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 /* 55 * * Main purpose of TIME-WAIT state is to close connection gracefully, 56 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 57 * (and, probably, tail of data) and one or more our ACKs are lost. 58 * * What is TIME-WAIT timeout? It is associated with maximal packet 59 * lifetime in the internet, which results in wrong conclusion, that 60 * it is set to catch "old duplicate segments" wandering out of their path. 61 * It is not quite correct. This timeout is calculated so that it exceeds 62 * maximal retransmission timeout enough to allow to lose one (or more) 63 * segments sent by peer and our ACKs. This time may be calculated from RTO. 64 * * When TIME-WAIT socket receives RST, it means that another end 65 * finally closed and we are allowed to kill TIME-WAIT too. 66 * * Second purpose of TIME-WAIT is catching old duplicate segments. 67 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 68 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 69 * * If we invented some more clever way to catch duplicates 70 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 71 * 72 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 73 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 74 * from the very beginning. 75 * 76 * NOTE. With recycling (and later with fin-wait-2) TW bucket 77 * is _not_ stateless. It means, that strictly speaking we must 78 * spinlock it. I do not want! Well, probability of misbehaviour 79 * is ridiculously low and, seems, we could use some mb() tricks 80 * to avoid misread sequence numbers, states etc. --ANK 81 * 82 * We don't need to initialize tmp_out.sack_ok as we don't use the results 83 */ 84 enum tcp_tw_status 85 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 86 const struct tcphdr *th) 87 { 88 struct tcp_options_received tmp_opt; 89 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 90 bool paws_reject = false; 91 92 tmp_opt.saw_tstamp = 0; 93 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 94 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 95 96 if (tmp_opt.saw_tstamp) { 97 if (tmp_opt.rcv_tsecr) 98 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 99 tmp_opt.ts_recent = tcptw->tw_ts_recent; 100 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 101 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 102 } 103 } 104 105 if (tw->tw_substate == TCP_FIN_WAIT2) { 106 /* Just repeat all the checks of tcp_rcv_state_process() */ 107 108 /* Out of window, send ACK */ 109 if (paws_reject || 110 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 111 tcptw->tw_rcv_nxt, 112 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 113 return tcp_timewait_check_oow_rate_limit( 114 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 115 116 if (th->rst) 117 goto kill; 118 119 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 120 return TCP_TW_RST; 121 122 /* Dup ACK? */ 123 if (!th->ack || 124 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 125 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 126 inet_twsk_put(tw); 127 return TCP_TW_SUCCESS; 128 } 129 130 /* New data or FIN. If new data arrive after half-duplex close, 131 * reset. 132 */ 133 if (!th->fin || 134 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 135 return TCP_TW_RST; 136 137 /* FIN arrived, enter true time-wait state. */ 138 tw->tw_substate = TCP_TIME_WAIT; 139 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; 140 if (tmp_opt.saw_tstamp) { 141 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 142 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 143 } 144 145 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 146 return TCP_TW_ACK; 147 } 148 149 /* 150 * Now real TIME-WAIT state. 151 * 152 * RFC 1122: 153 * "When a connection is [...] on TIME-WAIT state [...] 154 * [a TCP] MAY accept a new SYN from the remote TCP to 155 * reopen the connection directly, if it: 156 * 157 * (1) assigns its initial sequence number for the new 158 * connection to be larger than the largest sequence 159 * number it used on the previous connection incarnation, 160 * and 161 * 162 * (2) returns to TIME-WAIT state if the SYN turns out 163 * to be an old duplicate". 164 */ 165 166 if (!paws_reject && 167 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 168 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 169 /* In window segment, it may be only reset or bare ack. */ 170 171 if (th->rst) { 172 /* This is TIME_WAIT assassination, in two flavors. 