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/mm.h> 22 #include <linux/module.h> 23 #include <linux/slab.h> 24 #include <linux/sysctl.h> 25 #include <linux/workqueue.h> 26 #include <linux/static_key.h> 27 #include <net/tcp.h> 28 #include <net/inet_common.h> 29 #include <net/xfrm.h> 30 #include <net/busy_poll.h> 31 32 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 33 { 34 if (seq == s_win) 35 return true; 36 if (after(end_seq, s_win) && before(seq, e_win)) 37 return true; 38 return seq == e_win && seq == end_seq; 39 } 40 41 static enum tcp_tw_status 42 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 43 const struct sk_buff *skb, int mib_idx) 44 { 45 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 46 47 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 48 &tcptw->tw_last_oow_ack_time)) { 49 /* Send ACK. Note, we do not put the bucket, 50 * it will be released by caller. 51 */ 52 return TCP_TW_ACK; 53 } 54 55 /* We are rate-limiting, so just release the tw sock and drop skb. */ 56 inet_twsk_put(tw); 57 return TCP_TW_SUCCESS; 58 } 59 60 /* 61 * * Main purpose of TIME-WAIT state is to close connection gracefully, 62 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 63 * (and, probably, tail of data) and one or more our ACKs are lost. 64 * * What is TIME-WAIT timeout? It is associated with maximal packet 65 * lifetime in the internet, which results in wrong conclusion, that 66 * it is set to catch "old duplicate segments" wandering out of their path. 67 * It is not quite correct. This timeout is calculated so that it exceeds 68 * maximal retransmission timeout enough to allow to lose one (or more) 69 * segments sent by peer and our ACKs. This time may be calculated from RTO. 70 * * When TIME-WAIT socket receives RST, it means that another end 71 * finally closed and we are allowed to kill TIME-WAIT too. 72 * * Second purpose of TIME-WAIT is catching old duplicate segments. 73 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 74 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 75 * * If we invented some more clever way to catch duplicates 76 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 77 * 78 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 79 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 80 * from the very beginning. 81 * 82 * NOTE. With recycling (and later with fin-wait-2) TW bucket 83 * is _not_ stateless. It means, that strictly speaking we must 84 * spinlock it. I do not want! Well, probability of misbehaviour 85 * is ridiculously low and, seems, we could use some mb() tricks 86 * to avoid misread sequence numbers, states etc. --ANK 87 * 88 * We don't need to initialize tmp_out.sack_ok as we don't use the results 89 */ 90 enum tcp_tw_status 91 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 92 const struct tcphdr *th) 93 { 94 struct tcp_options_received tmp_opt; 95 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 96 bool paws_reject = false; 97 98 tmp_opt.saw_tstamp = 0; 99 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 100 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 101 102 if (tmp_opt.saw_tstamp) { 103 if (tmp_opt.rcv_tsecr) 104 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 105 tmp_opt.ts_recent = tcptw->tw_ts_recent; 106 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 107 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 108 } 109 } 110 111 if (tw->tw_substate == TCP_FIN_WAIT2) { 112 /* Just repeat all the checks of tcp_rcv_state_process() */ 113 114 /* Out of window, send ACK */ 115 if (paws_reject || 116 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 117 tcptw->tw_rcv_nxt, 118 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 119 return tcp_timewait_check_oow_rate_limit( 120 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 121 122 if (th->rst) 123 goto kill; 124 125 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 126 return TCP_TW_RST; 127 128 /* Dup ACK? */ 129 if (!th->ack || 130 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 131 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 132 inet_twsk_put(tw); 133 return TCP_TW_SUCCESS; 134 } 135 136 /* New data or FIN. If new data arrive after half-duplex close, 137 * reset. 