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 <net/tcp.h> 23 #include <net/xfrm.h> 24 #include <net/busy_poll.h> 25 #include <net/rstreason.h> 26 27 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 28 { 29 if (seq == s_win) 30 return true; 31 if (after(end_seq, s_win) && before(seq, e_win)) 32 return true; 33 return seq == e_win && seq == end_seq; 34 } 35 36 static enum tcp_tw_status 37 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 38 const struct sk_buff *skb, int mib_idx) 39 { 40 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 41 42 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 43 &tcptw->tw_last_oow_ack_time)) { 44 /* Send ACK. Note, we do not put the bucket, 45 * it will be released by caller. 46 */ 47 return TCP_TW_ACK; 48 } 49 50 /* We are rate-limiting, so just release the tw sock and drop skb. */ 51 inet_twsk_put(tw); 52 return TCP_TW_SUCCESS; 53 } 54 55 static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq) 56 { 57 #ifdef CONFIG_TCP_AO 58 struct tcp_ao_info *ao; 59 60 ao = rcu_dereference(tcptw->ao_info); 61 if (unlikely(ao && seq < tcptw->tw_rcv_nxt)) 62 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1); 63 #endif 64 tcptw->tw_rcv_nxt = seq; 65 } 66 67 /* 68 * * Main purpose of TIME-WAIT state is to close connection gracefully, 69 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 70 * (and, probably, tail of data) and one or more our ACKs are lost. 71 * * What is TIME-WAIT timeout? It is associated with maximal packet 72 * lifetime in the internet, which results in wrong conclusion, that 73 * it is set to catch "old duplicate segments" wandering out of their path. 74 * It is not quite correct. This timeout is calculated so that it exceeds 75 * maximal retransmission timeout enough to allow to lose one (or more) 76 * segments sent by peer and our ACKs. This time may be calculated from RTO. 77 * * When TIME-WAIT socket receives RST, it means that another end 78 * finally closed and we are allowed to kill TIME-WAIT too. 79 * * Second purpose of TIME-WAIT is catching old duplicate segments. 80 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 81 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 82 * * If we invented some more clever way to catch duplicates 83 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 84 * 85 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 86 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 87 * from the very beginning. 88 * 89 * NOTE. With recycling (and later with fin-wait-2) TW bucket 90 * is _not_ stateless. It means, that strictly speaking we must 91 * spinlock it. I do not want! Well, probability of misbehaviour 92 * is ridiculously low and, seems, we could use some mb() tricks 93 * to avoid misread sequence numbers, states etc. --ANK 94 * 95 * We don't need to initialize tmp_out.sack_ok as we don't use the results 96 */ 97 enum tcp_tw_status 98 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 99 const struct tcphdr *th, u32 *tw_isn) 100 { 101 struct tcp_options_received tmp_opt; 102 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 103 bool paws_reject = false; 104 105 tmp_opt.saw_tstamp = 0; 106 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 107 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 108 109 if (tmp_opt.saw_tstamp) { 110 if (tmp_opt.rcv_tsecr) 111 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 112 tmp_opt.ts_recent = tcptw->tw_ts_recent; 113 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 114 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 115 } 116 } 117 118 if (tw->tw_substate == TCP_FIN_WAIT2) { 119 /* Just repeat all the checks of tcp_rcv_state_process() */ 120 121 /* Out of window, send ACK */ 122 if (paws_reject || 123 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 124 tcptw->tw_rcv_nxt, 125 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 126 return tcp_timewait_check_oow_rate_limit( 127 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 128 129 if (th->rst) 130 goto kill; 131 132 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 133 return TCP_TW_RST; 134 135 /* Dup ACK? */ 136 if (!th->ack || 137 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 138 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 139 inet_twsk_put(tw); 140 return TCP_TW_SUCCESS; 141 } 142 143 /* New data or FIN. If new data arrive after half-duplex close, 144 * reset. 