173 * Oh well... nobody has a sufficient solution to this 174 * protocol bug yet. 175 */ 176 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 177 kill: 178 inet_twsk_deschedule_put(tw); 179 return TCP_TW_SUCCESS; 180 } 181 } else { 182 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 183 } 184 185 if (tmp_opt.saw_tstamp) { 186 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 187 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 188 } 189 190 inet_twsk_put(tw); 191 return TCP_TW_SUCCESS; 192 } 193 194 /* Out of window segment. 195 196 All the segments are ACKed immediately. 197 198 The only exception is new SYN. We accept it, if it is 199 not old duplicate and we are not in danger to be killed 200 by delayed old duplicates. RFC check is that it has 201 newer sequence number works at rates <40Mbit/sec. 202 However, if paws works, it is reliable AND even more, 203 we even may relax silly seq space cutoff. 204 205 RED-PEN: we violate main RFC requirement, if this SYN will appear 206 old duplicate (i.e. we receive RST in reply to SYN-ACK), 207 we must return socket to time-wait state. It is not good, 208 but not fatal yet. 209 */ 210 211 if (th->syn && !th->rst && !th->ack && !paws_reject && 212 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 213 (tmp_opt.saw_tstamp && 214 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 215 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 216 if (isn == 0) 217 isn++; 218 TCP_SKB_CB(skb)->tcp_tw_isn = isn; 219 return TCP_TW_SYN; 220 } 221 222 if (paws_reject) 223 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 224 225 if (!th->rst) { 226 /* In this case we must reset the TIMEWAIT timer. 227 * 228 * If it is ACKless SYN it may be both old duplicate 229 * and new good SYN with random sequence number <rcv_nxt. 230 * Do not reschedule in the last case. 231 */ 232 if (paws_reject || th->ack) 233 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 234 235 return tcp_timewait_check_oow_rate_limit( 236 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 237 } 238 inet_twsk_put(tw); 239 return TCP_TW_SUCCESS; 240 } 241 EXPORT_SYMBOL(tcp_timewait_state_process); 242 243 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 244 { 245 #ifdef CONFIG_TCP_MD5SIG 246 const struct tcp_sock *tp = tcp_sk(sk); 247 struct tcp_md5sig_key *key; 248 249 /* 250 * The timewait bucket does not have the key DB from the 251 * sock structure. We just make a quick copy of the 252 * md5 key being used (if indeed we are using one) 253 * so the timewait ack generating code has the key. 254 */ 255 tcptw->tw_md5_key = NULL; 256 if (!static_branch_unlikely(&tcp_md5_needed.key)) 257 return; 258 259 key = tp->af_specific->md5_lookup(sk, sk); 260 if (key) { 261 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 262 if (!tcptw->tw_md5_key) 263 return; 264 if (!tcp_alloc_md5sig_pool()) 265 goto out_free; 266 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 267 goto out_free; 268 } 269 return; 270 out_free: 271 WARN_ON_ONCE(1); 272 kfree(tcptw->tw_md5_key); 273 tcptw->tw_md5_key = NULL; 274 #endif 275 } 276 277 /* 278 * Move a socket to time-wait or dead fin-wait-2 state. 279 */ 280 void tcp_time_wait(struct sock *sk, int state, int timeo) 281 { 282 const struct inet_connection_sock *icsk = inet_csk(sk); 283 const struct tcp_sock *tp = tcp_sk(sk); 284 struct net *net = sock_net(sk); 285 struct inet_timewait_sock *tw; 286 287 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 288 289 if (tw) { 290 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 291 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 292 293 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 294 tw->tw_mark = sk->sk_mark; 295 tw->tw_priority = sk->sk_priority; 296 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 297 tcptw->tw_rcv_nxt = tp->rcv_nxt; 298 tcptw->tw_snd_nxt = tp->snd_nxt; 299 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 300 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 301 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 302 tcptw->tw_ts_offset = tp->tsoffset; 303 tcptw->tw_last_oow_ack_time = 0; 304 tcptw->tw_tx_delay = tp->tcp_tx_delay; 305 tw->tw_txhash = sk->sk_txhash; 306 #if IS_ENABLED(CONFIG_IPV6) 307 if (tw->tw_family == PF_INET6) { 308 struct ipv6_pinfo *np = inet6_sk(sk); 309 310 tw->tw_v6_daddr = sk->sk_v6_daddr; 311 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 312 tw->tw_tclass = np->tclass; 313 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 314 tw->tw_ipv6only = sk->sk_ipv6only; 315 } 316 #endif 317 318 tcp_time_wait_init(sk, tcptw); 319 320 /* Get the TIME_WAIT timeout firing. */ 321 if (timeo < rto) 322 timeo = rto; 323 324 if (state == TCP_TIME_WAIT) 325 timeo = TCP_TIMEWAIT_LEN; 326 327 /* tw_timer is pinned, so we need to make sure BH are disabled 328 * in following section, otherwise timer handler could run before 329 * we complete the initialization. 