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 u32 rcv_nxt) 57 { 58 #ifdef CONFIG_TCP_AO 59 struct tcp_ao_info *ao; 60 61 ao = rcu_dereference(tcptw->ao_info); 62 if (unlikely(ao && seq < rcv_nxt)) 63 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1); 64 #endif 65 WRITE_ONCE(tcptw->tw_rcv_nxt, seq); 66 } 67 68 /* 69 * * Main purpose of TIME-WAIT state is to close connection gracefully, 70 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 71 * (and, probably, tail of data) and one or more our ACKs are lost. 72 * * What is TIME-WAIT timeout? It is associated with maximal packet 73 * lifetime in the internet, which results in wrong conclusion, that 74 * it is set to catch "old duplicate segments" wandering out of their path. 75 * It is not quite correct. This timeout is calculated so that it exceeds 76 * maximal retransmission timeout enough to allow to lose one (or more) 77 * segments sent by peer and our ACKs. This time may be calculated from RTO. 78 * * When TIME-WAIT socket receives RST, it means that another end 79 * finally closed and we are allowed to kill TIME-WAIT too. 80 * * Second purpose of TIME-WAIT is catching old duplicate segments. 81 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 82 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 83 * * If we invented some more clever way to catch duplicates 84 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 85 * 86 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 87 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 88 * from the very beginning. 89 * 90 * NOTE. With recycling (and later with fin-wait-2) TW bucket 91 * is _not_ stateless. It means, that strictly speaking we must 92 * spinlock it. I do not want! Well, probability of misbehaviour 93 * is ridiculously low and, seems, we could use some mb() tricks 94 * to avoid misread sequence numbers, states etc. --ANK 95 * 96 * We don't need to initialize tmp_out.sack_ok as we don't use the results 97 */ 98 enum tcp_tw_status 99 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 100 const struct tcphdr *th, u32 *tw_isn) 101 { 102 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 103 u32 rcv_nxt = READ_ONCE(tcptw->tw_rcv_nxt); 104 struct tcp_options_received tmp_opt; 105 bool paws_reject = false; 106 int ts_recent_stamp; 107 108 tmp_opt.saw_tstamp = 0; 109 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp); 110 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) { 111 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 112 113 if (tmp_opt.saw_tstamp) { 114 if (tmp_opt.rcv_tsecr) 115 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 116 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent); 117 tmp_opt.ts_recent_stamp = ts_recent_stamp; 118 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 119 } 120 } 121 122 if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) { 123 /* Just repeat all the checks of tcp_rcv_state_process() */ 124 125 /* Out of window, send ACK */ 126 if (paws_reject || 127 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 128 rcv_nxt, 129 rcv_nxt + tcptw->tw_rcv_wnd)) 130 return tcp_timewait_check_oow_rate_limit( 131 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 132 133 if (th->rst) 134 goto kill; 135 136 if (th->syn && !before(TCP_SKB_CB(skb)->seq, rcv_nxt)) 137 return TCP_TW_RST; 138 139 /* Dup ACK? */ 140 if (!th->ack || 141 !after(TCP_SKB_CB(skb)->end_seq, rcv_nxt) || 142 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 143 inet_twsk_put(tw); 144 return TCP_TW_SUCCESS; 145 } 146 147 /* New data or FIN. If new data arrive after half-duplex close, 148 * reset. 149 */ 150 if (!th->fin || 151 TCP_SKB_CB(skb)->end_seq != rcv_nxt + 1) 152 return TCP_TW_RST; 153 154 /* FIN arrived, enter true time-wait state. */ 155 WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT); 156 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq, 157 rcv_nxt); 158 159 if (tmp_opt.saw_tstamp) { 160 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 161 ktime_get_seconds()); 162 WRITE_ONCE(tcptw->tw_ts_recent, 163 tmp_opt.rcv_tsval); 164 } 165 166 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 167 return TCP_TW_ACK; 168 } 169 170 /* 171 * Now real TIME-WAIT state. 