138 */ 139 if (!th->fin || 140 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 141 return TCP_TW_RST; 142 143 /* FIN arrived, enter true time-wait state. */ 144 tw->tw_substate = TCP_TIME_WAIT; 145 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; 146 if (tmp_opt.saw_tstamp) { 147 tcptw->tw_ts_recent_stamp = get_seconds(); 148 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 149 } 150 151 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 152 return TCP_TW_ACK; 153 } 154 155 /* 156 * Now real TIME-WAIT state. 157 * 158 * RFC 1122: 159 * "When a connection is [...] on TIME-WAIT state [...] 160 * [a TCP] MAY accept a new SYN from the remote TCP to 161 * reopen the connection directly, if it: 162 * 163 * (1) assigns its initial sequence number for the new 164 * connection to be larger than the largest sequence 165 * number it used on the previous connection incarnation, 166 * and 167 * 168 * (2) returns to TIME-WAIT state if the SYN turns out 169 * to be an old duplicate". 170 */ 171 172 if (!paws_reject && 173 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 174 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 175 /* In window segment, it may be only reset or bare ack. */ 176 177 if (th->rst) { 178 /* This is TIME_WAIT assassination, in two flavors. 179 * Oh well... nobody has a sufficient solution to this 180 * protocol bug yet. 181 */ 182 if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) { 183 kill: 184 inet_twsk_deschedule_put(tw); 185 return TCP_TW_SUCCESS; 186 } 187 } 188 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 189 190 if (tmp_opt.saw_tstamp) { 191 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 192 tcptw->tw_ts_recent_stamp = get_seconds(); 193 } 194 195 inet_twsk_put(tw); 196 return TCP_TW_SUCCESS; 197 } 198 199 /* Out of window segment. 200 201 All the segments are ACKed immediately. 202 203 The only exception is new SYN. We accept it, if it is 204 not old duplicate and we are not in danger to be killed 205 by delayed old duplicates. RFC check is that it has 206 newer sequence number works at rates <40Mbit/sec. 207 However, if paws works, it is reliable AND even more, 208 we even may relax silly seq space cutoff. 209 210 RED-PEN: we violate main RFC requirement, if this SYN will appear 211 old duplicate (i.e. we receive RST in reply to SYN-ACK), 212 we must return socket to time-wait state. It is not good, 213 but not fatal yet. 214 */ 215 216 if (th->syn && !th->rst && !th->ack && !paws_reject && 217 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 218 (tmp_opt.saw_tstamp && 219 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 220 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 221 if (isn == 0) 222 isn++; 223 TCP_SKB_CB(skb)->tcp_tw_isn = isn; 224 return TCP_TW_SYN; 225 } 226 227 if (paws_reject) 228 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 229 230 if (!th->rst) { 231 /* In this case we must reset the TIMEWAIT timer. 232 * 233 * If it is ACKless SYN it may be both old duplicate 234 * and new good SYN with random sequence number <rcv_nxt. 235 * Do not reschedule in the last case. 236 */ 237 if (paws_reject || th->ack) 238 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 239 240 return tcp_timewait_check_oow_rate_limit( 241 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 242 } 243 inet_twsk_put(tw); 244 return TCP_TW_SUCCESS; 245 } 246 EXPORT_SYMBOL(tcp_timewait_state_process); 247 248 /* 249 * Move a socket to time-wait or dead fin-wait-2 state. 