330 */ 331 local_bh_disable(); 332 inet_twsk_schedule(tw, timeo); 333 /* Linkage updates. 334 * Note that access to tw after this point is illegal. 335 */ 336 inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); 337 local_bh_enable(); 338 } else { 339 /* Sorry, if we're out of memory, just CLOSE this 340 * socket up. We've got bigger problems than 341 * non-graceful socket closings. 342 */ 343 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 344 } 345 346 tcp_update_metrics(sk); 347 tcp_done(sk); 348 } 349 EXPORT_SYMBOL(tcp_time_wait); 350 351 void tcp_twsk_destructor(struct sock *sk) 352 { 353 #ifdef CONFIG_TCP_MD5SIG 354 if (static_branch_unlikely(&tcp_md5_needed.key)) { 355 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 356 357 if (twsk->tw_md5_key) { 358 kfree_rcu(twsk->tw_md5_key, rcu); 359 static_branch_slow_dec_deferred(&tcp_md5_needed); 360 } 361 } 362 #endif 363 } 364 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 365 366 void tcp_twsk_purge(struct list_head *net_exit_list, int family) 367 { 368 bool purged_once = false; 369 struct net *net; 370 371 list_for_each_entry(net, net_exit_list, exit_list) { 372 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 373 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 374 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family); 375 } else if (!purged_once) { 376 /* The last refcount is decremented in tcp_sk_exit_batch() */ 377 if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) 378 continue; 379 380 inet_twsk_purge(&tcp_hashinfo, family); 381 purged_once = true; 382 } 383 } 384 } 385 EXPORT_SYMBOL_GPL(tcp_twsk_purge); 386 387 /* Warning : This function is called without sk_listener being locked. 388 * Be sure to read socket fields once, as their value could change under us. 389 */ 390 void tcp_openreq_init_rwin(struct request_sock *req, 391 const struct sock *sk_listener, 392 const struct dst_entry *dst) 393 { 394 struct inet_request_sock *ireq = inet_rsk(req); 395 const struct tcp_sock *tp = tcp_sk(sk_listener); 396 int full_space = tcp_full_space(sk_listener); 397 u32 window_clamp; 398 __u8 rcv_wscale; 399 u32 rcv_wnd; 400 int mss; 401 402 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 403 window_clamp = READ_ONCE(tp->window_clamp); 404 /* Set this up on the first call only */ 405 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 406 407 /* limit the window selection if the user enforce a smaller rx buffer */ 408 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 409 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 410 req->rsk_window_clamp = full_space; 411 412 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 413 if (rcv_wnd == 0) 414 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 415 else if (full_space < rcv_wnd * mss) 416 full_space = rcv_wnd * mss; 417 418 /* tcp_full_space because it is guaranteed to be the first packet */ 419 tcp_select_initial_window(sk_listener, full_space, 420 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 421 &req->rsk_rcv_wnd, 422 &req->rsk_window_clamp, 423 ireq->wscale_ok, 424 &rcv_wscale, 425 rcv_wnd); 426 ireq->rcv_wscale = rcv_wscale; 427 } 428 EXPORT_SYMBOL(tcp_openreq_init_rwin); 429 430 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 431 const struct request_sock *req) 432 { 433 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 434 } 435 436 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 437 { 438 struct inet_connection_sock *icsk = inet_csk(sk); 439 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 440 bool ca_got_dst = false; 441 442 if (ca_key != TCP_CA_UNSPEC) { 443 const struct tcp_congestion_ops *ca; 444 445 rcu_read_lock(); 446 ca = tcp_ca_find_key(ca_key); 447 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 448 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 449 icsk->icsk_ca_ops = ca; 450 ca_got_dst = true; 451 } 452 rcu_read_unlock(); 453 } 454 455 /* If no valid choice made yet, assign current system default ca. */ 456 if (!ca_got_dst && 457 (!icsk->icsk_ca_setsockopt || 458 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 459 tcp_assign_congestion_control(sk); 460 461 tcp_set_ca_state(sk, TCP_CA_Open); 462 } 463 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 464 465 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 466 struct request_sock *req, 467 struct tcp_sock *newtp) 468 { 469 #if IS_ENABLED(CONFIG_SMC) 470 struct inet_request_sock *ireq; 471 472 if (static_branch_unlikely(&tcp_have_smc)) { 473 ireq = inet_rsk(req); 474 if (oldtp->syn_smc && !ireq->smc_ok) 475 newtp->syn_smc = 0; 476 } 477 #endif 478 } 479 480 /* This is not only more efficient than what we used to do, it eliminates 481 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 482 * 483 * Actually, we could lots of memory writes here. tp of listening 484 * socket contains all necessary default parameters. 