145 */ 146 if (!th->fin || 147 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 148 return TCP_TW_RST; 149 150 /* FIN arrived, enter true time-wait state. */ 151 tw->tw_substate = TCP_TIME_WAIT; 152 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq); 153 154 if (tmp_opt.saw_tstamp) { 155 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 156 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 157 } 158 159 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 160 return TCP_TW_ACK; 161 } 162 163 /* 164 * Now real TIME-WAIT state. 165 * 166 * RFC 1122: 167 * "When a connection is [...] on TIME-WAIT state [...] 168 * [a TCP] MAY accept a new SYN from the remote TCP to 169 * reopen the connection directly, if it: 170 * 171 * (1) assigns its initial sequence number for the new 172 * connection to be larger than the largest sequence 173 * number it used on the previous connection incarnation, 174 * and 175 * 176 * (2) returns to TIME-WAIT state if the SYN turns out 177 * to be an old duplicate". 178 */ 179 180 if (!paws_reject && 181 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 182 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 183 /* In window segment, it may be only reset or bare ack. */ 184 185 if (th->rst) { 186 /* This is TIME_WAIT assassination, in two flavors. 187 * Oh well... nobody has a sufficient solution to this 188 * protocol bug yet. 189 */ 190 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 191 kill: 192 inet_twsk_deschedule_put(tw); 193 return TCP_TW_SUCCESS; 194 } 195 } else { 196 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 197 } 198 199 if (tmp_opt.saw_tstamp) { 200 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 201 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 202 } 203 204 inet_twsk_put(tw); 205 return TCP_TW_SUCCESS; 206 } 207 208 /* Out of window segment. 209 210 All the segments are ACKed immediately. 211 212 The only exception is new SYN. We accept it, if it is 213 not old duplicate and we are not in danger to be killed 214 by delayed old duplicates. RFC check is that it has 215 newer sequence number works at rates <40Mbit/sec. 216 However, if paws works, it is reliable AND even more, 217 we even may relax silly seq space cutoff. 218 219 RED-PEN: we violate main RFC requirement, if this SYN will appear 220 old duplicate (i.e. we receive RST in reply to SYN-ACK), 221 we must return socket to time-wait state. It is not good, 222 but not fatal yet. 223 */ 224 225 if (th->syn && !th->rst && !th->ack && !paws_reject && 226 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 227 (tmp_opt.saw_tstamp && 228 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 229 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 230 if (isn == 0) 231 isn++; 232 *tw_isn = isn; 233 return TCP_TW_SYN; 234 } 235 236 if (paws_reject) 237 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 238 239 if (!th->rst) { 240 /* In this case we must reset the TIMEWAIT timer. 241 * 242 * If it is ACKless SYN it may be both old duplicate 243 * and new good SYN with random sequence number <rcv_nxt. 244 * Do not reschedule in the last case. 245 */ 246 if (paws_reject || th->ack) 247 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 248 249 return tcp_timewait_check_oow_rate_limit( 250 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 251 } 252 inet_twsk_put(tw); 253 return TCP_TW_SUCCESS; 254 } 255 EXPORT_SYMBOL(tcp_timewait_state_process); 256 257 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 258 { 259 #ifdef CONFIG_TCP_MD5SIG 260 const struct tcp_sock *tp = tcp_sk(sk); 261 struct tcp_md5sig_key *key; 262 263 /* 264 * The timewait bucket does not have the key DB from the 265 * sock structure. We just make a quick copy of the 266 * md5 key being used (if indeed we are using one) 267 * so the timewait ack generating code has the key. 268 */ 269 tcptw->tw_md5_key = NULL; 270 if (!static_branch_unlikely(&tcp_md5_needed.key)) 271 return; 272 273 key = tp->af_specific->md5_lookup(sk, sk); 274 if (key) { 275 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 276 if (!tcptw->tw_md5_key) 277 return; 278 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 279 goto out_free; 280 tcp_md5_add_sigpool(); 281 } 282 return; 283 out_free: 284 WARN_ON_ONCE(1); 285 kfree(tcptw->tw_md5_key); 286 tcptw->tw_md5_key = NULL; 287 #endif 288 } 289 290 /* 291 * Move a socket to time-wait or dead fin-wait-2 state. 