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 <net/tcp.h> 23 24 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES; 25 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; 26 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; 27 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; 28 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; 29 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; 30 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; 31 int sysctl_tcp_orphan_retries __read_mostly; 32 33 static void tcp_write_timer(unsigned long); 34 static void tcp_delack_timer(unsigned long); 35 static void tcp_keepalive_timer (unsigned long data); 36 37 void tcp_init_xmit_timers(struct sock *sk) 38 { 39 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 40 &tcp_keepalive_timer); 41 } 42 43 EXPORT_SYMBOL(tcp_init_xmit_timers); 44 45 static void tcp_write_err(struct sock *sk) 46 { 47 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 48 sk->sk_error_report(sk); 49 50 tcp_done(sk); 51 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); 52 } 53 54 /* Do not allow orphaned sockets to eat all our resources. 55 * This is direct violation of TCP specs, but it is required 56 * to prevent DoS attacks. It is called when a retransmission timeout 57 * or zero probe timeout occurs on orphaned socket. 58 * 59 * Criteria is still not confirmed experimentally and may change. 60 * We kill the socket, if: 61 * 1. If number of orphaned sockets exceeds an administratively configured 62 * limit. 63 * 2. If we have strong memory pressure. 64 */ 65 static int tcp_out_of_resources(struct sock *sk, int do_reset) 66 { 67 struct tcp_sock *tp = tcp_sk(sk); 68 int orphans = percpu_counter_read_positive(&tcp_orphan_count); 69 70 /* If peer does not open window for long time, or did not transmit 71 * anything for long time, penalize it. */ 72 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 73 orphans <<= 1; 74 75 /* If some dubious ICMP arrived, penalize even more. */ 76 if (sk->sk_err_soft) 77 orphans <<= 1; 78 79 if (tcp_too_many_orphans(sk, orphans)) { 80 if (net_ratelimit()) 81 printk(KERN_INFO "Out of socket memory\n"); 82 83 /* Catch exceptional cases, when connection requires reset. 84 * 1. Last segment was sent recently. */ 85 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 86 /* 2. Window is closed. */ 87 (!tp->snd_wnd && !tp->packets_out)) 88 do_reset = 1; 89 if (do_reset) 90 tcp_send_active_reset(sk, GFP_ATOMIC); 91 tcp_done(sk); 92 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 93 return 1; 94 } 95 return 0; 96 } 97 98 /* Calculate maximal number or retries on an orphaned socket. */ 99 static int tcp_orphan_retries(struct sock *sk, int alive) 100 { 101 int retries = sysctl_tcp_orphan_retries; /* May be zero. */ 102 103 /* We know from an ICMP that something is wrong. */ 104 if (sk->sk_err_soft && !alive) 105 retries = 0; 106 107 /* However, if socket sent something recently, select some safe 108 * number of retries. 8 corresponds to >100 seconds with minimal 109 * RTO of 200msec. */ 110 if (retries == 0 && alive) 111 retries = 8; 112 return retries; 113 } 114 115 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 116 { 117 /* Black hole detection */ 118 if (sysctl_tcp_mtu_probing) { 119 if (!icsk->icsk_mtup.enabled) { 120 icsk->icsk_mtup.enabled = 1; 121 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 122 } else { 123 struct tcp_sock *tp = tcp_sk(sk); 124 int mss; 125 126 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 127 mss = min(sysctl_tcp_base_mss, mss); 128 mss = max(mss, 68 - tp->tcp_header_len); 129 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 130 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 131 } 132 } 133 } 134 135 /* A write timeout has occurred. Process the after effects. */ 136 static int tcp_write_timeout(struct sock *sk) 137 { 138 struct inet_connection_sock *icsk = inet_csk(sk); 139 int retry_until; 140 141 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 142 if (icsk->icsk_retransmits) 143 dst_negative_advice(&sk->sk_dst_cache); 144 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 145 } else { 146 if (icsk->icsk_retransmits >= sysctl_tcp_retries1) { 147 /* Black hole detection */ 148 tcp_mtu_probing(icsk, sk); 149 150 dst_negative_advice(&sk->sk_dst_cache); 151 } 152 153 retry_until = sysctl_tcp_retries2; 154 if (sock_flag(sk, SOCK_DEAD)) { 155 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 156 157 retry_until = tcp_orphan_retries(sk, alive); 158 159 if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until)) 160 return 1; 161 } 162 } 163 164 if (icsk->icsk_retransmits >= retry_until) { 165 /* Has it gone just too far? */ 166 tcp_write_err(sk); 167 return 1; 168 } 169 return 0; 170 } 171 172 static void tcp_delack_timer(unsigned long data) 173 { 174 struct sock *sk = (struct sock *)data; 175 struct tcp_sock *tp = tcp_sk(sk); 176 struct inet_connection_sock *icsk = inet_csk(sk); 177 178 bh_lock_sock(sk); 179 