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 int ts_recent_stamp; 105 106 tmp_opt.saw_tstamp = 0; 107 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp); 108 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) { 109 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 110 111 if (tmp_opt.saw_tstamp) { 112 if (tmp_opt.rcv_tsecr) 113 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 114 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent); 115 tmp_opt.ts_recent_stamp = ts_recent_stamp; 116 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 117 } 118 } 119 120 if (tw->tw_substate == TCP_FIN_WAIT2) { 121 /* Just repeat all the checks of tcp_rcv_state_process() */ 122 123 /* Out of window, send ACK */ 124 if (paws_reject || 125 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 126 tcptw->tw_rcv_nxt, 127 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 128 return tcp_timewait_check_oow_rate_limit( 129 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 130 131 if (th->rst) 132 goto kill; 133 134 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 135 return TCP_TW_RST; 136 137 /* Dup ACK? */ 138 if (!th->ack || 139 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 140 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 141 inet_twsk_put(tw); 142 return TCP_TW_SUCCESS; 143 } 144 145 /* New data or FIN. If new data arrive after half-duplex close, 146 * reset. 147 */ 148 if (!th->fin || 149 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 150 return TCP_TW_RST; 151 152 /* FIN arrived, enter true time-wait state. */ 153 tw->tw_substate = TCP_TIME_WAIT; 154 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq); 155 156 if (tmp_opt.saw_tstamp) { 157 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 158 ktime_get_seconds()); 159 WRITE_ONCE(tcptw->tw_ts_recent, 160 tmp_opt.rcv_tsval); 161 } 162 163 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 164 return TCP_TW_ACK; 165 } 166 167 /* 168 * Now real TIME-WAIT state. 169 * 170 * RFC 1122: 171 * "When a connection is [...] on TIME-WAIT state [...] 172 * [a TCP] MAY accept a new SYN from the remote TCP to 173 * reopen the connection directly, if it: 174 * 175 * (1) assigns its initial sequence number for the new 176 * connection to be larger than the largest sequence 177 * number it used on the previous connection incarnation, 178 * and 179 * 180 * (2) returns to TIME-WAIT state if the SYN turns out 181 * to be an old duplicate". 182 */ 183 184 if (!paws_reject && 185 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 186 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 187 /* In window segment, it may be only reset or bare ack. */ 188 189 if (th->rst) { 190 /* This is TIME_WAIT assassination, in two flavors. 191 * Oh well... nobody has a sufficient solution to this 192 * protocol bug yet. 193 */ 194 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 195 kill: 196 inet_twsk_deschedule_put(tw); 197 return TCP_TW_SUCCESS; 198 } 199 } else { 200 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 201 } 202 203 if (tmp_opt.saw_tstamp) { 204 WRITE_ONCE(tcptw->tw_ts_recent, 205 tmp_opt.rcv_tsval); 206 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 207 ktime_get_seconds()); 208 } 209 210 inet_twsk_put(tw); 211 return TCP_TW_SUCCESS; 212 } 213 214 /* Out of window segment. 215 216 All the segments are ACKed immediately. 217 218 The only exception is new SYN. We accept it, if it is 219 not old duplicate and we are not in danger to be killed 220 by delayed old duplicates. RFC check is that it has 221 newer sequence number works at rates <40Mbit/sec. 222 However, if paws works, it is reliable AND even more, 223 we even may relax silly seq space cutoff. 224 225 RED-PEN: we violate main RFC requirement, if this SYN will appear 226 old duplicate (i.e. we receive RST in reply to SYN-ACK), 227 we must return socket to time-wait state. It is not good, 228 but not fatal yet. 229 */ 230 231 if (th->syn && !th->rst && !th->ack && !paws_reject && 232 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 233 (tmp_opt.saw_tstamp && 234 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) { 235 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 236 if (isn == 0) 237 isn++; 238 *tw_isn = isn; 239 return TCP_TW_SYN; 240 } 241 242 if (paws_reject) 243 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 244 245 if (!th->rst) { 246 /* In this case we must reset the TIMEWAIT timer. 