292 */ 293 void tcp_time_wait(struct sock *sk, int state, int timeo) 294 { 295 const struct inet_connection_sock *icsk = inet_csk(sk); 296 struct tcp_sock *tp = tcp_sk(sk); 297 struct net *net = sock_net(sk); 298 struct inet_timewait_sock *tw; 299 300 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 301 302 if (tw) { 303 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 304 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 305 306 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 307 tw->tw_mark = sk->sk_mark; 308 tw->tw_priority = READ_ONCE(sk->sk_priority); 309 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 310 tcptw->tw_rcv_nxt = tp->rcv_nxt; 311 tcptw->tw_snd_nxt = tp->snd_nxt; 312 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 313 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 314 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 315 tcptw->tw_ts_offset = tp->tsoffset; 316 tw->tw_usec_ts = tp->tcp_usec_ts; 317 tcptw->tw_last_oow_ack_time = 0; 318 tcptw->tw_tx_delay = tp->tcp_tx_delay; 319 tw->tw_txhash = sk->sk_txhash; 320 #if IS_ENABLED(CONFIG_IPV6) 321 if (tw->tw_family == PF_INET6) { 322 struct ipv6_pinfo *np = inet6_sk(sk); 323 324 tw->tw_v6_daddr = sk->sk_v6_daddr; 325 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 326 tw->tw_tclass = np->tclass; 327 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 328 tw->tw_ipv6only = sk->sk_ipv6only; 329 } 330 #endif 331 332 tcp_time_wait_init(sk, tcptw); 333 tcp_ao_time_wait(tcptw, tp); 334 335 /* Get the TIME_WAIT timeout firing. */ 336 if (timeo < rto) 337 timeo = rto; 338 339 if (state == TCP_TIME_WAIT) 340 timeo = TCP_TIMEWAIT_LEN; 341 342 /* tw_timer is pinned, so we need to make sure BH are disabled 343 * in following section, otherwise timer handler could run before 344 * we complete the initialization. 345 */ 346 local_bh_disable(); 347 inet_twsk_schedule(tw, timeo); 348 /* Linkage updates. 349 * Note that access to tw after this point is illegal. 350 */ 351 inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); 352 local_bh_enable(); 353 } else { 354 /* Sorry, if we're out of memory, just CLOSE this 355 * socket up. We've got bigger problems than 356 * non-graceful socket closings. 357 */ 358 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 359 } 360 361 tcp_update_metrics(sk); 362 tcp_done(sk); 363 } 364 EXPORT_SYMBOL(tcp_time_wait); 365 366 #ifdef CONFIG_TCP_MD5SIG 367 static void tcp_md5_twsk_free_rcu(struct rcu_head *head) 368 { 369 struct tcp_md5sig_key *key; 370 371 key = container_of(head, struct tcp_md5sig_key, rcu); 372 kfree(key); 373 static_branch_slow_dec_deferred(&tcp_md5_needed); 374 tcp_md5_release_sigpool(); 375 } 376 #endif 377 378 void tcp_twsk_destructor(struct sock *sk) 379 { 380 #ifdef CONFIG_TCP_MD5SIG 381 if (static_branch_unlikely(&tcp_md5_needed.key)) { 382 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 383 384 if (twsk->tw_md5_key) 385 call_rcu(&twsk->tw_md5_key->rcu, tcp_md5_twsk_free_rcu); 386 } 387 #endif 388 tcp_ao_destroy_sock(sk, true); 389 } 390 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 391 392 void tcp_twsk_purge(struct list_head *net_exit_list) 393 { 394 bool purged_once = false; 395 struct net *net; 396 397 list_for_each_entry(net, net_exit_list, exit_list) { 398 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 399 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 400 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 401 } else if (!purged_once) { 402 inet_twsk_purge(&tcp_hashinfo); 403 purged_once = true; 404 } 405 } 406 } 407 408 /* Warning : This function is called without sk_listener being locked. 