250 */ 251 void tcp_time_wait(struct sock *sk, int state, int timeo) 252 { 253 const struct inet_connection_sock *icsk = inet_csk(sk); 254 const struct tcp_sock *tp = tcp_sk(sk); 255 struct inet_timewait_sock *tw; 256 struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row; 257 258 tw = inet_twsk_alloc(sk, tcp_death_row, state); 259 260 if (tw) { 261 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 262 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 263 struct inet_sock *inet = inet_sk(sk); 264 265 tw->tw_transparent = inet->transparent; 266 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 267 tcptw->tw_rcv_nxt = tp->rcv_nxt; 268 tcptw->tw_snd_nxt = tp->snd_nxt; 269 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 270 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 271 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 272 tcptw->tw_ts_offset = tp->tsoffset; 273 tcptw->tw_last_oow_ack_time = 0; 274 275 #if IS_ENABLED(CONFIG_IPV6) 276 if (tw->tw_family == PF_INET6) { 277 struct ipv6_pinfo *np = inet6_sk(sk); 278 279 tw->tw_v6_daddr = sk->sk_v6_daddr; 280 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 281 tw->tw_tclass = np->tclass; 282 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 283 tw->tw_ipv6only = sk->sk_ipv6only; 284 } 285 #endif 286 287 #ifdef CONFIG_TCP_MD5SIG 288 /* 289 * The timewait bucket does not have the key DB from the 290 * sock structure. We just make a quick copy of the 291 * md5 key being used (if indeed we are using one) 292 * so the timewait ack generating code has the key. 293 */ 294 do { 295 struct tcp_md5sig_key *key; 296 tcptw->tw_md5_key = NULL; 297 key = tp->af_specific->md5_lookup(sk, sk); 298 if (key) { 299 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 300 BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool()); 301 } 302 } while (0); 303 #endif 304 305 /* Get the TIME_WAIT timeout firing. */ 306 if (timeo < rto) 307 timeo = rto; 308 309 tw->tw_timeout = TCP_TIMEWAIT_LEN; 310 if (state == TCP_TIME_WAIT) 311 timeo = TCP_TIMEWAIT_LEN; 312 313 inet_twsk_schedule(tw, timeo); 314 /* Linkage updates. */ 315 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo); 316 inet_twsk_put(tw); 317 } else { 318 /* Sorry, if we're out of memory, just CLOSE this 319 * socket up. We've got bigger problems than 320 * non-graceful socket closings. 321 */ 322 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW); 323 } 324 325 tcp_update_metrics(sk); 326 tcp_done(sk); 327 } 328 329 void tcp_twsk_destructor(struct sock *sk) 330 { 331 #ifdef CONFIG_TCP_MD5SIG 332 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 333 334 if (twsk->tw_md5_key) 335 kfree_rcu(twsk->tw_md5_key, rcu); 336 #endif 337 } 338 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 339 340 /* Warning : This function is called without sk_listener being locked. 341 * Be sure to read socket fields once, as their value could change under us. 342 */ 343 void tcp_openreq_init_rwin(struct request_sock *req, 344 const struct sock *sk_listener, 345 const struct dst_entry *dst) 346 { 347 struct inet_request_sock *ireq = inet_rsk(req); 348 const struct tcp_sock *tp = tcp_sk(sk_listener); 349 int full_space = tcp_full_space(sk_listener); 350 u32 window_clamp; 351 __u8 rcv_wscale; 352 u32 rcv_wnd; 353 int mss; 354 355 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 356 window_clamp = READ_ONCE(tp->window_clamp); 357 /* Set this up on the first call only */ 358 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 359 360 /* limit the window selection if the user enforce a smaller rx buffer */ 361 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 362 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 363 req->rsk_window_clamp = full_space; 364 365 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 366 if (rcv_wnd == 0) 367 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 368 else if (full_space < rcv_wnd * mss) 369 full_space = rcv_wnd * mss; 370 371 /* tcp_full_space because it is guaranteed to be the first packet */ 372 tcp_select_initial_window(full_space, 373 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 