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 26static 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 35static enum tcp_tw_status 36tcp_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 */ 84enum tcp_tw_status 85tcp_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)) { 177kill: 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} 241EXPORT_SYMBOL(tcp_timewait_state_process); 242 243static 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; 270out_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 */ 280void 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} 349EXPORT_SYMBOL(tcp_time_wait); 350 351void 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} 364EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 365 366void 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 inet_twsk_purge(&tcp_hashinfo, family); 377 purged_once = true; 378 } 379 } 380} 381EXPORT_SYMBOL_GPL(tcp_twsk_purge); 382 383/* Warning : This function is called without sk_listener being locked. 384 * Be sure to read socket fields once, as their value could change under us. 385 */ 386void tcp_openreq_init_rwin(struct request_sock *req, 387 const struct sock *sk_listener, 388 const struct dst_entry *dst) 389{ 390 struct inet_request_sock *ireq = inet_rsk(req); 391 const struct tcp_sock *tp = tcp_sk(sk_listener); 392 int full_space = tcp_full_space(sk_listener); 393 u32 window_clamp; 394 __u8 rcv_wscale; 395 u32 rcv_wnd; 396 int mss; 397 398 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 399 window_clamp = READ_ONCE(tp->window_clamp); 400 /* Set this up on the first call only */ 401 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 402 403 /* limit the window selection if the user enforce a smaller rx buffer */ 404 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 405 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 406 req->rsk_window_clamp = full_space; 407 408 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 409 if (rcv_wnd == 0) 410 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 411 else if (full_space < rcv_wnd * mss) 412 full_space = rcv_wnd * mss; 413 414 /* tcp_full_space because it is guaranteed to be the first packet */ 415 tcp_select_initial_window(sk_listener, full_space, 416 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 417 &req->rsk_rcv_wnd, 418 &req->rsk_window_clamp, 419 ireq->wscale_ok, 420 &rcv_wscale, 421 rcv_wnd); 422 ireq->rcv_wscale = rcv_wscale; 423} 424EXPORT_SYMBOL(tcp_openreq_init_rwin); 425 426static void tcp_ecn_openreq_child(struct tcp_sock *tp, 427 const struct request_sock *req) 428{ 429 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 430} 431 432void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 433{ 434 struct inet_connection_sock *icsk = inet_csk(sk); 435 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 436 bool ca_got_dst = false; 437 438 if (ca_key != TCP_CA_UNSPEC) { 439 const struct tcp_congestion_ops *ca; 440 441 rcu_read_lock(); 442 ca = tcp_ca_find_key(ca_key); 443 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 444 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 445 icsk->icsk_ca_ops = ca; 446 ca_got_dst = true; 447 } 448 rcu_read_unlock(); 449 } 450 451 /* If no valid choice made yet, assign current system default ca. */ 452 if (!ca_got_dst && 453 (!icsk->icsk_ca_setsockopt || 454 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 455 tcp_assign_congestion_control(sk); 456 457 tcp_set_ca_state(sk, TCP_CA_Open); 458} 459EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 460 461static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 462 struct request_sock *req, 463 struct tcp_sock *newtp) 464{ 465#if IS_ENABLED(CONFIG_SMC) 466 struct inet_request_sock *ireq; 467 468 if (static_branch_unlikely(&tcp_have_smc)) { 469 ireq = inet_rsk(req); 470 if (oldtp->syn_smc && !ireq->smc_ok) 471 newtp->syn_smc = 0; 472 } 473#endif 474} 475 476/* This is not only more efficient than what we used to do, it eliminates 477 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 478 * 479 * Actually, we could lots of memory writes here. tp of listening 480 * socket contains all necessary default parameters. 