409 * Be sure to read socket fields once, as their value could change under us. 410 */ 411 void tcp_openreq_init_rwin(struct request_sock *req, 412 const struct sock *sk_listener, 413 const struct dst_entry *dst) 414 { 415 struct inet_request_sock *ireq = inet_rsk(req); 416 const struct tcp_sock *tp = tcp_sk(sk_listener); 417 int full_space = tcp_full_space(sk_listener); 418 u32 window_clamp; 419 __u8 rcv_wscale; 420 u32 rcv_wnd; 421 int mss; 422 423 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 424 window_clamp = READ_ONCE(tp->window_clamp); 425 /* Set this up on the first call only */ 426 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 427 428 /* limit the window selection if the user enforce a smaller rx buffer */ 429 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 430 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 431 req->rsk_window_clamp = full_space; 432 433 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 434 if (rcv_wnd == 0) 435 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 436 else if (full_space < rcv_wnd * mss) 437 full_space = rcv_wnd * mss; 438 439 /* tcp_full_space because it is guaranteed to be the first packet */ 440 tcp_select_initial_window(sk_listener, full_space, 441 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 442 &req->rsk_rcv_wnd, 443 &req->rsk_window_clamp, 444 ireq->wscale_ok, 445 &rcv_wscale, 446 rcv_wnd); 447 ireq->rcv_wscale = rcv_wscale; 448 } 449 EXPORT_SYMBOL(tcp_openreq_init_rwin); 450 451 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 452 const struct request_sock *req) 453 { 454 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 455 } 456 457 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 458 { 459 struct inet_connection_sock *icsk = inet_csk(sk); 460 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 461 bool ca_got_dst = false; 462 463 if (ca_key != TCP_CA_UNSPEC) { 464 const struct tcp_congestion_ops *ca; 465 466 rcu_read_lock(); 467 ca = tcp_ca_find_key(ca_key); 468 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 469 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 470 icsk->icsk_ca_ops = ca; 471 ca_got_dst = true; 472 } 473 rcu_read_unlock(); 474 } 475 476 /* If no valid choice made yet, assign current system default ca. */ 477 if (!ca_got_dst && 478 (!icsk->icsk_ca_setsockopt || 479 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 480 tcp_assign_congestion_control(sk); 481 482 tcp_set_ca_state(sk, TCP_CA_Open); 483 } 484 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 485 486 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 487 struct request_sock *req, 488 struct tcp_sock *newtp) 489 { 490 #if IS_ENABLED(CONFIG_SMC) 491 struct inet_request_sock *ireq; 492 493 if (static_branch_unlikely(&tcp_have_smc)) { 494 ireq = inet_rsk(req); 495 if (oldtp->syn_smc && !ireq->smc_ok) 496 newtp->syn_smc = 0; 497 } 498 #endif 499 } 500 501 /* This is not only more efficient than what we used to do, it eliminates 502 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 503 * 504 * Actually, we could lots of memory writes here. tp of listening 505 * socket contains all necessary default parameters. 506 */ 507 struct sock *tcp_create_openreq_child(const struct sock *sk, 508 struct request_sock *req, 509 struct sk_buff *skb) 510 { 511 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 512 const struct inet_request_sock *ireq = inet_rsk(req); 513 struct tcp_request_sock *treq = tcp_rsk(req); 514 struct inet_connection_sock *newicsk; 515 const struct tcp_sock *oldtp; 516 struct tcp_sock *newtp; 517 u32 seq; 518 #ifdef CONFIG_TCP_AO 519 struct tcp_ao_key *ao_key; 520 #endif 521 522 if (!newsk) 523 return NULL; 524 525 newicsk = inet_csk(newsk); 526 newtp = tcp_sk(newsk); 527 oldtp = tcp_sk(sk); 528 529 smc_check_reset_syn_req(oldtp, req, newtp); 530 531 /* Now setup tcp_sock */ 532 newtp->pred_flags = 0; 533 534 seq = treq->rcv_isn + 1; 535 newtp->rcv_wup = seq; 536 WRITE_ONCE(newtp->copied_seq, seq); 537 WRITE_ONCE(newtp->rcv_nxt, seq); 538 newtp->segs_in = 1; 539 540 seq = treq->snt_isn + 1; 541 newtp->snd_sml = newtp->snd_una = seq; 542 WRITE_ONCE(newtp->snd_nxt, seq); 543 newtp->snd_up = seq; 544 545 INIT_LIST_HEAD(&newtp->tsq_node); 546 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 547 548 tcp_init_wl(newtp, treq->rcv_isn); 549 550 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 551 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 552 553 newtp->lsndtime = tcp_jiffies32; 554 newsk->sk_txhash = READ_ONCE(treq->txhash); 555 newtp->total_retrans = req->num_retrans; 556 557 tcp_init_xmit_timers(newsk); 558 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 559 560 if (sock_flag(newsk, SOCK_KEEPOPEN)) 561 inet_csk_reset_keepalive_timer(newsk, 562 keepalive_time_when(newtp)); 