374 &req->rsk_rcv_wnd, 375 &req->rsk_window_clamp, 376 ireq->wscale_ok, 377 &rcv_wscale, 378 rcv_wnd); 379 ireq->rcv_wscale = rcv_wscale; 380 } 381 EXPORT_SYMBOL(tcp_openreq_init_rwin); 382 383 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 384 const struct request_sock *req) 385 { 386 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 387 } 388 389 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 390 { 391 struct inet_connection_sock *icsk = inet_csk(sk); 392 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 393 bool ca_got_dst = false; 394 395 if (ca_key != TCP_CA_UNSPEC) { 396 const struct tcp_congestion_ops *ca; 397 398 rcu_read_lock(); 399 ca = tcp_ca_find_key(ca_key); 400 if (likely(ca && try_module_get(ca->owner))) { 401 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 402 icsk->icsk_ca_ops = ca; 403 ca_got_dst = true; 404 } 405 rcu_read_unlock(); 406 } 407 408 /* If no valid choice made yet, assign current system default ca. */ 409 if (!ca_got_dst && 410 (!icsk->icsk_ca_setsockopt || 411 !try_module_get(icsk->icsk_ca_ops->owner))) 412 tcp_assign_congestion_control(sk); 413 414 tcp_set_ca_state(sk, TCP_CA_Open); 415 } 416 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 417 418 static void smc_check_reset_syn_req(struct tcp_sock *oldtp, 419 struct request_sock *req, 420 struct tcp_sock *newtp) 421 { 422 #if IS_ENABLED(CONFIG_SMC) 423 struct inet_request_sock *ireq; 424 425 if (static_branch_unlikely(&tcp_have_smc)) { 426 ireq = inet_rsk(req); 427 if (oldtp->syn_smc && !ireq->smc_ok) 428 newtp->syn_smc = 0; 429 } 430 #endif 431 } 432 433 /* This is not only more efficient than what we used to do, it eliminates 434 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 435 * 436 * Actually, we could lots of memory writes here. tp of listening 437 * socket contains all necessary default parameters. 438 */ 439 struct sock *tcp_create_openreq_child(const struct sock *sk, 440 struct request_sock *req, 441 struct sk_buff *skb) 442 { 443 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 444 445 if (newsk) { 446 const struct inet_request_sock *ireq = inet_rsk(req); 447 struct tcp_request_sock *treq = tcp_rsk(req); 448 struct inet_connection_sock *newicsk = inet_csk(newsk); 449 struct tcp_sock *newtp = tcp_sk(newsk); 450 struct tcp_sock *oldtp = tcp_sk(sk); 451 452 smc_check_reset_syn_req(oldtp, req, newtp); 453 454 /* Now setup tcp_sock */ 455 newtp->pred_flags = 0; 456 457 newtp->rcv_wup = newtp->copied_seq = 458 newtp->rcv_nxt = treq->rcv_isn + 1; 459 newtp->segs_in = 1; 460 461 newtp->snd_sml = newtp->snd_una = 462 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1; 463 464 INIT_LIST_HEAD(&newtp->tsq_node); 465 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 466 467 tcp_init_wl(newtp, treq->rcv_isn); 468 469 newtp->srtt_us = 0; 470 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT); 471 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 472 newicsk->icsk_rto = TCP_TIMEOUT_INIT; 473 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 474 475 newtp->packets_out = 0; 476 newtp->retrans_out = 0; 477 newtp->sacked_out = 0; 478 newtp->fackets_out = 0; 479 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH; 480 newtp->tlp_high_seq = 0; 481 newtp->lsndtime = tcp_jiffies32; 482 newsk->sk_txhash = treq->txhash; 483 newtp->last_oow_ack_time = 0; 484 newtp->total_retrans = req->num_retrans; 485 486 /* So many TCP implementations out there (incorrectly) count the 487 * initial SYN frame in their delayed-ACK and congestion control 488 * algorithms that we must have the following bandaid to talk 489 * efficiently to them. -DaveM 490 */ 491 newtp->snd_cwnd = TCP_INIT_CWND; 492 newtp->snd_cwnd_cnt = 0; 493 494 /* There's a bubble in the pipe until at least the first ACK. */ 495 newtp->app_limited = ~0U; 496 497 tcp_init_xmit_timers(newsk); 498 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1; 499 500 newtp->rx_opt.saw_tstamp = 0; 501 502 newtp->rx_opt.dsack = 0; 503 newtp->rx_opt.num_sacks = 0; 504 505 newtp->urg_data = 0; 506 507 if (sock_flag(newsk, SOCK_KEEPOPEN)) 508 inet_csk_reset_keepalive_timer(newsk, 509 keepalive_time_when(newtp)); 510 511 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 512 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) { 513 if (sock_net(sk)->ipv4.sysctl_tcp_fack) 514 tcp_enable_fack(newtp); 515 } 516 newtp->window_clamp = req->rsk_window_clamp; 517 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 518 newtp->rcv_wnd = req->rsk_rcv_wnd; 519 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 520 if (newtp->rx_opt.wscale_ok) { 521 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 522 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 523 } else { 524 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 525 newtp->window_clamp = min(newtp->window_clamp, 65535U); 526 } 527 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) << 528 newtp->rx_opt.snd_wscale); 529 newtp->max_window = newtp->snd_wnd; 530 531 if (newtp->rx_opt.tstamp_ok) { 532 newtp->rx_opt.ts_recent = req->ts_recent; 533 newtp->rx_opt.ts_recent_stamp = get_seconds(); 534 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 535 } else { 536 newtp->rx_opt.ts_recent_stamp = 0; 537 newtp->tcp_header_len = sizeof(struct tcphdr); 538 } 539 newtp->tsoffset = treq->ts_off; 540 #ifdef CONFIG_TCP_MD5SIG 541 newtp->md5sig_info = NULL; /*XXX*/ 542 if (newtp->af_specific->md5_lookup(sk, newsk)) 543 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 544 #endif 545 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 546 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 547 newtp->rx_opt.mss_clamp = req->mss; 548 tcp_ecn_openreq_child(newtp, req); 549 newtp->fastopen_req = NULL; 550 newtp->fastopen_rsk = NULL; 551 newtp->syn_data_acked = 0; 552 newtp->rack.mstamp = 0; 553 newtp->rack.advanced = 0; 554 555 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 556 } 557 return newsk; 558 } 559 EXPORT_SYMBOL(tcp_create_openreq_child); 560 561 /* 562 * Process an incoming packet for SYN_RECV sockets represented as a 563 * request_sock. Normally sk is the listener socket but for TFO it 564 * points to the child socket. 565 * 566 * XXX (TFO) - The current impl contains a special check for ack 567 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 568 * 569 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 570 */ 571 572 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 573 struct request_sock *req, 574 bool fastopen) 575 { 576 struct tcp_options_received tmp_opt; 577 struct sock *child; 578 const struct tcphdr *th = tcp_hdr(skb); 579 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 580 bool paws_reject = false; 581 bool own_req; 582 583 tmp_opt.saw_tstamp = 0; 584 if (th->doff > (sizeof(struct tcphdr)>>2)) { 585 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 586 587 if (tmp_opt.saw_tstamp) { 588 tmp_opt.ts_recent = req->ts_recent; 589 if (tmp_opt.rcv_tsecr) 590 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 591 /* We do not store true stamp, but it is not required, 592 * it can be estimated (approximately) 593 * from another data. 594 */ 595 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout); 596 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 597 } 598 } 599 600 /* Check for pure retransmitted SYN. */ 601 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 602 flg == TCP_FLAG_SYN && 603 !paws_reject) { 604 /* 605 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 606 * this case on figure 6 and figure 8, but formal 607 * protocol description says NOTHING. 608 * To be more exact, it says that we should send ACK, 609 * because this segment (at least, if it has no data) 610 * is out of window. 611 * 612 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 613 * describe SYN-RECV state. All the description 614 * is wrong, we cannot believe to it and should 615 * rely only on common sense and implementation 616 * experience. 