if (sock_owned_by_user(sk)) { 180 /* Try again later. */ 181 icsk->icsk_ack.blocked = 1; 182 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 183 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); 184 goto out_unlock; 185 } 186 187 sk_mem_reclaim_partial(sk); 188 189 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 190 goto out; 191 192 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 193 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 194 goto out; 195 } 196 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 197 198 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 199 struct sk_buff *skb; 200 201 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 202 203 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 204 sk_backlog_rcv(sk, skb); 205 206 tp->ucopy.memory = 0; 207 } 208 209 if (inet_csk_ack_scheduled(sk)) { 210 if (!icsk->icsk_ack.pingpong) { 211 /* Delayed ACK missed: inflate ATO. */ 212 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 213 } else { 214 /* Delayed ACK missed: leave pingpong mode and 215 * deflate ATO. 216 */ 217 icsk->icsk_ack.pingpong = 0; 218 icsk->icsk_ack.ato = TCP_ATO_MIN; 219 } 220 tcp_send_ack(sk); 221 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); 222 } 223 TCP_CHECK_TIMER(sk); 224 225 out: 226 if (tcp_memory_pressure) 227 sk_mem_reclaim(sk); 228 out_unlock: 229 bh_unlock_sock(sk); 230 sock_put(sk); 231 } 232 233 static void tcp_probe_timer(struct sock *sk) 234 { 235 struct inet_connection_sock *icsk = inet_csk(sk); 236 struct tcp_sock *tp = tcp_sk(sk); 237 int max_probes; 238 239 if (tp->packets_out || !tcp_send_head(sk)) { 240 icsk->icsk_probes_out = 0; 241 return; 242 } 243 244 /* *WARNING* RFC 1122 forbids this 245 * 246 * It doesn't AFAIK, because we kill the retransmit timer -AK 247 * 248 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 249 * this behaviour in Solaris down as a bug fix. [AC] 250 * 251 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 252 * even if they advertise zero window. Hence, connection is killed only 253 * if we received no ACKs for normal connection timeout. It is not killed 254 * only because window stays zero for some time, window may be zero 255 * until armageddon and even later. We are in full accordance 256 * with RFCs, only probe timer combines both retransmission timeout 257 * and probe timeout in one bottle. --ANK 258 */ 259 max_probes = sysctl_tcp_retries2; 260 261 if (sock_flag(sk, SOCK_DEAD)) { 262 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 263 264 max_probes = tcp_orphan_retries(sk, alive); 265 266 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 267 return; 268 } 269 270 if (icsk->icsk_probes_out > max_probes) { 271 tcp_write_err(sk); 272 } else { 273 /* Only send another probe if we didn't close things up. */ 274 tcp_send_probe0(sk); 275 } 276 } 277 278 /* 279 * The TCP retransmit timer. 280 */ 281 282 static void tcp_retransmit_timer(struct sock *sk) 283 { 284 struct tcp_sock *tp = tcp_sk(sk); 285 struct inet_connection_sock *icsk = inet_csk(sk); 286 287 if (!tp->packets_out) 288 goto out; 289 290 WARN_ON(tcp_write_queue_empty(sk)); 291 292 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 293 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 294 /* Receiver dastardly shrinks window. Our retransmits 295 * become zero probes, but we should not timeout this 296 * connection. If the socket is an orphan, time it out, 297 * we cannot allow such beasts to hang infinitely. 298 */ 299 #ifdef TCP_DEBUG 300 struct inet_sock *inet = inet_sk(sk); 301 if (sk->sk_family == AF_INET) { 302 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 303 &inet->daddr, ntohs(inet->dport), 304 inet->num, tp->snd_una, tp->snd_nxt); 305 } 306 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) 307 else if (sk->sk_family == AF_INET6) { 308 struct ipv6_pinfo *np = inet6_sk(sk); 309 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 310 &np->daddr, ntohs(inet->dport), 311 inet->num, tp->snd_una, tp->snd_nxt); 312 } 313 #endif 314 #endif 315 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 316 tcp_write_err(sk); 317 goto out; 318 } 319 tcp_enter_loss(sk, 0); 320 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 321 __sk_dst_reset(sk); 322 goto out_reset_timer; 323 } 324 325 if (tcp_write_timeout(sk)) 326 goto out; 327 328 if (icsk->icsk_retransmits == 0) { 329 int mib_idx; 330 331 if (icsk->icsk_ca_state == TCP_CA_Disorder) { 332 if (tcp_is_sack(tp)) 333 mib_idx = LINUX_MIB_TCPSACKFAILURES; 334 else 335 mib_idx = LINUX_MIB_TCPRENOFAILURES; 336 } else if (icsk->icsk_ca_state == TCP_CA_Recovery) { 337 if (tcp_is_sack(tp)) 338 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 339 else 340 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 341 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 342 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 343 } else { 344 mib_idx = LINUX_MIB_TCPTIMEOUTS; 345 } 346 NET_INC_STATS_BH(sock_net(sk), mib_idx); 347 } 348 349 if (tcp_use_frto(sk)) { 350 tcp_enter_frto(sk); 351 } else { 352 tcp_enter_loss(sk, 0); 353 } 354 355 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 356 /* Retransmission failed because of local congestion, 357 * do not backoff. 