172 * 173 * RFC 1122: 174 * "When a connection is [...] on TIME-WAIT state [...] 175 * [a TCP] MAY accept a new SYN from the remote TCP to 176 * reopen the connection directly, if it: 177 * 178 * (1) assigns its initial sequence number for the new 179 * connection to be larger than the largest sequence 180 * number it used on the previous connection incarnation, 181 * and 182 * 183 * (2) returns to TIME-WAIT state if the SYN turns out 184 * to be an old duplicate". 185 */ 186 187 if (!paws_reject && 188 (TCP_SKB_CB(skb)->seq == rcv_nxt && 189 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 190 /* In window segment, it may be only reset or bare ack. */ 191 192 if (th->rst) { 193 /* This is TIME_WAIT assassination, in two flavors. 194 * Oh well... nobody has a sufficient solution to this 195 * protocol bug yet. 196 */ 197 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 198 kill: 199 inet_twsk_deschedule_put(tw); 200 return TCP_TW_SUCCESS; 201 } 202 } else { 203 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 204 } 205 206 if (tmp_opt.saw_tstamp) { 207 WRITE_ONCE(tcptw->tw_ts_recent, 208 tmp_opt.rcv_tsval); 209 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 210 ktime_get_seconds()); 211 } 212 213 inet_twsk_put(tw); 214 return TCP_TW_SUCCESS; 215 } 216 217 /* Out of window segment. 218 219 All the segments are ACKed immediately. 220 221 The only exception is new SYN. We accept it, if it is 222 not old duplicate and we are not in danger to be killed 223 by delayed old duplicates. RFC check is that it has 224 newer sequence number works at rates <40Mbit/sec. 225 However, if paws works, it is reliable AND even more, 226 we even may relax silly seq space cutoff. 227 228 RED-PEN: we violate main RFC requirement, if this SYN will appear 229 old duplicate (i.e. we receive RST in reply to SYN-ACK), 230 we must return socket to time-wait state. It is not good, 231 but not fatal yet. 232 */ 233 234 if (th->syn && !th->rst && !th->ack && !paws_reject && 235 (after(TCP_SKB_CB(skb)->seq, rcv_nxt) || 236 (tmp_opt.saw_tstamp && 237 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) { 238 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 239 if (isn == 0) 240 isn++; 241 *tw_isn = isn; 242 return TCP_TW_SYN; 243 } 244 245 if (paws_reject) 246 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 247 248 if (!th->rst) { 249 /* In this case we must reset the TIMEWAIT timer. 250 * 251 * If it is ACKless SYN it may be both old duplicate 252 * and new good SYN with random sequence number <rcv_nxt. 253 * Do not reschedule in the last case. 254 */ 255 if (paws_reject || th->ack) 256 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 257 258 return tcp_timewait_check_oow_rate_limit( 259 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 260 } 261 inet_twsk_put(tw); 262 return TCP_TW_SUCCESS; 263 } 264 EXPORT_SYMBOL(tcp_timewait_state_process); 265 266 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 267 { 268 #ifdef CONFIG_TCP_MD5SIG 269 const struct tcp_sock *tp = tcp_sk(sk); 270 struct tcp_md5sig_key *key; 271 272 /* 273 * The timewait bucket does not have the key DB from the 274 * sock structure. We just make a quick copy of the 275 * md5 key being used (if indeed we are using one) 276 * so the timewait ack generating code has the key. 277 */ 278 tcptw->tw_md5_key = NULL; 279 if (!static_branch_unlikely(&tcp_md5_needed.key)) 280 return; 281 282 key = tp->af_specific->md5_lookup(sk, sk); 283 if (key) { 284 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 285 if (!tcptw->tw_md5_key) 286 return; 287 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 288 goto out_free; 289 tcp_md5_add_sigpool(); 290 } 291 return; 292 out_free: 293 WARN_ON_ONCE(1); 294 kfree(tcptw->tw_md5_key); 295 tcptw->tw_md5_key = NULL; 296 #endif 297 } 298 299 /* 300 * Move a socket to time-wait or dead fin-wait-2 state. 