247 * 248 * If it is ACKless SYN it may be both old duplicate 249 * and new good SYN with random sequence number <rcv_nxt. 250 * Do not reschedule in the last case. 251 */ 252 if (paws_reject || th->ack) 253 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 254 255 return tcp_timewait_check_oow_rate_limit( 256 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 257 } 258 inet_twsk_put(tw); 259 return TCP_TW_SUCCESS; 260 } 261 EXPORT_SYMBOL(tcp_timewait_state_process); 262 263 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 264 { 265 #ifdef CONFIG_TCP_MD5SIG 266 const struct tcp_sock *tp = tcp_sk(sk); 267 struct tcp_md5sig_key *key; 268 269 /* 270 * The timewait bucket does not have the key DB from the 271 * sock structure. We just make a quick copy of the 272 * md5 key being used (if indeed we are using one) 273 * so the timewait ack generating code has the key. 274 */ 275 tcptw->tw_md5_key = NULL; 276 if (!static_branch_unlikely(&tcp_md5_needed.key)) 277 return; 278 279 key = tp->af_specific->md5_lookup(sk, sk); 280 if (key) { 281 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 282 if (!tcptw->tw_md5_key) 283 return; 284 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 285 goto out_free; 286 tcp_md5_add_sigpool(); 287 } 288 return; 289 out_free: 290 WARN_ON_ONCE(1); 291 kfree(tcptw->tw_md5_key); 292 tcptw->tw_md5_key = NULL; 293 #endif 294 } 295 296 /* 297 * Move a socket to time-wait or dead fin-wait-2 state. 298 */ 299 void tcp_time_wait(struct sock *sk, int state, int timeo) 300 { 301 const struct inet_connection_sock *icsk = inet_csk(sk); 302 struct tcp_sock *tp = tcp_sk(sk); 303 struct net *net = sock_net(sk); 304 struct inet_timewait_sock *tw; 305 306 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 307 308 if (tw) { 309 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 310 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 311 312 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 313 tw->tw_mark = sk->sk_mark; 314 tw->tw_priority = READ_ONCE(sk->sk_priority); 315 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 316 tcptw->tw_rcv_nxt = tp->rcv_nxt; 317 tcptw->tw_snd_nxt = tp->snd_nxt; 318 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 319 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 320 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 321 tcptw->tw_ts_offset = tp->tsoffset; 322 tw->tw_usec_ts = tp->tcp_usec_ts; 323 tcptw->tw_last_oow_ack_time = 0; 324 tcptw->tw_tx_delay = tp->tcp_tx_delay; 325 tw->tw_txhash = sk->sk_txhash; 326 #if IS_ENABLED(CONFIG_IPV6) 327 if (tw->tw_family == PF_INET6) { 328 struct ipv6_pinfo *np = inet6_sk(sk); 329 330 tw->tw_v6_daddr = sk->sk_v6_daddr; 331 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 332 tw->tw_tclass = np->tclass; 333 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 334 tw->tw_ipv6only = sk->sk_ipv6only; 335 } 336 #endif 337 338 tcp_time_wait_init(sk, tcptw); 339 tcp_ao_time_wait(tcptw, tp); 340 341 /* Get the TIME_WAIT timeout firing. */ 342 if (timeo < rto) 343 timeo = rto; 344 345 if (state == TCP_TIME_WAIT) 346 timeo = TCP_TIMEWAIT_LEN; 347 348 /* Linkage updates. 349 * Note that access to tw after this point is illegal. 350 */ 351 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 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) 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); 400 } else if (!purged_once) { 401 inet_twsk_purge(&tcp_hashinfo); 402 purged_once = true; 403 } 404 } 405 } 406 407 /* Warning : This function is called without sk_listener being locked. 408 * Be sure to read socket fields once, as their value could change under us. 409 */ 410 void tcp_openreq_init_rwin(struct request_sock *req, 411 const struct sock *sk_listener, 412 const struct dst_entry *dst) 413 { 414 struct inet_request_sock *ireq = inet_rsk(req); 415 const struct tcp_sock *tp = tcp_sk(sk_listener); 416 int full_space = tcp_full_space(sk_listener); 417 u32 window_clamp; 418 __u8 rcv_wscale; 419 u32 rcv_wnd; 420 int mss; 421 422 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 423 window_clamp = READ_ONCE(tp->window_clamp); 424 /* Set this up on the first call only */ 425 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 426 427 /* limit the window selection if the user enforce a smaller rx buffer */ 428 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 429 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 430 req->rsk_window_clamp = full_space; 431 432 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 433 if (rcv_wnd == 0) 434 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 435 else if (full_space < rcv_wnd * mss) 436 full_space = rcv_wnd * mss; 437 438 /* tcp_full_space because it is guaranteed to be the first packet */ 439 tcp_select_initial_window(sk_listener, full_space, 440 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 441 &req->rsk_rcv_wnd, 442 &req->rsk_window_clamp, 443 ireq->wscale_ok, 444 &rcv_wscale, 445 rcv_wnd); 446 ireq->rcv_wscale = rcv_wscale; 447 } 448 EXPORT_SYMBOL(tcp_openreq_init_rwin); 449 450 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 451 const struct request_sock *req) 452 { 453 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 454 } 455 456 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 457 { 458 struct inet_connection_sock *icsk = inet_csk(sk); 459 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 