481 */ 482struct sock *tcp_create_openreq_child(const struct sock *sk, 483 struct request_sock *req, 484 struct sk_buff *skb) 485{ 486 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 487 const struct inet_request_sock *ireq = inet_rsk(req); 488 struct tcp_request_sock *treq = tcp_rsk(req); 489 struct inet_connection_sock *newicsk; 490 const struct tcp_sock *oldtp; 491 struct tcp_sock *newtp; 492 u32 seq; 493 494 if (!newsk) 495 return NULL; 496 497 newicsk = inet_csk(newsk); 498 newtp = tcp_sk(newsk); 499 oldtp = tcp_sk(sk); 500 501 smc_check_reset_syn_req(oldtp, req, newtp); 502 503 /* Now setup tcp_sock */ 504 newtp->pred_flags = 0; 505 506 seq = treq->rcv_isn + 1; 507 newtp->rcv_wup = seq; 508 WRITE_ONCE(newtp->copied_seq, seq); 509 WRITE_ONCE(newtp->rcv_nxt, seq); 510 newtp->segs_in = 1; 511 512 seq = treq->snt_isn + 1; 513 newtp->snd_sml = newtp->snd_una = seq; 514 WRITE_ONCE(newtp->snd_nxt, seq); 515 newtp->snd_up = seq; 516 517 INIT_LIST_HEAD(&newtp->tsq_node); 518 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 519 520 tcp_init_wl(newtp, treq->rcv_isn); 521 522 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 523 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 524 525 newtp->lsndtime = tcp_jiffies32; 526 newsk->sk_txhash = READ_ONCE(treq->txhash); 527 newtp->total_retrans = req->num_retrans; 528 529 tcp_init_xmit_timers(newsk); 530 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 531 532 if (sock_flag(newsk, SOCK_KEEPOPEN)) 533 inet_csk_reset_keepalive_timer(newsk, 534 keepalive_time_when(newtp)); 535 536 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 537 newtp->rx_opt.sack_ok = ireq->sack_ok; 538 newtp->window_clamp = req->rsk_window_clamp; 539 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 540 newtp->rcv_wnd = req->rsk_rcv_wnd; 541 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 542 if (newtp->rx_opt.wscale_ok) { 543 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 544 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 545 } else { 546 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 547 newtp->window_clamp = min(newtp->window_clamp, 65535U); 548 } 549 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 550 newtp->max_window = newtp->snd_wnd; 551 552 if (newtp->rx_opt.tstamp_ok) { 553 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 554 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 555 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 556 } else { 557 newtp->rx_opt.ts_recent_stamp = 0; 558 newtp->tcp_header_len = sizeof(struct tcphdr); 559 } 560 if (req->num_timeout) { 561 newtp->undo_marker = treq->snt_isn; 562 newtp->retrans_stamp = div_u64(treq->snt_synack, 563 USEC_PER_SEC / TCP_TS_HZ); 564 } 565 newtp->tsoffset = treq->ts_off; 566#ifdef CONFIG_TCP_MD5SIG 567 newtp->md5sig_info = NULL; /*XXX*/ 568#endif 569 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 570 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 571 newtp->rx_opt.mss_clamp = req->mss; 572 tcp_ecn_openreq_child(newtp, req); 573 newtp->fastopen_req = NULL; 574 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 575 576 newtp->bpf_chg_cc_inprogress = 0; 577 tcp_bpf_clone(sk, newsk); 578 579 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 580 581 return newsk; 582} 583EXPORT_SYMBOL(tcp_create_openreq_child); 584 585/* 586 * Process an incoming packet for SYN_RECV sockets represented as a 587 * request_sock. Normally sk is the listener socket but for TFO it 588 * points to the child socket. 589 * 590 * XXX (TFO) - The current impl contains a special check for ack 591 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 592 * 593 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 594 * 595 * Note: If @fastopen is true, this can be called from process context. 596 * Otherwise, this is from BH context. 597 */ 598 599struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 600 struct request_sock *req, 601 bool fastopen, bool *req_stolen) 602{ 603 struct tcp_options_received tmp_opt; 604 struct sock *child; 605 const struct tcphdr *th = tcp_hdr(skb); 606 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 607 bool paws_reject = false; 608 bool own_req; 609 610 tmp_opt.saw_tstamp = 0; 611 if (th->doff > (sizeof(struct tcphdr)>>2)) { 612 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 613 614 if (tmp_opt.saw_tstamp) { 615 tmp_opt.ts_recent = READ_ONCE(req->ts_recent); 616 if (tmp_opt.rcv_tsecr) 617 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 618 /* We do not store true stamp, but it is not required, 619 * it can be estimated (approximately) 620 * from another data. 621 */ 622 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 623 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 624 } 625 } 626 627 /* Check for pure retransmitted SYN. */ 628 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 629 flg == TCP_FLAG_SYN && 630 !paws_reject) { 631 /* 632 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 633 * this case on figure 6 and figure 8, but formal 634 * protocol description says NOTHING. 