301 */ 302 void tcp_time_wait(struct sock *sk, int state, int timeo) 303 { 304 const struct inet_connection_sock *icsk = inet_csk(sk); 305 struct tcp_sock *tp = tcp_sk(sk); 306 struct net *net = sock_net(sk); 307 struct inet_timewait_sock *tw; 308 309 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 310 311 if (tw) { 312 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 313 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 314 315 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 316 tw->tw_mark = sk->sk_mark; 317 tw->tw_priority = READ_ONCE(sk->sk_priority); 318 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 319 tcptw->tw_rcv_nxt = tp->rcv_nxt; 320 tcptw->tw_snd_nxt = tp->snd_nxt; 321 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 322 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 323 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 324 tcptw->tw_ts_offset = tp->tsoffset; 325 tw->tw_usec_ts = tp->tcp_usec_ts; 326 tcptw->tw_last_oow_ack_time = 0; 327 tcptw->tw_tx_delay = tp->tcp_tx_delay; 328 tw->tw_txhash = sk->sk_txhash; 329 #if IS_ENABLED(CONFIG_IPV6) 330 if (tw->tw_family == PF_INET6) { 331 struct ipv6_pinfo *np = inet6_sk(sk); 332 333 tw->tw_v6_daddr = sk->sk_v6_daddr; 334 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 335 tw->tw_tclass = np->tclass; 336 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 337 tw->tw_ipv6only = sk->sk_ipv6only; 338 } 339 #endif 340 341 tcp_time_wait_init(sk, tcptw); 342 tcp_ao_time_wait(tcptw, tp); 343 344 /* Get the TIME_WAIT timeout firing. */ 345 if (timeo < rto) 346 timeo = rto; 347 348 if (state == TCP_TIME_WAIT) 349 timeo = TCP_TIMEWAIT_LEN; 350 351 /* Linkage updates. 352 * Note that access to tw after this point is illegal. 353 */ 354 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 355 } else { 356 /* Sorry, if we're out of memory, just CLOSE this 357 * socket up. We've got bigger problems than 358 * non-graceful socket closings. 359 */ 360 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 361 } 362 363 tcp_update_metrics(sk); 364 tcp_done(sk); 365 } 366 EXPORT_SYMBOL(tcp_time_wait); 367 368 #ifdef CONFIG_TCP_MD5SIG 369 static void tcp_md5_twsk_free_rcu(struct rcu_head *head) 370 { 371 struct tcp_md5sig_key *key; 372 373 key = container_of(head, struct tcp_md5sig_key, rcu); 374 kfree(key); 375 static_branch_slow_dec_deferred(&tcp_md5_needed); 376 tcp_md5_release_sigpool(); 377 } 378 #endif 379 380 void tcp_twsk_destructor(struct sock *sk) 381 { 382 #ifdef CONFIG_TCP_MD5SIG 383 if (static_branch_unlikely(&tcp_md5_needed.key)) { 384 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 385 386 if (twsk->tw_md5_key) 387 call_rcu(&twsk->tw_md5_key->rcu, tcp_md5_twsk_free_rcu); 388 } 389 #endif 390 tcp_ao_destroy_sock(sk, true); 391 } 392 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 393 394 void tcp_twsk_purge(struct list_head *net_exit_list) 395 { 396 bool purged_once = false; 397 struct net *net; 398 399 list_for_each_entry(net, net_exit_list, exit_list) { 400 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 401 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 402 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 403 } else if (!purged_once) { 404 inet_twsk_purge(&tcp_hashinfo); 405 purged_once = true; 406 } 407 } 408 } 409 410 /* Warning : This function is called without sk_listener being locked. 411 * Be sure to read socket fields once, as their value could change under us. 412 */ 413 void tcp_openreq_init_rwin(struct request_sock *req, 414 const struct sock *sk_listener, 415 const struct dst_entry *dst) 416 { 417 struct inet_request_sock *ireq = inet_rsk(req); 418 const struct tcp_sock *tp = tcp_sk(sk_listener); 419 int full_space = tcp_full_space(sk_listener); 420 u32 window_clamp; 421 __u8 rcv_wscale; 422 u32 rcv_wnd; 423 int mss; 424 425 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 426 window_clamp = READ_ONCE(tp->window_clamp); 427 /* Set this up on the first call only */ 428 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 429 430 /* limit the window selection if the user enforce a smaller rx buffer */ 431 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 432 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 433 req->rsk_window_clamp = full_space; 434 435 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 436 if (rcv_wnd == 0) 437 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 438 else if (full_space < rcv_wnd * mss) 439 