460 bool ca_got_dst = false; 461 462 if (ca_key != TCP_CA_UNSPEC) { 463 const struct tcp_congestion_ops *ca; 464 465 rcu_read_lock(); 466 ca = tcp_ca_find_key(ca_key); 467 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 468 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 469 icsk->icsk_ca_ops = ca; 470 ca_got_dst = true; 471 } 472 rcu_read_unlock(); 473 } 474 475 /* If no valid choice made yet, assign current system default ca. */ 476 if (!ca_got_dst && 477 (!icsk->icsk_ca_setsockopt || 478 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 479 tcp_assign_congestion_control(sk); 480 481 tcp_set_ca_state(sk, TCP_CA_Open); 482 } 483 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 484 485 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 486 struct request_sock *req, 487 struct tcp_sock *newtp) 488 { 489 #if IS_ENABLED(CONFIG_SMC) 490 struct inet_request_sock *ireq; 491 492 if (static_branch_unlikely(&tcp_have_smc)) { 493 ireq = inet_rsk(req); 494 if (oldtp->syn_smc && !ireq->smc_ok) 495 newtp->syn_smc = 0; 496 } 497 #endif 498 } 499 500 /* This is not only more efficient than what we used to do, it eliminates 501 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 502 * 503 * Actually, we could lots of memory writes here. tp of listening 504 * socket contains all necessary default parameters. 505 */ 506 struct sock *tcp_create_openreq_child(const struct sock *sk, 507 struct request_sock *req, 508 struct sk_buff *skb) 509 { 510 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 511 const struct inet_request_sock *ireq = inet_rsk(req); 512 struct tcp_request_sock *treq = tcp_rsk(req); 513 struct inet_connection_sock *newicsk; 514 const struct tcp_sock *oldtp; 515 struct tcp_sock *newtp; 516 u32 seq; 517 518 if (!newsk) 519 return NULL; 520 521 newicsk = inet_csk(newsk); 522 newtp = tcp_sk(newsk); 523 oldtp = tcp_sk(sk); 524 525 smc_check_reset_syn_req(oldtp, req, newtp); 526 527 /* Now setup tcp_sock */ 528 newtp->pred_flags = 0; 529 530 seq = treq->rcv_isn + 1; 531 newtp->rcv_wup = seq; 532 WRITE_ONCE(newtp->copied_seq, seq); 533 WRITE_ONCE(newtp->rcv_nxt, seq); 534 newtp->segs_in = 1; 535 536 seq = treq->snt_isn + 1; 537 newtp->snd_sml = newtp->snd_una = seq; 538 WRITE_ONCE(newtp->snd_nxt, seq); 539 newtp->snd_up = seq; 540 541 INIT_LIST_HEAD(&newtp->tsq_node); 542 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 543 544 tcp_init_wl(newtp, treq->rcv_isn); 545 546 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 547 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 548 549 newtp->lsndtime = tcp_jiffies32; 550 newsk->sk_txhash = READ_ONCE(treq->txhash); 551 newtp->total_retrans = req->num_retrans; 552 553 tcp_init_xmit_timers(newsk); 554 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 555 556 if (sock_flag(newsk, SOCK_KEEPOPEN)) 557 inet_csk_reset_keepalive_timer(newsk, 558 keepalive_time_when(newtp)); 559 560 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 561 newtp->rx_opt.sack_ok = ireq->sack_ok; 562 newtp->window_clamp = req->rsk_window_clamp; 563 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 564 newtp->rcv_wnd = req->rsk_rcv_wnd; 565 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 566 if (newtp->rx_opt.wscale_ok) { 567 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 568 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 569 } else { 570 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 571 newtp->window_clamp = min(newtp->window_clamp, 65535U); 572 } 573 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 574 newtp->max_window = newtp->snd_wnd; 575 576 if (newtp->rx_opt.tstamp_ok) { 577 newtp->tcp_usec_ts = treq->req_usec_ts; 578 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 579 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 580 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 581 } else { 582 newtp->tcp_usec_ts = 0; 583 newtp->rx_opt.ts_recent_stamp = 0; 584 newtp->tcp_header_len = sizeof(struct tcphdr); 585 } 586 if (req->num_timeout) { 587 newtp->total_rto = req->num_timeout; 588 newtp->undo_marker = treq->snt_isn; 589 if (newtp->tcp_usec_ts) { 590 newtp->retrans_stamp = treq->snt_synack; 591 newtp->total_rto_time = (u32)(tcp_clock_us() - 592 newtp->retrans_stamp) / USEC_PER_MSEC; 593 } else { 594 newtp->retrans_stamp = div_u64(treq->snt_synack, 595 USEC_PER_SEC / TCP_TS_HZ); 596 newtp->total_rto_time = tcp_clock_ms() - 597 newtp->retrans_stamp; 598 } 599 newtp->total_rto_recoveries = 1; 600 } 601 newtp->tsoffset = treq->ts_off; 602 #ifdef CONFIG_TCP_MD5SIG 603 newtp->md5sig_info = NULL; /*XXX*/ 604 #endif 605 #ifdef CONFIG_TCP_AO 606 newtp->ao_info = NULL; 607 608 if (tcp_rsk_used_ao(req)) { 609 struct tcp_ao_key *ao_key; 610 611 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 612 if (ao_key) 613 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 614 } 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, 787 TCP_SKB_CB(skb)->end_seq, 788 tcp_rsk(req)->rcv_nxt, 789 tcp_rsk(req)->rcv_nxt + 790 tcp_synack_window(req))) { 791 /* Out of window: send ACK and drop. */ 792 if (!