563 564 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 565 newtp->rx_opt.sack_ok = ireq->sack_ok; 566 newtp->window_clamp = req->rsk_window_clamp; 567 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 568 newtp->rcv_wnd = req->rsk_rcv_wnd; 569 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 570 if (newtp->rx_opt.wscale_ok) { 571 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 572 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 573 } else { 574 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 575 newtp->window_clamp = min(newtp->window_clamp, 65535U); 576 } 577 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 578 newtp->max_window = newtp->snd_wnd; 579 580 if (newtp->rx_opt.tstamp_ok) { 581 newtp->tcp_usec_ts = treq->req_usec_ts; 582 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 583 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 584 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 585 } else { 586 newtp->tcp_usec_ts = 0; 587 newtp->rx_opt.ts_recent_stamp = 0; 588 newtp->tcp_header_len = sizeof(struct tcphdr); 589 } 590 if (req->num_timeout) { 591 newtp->total_rto = req->num_timeout; 592 newtp->undo_marker = treq->snt_isn; 593 if (newtp->tcp_usec_ts) { 594 newtp->retrans_stamp = treq->snt_synack; 595 newtp->total_rto_time = (u32)(tcp_clock_us() - 596 newtp->retrans_stamp) / USEC_PER_MSEC; 597 } else { 598 newtp->retrans_stamp = div_u64(treq->snt_synack, 599 USEC_PER_SEC / TCP_TS_HZ); 600 newtp->total_rto_time = tcp_clock_ms() - 601 newtp->retrans_stamp; 602 } 603 newtp->total_rto_recoveries = 1; 604 } 605 newtp->tsoffset = treq->ts_off; 606 #ifdef CONFIG_TCP_MD5SIG 607 newtp->md5sig_info = NULL; /*XXX*/ 608 #endif 609 #ifdef CONFIG_TCP_AO 610 newtp->ao_info = NULL; 611 ao_key = treq->af_specific->ao_lookup(sk, req, 612 tcp_rsk(req)->ao_keyid, -1); 613 if (ao_key) 614 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 615 #endif 616 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 617 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 618 newtp->rx_opt.mss_clamp = req->mss; 619 tcp_ecn_openreq_child(newtp, req); 620 newtp->fastopen_req = NULL; 621 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 622 623 newtp->bpf_chg_cc_inprogress = 0; 624 tcp_bpf_clone(sk, newsk); 625 626 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 627 628 return newsk; 629 } 630 EXPORT_SYMBOL(tcp_create_openreq_child); 631 632 /* 633 * Process an incoming packet for SYN_RECV sockets represented as a 634 * request_sock. Normally sk is the listener socket but for TFO it 635 * points to the child socket. 636 * 637 * XXX (TFO) - The current impl contains a special check for ack 638 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 639 * 640 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 641 * 642 * Note: If @fastopen is true, this can be called from process context. 643 * Otherwise, this is from BH context. 644 */ 645 646 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 647 struct request_sock *req, 648 bool fastopen, bool *req_stolen) 649 { 650 struct tcp_options_received tmp_opt; 651 struct sock *child; 652 const struct tcphdr *th = tcp_hdr(skb); 653 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 654 bool paws_reject = false; 655 bool own_req; 656 657 tmp_opt.saw_tstamp = 0; 658 if (th->doff > (sizeof(struct tcphdr)>>2)) { 659 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 660 661 if (tmp_opt.saw_tstamp) { 662 tmp_opt.ts_recent = READ_ONCE(req->ts_recent); 663 if (tmp_opt.rcv_tsecr) 664 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 665 /* We do not store true stamp, but it is not required, 666 * it can be estimated (approximately) 667 * from another data. 668 */ 669 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 670 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 671 } 672 } 673 674 /* Check for pure retransmitted SYN. */ 675 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 676 flg == TCP_FLAG_SYN && 677 !paws_reject) { 678 /* 679 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 680 * this case on figure 6 and figure 8, but formal 681 * protocol description says NOTHING. 682 * To be more exact, it says that we should send ACK, 683 * because this segment (at least, if it has no data) 684 * is out of window. 