485 */ 486 struct sock *tcp_create_openreq_child(const struct sock *sk, 487 struct request_sock *req, 488 struct sk_buff *skb) 489 { 490 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 491 const struct inet_request_sock *ireq = inet_rsk(req); 492 struct tcp_request_sock *treq = tcp_rsk(req); 493 struct inet_connection_sock *newicsk; 494 const struct tcp_sock *oldtp; 495 struct tcp_sock *newtp; 496 u32 seq; 497 498 if (!newsk) 499 return NULL; 500 501 newicsk = inet_csk(newsk); 502 newtp = tcp_sk(newsk); 503 oldtp = tcp_sk(sk); 504 505 smc_check_reset_syn_req(oldtp, req, newtp); 506 507 /* Now setup tcp_sock */ 508 newtp->pred_flags = 0; 509 510 seq = treq->rcv_isn + 1; 511 newtp->rcv_wup = seq; 512 WRITE_ONCE(newtp->copied_seq, seq); 513 WRITE_ONCE(newtp->rcv_nxt, seq); 514 newtp->segs_in = 1; 515 516 seq = treq->snt_isn + 1; 517 newtp->snd_sml = newtp->snd_una = seq; 518 WRITE_ONCE(newtp->snd_nxt, seq); 519 newtp->snd_up = seq; 520 521 INIT_LIST_HEAD(&newtp->tsq_node); 522 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 523 524 tcp_init_wl(newtp, treq->rcv_isn); 525 526 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 527 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 528 529 newtp->lsndtime = tcp_jiffies32; 530 newsk->sk_txhash = READ_ONCE(treq->txhash); 531 newtp->total_retrans = req->num_retrans; 532 533 tcp_init_xmit_timers(newsk); 534 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 535 536 if (sock_flag(newsk, SOCK_KEEPOPEN)) 537 inet_csk_reset_keepalive_timer(newsk, 538 keepalive_time_when(newtp)); 539 540 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 541 newtp->rx_opt.sack_ok = ireq->sack_ok; 542 newtp->window_clamp = req->rsk_window_clamp; 543 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 544 newtp->rcv_wnd = req->rsk_rcv_wnd; 545 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 546 if (newtp->rx_opt.wscale_ok) { 547 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 548 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 549 } else { 550 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 551 newtp->window_clamp = min(newtp->window_clamp, 65535U); 552 } 553 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 554 newtp->max_window = newtp->snd_wnd; 555 556 if (newtp->rx_opt.tstamp_ok) { 557 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 558 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 559 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 560 } else { 561 newtp->rx_opt.ts_recent_stamp = 0; 562 newtp->tcp_header_len = sizeof(struct tcphdr); 563 } 564 if (req->num_timeout) { 565 newtp->undo_marker = treq->snt_isn; 566 newtp->retrans_stamp = div_u64(treq->snt_synack, 567 USEC_PER_SEC / TCP_TS_HZ); 568 } 569 newtp->tsoffset = treq->ts_off; 570 #ifdef CONFIG_TCP_MD5SIG 571 newtp->md5sig_info = NULL; /*XXX*/ 572 #endif 573 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 574 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 575 newtp->rx_opt.mss_clamp = req->mss; 576 tcp_ecn_openreq_child(newtp, req); 577 newtp->fastopen_req = NULL; 578 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 579 580 newtp->bpf_chg_cc_inprogress = 0; 581 tcp_bpf_clone(sk, newsk); 582 583 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 584 585 return newsk; 586 } 587 EXPORT_SYMBOL(tcp_create_openreq_child); 588 589 /* 590 * Process an incoming packet for SYN_RECV sockets represented as a 591 * request_sock. Normally sk is the listener socket but for TFO it 592 * points to the child socket. 593 * 594 * XXX (TFO) - The current impl contains a special check for ack 595 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 596 * 597 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 598 * 599 * Note: If @fastopen is true, this can be called from process context. 600 * Otherwise, this is from BH context. 