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 26 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 27 { 28 if (seq == s_win) 29 return true; 30 if (after(end_seq, s_win) && before(seq, e_win)) 31 return true; 32 return seq == e_win && seq == end_seq; 33 } 34 35 static enum tcp_tw_status 36 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 37 const struct sk_buff *skb, int mib_idx) 38 { 39 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 40 41 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 42 &tcptw->tw_last_oow_ack_time)) { 43 /* Send ACK. Note, we do not put the bucket, 44 * it will be released by caller. 45 */ 46 return TCP_TW_ACK; 47 } 48 49 /* We are rate-limiting, so just release the tw sock and drop skb. */ 50 inet_twsk_put(tw); 51 return TCP_TW_SUCCESS; 52 } 53 54 static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq) 55 { 56 #ifdef CONFIG_TCP_AO 57 struct tcp_ao_info *ao; 58 59 ao = rcu_dereference(tcptw->ao_info); 60 if (unlikely(ao && seq < tcptw->tw_rcv_nxt)) 61 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1); 62 #endif 63 tcptw->tw_rcv_nxt = seq; 64 } 65 66 /* 67 * * Main purpose of TIME-WAIT state is to close connection gracefully, 68 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 69 * (and, probably, tail of data) and one or more our ACKs are lost. 70 * * What is TIME-WAIT timeout? It is associated with maximal packet 71 * lifetime in the internet, which results in wrong conclusion, that 72 * it is set to catch "old duplicate segments" wandering out of their path. 73 * It is not quite correct. This timeout is calculated so that it exceeds 74 * maximal retransmission timeout enough to allow to lose one (or more) 75 * segments sent by peer and our ACKs. This time may be calculated from RTO. 76 * * When TIME-WAIT socket receives RST, it means that another end 77 * finally closed and we are allowed to kill TIME-WAIT too. 78 * * Second purpose of TIME-WAIT is catching old duplicate segments. 79 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 80 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 81 * * If we invented some more clever way to catch duplicates 82 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 83 * 84 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 85 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 86 * from the very beginning. 87 * 88 * NOTE. With recycling (and later with fin-wait-2) TW bucket 89 * is _not_ stateless. It means, that strictly speaking we must 90 * spinlock it. I do not want! Well, probability of misbehaviour 91 * is ridiculously low and, seems, we could use some mb() tricks 92 * to avoid misread sequence numbers, states etc. --ANK 93 * 94 * We don't need to initialize tmp_out.sack_ok as we don't use the results 95 */ 96 enum tcp_tw_status 97 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 98 const struct tcphdr *th) 99 { 100 struct tcp_options_received tmp_opt; 101 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 102 bool paws_reject = false; 103 104 tmp_opt.saw_tstamp = 0; 105 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 106 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 107 108 if (tmp_opt.saw_tstamp) { 109 if (tmp_opt.rcv_tsecr) 110 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 111 tmp_opt.ts_recent = tcptw->tw_ts_recent; 112 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 113 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 114 } 115 } 116 117 if (tw->tw_substate == TCP_FIN_WAIT2) { 118 /* Just repeat all the checks of tcp_rcv_state_process() */ 119 120 /* Out of window, send ACK */ 121 if (paws_reject || 122 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 123 tcptw->tw_rcv_nxt, 124 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 125 return tcp_timewait_check_oow_rate_limit( 126 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 127 128 if (th->rst) 129 goto kill; 130 131 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 132 return TCP_TW_RST; 133 134 /* Dup ACK? */ 135 if (!th->ack || 136 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 137 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 138 inet_twsk_put(tw); 139 return TCP_TW_SUCCESS; 140 } 141 142 /* New data or FIN. If new data arrive after half-duplex close, 143 * reset. 