685 * 686 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 687 * describe SYN-RECV state. All the description 688 * is wrong, we cannot believe to it and should 689 * rely only on common sense and implementation 690 * experience. 691 * 692 * Enforce "SYN-ACK" according to figure 8, figure 6 693 * of RFC793, fixed by RFC1122. 694 * 695 * Note that even if there is new data in the SYN packet 696 * they will be thrown away too. 697 * 698 * Reset timer after retransmitting SYNACK, similar to 699 * the idea of fast retransmit in recovery. 700 */ 701 if (!tcp_oow_rate_limited(sock_net(sk), skb, 702 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 703 &tcp_rsk(req)->last_oow_ack_time) && 704 705 !inet_rtx_syn_ack(sk, req)) { 706 unsigned long expires = jiffies; 707 708 expires += reqsk_timeout(req, TCP_RTO_MAX); 709 if (!fastopen) 710 mod_timer_pending(&req->rsk_timer, expires); 711 else 712 req->rsk_timer.expires = expires; 713 } 714 return NULL; 715 } 716 717 /* Further reproduces section "SEGMENT ARRIVES" 718 for state SYN-RECEIVED of RFC793. 719 It is broken, however, it does not work only 720 when SYNs are crossed. 721 722 You would think that SYN crossing is impossible here, since 723 we should have a SYN_SENT socket (from connect()) on our end, 724 but this is not true if the crossed SYNs were sent to both 725 ends by a malicious third party. We must defend against this, 726 and to do that we first verify the ACK (as per RFC793, page 727 36) and reset if it is invalid. Is this a true full defense? 728 To convince ourselves, let us consider a way in which the ACK 729 test can still pass in this 'malicious crossed SYNs' case. 730 Malicious sender sends identical SYNs (and thus identical sequence 731 numbers) to both A and B: 732 733 A: gets SYN, seq=7 734 B: gets SYN, seq=7 735 736 By our good fortune, both A and B select the same initial 737 send sequence number of seven :-) 738 739 A: sends SYN|ACK, seq=7, ack_seq=8 740 B: sends SYN|ACK, seq=7, ack_seq=8 741 742 So we are now A eating this SYN|ACK, ACK test passes. So 743 does sequence test, SYN is truncated, and thus we consider 744 it a bare ACK. 745 746 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 747 bare ACK. Otherwise, we create an established connection. Both 748 ends (listening sockets) accept the new incoming connection and try 749 to talk to each other. 8-) 750 751 Note: This case is both harmless, and rare. Possibility is about the 752 same as us discovering intelligent life on another plant tomorrow. 753 754 But generally, we should (RFC lies!) to accept ACK 755 from SYNACK both here and in tcp_rcv_state_process(). 756 tcp_rcv_state_process() does not, hence, we do not too. 757 758 Note that the case is absolutely generic: 759 we cannot optimize anything here without 760 violating protocol. All the checks must be made 761 before attempt to create socket. 762 */ 763 764 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 765 * and the incoming segment acknowledges something not yet 766 * sent (the segment carries an unacceptable ACK) ... 767 * a reset is sent." 768 * 769 * Invalid ACK: reset will be sent by listening socket. 770 * Note that the ACK validity check for a Fast Open socket is done 771 * elsewhere and is checked directly against the child socket rather 772 * than req because user data may have been sent out. 773 */ 774 if ((flg & TCP_FLAG_ACK) && !fastopen && 775 (TCP_SKB_CB(skb)->ack_seq != 776 tcp_rsk(req)->snt_isn + 1)) 777 return sk; 778 779 /* Also, it would be not so bad idea to check rcv_tsecr, which 780 * is essentially ACK extension and too early or too late values 781 * should cause reset in unsynchronized states. 782 */ 783 784 /* RFC793: "first check sequence number". */ 785 786 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 787 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 788 /* Out of window: send ACK and drop. */ 789 if (!