(flg & TCP_FLAG_RST) && 793 !tcp_oow_rate_limited(sock_net(sk), skb, 794 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 795 &tcp_rsk(req)->last_oow_ack_time)) 796 req->rsk_ops->send_ack(sk, skb, req); 797 if (paws_reject) 798 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 799 return NULL; 800 } 801 802 /* In sequence, PAWS is OK. */ 803 804 /* TODO: We probably should defer ts_recent change once 805 * we take ownership of @req. 806 */ 807 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 808 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 809 810 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 811 /* Truncate SYN, it is out of window starting 812 at tcp_rsk(req)->rcv_isn + 1. */ 813 flg &= ~TCP_FLAG_SYN; 814 } 815 816 /* RFC793: "second check the RST bit" and 817 * "fourth, check the SYN bit" 818 */ 819 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 820 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 821 goto embryonic_reset; 822 } 823 824 /* ACK sequence verified above, just make sure ACK is 825 * set. If ACK not set, just silently drop the packet. 826 * 827 * XXX (TFO) - if we ever allow "data after SYN", the 828 * following check needs to be removed. 829 */ 830 if (!(flg & TCP_FLAG_ACK)) 831 return NULL; 832 833 /* For Fast Open no more processing is needed (sk is the 834 * child socket). 835 */ 836 if (fastopen) 837 return sk; 838 839 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 840 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 841 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 842 inet_rsk(req)->acked = 1; 843 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 844 return NULL; 845 } 846 847 /* OK, ACK is valid, create big socket and 848 * feed this segment to it. It will repeat all 849 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 850 * ESTABLISHED STATE. If it will be dropped after 851 * socket is created, wait for troubles. 852 */ 853 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 854 req, &own_req); 855 if (!child) 856 goto listen_overflow; 857 858 if (own_req && rsk_drop_req(req)) { 859 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 860 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 861 return child; 862 } 863 864 sock_rps_save_rxhash(child, skb); 865 tcp_synack_rtt_meas(child, req); 866 *req_stolen = !own_req; 867 return inet_csk_complete_hashdance(sk, child, req, own_req); 868 869 listen_overflow: 870 if (sk != req->rsk_listener) 871 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 872 873 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 874 inet_rsk(req)->acked = 1; 875 return NULL; 876 } 877 878 embryonic_reset: 879 if (!(flg & TCP_FLAG_RST)) { 880 /* Received a bad SYN pkt - for TFO We try not to reset 881 * the local connection unless it's really necessary to 882 * avoid becoming vulnerable to outside attack aiming at 883 * resetting legit local connections. 884 */ 885 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 886 } else if (fastopen) { /* received a valid RST pkt */ 887 reqsk_fastopen_remove(sk, req, true); 888 tcp_reset(sk, skb); 889 } 890 if (!fastopen) { 891 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 892 893 if (unlinked) 894 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 895 *req_stolen = !unlinked; 896 } 897 return NULL; 898 } 899 EXPORT_SYMBOL(tcp_check_req); 900 901 /* 902 * Queue segment on the new socket if the new socket is active, 903 * otherwise we just shortcircuit this and continue with 904 * the new socket. 905 * 906 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 907 * when entering. But other states are possible due to a race condition 908 * where after __inet_lookup_established() fails but before the listener 909 * locked is obtained, other packets cause the same connection to 910 * be created. 911 */ 912 913 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 914 struct sk_buff *skb) 915 __releases(&((child)->sk_lock.slock)) 916 { 917 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 918 int state = child->sk_state; 919 920 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 921 sk_mark_napi_id_set(child, skb); 922 923 tcp_segs_in(tcp_sk(child), skb); 924 if (!sock_owned_by_user(child)) { 925 reason = tcp_rcv_state_process(child, skb); 926 /* Wakeup parent, send SIGIO */ 927 if (state == TCP_SYN_RECV && child->sk_state != state) 928 parent->sk_data_ready(parent); 929 } else { 930 /* Alas, it is possible again, because we do lookup 931 * in main socket hash table and lock on listening 932 * socket does not protect us more. 933 */ 934 __sk_add_backlog(child, skb); 935 } 936 937 bh_unlock_sock(child); 938 sock_put(child); 939 return reason; 940 } 941 EXPORT_SYMBOL(tcp_child_process); 942