144 */ 145 if (!th->fin || 146 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 147 return TCP_TW_RST; 148 149 /* FIN arrived, enter true time-wait state. */ 150 tw->tw_substate = TCP_TIME_WAIT; 151 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq); 152 153 if (tmp_opt.saw_tstamp) { 154 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 155 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 156 } 157 158 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 159 return TCP_TW_ACK; 160 } 161 162 /* 163 * Now real TIME-WAIT state. 164 * 165 * RFC 1122: 166 * "When a connection is [...] on TIME-WAIT state [...] 167 * [a TCP] MAY accept a new SYN from the remote TCP to 168 * reopen the connection directly, if it: 169 * 170 * (1) assigns its initial sequence number for the new 171 * connection to be larger than the largest sequence 172 * number it used on the previous connection incarnation, 173 * and 174 * 175 * (2) returns to TIME-WAIT state if the SYN turns out 176 * to be an old duplicate". 177 */ 178 179 if (!paws_reject && 180 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 181 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 182 /* In window segment, it may be only reset or bare ack. */ 183 184 if (th->rst) { 185 /* This is TIME_WAIT assassination, in two flavors. 186 * Oh well... nobody has a sufficient solution to this 187 * protocol bug yet. 188 */ 189 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 190 kill: 191 inet_twsk_deschedule_put(tw); 192 return TCP_TW_SUCCESS; 193 } 194 } else { 195 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 196 } 197 198 if (tmp_opt.saw_tstamp) { 199 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 200 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 201 } 202 203 inet_twsk_put(tw); 204 return TCP_TW_SUCCESS; 205 } 206 207 /* Out of window segment. 208 209 All the segments are ACKed immediately. 210 211 The only exception is new SYN. We accept it, if it is 212 not old duplicate and we are not in danger to be killed 213 by delayed old duplicates. RFC check is that it has 214 newer sequence number works at rates <40Mbit/sec. 215 However, if paws works, it is reliable AND even more, 216 we even may relax silly seq space cutoff. 217 218 RED-PEN: we violate main RFC requirement, if this SYN will appear 219 old duplicate (i.e. we receive RST in reply to SYN-ACK), 220 we must return socket to time-wait state. It is not good, 221 but not fatal yet. 222 */ 223 224 if (th->syn && !th->rst && !th->ack && !paws_reject && 225 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 226 (tmp_opt.saw_tstamp && 227 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 228 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 229 if (isn == 0) 230 isn++; 231 TCP_SKB_CB(skb)->tcp_tw_isn = isn; 232 return TCP_TW_SYN; 233 } 234 235 if (paws_reject) 236 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 237 238 if (!th->rst) { 239 /* In this case we must reset the TIMEWAIT timer. 240 * 241 * If it is ACKless SYN it may be both old duplicate 242 * and new good SYN with random sequence number <rcv_nxt. 243 * Do not reschedule in the last case. 244 */ 245 if (paws_reject || th->ack) 246 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 247 248 return tcp_timewait_check_oow_rate_limit( 249 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 250 } 251 inet_twsk_put(tw); 252 return TCP_TW_SUCCESS; 253 } 254 EXPORT_SYMBOL(tcp_timewait_state_process); 255 256 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 257 { 258 #ifdef CONFIG_TCP_MD5SIG 259 const struct tcp_sock *tp = tcp_sk(sk); 260 struct tcp_md5sig_key *key; 261 262 /* 263 * The timewait bucket does not have the key DB from the 264 * sock structure. We just make a quick copy of the 265 * md5 key being used (if indeed we are using one) 266 * so the timewait ack generating code has the key. 267 */ 268 tcptw->tw_md5_key = NULL; 269 if (!static_branch_unlikely(&tcp_md5_needed.key)) 270 return; 271 272 key = tp->af_specific->md5_lookup(sk, sk); 273 if (key) { 274 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 275 if (!tcptw->tw_md5_key) 276 return; 277 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 278 goto out_free; 279 tcp_md5_add_sigpool(); 280 } 281 return; 282 out_free: 283 WARN_ON_ONCE(1); 284 kfree(tcptw->tw_md5_key); 285 tcptw->tw_md5_key = NULL; 286 #endif 287 } 288 289 /* 290 * Move a socket to time-wait or dead fin-wait-2 state. 