601 */ 602 603 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 604 struct request_sock *req, 605 bool fastopen, bool *req_stolen) 606 { 607 struct tcp_options_received tmp_opt; 608 struct sock *child; 609 const struct tcphdr *th = tcp_hdr(skb); 610 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 611 bool paws_reject = false; 612 bool own_req; 613 614 tmp_opt.saw_tstamp = 0; 615 if (th->doff > (sizeof(struct tcphdr)>>2)) { 616 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 617 618 if (tmp_opt.saw_tstamp) { 619 tmp_opt.ts_recent = READ_ONCE(req->ts_recent); 620 if (tmp_opt.rcv_tsecr) 621 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 622 /* We do not store true stamp, but it is not required, 623 * it can be estimated (approximately) 624 * from another data. 625 */ 626 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 627 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 628 } 629 } 630 631 /* Check for pure retransmitted SYN. */ 632 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 633 flg == TCP_FLAG_SYN && 634 !paws_reject) { 635 /* 636 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 637 * this case on figure 6 and figure 8, but formal 638 * protocol description says NOTHING. 639 * To be more exact, it says that we should send ACK, 640 * because this segment (at least, if it has no data) 641 * is out of window. 642 * 643 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 644 * describe SYN-RECV state. All the description 645 * is wrong, we cannot believe to it and should 646 * rely only on common sense and implementation 647 * experience. 648 * 649 * Enforce "SYN-ACK" according to figure 8, figure 6 650 * of RFC793, fixed by RFC1122. 651 * 652 * Note that even if there is new data in the SYN packet 653 * they will be thrown away too. 654 * 655 * Reset timer after retransmitting SYNACK, similar to 656 * the idea of fast retransmit in recovery. 657 */ 658 if (!tcp_oow_rate_limited(sock_net(sk), skb, 659 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 660 &tcp_rsk(req)->last_oow_ack_time) && 661 662 !inet_rtx_syn_ack(sk, req)) { 663 unsigned long expires = jiffies; 664 665 expires += reqsk_timeout(req, TCP_RTO_MAX); 666 if (!fastopen) 667 mod_timer_pending(&req->rsk_timer, expires); 668 else 669 req->rsk_timer.expires = expires; 670 } 671 return NULL; 672 } 673 674 /* Further reproduces section "SEGMENT ARRIVES" 675 for state SYN-RECEIVED of RFC793. 676 It is broken, however, it does not work only 677 when SYNs are crossed. 678 679 You would think that SYN crossing is impossible here, since 680 we should have a SYN_SENT socket (from connect()) on our end, 681 but this is not true if the crossed SYNs were sent to both 682 ends by a malicious third party. We must defend against this, 683 and to do that we first verify the ACK (as per RFC793, page 684 36) and reset if it is invalid. Is this a true full defense? 685 To convince ourselves, let us consider a way in which the ACK 686 test can still pass in this 'malicious crossed SYNs' case. 687 Malicious sender sends identical SYNs (and thus identical sequence 688 numbers) to both A and B: 689 690 A: gets SYN, seq=7 691 B: gets SYN, seq=7 692 693 By our good fortune, both A and B select the same initial 694 send sequence number of seven :-) 695 696 A: sends SYN|ACK, seq=7, ack_seq=8 697 B: sends SYN|ACK, seq=7, ack_seq=8 698 699 So we are now A eating this SYN|ACK, ACK test passes. So 700 does sequence test, SYN is truncated, and thus we consider 701 it a bare ACK. 702 703 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 704 bare ACK. Otherwise, we create an established connection. Both 705 ends (listening sockets) accept the new incoming connection and try 706 to talk to each other. 8-) 707 708 Note: This case is both harmless, and rare. Possibility is about the 709 same as us discovering intelligent life on another plant tomorrow. 710 711 But generally, we should (RFC lies!) to accept ACK 712 from SYNACK both here and in tcp_rcv_state_process(). 713 tcp_rcv_state_process() does not, hence, we do not too. 714 715 Note that the case is absolutely generic: 716 we cannot optimize anything here without 717 violating protocol. All the checks must be made 718 before attempt to create socket. 719 */ 720 721 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 722 * and the incoming segment acknowledges something not yet 723 * sent (the segment carries an unacceptable ACK) ... 724 * a reset is sent." 725 * 726 * Invalid ACK: reset will be sent by listening socket. 727 * Note that the ACK validity check for a Fast Open socket is done 728 * elsewhere and is checked directly against the child socket rather 729 * than req because user data may have been sent out. 730 */ 731 if ((flg & TCP_FLAG_ACK) && !fastopen && 732 (TCP_SKB_CB(skb)->ack_seq != 733 tcp_rsk(req)->snt_isn + 1)) 734 return sk; 735 736 /* Also, it would be not so bad idea to check rcv_tsecr, which 737 * is essentially ACK extension and too early or too late values 738 * should cause reset in unsynchronized states. 739 */ 740 741 /* RFC793: "first check sequence number". */ 742 743 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 744 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 745 /* Out of window: send ACK and drop. */ 746 if (!