617 * 618 * Enforce "SYN-ACK" according to figure 8, figure 6 619 * of RFC793, fixed by RFC1122. 620 * 621 * Note that even if there is new data in the SYN packet 622 * they will be thrown away too. 623 * 624 * Reset timer after retransmitting SYNACK, similar to 625 * the idea of fast retransmit in recovery. 626 */ 627 if (!tcp_oow_rate_limited(sock_net(sk), skb, 628 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 629 &tcp_rsk(req)->last_oow_ack_time) && 630 631 !inet_rtx_syn_ack(sk, req)) { 632 unsigned long expires = jiffies; 633 634 expires += min(TCP_TIMEOUT_INIT << req->num_timeout, 635 TCP_RTO_MAX); 636 if (!fastopen) 637 mod_timer_pending(&req->rsk_timer, expires); 638 else 639 req->rsk_timer.expires = expires; 640 } 641 return NULL; 642 } 643 644 /* Further reproduces section "SEGMENT ARRIVES" 645 for state SYN-RECEIVED of RFC793. 646 It is broken, however, it does not work only 647 when SYNs are crossed. 648 649 You would think that SYN crossing is impossible here, since 650 we should have a SYN_SENT socket (from connect()) on our end, 651 but this is not true if the crossed SYNs were sent to both 652 ends by a malicious third party. We must defend against this, 653 and to do that we first verify the ACK (as per RFC793, page 654 36) and reset if it is invalid. Is this a true full defense? 655 To convince ourselves, let us consider a way in which the ACK 656 test can still pass in this 'malicious crossed SYNs' case. 657 Malicious sender sends identical SYNs (and thus identical sequence 658 numbers) to both A and B: 659 660 A: gets SYN, seq=7 661 B: gets SYN, seq=7 662 663 By our good fortune, both A and B select the same initial 664 send sequence number of seven :-) 665 666 A: sends SYN|ACK, seq=7, ack_seq=8 667 B: sends SYN|ACK, seq=7, ack_seq=8 668 669 So we are now A eating this SYN|ACK, ACK test passes. So 670 does sequence test, SYN is truncated, and thus we consider 671 it a bare ACK. 672 673 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 674 bare ACK. Otherwise, we create an established connection. Both 675 ends (listening sockets) accept the new incoming connection and try 676 to talk to each other. 8-) 677 678 Note: This case is both harmless, and rare. Possibility is about the 679 same as us discovering intelligent life on another plant tomorrow. 680 681 But generally, we should (RFC lies!) to accept ACK 682 from SYNACK both here and in tcp_rcv_state_process(). 683 tcp_rcv_state_process() does not, hence, we do not too. 684 685 Note that the case is absolutely generic: 686 we cannot optimize anything here without 687 violating protocol. All the checks must be made 688 before attempt to create socket. 689 */ 690 691 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 692 * and the incoming segment acknowledges something not yet 693 * sent (the segment carries an unacceptable ACK) ... 694 * a reset is sent." 695 * 696 * Invalid ACK: reset will be sent by listening socket. 697 * Note that the ACK validity check for a Fast Open socket is done 698 * elsewhere and is checked directly against the child socket rather 699 * than req because user data may have been sent out. 700 */ 701 if ((flg & TCP_FLAG_ACK) && !fastopen && 702 (TCP_SKB_CB(skb)->ack_seq != 703 tcp_rsk(req)->snt_isn + 1)) 704 return sk; 705 706 /* Also, it would be not so bad idea to check rcv_tsecr, which 707 * is essentially ACK extension and too early or too late values 708 * should cause reset in unsynchronized states. 709 */ 710 711 /* RFC793: "first check sequence number". */ 712 713 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 714 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 715 /* Out of window: send ACK and drop. */ 716 if (!