291 */ 292 void tcp_time_wait(struct sock *sk, int state, int timeo) 293 { 294 const struct inet_connection_sock *icsk = inet_csk(sk); 295 struct tcp_sock *tp = tcp_sk(sk); 296 struct net *net = sock_net(sk); 297 struct inet_timewait_sock *tw; 298 299 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 300 301 if (tw) { 302 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 303 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 304 305 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 306 tw->tw_mark = sk->sk_mark; 307 tw->tw_priority = READ_ONCE(sk->sk_priority); 308 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 309 tcptw->tw_rcv_nxt = tp->rcv_nxt; 310 tcptw->tw_snd_nxt = tp->snd_nxt; 311 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 312 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 313 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 314 tcptw->tw_ts_offset = tp->tsoffset; 315 tw->tw_usec_ts = tp->tcp_usec_ts; 316 tcptw->tw_last_oow_ack_time = 0; 317 tcptw->tw_tx_delay = tp->tcp_tx_delay; 318 tw->tw_txhash = sk->sk_txhash; 319 #if IS_ENABLED(CONFIG_IPV6) 320 if (tw->tw_family == PF_INET6) { 321 struct ipv6_pinfo *np = inet6_sk(sk); 322 323 tw->tw_v6_daddr = sk->sk_v6_daddr; 324 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 325 tw->tw_tclass = np->tclass; 326 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 327 tw->tw_ipv6only = sk->sk_ipv6only; 328 } 329 #endif 330 331 tcp_time_wait_init(sk, tcptw); 332 tcp_ao_time_wait(tcptw, tp); 333 334 /* Get the TIME_WAIT timeout firing. */ 335 if (timeo < rto) 336 timeo = rto; 337 338 if (state == TCP_TIME_WAIT) 339 timeo = TCP_TIMEWAIT_LEN; 340 341 /* tw_timer is pinned, so we need to make sure BH are disabled 342 * in following section, otherwise timer handler could run before 343 * we complete the initialization. 344 */ 345 local_bh_disable(); 346 inet_twsk_schedule(tw, timeo); 347 /* Linkage updates. 348 * Note that access to tw after this point is illegal. 349 */ 350 inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); 351 local_bh_enable(); 352 } else { 353 /* Sorry, if we're out of memory, just CLOSE this 354 * socket up. We've got bigger problems than 355 * non-graceful socket closings. 356 */ 357 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 358 } 359 360 tcp_update_metrics(sk); 361 tcp_done(sk); 362 } 363 EXPORT_SYMBOL(tcp_time_wait); 364 365 #ifdef CONFIG_TCP_MD5SIG 366 static void tcp_md5_twsk_free_rcu(struct rcu_head *head) 367 { 368 struct tcp_md5sig_key *key; 369 370 key = container_of(head, struct tcp_md5sig_key, rcu); 371 kfree(key); 372 static_branch_slow_dec_deferred(&tcp_md5_needed); 373 tcp_md5_release_sigpool(); 374 } 375 #endif 376 377 void tcp_twsk_destructor(struct sock *sk) 378 { 379 #ifdef CONFIG_TCP_MD5SIG 380 if (static_branch_unlikely(&tcp_md5_needed.key)) { 381 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 382 383 if (twsk->tw_md5_key) 384 call_rcu(&twsk->tw_md5_key->rcu, tcp_md5_twsk_free_rcu); 385 } 386 #endif 387 tcp_ao_destroy_sock(sk, true); 388 } 389 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 390 391 void tcp_twsk_purge(struct list_head *net_exit_list, int family) 392 { 393 bool purged_once = false; 394 struct net *net; 395 396 list_for_each_entry(net, net_exit_list, exit_list) { 397 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 398 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 399 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family); 400 } else if (!purged_once) { 401 /* The last refcount is decremented in tcp_sk_exit_batch() */ 402 if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) 403 continue; 404 405 inet_twsk_purge(&tcp_hashinfo, family); 406 purged_once = true; 407 } 408 } 409 } 410 EXPORT_SYMBOL_GPL(tcp_twsk_purge); 411 412 /* Warning : This function is called without sk_listener being locked. 