full_space = rcv_wnd * mss; 440 441 /* tcp_full_space because it is guaranteed to be the first packet */ 442 tcp_select_initial_window(sk_listener, full_space, 443 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 444 &req->rsk_rcv_wnd, 445 &req->rsk_window_clamp, 446 ireq->wscale_ok, 447 &rcv_wscale, 448 rcv_wnd); 449 ireq->rcv_wscale = rcv_wscale; 450 } 451 EXPORT_SYMBOL(tcp_openreq_init_rwin); 452 453 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 454 const struct request_sock *req) 455 { 456 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 457 } 458 459 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 460 { 461 struct inet_connection_sock *icsk = inet_csk(sk); 462 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 463 bool ca_got_dst = false; 464 465 if (ca_key != TCP_CA_UNSPEC) { 466 const struct tcp_congestion_ops *ca; 467 468 rcu_read_lock(); 469 ca = tcp_ca_find_key(ca_key); 470 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 471 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 472 icsk->icsk_ca_ops = ca; 473 ca_got_dst = true; 474 } 475 rcu_read_unlock(); 476 } 477 478 /* If no valid choice made yet, assign current system default ca. */ 479 if (!ca_got_dst && 480 (!icsk->icsk_ca_setsockopt || 481 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 482 tcp_assign_congestion_control(sk); 483 484 tcp_set_ca_state(sk, TCP_CA_Open); 485 } 486 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 487 488 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 489 struct request_sock *req, 490 struct tcp_sock *newtp) 491 { 492 #if IS_ENABLED(CONFIG_SMC) 493 struct inet_request_sock *ireq; 494 495 if (static_branch_unlikely(&tcp_have_smc)) { 496 ireq = inet_rsk(req); 497 if (oldtp->syn_smc && !ireq->smc_ok) 498 newtp->syn_smc = 0; 499 } 500 #endif 501 } 502 503 /* This is not only more efficient than what we used to do, it eliminates 504 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 505 * 506 * Actually, we could lots of memory writes here. tp of listening 507 * socket contains all necessary default parameters. 508 */ 509 struct sock *tcp_create_openreq_child(const struct sock *sk, 510 struct request_sock *req, 511 struct sk_buff *skb) 512 { 513 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 514 const struct inet_request_sock *ireq = inet_rsk(req); 515 struct tcp_request_sock *treq = tcp_rsk(req); 516 struct inet_connection_sock *newicsk; 517 const struct tcp_sock *oldtp; 518 struct tcp_sock *newtp; 519 u32 seq; 520 521 if (!newsk) 522 return NULL; 523 524 newicsk = inet_csk(newsk); 525 newtp = tcp_sk(newsk); 526 oldtp = tcp_sk(sk); 527 528 smc_check_reset_syn_req(oldtp, req, newtp); 529 530 /* Now setup tcp_sock */ 531 newtp->pred_flags = 0; 532 533 seq = treq->rcv_isn + 1; 534 newtp->rcv_wup = seq; 535 WRITE_ONCE(newtp->copied_seq, seq); 536 WRITE_ONCE(newtp->rcv_nxt, seq); 537 newtp->segs_in = 1; 538 539 seq = treq->snt_isn + 1; 540 newtp->snd_sml = newtp->snd_una = seq; 541 WRITE_ONCE(newtp->snd_nxt, seq); 542 newtp->snd_up = seq; 543 544 INIT_LIST_HEAD(&newtp->tsq_node); 545 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 546 547 tcp_init_wl(newtp, treq->rcv_isn); 548 549 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 550 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 551 552 newtp->lsndtime = tcp_jiffies32; 553 newsk->sk_txhash = READ_ONCE(treq->txhash); 554 newtp->total_retrans = req->num_retrans; 555 556 tcp_init_xmit_timers(newsk); 557 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 558 559 if (sock_flag(newsk, SOCK_KEEPOPEN)) 560 inet_csk_reset_keepalive_timer(newsk, 561 keepalive_time_when(newtp)); 562 563 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 564 newtp->rx_opt.sack_ok = ireq->sack_ok; 565 newtp->window_clamp = req->rsk_window_clamp; 566 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 567 newtp->rcv_wnd = req->rsk_rcv_wnd; 568 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 569 if (newtp->rx_opt.wscale_ok) { 570 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 571 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 572 } else { 573 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 574 newtp->window_clamp = min(newtp->window_clamp, 65535U); 575 } 576 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 577 newtp->max_window = newtp->snd_wnd; 578 579 if (newtp->rx_opt.tstamp_ok) { 580 newtp->tcp_usec_ts = treq->req_usec_ts; 581 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 582 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 583 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 584 } else { 585 newtp->tcp_usec_ts = 0; 586 newtp->rx_opt.ts_recent_stamp = 0; 587 newtp->tcp_header_len = sizeof(struct tcphdr); 588 } 589 if (req->num_timeout) { 590 newtp->total_rto = req->num_timeout; 591 newtp->undo_marker = treq->snt_isn; 592 if (newtp->tcp_usec_ts) { 593 newtp->retrans_stamp = treq->snt_synack; 594 newtp->total_rto_time = (u32)(tcp_clock_us() - 595 newtp->retrans_stamp) / USEC_PER_MSEC; 596 } else { 597 newtp->retrans_stamp = div_u64(treq->snt_synack, 598 USEC_PER_SEC / TCP_TS_HZ); 599 newtp->total_rto_time = tcp_clock_ms() - 600 newtp->retrans_stamp; 601 } 602 newtp->total_rto_recoveries = 1; 603 } 604 newtp->tsoffset = treq->ts_off; 605 #ifdef CONFIG_TCP_MD5SIG 606 newtp->md5sig_info = NULL; /*XXX*/ 607 #endif 608 #ifdef CONFIG_TCP_AO 609 newtp->ao_info = NULL; 610 611 if (tcp_rsk_used_ao(req)) { 612 struct tcp_ao_key *ao_key; 613 614 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 615 if (ao_key) 616 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 617 } 618 #endif 619 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 620 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 621 newtp->rx_opt.mss_clamp = req->mss; 622 tcp_ecn_openreq_child(newtp, req); 623 newtp->fastopen_req = NULL; 624 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 625 626 newtp->bpf_chg_cc_inprogress = 0; 627 tcp_bpf_clone(sk, newsk); 628 629 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 630 631 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 632 633 return newsk; 634 } 635 EXPORT_SYMBOL(tcp_create_openreq_child); 636 637 /* 638 * Process an incoming packet for SYN_RECV sockets represented as a 639 * request_sock. Normally sk is the listener socket but for TFO it 640 * points to the child socket. 641 * 642 * XXX (TFO) - The current impl contains a special check for ack 643 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 644 * 645 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 646 * 647 * Note: If @fastopen is true, this can be called from process context. 648 * Otherwise, this is from BH context. 649 */ 650 651 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 652 struct request_sock *req, 653 bool fastopen, bool *req_stolen) 654 { 655 struct tcp_options_received tmp_opt; 656 struct sock *child; 657 const struct tcphdr *th = tcp_hdr(skb); 658 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 659 bool paws_reject = false; 660 bool own_req; 661 662 tmp_opt.saw_tstamp = 0; 663 if (th->doff > (sizeof(struct tcphdr)>>2)) { 664 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 665 666 if (tmp_opt.saw_tstamp) { 667 tmp_opt.ts_recent = READ_ONCE(req->ts_recent); 668 if (tmp_opt.rcv_tsecr) 669 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 670 /* We do not store true stamp, but it is not required, 671 * it can be estimated (approximately) 672 * from another data. 673 */ 674 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 675 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 676 } 677 } 678 679 /* Check for pure retransmitted SYN. */ 680 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 681 flg == TCP_FLAG_SYN && 682 !paws_reject) { 683 /* 684 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 685 * this case on figure 6 and figure 8, but formal 686 * protocol description says NOTHING. 687 * To be more exact, it says that we should send ACK, 688 * because this segment (at least, if it has no data) 689 * is out of window. 690 * 691 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 692 * describe SYN-RECV state. All the description 693 * is wrong, we cannot believe to it and should 694 * rely only on common sense and implementation 695 * experience. 696 * 697 * Enforce "SYN-ACK" according to figure 8, figure 6 698 * of RFC793, fixed by RFC1122. 