK_TIME_RETRANS: 409 tcp_retransmit_timer(sk); 410 break; 411 case ICSK_TIME_PROBE0: 412 tcp_probe_timer(sk); 413 break; 414 } 415 TCP_CHECK_TIMER(sk); 416 417 out: 418 sk_stream_mem_reclaim(sk); 419 out_unlock: 420 bh_unlock_sock(sk); 421 sock_put(sk); 422 } 423 424 /* 425 * Timer for listening sockets 426 */ 427 428 static void tcp_synack_timer(struct sock *sk) 429 { 430 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 431 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 432 } 433 434 void tcp_set_keepalive(struct sock *sk, int val) 435 { 436 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 437 return; 438 439 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 440 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 441 else if (!val) 442 inet_csk_delete_keepalive_timer(sk); 443 } 444 445 446 static void tcp_keepalive_timer (unsigned long data) 447 { 448 struct sock *sk = (struct sock *) data; 449 struct inet_connection_sock *icsk = inet_csk(sk); 450 struct tcp_sock *tp = tcp_sk(sk); 451 __u32 elapsed; 452 453 /* Only process if socket is not in use. */ 454 bh_lock_sock(sk); 455 if (sock_owned_by_user(sk)) { 456 /* Try again later. */ 457 inet_csk_reset_keepalive_timer (sk, HZ/20); 458 goto out; 459 } 460 461 if (sk->sk_state == TCP_LISTEN) { 462 tcp_synack_timer(sk); 463 goto out; 464 } 465 466 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 467 if (tp->linger2 >= 0) { 468 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 469 470 if (tmo > 0) { 471 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 472 goto out; 473 } 474 } 475 tcp_send_active_reset(sk, GFP_ATOMIC); 476 goto death; 477 } 478 479 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 480 goto out; 481 482 elapsed = keepalive_time_when(tp); 483 484 /* It is alive without keepalive 8) */ 485 if (tp->packets_out || sk->sk_send_head) 486 goto resched; 487 488 elapsed = tcp_time_stamp - tp->rcv_tstamp; 489 490 if (elapsed >= keepalive_time_when(tp)) { 491 if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) || 492 (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) { 493 tcp_send_active_reset(sk, GFP_ATOMIC); 494 tcp_write_err(sk); 495 goto out; 496 } 497 if (tcp_write_wakeup(sk) <= 0) { 498 icsk->icsk_probes_out++; 499 elapsed = keepalive_intvl_when(tp); 500 } else { 501 /* If keepalive was lost due to local congestion, 502 * try harder. 503 */ 504 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 505 } 506 } else { 507 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 508 elapsed = keepalive_time_when(tp) - elapsed; 509 } 510 511 TCP_CHECK_TIMER(sk); 512 sk_stream_mem_reclaim(sk); 513 514 resched: 515 inet_csk_reset_keepalive_timer (sk, elapsed); 516 goto out; 517 518 death: 519 tcp_done(sk); 520 521 out: 522 bh_unlock_sock(sk); 523 sock_put(sk); 524 } 525