413 * Be sure to read socket fields once, as their value could change under us. 414 */ 415 void tcp_openreq_init_rwin(struct request_sock *req, 416 const struct sock *sk_listener, 417 const struct dst_entry *dst) 418 { 419 struct inet_request_sock *ireq = inet_rsk(req); 420 const struct tcp_sock *tp = tcp_sk(sk_listener); 421 int full_space = tcp_full_space(sk_listener); 422 u32 window_clamp; 423 __u8 rcv_wscale; 424 u32 rcv_wnd; 425 int mss; 426 427 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 428 window_clamp = READ_ONCE(tp->window_clamp); 429 /* Set this up on the first call only */ 430 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 431 432 /* limit the window selection if the user enforce a smaller rx buffer */ 433 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 434 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 435 req->rsk_window_clamp = full_space; 436 437 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 438 if (rcv_wnd == 0) 439 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 440 else if (full_space < rcv_wnd * mss) 441 full_space = rcv_wnd * mss; 442 443 /* tcp_full_space because it is guaranteed to be the first packet */ 444 tcp_select_initial_window(sk_listener, full_space, 445 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 446 &req->rsk_rcv_wnd, 447 &req->rsk_window_clamp, 448 ireq->wscale_ok, 449 &rcv_wscale, 450 rcv_wnd); 451 ireq->rcv_wscale = rcv_wscale; 452 } 453 EXPORT_SYMBOL(tcp_openreq_init_rwin); 454 455 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 456 const struct request_sock *req) 457 { 458 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 459 } 460 461 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 462 { 463 struct inet_connection_sock *icsk = inet_csk(sk); 464 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 465 bool ca_got_dst = false; 466 467 if (ca_key != TCP_CA_UNSPEC) { 468 const struct tcp_congestion_ops *ca; 469 470 rcu_read_lock(); 471 ca = tcp_ca_find_key(ca_key); 472 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 473 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 474 icsk->icsk_ca_ops = ca; 475 ca_got_dst = true; 476 } 477 rcu_read_unlock(); 478 } 479 480 /* If no valid choice made yet, assign current system default ca. */ 481 if (!ca_got_dst && 482 (!icsk->icsk_ca_setsockopt || 483 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 484 tcp_assign_congestion_control(sk); 485 486 tcp_set_ca_state(sk, TCP_CA_Open); 487 } 488 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 489 490 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 491 struct request_sock *req, 492 struct tcp_sock *newtp) 493 { 494 #if IS_ENABLED(CONFIG_SMC) 495 struct inet_request_sock *ireq; 496 497 if (static_branch_unlikely(&tcp_have_smc)) { 498 ireq = inet_rsk(req); 499 if (oldtp->syn_smc && !ireq->smc_ok) 500 newtp->syn_smc = 0; 501 } 502 #endif 503 } 504 505 /* This is not only more efficient than what we used to do, it eliminates 506 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 507 * 508 * Actually, we could lots of memory writes here. tp of listening 509 * socket contains all necessary default parameters. 510 */ 511 struct sock *tcp_create_openreq_child(const struct sock *sk, 512 struct request_sock *req, 513 struct sk_buff *skb) 514 { 515 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 516 const struct inet_request_sock *ireq = inet_rsk(req); 517 struct tcp_request_sock *treq = tcp_rsk(req); 518 struct inet_connection_sock *newicsk; 519 const struct tcp_sock *oldtp; 520 struct tcp_sock *newtp; 521 u32 seq; 522 #ifdef CONFIG_TCP_AO 523 struct tcp_ao_key *ao_key; 524 #endif 525 526 if (!newsk) 527 return NULL; 528 529 newicsk = inet_csk(newsk); 530 newtp = tcp_sk(newsk); 531 oldtp = tcp_sk(sk); 532 533 smc_check_reset_syn_req(oldtp, req, newtp); 534 535 /* Now setup tcp_sock */ 536 newtp->pred_flags = 0; 537 538 seq = treq->rcv_isn + 1; 539 newtp->rcv_wup = seq; 540 WRITE_ONCE(newtp->copied_seq, seq); 541 WRITE_ONCE(newtp->rcv_nxt, seq); 542 newtp->segs_in = 1; 543 544 seq = treq->snt_isn + 1; 545 newtp->snd_sml = newtp->snd_una = seq; 546 WRITE_ONCE(newtp->snd_nxt, seq); 547 newtp->snd_up = seq; 548 549 INIT_LIST_HEAD(&newtp->tsq_node); 550 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 551 552 tcp_init_wl(newtp, treq->rcv_isn); 553 554 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 555 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 556 557 newtp->lsndtime = tcp_jiffies32; 558 newsk->sk_txhash = READ_ONCE(treq->txhash); 559 newtp->total_retrans = req->num_retrans; 560 561 tcp_init_xmit_timers(newsk); 562 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 563 564 if (sock_flag(newsk, SOCK_KEEPOPEN)) 565 inet_csk_reset_keepalive_timer(newsk, 566 keepalive_time_when(newtp)); 567 568 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 569 newtp->rx_opt.sack_ok = ireq->sack_ok; 570 newtp->window_clamp = req->rsk_window_clamp; 571 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 572 newtp->rcv_wnd = req->rsk_rcv_wnd; 573 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 574 if (newtp->rx_opt.wscale_ok) { 575 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 576 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 577 } else { 578 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 579 newtp->window_clamp = min(newtp->window_clamp, 65535U); 580 } 581 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 582 newtp->max_window = newtp->snd_wnd; 583 584 if (newtp->rx_opt.tstamp_ok) { 585 newtp->tcp_usec_ts = treq->req_usec_ts; 586 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 587 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 588 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 589 } else { 590 newtp->tcp_usec_ts = 0; 591 newtp->rx_opt.ts_recent_stamp = 0; 592 newtp->tcp_header_len = sizeof(struct tcphdr); 593 } 594 if (req->num_timeout) { 595 newtp->total_rto = req->num_timeout; 596 newtp->undo_marker = treq->snt_isn; 597 if (newtp->tcp_usec_ts) { 598 newtp->retrans_stamp = treq->snt_synack; 599 newtp->total_rto_time = (u32)(tcp_clock_us() - 600 newtp->retrans_stamp) / USEC_PER_MSEC; 601 } else { 602 newtp->retrans_stamp = div_u64(treq->snt_synack, 603 USEC_PER_SEC / TCP_TS_HZ); 604 newtp->total_rto_time = tcp_clock_ms() - 605 newtp->retrans_stamp; 606 } 607 newtp->total_rto_recoveries = 1; 608 } 609 newtp->tsoffset = treq->ts_off; 610 #ifdef CONFIG_TCP_MD5SIG 611 newtp->md5sig_info = NULL; /*XXX*/ 612 #endif 613 #ifdef CONFIG_TCP_AO 614 newtp->ao_info = NULL; 615 ao_key = treq->af_specific->ao_lookup(sk, req, 616 tcp_rsk(req)->ao_keyid, -1); 617 if (ao_key) 618 newtp->tcp_header_len += tcp_ao_len(ao_key); 619 #endif 620 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 621 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 622 newtp->rx_opt.mss_clamp = req->mss; 623 tcp_ecn_openreq_child(newtp, req); 624 newtp->fastopen_req = NULL; 625 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 626 627 newtp->bpf_chg_cc_inprogress = 0; 628 tcp_bpf_clone(sk, newsk); 629 630 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 631 632 return newsk; 633 } 634 EXPORT_SYMBOL(tcp_create_openreq_child); 635 636 /* 637 * Process an incoming packet for SYN_RECV sockets represented as a 638 * request_sock. Normally sk is the listener socket but for TFO it 639 * points to the child socket. 640 * 641 * XXX (TFO) - The current impl contains a special check for ack 642 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 643 * 644 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 645 * 646 * Note: If @fastopen is true, this can be called from process context. 647 * Otherwise, this is from BH context. 648 */ 649 650 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 651 struct request_sock *req, 652 bool fastopen, bool *req_stolen) 653 { 654 struct tcp_options_received tmp_opt; 655 struct sock *child; 656 const struct tcphdr *th = tcp_hdr(skb); 657 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 658 bool paws_reject = false; 659 bool own_req; 660 661 tmp_opt.saw_tstamp = 0; 662 if (th->doff > (sizeof(struct tcphdr)>>2)) { 663 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 664 665 if (tmp_opt.saw_tstamp) { 666 tmp_opt.ts_recent = READ_ONCE(req->ts_recent); 667 if (tmp_opt.rcv_tsecr) 668 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 669 /* We do not store true stamp, but it is not required, 670 * it can be estimated (approximately) 671 * from another data. 672 */ 673 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 674 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 675 } 676 } 677 678 /* Check for pure retransmitted SYN. */ 679 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 680 flg == TCP_FLAG_SYN && 681 !paws_reject) { 682 /* 683 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 684 * this case on figure 6 and figure 8, but formal 685 * protocol description says NOTHING. 686 * To be more exact, it says that we should send ACK, 687 * because this segment (at least, if it has no data) 688 * is out of window. 