(flg & TCP_FLAG_RST) && 717 !tcp_oow_rate_limited(sock_net(sk), skb, 718 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 719 &tcp_rsk(req)->last_oow_ack_time)) 720 req->rsk_ops->send_ack(sk, skb, req); 721 if (paws_reject) 722 __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 723 return NULL; 724 } 725 726 /* In sequence, PAWS is OK. */ 727 728 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 729 req->ts_recent = tmp_opt.rcv_tsval; 730 731 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 732 /* Truncate SYN, it is out of window starting 733 at tcp_rsk(req)->rcv_isn + 1. */ 734 flg &= ~TCP_FLAG_SYN; 735 } 736 737 /* RFC793: "second check the RST bit" and 738 * "fourth, check the SYN bit" 739 */ 740 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 741 __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 742 goto embryonic_reset; 743 } 744 745 /* ACK sequence verified above, just make sure ACK is 746 * set. If ACK not set, just silently drop the packet. 747 * 748 * XXX (TFO) - if we ever allow "data after SYN", the 749 * following check needs to be removed. 750 */ 751 if (!(flg & TCP_FLAG_ACK)) 752 return NULL; 753 754 /* For Fast Open no more processing is needed (sk is the 755 * child socket). 756 */ 757 if (fastopen) 758 return sk; 759 760 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 761 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && 762 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 763 inet_rsk(req)->acked = 1; 764 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 765 return NULL; 766 } 767 768 /* OK, ACK is valid, create big socket and 769 * feed this segment to it. It will repeat all 770 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 771 * ESTABLISHED STATE. If it will be dropped after 772 * socket is created, wait for troubles. 773 */ 774 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 775 req, &own_req); 776 if (!child) 777 goto listen_overflow; 778 779 sock_rps_save_rxhash(child, skb); 780 tcp_synack_rtt_meas(child, req); 781 return inet_csk_complete_hashdance(sk, child, req, own_req); 782 783 listen_overflow: 784 if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) { 785 inet_rsk(req)->acked = 1; 786 return NULL; 787 } 788 789 embryonic_reset: 790 if (!(flg & TCP_FLAG_RST)) { 791 /* Received a bad SYN pkt - for TFO We try not to reset 792 * the local connection unless it's really necessary to 793 * avoid becoming vulnerable to outside attack aiming at 794 * resetting legit local connections. 795 */ 796 req->rsk_ops->send_reset(sk, skb); 797 } else if (fastopen) { /* received a valid RST pkt */ 798 reqsk_fastopen_remove(sk, req, true); 799 tcp_reset(sk); 800 } 801 if (!fastopen) { 802 inet_csk_reqsk_queue_drop(sk, req); 803 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 804 } 805 return NULL; 806 } 807 EXPORT_SYMBOL(tcp_check_req); 808 809 /* 810 * Queue segment on the new socket if the new socket is active, 811 * otherwise we just shortcircuit this and continue with 812 * the new socket. 813 * 814 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 815 * when entering. But other states are possible due to a race condition 816 * where after __inet_lookup_established() fails but before the listener 817 * locked is obtained, other packets cause the same connection to 818 * be created. 819 */ 820 821 int tcp_child_process(struct sock *parent, struct sock *child, 822 struct sk_buff *skb) 823 { 824 int ret = 0; 825 int state = child->sk_state; 826 827 /* record NAPI ID of child */ 828 sk_mark_napi_id(child, skb); 829 830 tcp_segs_in(tcp_sk(child), skb); 831 if (!sock_owned_by_user(child)) { 832 ret = tcp_rcv_state_process(child, skb); 833 /* Wakeup parent, send SIGIO */ 834 if (state == TCP_SYN_RECV && child->sk_state != state) 835 parent->sk_data_ready(parent); 836 } else { 837 /* Alas, it is possible again, because we do lookup 838 * in main socket hash table and lock on listening 839 * socket does not protect us more. 840 */ 841 __sk_add_backlog(child, skb); 842 } 843 844 bh_unlock_sock(child); 845 sock_put(child); 846 return ret; 847 } 848 EXPORT_SYMBOL(tcp_child_process); 849