(flg & TCP_FLAG_RST) && 747 !tcp_oow_rate_limited(sock_net(sk), skb, 748 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 749 &tcp_rsk(req)->last_oow_ack_time)) 750 req->rsk_ops->send_ack(sk, skb, req); 751 if (paws_reject) 752 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 753 return NULL; 754 } 755 756 /* In sequence, PAWS is OK. */ 757 758 /* TODO: We probably should defer ts_recent change once 759 * we take ownership of @req. 760 */ 761 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 762 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 763 764 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 765 /* Truncate SYN, it is out of window starting 766 at tcp_rsk(req)->rcv_isn + 1. */ 767 flg &= ~TCP_FLAG_SYN; 768 } 769 770 /* RFC793: "second check the RST bit" and 771 * "fourth, check the SYN bit" 772 */ 773 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 774 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 775 goto embryonic_reset; 776 } 777 778 /* ACK sequence verified above, just make sure ACK is 779 * set. If ACK not set, just silently drop the packet. 780 * 781 * XXX (TFO) - if we ever allow "data after SYN", the 782 * following check needs to be removed. 783 */ 784 if (!(flg & TCP_FLAG_ACK)) 785 return NULL; 786 787 /* For Fast Open no more processing is needed (sk is the 788 * child socket). 789 */ 790 if (fastopen) 791 return sk; 792 793 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 794 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 795 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 796 inet_rsk(req)->acked = 1; 797 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 798 return NULL; 799 } 800 801 /* OK, ACK is valid, create big socket and 802 * feed this segment to it. It will repeat all 803 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 804 * ESTABLISHED STATE. If it will be dropped after 805 * socket is created, wait for troubles. 806 */ 807 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 808 req, &own_req); 809 if (!child) 810 goto listen_overflow; 811 812 if (own_req && rsk_drop_req(req)) { 813 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 814 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 815 return child; 816 } 817 818 sock_rps_save_rxhash(child, skb); 819 tcp_synack_rtt_meas(child, req); 820 *req_stolen = !own_req; 821 return inet_csk_complete_hashdance(sk, child, req, own_req); 822 823 listen_overflow: 824 if (sk != req->rsk_listener) 825 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 826 827 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 828 inet_rsk(req)->acked = 1; 829 return NULL; 830 } 831 832 embryonic_reset: 833 if (!(flg & TCP_FLAG_RST)) { 834 /* Received a bad SYN pkt - for TFO We try not to reset 835 * the local connection unless it's really necessary to 836 * avoid becoming vulnerable to outside attack aiming at 837 * resetting legit local connections. 838 */ 839 req->rsk_ops->send_reset(sk, skb); 840 } else if (fastopen) { /* received a valid RST pkt */ 841 reqsk_fastopen_remove(sk, req, true); 842 tcp_reset(sk, skb); 843 } 844 if (!fastopen) { 845 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 846 847 if (unlinked) 848 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 849 *req_stolen = !unlinked; 850 } 851 return NULL; 852 } 853 EXPORT_SYMBOL(tcp_check_req); 854 855 /* 856 * Queue segment on the new socket if the new socket is active, 857 * otherwise we just shortcircuit this and continue with 858 * the new socket. 859 * 860 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 861 * when entering. But other states are possible due to a race condition 862 * where after __inet_lookup_established() fails but before the listener 863 * locked is obtained, other packets cause the same connection to 864 * be created. 865 */ 866 867 int tcp_child_process(struct sock *parent, struct sock *child, 868 struct sk_buff *skb) 869 __releases(&((child)->sk_lock.slock)) 870 { 871 int ret = 0; 872 int state = child->sk_state; 873 874 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 875 sk_mark_napi_id_set(child, skb); 876 877 tcp_segs_in(tcp_sk(child), skb); 878 if (!sock_owned_by_user(child)) { 879 ret = tcp_rcv_state_process(child, skb); 880 /* Wakeup parent, send SIGIO */ 881 if (state == TCP_SYN_RECV && child->sk_state != state) 882 parent->sk_data_ready(parent); 883 } else { 884 /* Alas, it is possible again, because we do lookup 885 * in main socket hash table and lock on listening 886 * socket does not protect us more. 887 */ 888 __sk_add_backlog(child, skb); 889 } 890 891 bh_unlock_sock(child); 892 sock_put(child); 893 return ret; 894 } 895 EXPORT_SYMBOL(tcp_child_process); 896