689 * 690 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 691 * describe SYN-RECV state. All the description 692 * is wrong, we cannot believe to it and should 693 * rely only on common sense and implementation 694 * experience. 695 * 696 * Enforce "SYN-ACK" according to figure 8, figure 6 697 * of RFC793, fixed by RFC1122. 698 * 699 * Note that even if there is new data in the SYN packet 700 * they will be thrown away too. 701 * 702 * Reset timer after retransmitting SYNACK, similar to 703 * the idea of fast retransmit in recovery. 704 */ 705 if (!tcp_oow_rate_limited(sock_net(sk), skb, 706 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 707 &tcp_rsk(req)->last_oow_ack_time) && 708 709 !inet_rtx_syn_ack(sk, req)) { 710 unsigned long expires = jiffies; 711 712 expires += reqsk_timeout(req, TCP_RTO_MAX); 713 if (!fastopen) 714 mod_timer_pending(&req->rsk_timer, expires); 715 else 716 req->rsk_timer.expires = expires; 717 } 718 return NULL; 719 } 720 721 /* Further reproduces section "SEGMENT ARRIVES" 722 for state SYN-RECEIVED of RFC793. 723 It is broken, however, it does not work only 724 when SYNs are crossed. 725 726 You would think that SYN crossing is impossible here, since 727 we should have a SYN_SENT socket (from connect()) on our end, 728 but this is not true if the crossed SYNs were sent to both 729 ends by a malicious third party. We must defend against this, 730 and to do that we first verify the ACK (as per RFC793, page 731 36) and reset if it is invalid. Is this a true full defense? 732 To convince ourselves, let us consider a way in which the ACK 733 test can still pass in this 'malicious crossed SYNs' case. 734 Malicious sender sends identical SYNs (and thus identical sequence 735 numbers) to both A and B: 736 737 A: gets SYN, seq=7 738 B: gets SYN, seq=7 739 740 By our good fortune, both A and B select the same initial 741 send sequence number of seven :-) 742 743 A: sends SYN|ACK, seq=7, ack_seq=8 744 B: sends SYN|ACK, seq=7, ack_seq=8 745 746 So we are now A eating this SYN|ACK, ACK test passes. So 747 does sequence test, SYN is truncated, and thus we consider 748 it a bare ACK. 749 750 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 751 bare ACK. Otherwise, we create an established connection. Both 752 ends (listening sockets) accept the new incoming connection and try 753 to talk to each other. 8-) 754 755 Note: This case is both harmless, and rare. Possibility is about the 756 same as us discovering intelligent life on another plant tomorrow. 757 758 But generally, we should (RFC lies!) to accept ACK 759 from SYNACK both here and in tcp_rcv_state_process(). 760 tcp_rcv_state_process() does not, hence, we do not too. 761 762 Note that the case is absolutely generic: 763 we cannot optimize anything here without 764 violating protocol. All the checks must be made 765 before attempt to create socket. 766 */ 767 768 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 769 * and the incoming segment acknowledges something not yet 770 * sent (the segment carries an unacceptable ACK) ... 771 * a reset is sent." 772 * 773 * Invalid ACK: reset will be sent by listening socket. 774 * Note that the ACK validity check for a Fast Open socket is done 775 * elsewhere and is checked directly against the child socket rather 776 * than req because user data may have been sent out. 777 */ 778 if ((flg & TCP_FLAG_ACK) && !fastopen && 779 (TCP_SKB_CB(skb)->ack_seq != 780 tcp_rsk(req)->snt_isn + 1)) 781 return sk; 782 783 /* Also, it would be not so bad idea to check rcv_tsecr, which 784 * is essentially ACK extension and too early or too late values 785 * should cause reset in unsynchronized states. 786 */ 787 788 /* RFC793: "first check sequence number". */ 789 790 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 791 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 792 /* Out of window: send ACK and drop. */ 793 if (!