358 */ 359 if (!icsk->icsk_retransmits) 360 icsk->icsk_retransmits = 1; 361 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 362 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 363 TCP_RTO_MAX); 364 goto out; 365 } 366 367 /* Increase the timeout each time we retransmit. Note that 368 * we do not increase the rtt estimate. rto is initialized 369 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 370 * that doubling rto each time is the least we can get away with. 371 * In KA9Q, Karn uses this for the first few times, and then 372 * goes to quadratic. netBSD doubles, but only goes up to *64, 373 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 374 * defined in the protocol as the maximum possible RTT. I guess 375 * we'll have to use something other than TCP to talk to the 376 * University of Mars. 377 * 378 * PAWS allows us longer timeouts and large windows, so once 379 * implemented ftp to mars will work nicely. We will have to fix 380 * the 120 second clamps though! 381 */ 382 icsk->icsk_backoff++; 383 icsk->icsk_retransmits++; 384 385 out_reset_timer: 386 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 387 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 388 if (icsk->icsk_retransmits > sysctl_tcp_retries1) 389 __sk_dst_reset(sk); 390 391 out:; 392 } 393 394 static void tcp_write_timer(unsigned long data) 395 { 396 struct sock *sk = (struct sock *)data; 397 struct inet_connection_sock *icsk = inet_csk(sk); 398 int event; 399 400 bh_lock_sock(sk); 401 if (sock_owned_by_user(sk)) { 402 /* Try again later */ 403 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); 404 goto out_unlock; 405 } 406 407 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 408 goto out; 409 410 if (time_after(icsk->icsk_timeout, jiffies)) { 411 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 412 goto out; 413 } 414 415 event = icsk->icsk_pending; 416 icsk->icsk_pending = 0; 417 418 switch (event) { 419 case ICSK_TIME_RETRANS: 420 tcp_retransmit_timer(sk); 421 break; 422 case ICSK_TIME_PROBE0: 423 tcp_probe_timer(sk); 424 break; 425 } 426 TCP_CHECK_TIMER(sk); 427 428 out: 429 sk_mem_reclaim(sk); 430 out_unlock: 431 bh_unlock_sock(sk); 432 sock_put(sk); 433 } 434 435 /* 436 * Timer for listening sockets 437 */ 438 439 static void tcp_synack_timer(struct sock *sk) 440 { 441 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 442 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 443 } 444 445 void tcp_set_keepalive(struct sock *sk, int val) 446 { 447 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 448 return; 449 450 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 451 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 452 else if (!val) 453 inet_csk_delete_keepalive_timer(sk); 454 } 455 456 457 static void tcp_keepalive_timer (unsigned long data) 458 { 459 struct sock *sk = (struct sock *) data; 460 struct inet_connection_sock *icsk = inet_csk(sk); 461 struct tcp_sock *tp = tcp_sk(sk); 462 __u32 elapsed; 463 464 /* Only process if socket is not in use. */ 465 bh_lock_sock(sk); 466 if (sock_owned_by_user(sk)) { 467 /* Try again later. */ 468 inet_csk_reset_keepalive_timer (sk, HZ/20); 469 goto out; 470 } 471 472 if (sk->sk_state == TCP_LISTEN) { 473 tcp_synack_timer(sk); 474 goto out; 475 } 476 477 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 478 if (tp->linger2 >= 0) { 479 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 480 481 if (tmo > 0) { 482 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 483 goto out; 484 } 485 } 486 tcp_send_active_reset(sk, GFP_ATOMIC); 487 goto death; 488 } 489 490 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 491 goto out; 492 493 elapsed = keepalive_time_when(tp); 494 495 /* It is alive without keepalive 8) */ 496 if (tp->packets_out || tcp_send_head(sk)) 497 goto resched; 498 499 elapsed = tcp_time_stamp - tp->rcv_tstamp; 500 501 if (elapsed >= keepalive_time_when(tp)) { 502 if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) || 503 (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) { 504 tcp_send_active_reset(sk, GFP_ATOMIC); 505 tcp_write_err(sk); 506 goto out; 507 } 508 if (tcp_write_wakeup(sk) <= 0) { 509 icsk->icsk_probes_out++; 510 elapsed = keepalive_intvl_when(tp); 511 } else { 512 /* If keepalive was lost due to local congestion, 513 * try harder. 514 */ 515 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 516 } 517 } else { 518 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 519 elapsed = keepalive_time_when(tp) - elapsed; 520 } 521 522 TCP_CHECK_TIMER(sk); 523 sk_mem_reclaim(sk); 524 525 resched: 526 inet_csk_reset_keepalive_timer (sk, elapsed); 527 goto out; 528 529 death: 530 tcp_done(sk); 531 532 out: 533 bh_unlock_sock(sk); 534 sock_put(sk); 535 } 536