699 * 700 * Note that even if there is new data in the SYN packet 701 * they will be thrown away too. 702 * 703 * Reset timer after retransmitting SYNACK, similar to 704 * the idea of fast retransmit in recovery. 705 */ 706 if (!tcp_oow_rate_limited(sock_net(sk), skb, 707 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 708 &tcp_rsk(req)->last_oow_ack_time) && 709 710 !inet_rtx_syn_ack(sk, req)) { 711 unsigned long expires = jiffies; 712 713 expires += reqsk_timeout(req, TCP_RTO_MAX); 714 if (!fastopen) 715 mod_timer_pending(&req->rsk_timer, expires); 716 else 717 req->rsk_timer.expires = expires; 718 } 719 return NULL; 720 } 721 722 /* Further reproduces section "SEGMENT ARRIVES" 723 for state SYN-RECEIVED of RFC793. 724 It is broken, however, it does not work only 725 when SYNs are crossed. 726 727 You would think that SYN crossing is impossible here, since 728 we should have a SYN_SENT socket (from connect()) on our end, 729 but this is not true if the crossed SYNs were sent to both 730 ends by a malicious third party. We must defend against this, 731 and to do that we first verify the ACK (as per RFC793, page 732 36) and reset if it is invalid. Is this a true full defense? 733 To convince ourselves, let us consider a way in which the ACK 734 test can still pass in this 'malicious crossed SYNs' case. 735 Malicious sender sends identical SYNs (and thus identical sequence 736 numbers) to both A and B: 737 738 A: gets SYN, seq=7 739 B: gets SYN, seq=7 740 741 By our good fortune, both A and B select the same initial 742 send sequence number of seven :-) 743 744 A: sends SYN|ACK, seq=7, ack_seq=8 745 B: sends SYN|ACK, seq=7, ack_seq=8 746 747 So we are now A eating this SYN|ACK, ACK test passes. So 748 does sequence test, SYN is truncated, and thus we consider 749 it a bare ACK. 750 751 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 752 bare ACK. Otherwise, we create an established connection. Both 753 ends (listening sockets) accept the new incoming connection and try 754 to talk to each other. 8-) 755 756 Note: This case is both harmless, and rare. Possibility is about the 757 same as us discovering intelligent life on another plant tomorrow. 758 759 But generally, we should (RFC lies!) to accept ACK 760 from SYNACK both here and in tcp_rcv_state_process(). 761 tcp_rcv_state_process() does not, hence, we do not too. 762 763 Note that the case is absolutely generic: 764 we cannot optimize anything here without 765 violating protocol. All the checks must be made 766 before attempt to create socket. 767 */ 768 769 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 770 * and the incoming segment acknowledges something not yet 771 * sent (the segment carries an unacceptable ACK) ... 772 * a reset is sent." 773 * 774 * Invalid ACK: reset will be sent by listening socket. 775 * Note that the ACK validity check for a Fast Open socket is done 776 * elsewhere and is checked directly against the child socket rather 777 * than req because user data may have been sent out. 778 */ 779 if ((flg & TCP_FLAG_ACK) && !fastopen && 780 (TCP_SKB_CB(skb)->ack_seq != 781 tcp_rsk(req)->snt_isn + 1)) 782 return sk; 783 784 /* Also, it would be not so bad idea to check rcv_tsecr, which 785 * is essentially ACK extension and too early or too late values 786 * should cause reset in unsynchronized states. 787 */ 788 789 /* RFC793: "first check sequence number". */ 790 791 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, 792 TCP_SKB_CB(skb)->end_seq, 793 tcp_rsk(req)->rcv_nxt, 794 tcp_rsk(req)->rcv_nxt + 795 tcp_synack_window(req))) { 796 /* Out of window: send ACK and drop. */ 797 if (!(flg & TCP_FLAG_RST) && 798 !tcp_oow_rate_limited(sock_net(sk), skb, 799 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 800 &tcp_rsk(req)->last_oow_ack_time)) 801 req->rsk_ops->send_ack(sk, skb, req); 802 if (paws_reject) 803 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 804 return NULL; 805 } 806 807 /* In sequence, PAWS is OK. */ 808 809 /* TODO: We probably should defer ts_recent change once 810 * we take ownership of @req. 811 */ 812 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 813 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 814 815 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 816 /* Truncate SYN, it is out of window starting 817 at tcp_rsk(req)->rcv_isn + 1. */ 818 flg &= ~TCP_FLAG_SYN; 819 } 820 821 /* RFC793: "second check the RST bit" and 822 * "fourth, check the SYN bit" 823 */ 824 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 825 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 826 goto embryonic_reset; 827 } 828 829 /* ACK sequence verified above, just make sure ACK is 830 * set. If ACK not set, just silently drop the packet. 