(flg & TCP_FLAG_RST) && 790 !tcp_oow_rate_limited(sock_net(sk), skb, 791 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 792 &tcp_rsk(req)->last_oow_ack_time)) 793 req->rsk_ops->send_ack(sk, skb, req); 794 if (paws_reject) 795 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 796 return NULL; 797 } 798 799 /* In sequence, PAWS is OK. */ 800 801 /* TODO: We probably should defer ts_recent change once 802 * we take ownership of @req. 803 */ 804 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 805 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 806 807 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 808 /* Truncate SYN, it is out of window starting 809 at tcp_rsk(req)->rcv_isn + 1. */ 810 flg &= ~TCP_FLAG_SYN; 811 } 812 813 /* RFC793: "second check the RST bit" and 814 * "fourth, check the SYN bit" 815 */ 816 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 817 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 818 goto embryonic_reset; 819 } 820 821 /* ACK sequence verified above, just make sure ACK is 822 * set. If ACK not set, just silently drop the packet. 823 * 824 * XXX (TFO) - if we ever allow "data after SYN", the 825 * following check needs to be removed. 826 */ 827 if (!(flg & TCP_FLAG_ACK)) 828 return NULL; 829 830 /* For Fast Open no more processing is needed (sk is the 831 * child socket). 832 */ 833 if (fastopen) 834 return sk; 835 836 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 837 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 838 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 839 inet_rsk(req)->acked = 1; 840 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 841 return NULL; 842 } 843 844 /* OK, ACK is valid, create big socket and 845 * feed this segment to it. It will repeat all 846 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 847 * ESTABLISHED STATE. If it will be dropped after 848 * socket is created, wait for troubles. 849 */ 850 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 851 req, &own_req); 852 if (!child) 853 goto listen_overflow; 854 855 if (own_req && rsk_drop_req(req)) { 856 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 857 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 858 return child; 859 } 860 861 sock_rps_save_rxhash(child, skb); 862 tcp_synack_rtt_meas(child, req); 863 *req_stolen = !own_req; 864 return inet_csk_complete_hashdance(sk, child, req, own_req); 865 866 listen_overflow: 867 if (sk != req->rsk_listener) 868 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 869 870 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 871 inet_rsk(req)->acked = 1; 872 return NULL; 873 } 874 875 embryonic_reset: 876 if (!(flg & TCP_FLAG_RST)) { 877 /* Received a bad SYN pkt - for TFO We try not to reset 878 * the local connection unless it's really necessary to 879 * avoid becoming vulnerable to outside attack aiming at 880 * resetting legit local connections. 881 */ 882 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 883 } else if (fastopen) { /* received a valid RST pkt */ 884 reqsk_fastopen_remove(sk, req, true); 885 tcp_reset(sk, skb); 886 } 887 if (!fastopen) { 888 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 889 890 if (unlinked) 891 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 892 *req_stolen = !unlinked; 893 } 894 return NULL; 895 } 896 EXPORT_SYMBOL(tcp_check_req); 897 898 /* 899 * Queue segment on the new socket if the new socket is active, 900 * otherwise we just shortcircuit this and continue with 901 * the new socket. 902 * 903 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 904 * when entering. But other states are possible due to a race condition 905 * where after __inet_lookup_established() fails but before the listener 906 * locked is obtained, other packets cause the same connection to 907 * be created. 908 */ 909 910 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 911 struct sk_buff *skb) 912 __releases(&((child)->sk_lock.slock)) 913 { 914 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 915 int state = child->sk_state; 916 917 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 918 sk_mark_napi_id_set(child, skb); 919 920 tcp_segs_in(tcp_sk(child), skb); 921 if (!sock_owned_by_user(child)) { 922 reason = tcp_rcv_state_process(child, skb); 923 /* Wakeup parent, send SIGIO */ 924 if (state == TCP_SYN_RECV && child->sk_state != state) 925 parent->sk_data_ready(parent); 926 } else { 927 /* Alas, it is possible again, because we do lookup 928 * in main socket hash table and lock on listening 929 * socket does not protect us more. 930 */ 931 __sk_add_backlog(child, skb); 932 } 933 934 bh_unlock_sock(child); 935 sock_put(child); 936 return reason; 937 } 938 EXPORT_SYMBOL(tcp_child_process); 939