(flg & TCP_FLAG_RST) && 794 !tcp_oow_rate_limited(sock_net(sk), skb, 795 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 796 &tcp_rsk(req)->last_oow_ack_time)) 797 req->rsk_ops->send_ack(sk, skb, req); 798 if (paws_reject) 799 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 800 return NULL; 801 } 802 803 /* In sequence, PAWS is OK. */ 804 805 /* TODO: We probably should defer ts_recent change once 806 * we take ownership of @req. 807 */ 808 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 809 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 810 811 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 812 /* Truncate SYN, it is out of window starting 813 at tcp_rsk(req)->rcv_isn + 1. */ 814 flg &= ~TCP_FLAG_SYN; 815 } 816 817 /* RFC793: "second check the RST bit" and 818 * "fourth, check the SYN bit" 819 */ 820 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 821 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 822 goto embryonic_reset; 823 } 824 825 /* ACK sequence verified above, just make sure ACK is 826 * set. If ACK not set, just silently drop the packet. 827 * 828 * XXX (TFO) - if we ever allow "data after SYN", the 829 * following check needs to be removed. 830 */ 831 if (!(flg & TCP_FLAG_ACK)) 832 return NULL; 833 834 /* For Fast Open no more processing is needed (sk is the 835 * child socket). 836 */ 837 if (fastopen) 838 return sk; 839 840 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 841 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 842 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 843 inet_rsk(req)->acked = 1; 844 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 845 return NULL; 846 } 847 848 /* OK, ACK is valid, create big socket and 849 * feed this segment to it. It will repeat all 850 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 851 * ESTABLISHED STATE. If it will be dropped after 852 * socket is created, wait for troubles. 853 */ 854 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 855 req, &own_req); 856 if (!child) 857 goto listen_overflow; 858 859 if (own_req && rsk_drop_req(req)) { 860 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 861 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 862 return child; 863 } 864 865 sock_rps_save_rxhash(child, skb); 866 tcp_synack_rtt_meas(child, req); 867 *req_stolen = !own_req; 868 return inet_csk_complete_hashdance(sk, child, req, own_req); 869 870 listen_overflow: 871 if (sk != req->rsk_listener) 872 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 873 874 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 875 inet_rsk(req)->acked = 1; 876 return NULL; 877 } 878 879 embryonic_reset: 880 if (!(flg & TCP_FLAG_RST)) { 881 /* Received a bad SYN pkt - for TFO We try not to reset 882 * the local connection unless it's really necessary to 883 * avoid becoming vulnerable to outside attack aiming at 884 * resetting legit local connections. 885 */ 886 req->rsk_ops->send_reset(sk, skb); 887 } else if (fastopen) { /* received a valid RST pkt */ 888 reqsk_fastopen_remove(sk, req, true); 889 tcp_reset(sk, skb); 890 } 891 if (!fastopen) { 892 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 893 894 if (unlinked) 895 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 896 *req_stolen = !unlinked; 897 } 898 return NULL; 899 } 900 EXPORT_SYMBOL(tcp_check_req); 901 902 /* 903 * Queue segment on the new socket if the new socket is active, 904 * otherwise we just shortcircuit this and continue with 905 * the new socket. 906 * 907 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 908 * when entering. But other states are possible due to a race condition 909 * where after __inet_lookup_established() fails but before the listener 910 * locked is obtained, other packets cause the same connection to 911 * be created. 912 */ 913 914 int tcp_child_process(struct sock *parent, struct sock *child, 915 struct sk_buff *skb) 916 __releases(&((child)->sk_lock.slock)) 917 { 918 int ret = 0; 919 int state = child->sk_state; 920 921 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 922 sk_mark_napi_id_set(child, skb); 923 924 tcp_segs_in(tcp_sk(child), skb); 925 if (!sock_owned_by_user(child)) { 926 ret = tcp_rcv_state_process(child, skb); 927 /* Wakeup parent, send SIGIO */ 928 if (state == TCP_SYN_RECV && child->sk_state != state) 929 parent->sk_data_ready(parent); 930 } else { 931 /* Alas, it is possible again, because we do lookup 932 * in main socket hash table and lock on listening 933 * socket does not protect us more. 934 */ 935 __sk_add_backlog(child, skb); 936 } 937 938 bh_unlock_sock(child); 939 sock_put(child); 940 return ret; 941 } 942 EXPORT_SYMBOL(tcp_child_process); 943