831 * 832 * XXX (TFO) - if we ever allow "data after SYN", the 833 * following check needs to be removed. 834 */ 835 if (!(flg & TCP_FLAG_ACK)) 836 return NULL; 837 838 /* For Fast Open no more processing is needed (sk is the 839 * child socket). 840 */ 841 if (fastopen) 842 return sk; 843 844 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 845 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 846 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 847 inet_rsk(req)->acked = 1; 848 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 849 return NULL; 850 } 851 852 /* OK, ACK is valid, create big socket and 853 * feed this segment to it. It will repeat all 854 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 855 * ESTABLISHED STATE. If it will be dropped after 856 * socket is created, wait for troubles. 857 */ 858 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 859 req, &own_req); 860 if (!child) 861 goto listen_overflow; 862 863 if (own_req && rsk_drop_req(req)) { 864 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 865 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 866 return child; 867 } 868 869 sock_rps_save_rxhash(child, skb); 870 tcp_synack_rtt_meas(child, req); 871 *req_stolen = !own_req; 872 return inet_csk_complete_hashdance(sk, child, req, own_req); 873 874 listen_overflow: 875 if (sk != req->rsk_listener) 876 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 877 878 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 879 inet_rsk(req)->acked = 1; 880 return NULL; 881 } 882 883 embryonic_reset: 884 if (!(flg & TCP_FLAG_RST)) { 885 /* Received a bad SYN pkt - for TFO We try not to reset 886 * the local connection unless it's really necessary to 887 * avoid becoming vulnerable to outside attack aiming at 888 * resetting legit local connections. 889 */ 890 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 891 } else if (fastopen) { /* received a valid RST pkt */ 892 reqsk_fastopen_remove(sk, req, true); 893 tcp_reset(sk, skb); 894 } 895 if (!fastopen) { 896 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 897 898 if (unlinked) 899 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 900 *req_stolen = !unlinked; 901 } 902 return NULL; 903 } 904 EXPORT_SYMBOL(tcp_check_req); 905 906 /* 907 * Queue segment on the new socket if the new socket is active, 908 * otherwise we just shortcircuit this and continue with 909 * the new socket. 910 * 911 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 912 * when entering. But other states are possible due to a race condition 913 * where after __inet_lookup_established() fails but before the listener 914 * locked is obtained, other packets cause the same connection to 915 * be created. 916 */ 917 918 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 919 struct sk_buff *skb) 920 __releases(&((child)->sk_lock.slock)) 921 { 922 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 923 int state = child->sk_state; 924 925 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 926 sk_mark_napi_id_set(child, skb); 927 928 tcp_segs_in(tcp_sk(child), skb); 929 if (!sock_owned_by_user(child)) { 930 reason = tcp_rcv_state_process(child, skb); 931 /* Wakeup parent, send SIGIO */ 932 if (state == TCP_SYN_RECV && child->sk_state != state) 933 parent->sk_data_ready(parent); 934 } else { 935 /* Alas, it is possible again, because we do lookup 936 * in main socket hash table and lock on listening 937 * socket does not protect us more. 938 */ 939 __sk_add_backlog(child, skb); 940 } 941 942 bh_unlock_sock(child); 943 sock_put(child); 944 return reason; 945 } 946 EXPORT_SYMBOL(tcp_child_process); 947