635 * To be more exact, it says that we should send ACK, 636 * because this segment (at least, if it has no data) 637 * is out of window. 638 * 639 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 640 * describe SYN-RECV state. All the description 641 * is wrong, we cannot believe to it and should 642 * rely only on common sense and implementation 643 * experience. 644 * 645 * Enforce "SYN-ACK" according to figure 8, figure 6 646 * of RFC793, fixed by RFC1122. 647 * 648 * Note that even if there is new data in the SYN packet 649 * they will be thrown away too. 650 * 651 * Reset timer after retransmitting SYNACK, similar to 652 * the idea of fast retransmit in recovery. 653 */ 654 if (!tcp_oow_rate_limited(sock_net(sk), skb, 655 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 656 &tcp_rsk(req)->last_oow_ack_time) && 657 658 !inet_rtx_syn_ack(sk, req)) { 659 unsigned long expires = jiffies; 660 661 expires += reqsk_timeout(req, TCP_RTO_MAX); 662 if (!fastopen) 663 mod_timer_pending(&req->rsk_timer, expires); 664 else 665 req->rsk_timer.expires = expires; 666 } 667 return NULL; 668 } 669 670 /* Further reproduces section "SEGMENT ARRIVES" 671 for state SYN-RECEIVED of RFC793. 672 It is broken, however, it does not work only 673 when SYNs are crossed. 674 675 You would think that SYN crossing is impossible here, since 676 we should have a SYN_SENT socket (from connect()) on our end, 677 but this is not true if the crossed SYNs were sent to both 678 ends by a malicious third party. We must defend against this, 679 and to do that we first verify the ACK (as per RFC793, page 680 36) and reset if it is invalid. Is this a true full defense? 681 To convince ourselves, let us consider a way in which the ACK 682 test can still pass in this 'malicious crossed SYNs' case. 683 Malicious sender sends identical SYNs (and thus identical sequence 684 numbers) to both A and B: 685 686 A: gets SYN, seq=7 687 B: gets SYN, seq=7 688 689 By our good fortune, both A and B select the same initial 690 send sequence number of seven :-) 691 692 A: sends SYN|ACK, seq=7, ack_seq=8 693 B: sends SYN|ACK, seq=7, ack_seq=8 694 695 So we are now A eating this SYN|ACK, ACK test passes. So 696 does sequence test, SYN is truncated, and thus we consider 697 it a bare ACK. 698 699 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 700 bare ACK. Otherwise, we create an established connection. Both 701 ends (listening sockets) accept the new incoming connection and try 702 to talk to each other. 8-) 703 704 Note: This case is both harmless, and rare. Possibility is about the 705 same as us discovering intelligent life on another plant tomorrow. 706 707 But generally, we should (RFC lies!) to accept ACK 708 from SYNACK both here and in tcp_rcv_state_process(). 709 tcp_rcv_state_process() does not, hence, we do not too. 710 711 Note that the case is absolutely generic: 712 we cannot optimize anything here without 713 violating protocol. All the checks must be made 714 before attempt to create socket. 715 */ 716 717 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 718 * and the incoming segment acknowledges something not yet 719 * sent (the segment carries an unacceptable ACK) ... 720 * a reset is sent." 721 * 722 * Invalid ACK: reset will be sent by listening socket. 723 * Note that the ACK validity check for a Fast Open socket is done 724 * elsewhere and is checked directly against the child socket rather 725 * than req because user data may have been sent out. 726 */ 727 if ((flg & TCP_FLAG_ACK) && !fastopen && 728 (TCP_SKB_CB(skb)->ack_seq != 729 tcp_rsk(req)->snt_isn + 1)) 730 return sk; 731 732 /* Also, it would be not so bad idea to check rcv_tsecr, which 733 * is essentially ACK extension and too early or too late values 734 * should cause reset in unsynchronized states. 735 */ 736 737 /* RFC793: "first check sequence number". */ 738 739 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 740 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 741 /* Out of window: send ACK and drop. */ 742 if (!(flg & TCP_FLAG_RST) && 743 !tcp_oow_rate_limited(sock_net(sk), skb, 744 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 745 &tcp_rsk(req)->last_oow_ack_time)) 746 req->rsk_ops->send_ack(sk, skb, req); 747 if (paws_reject) 748 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 749 return NULL; 750 } 751 752 /* In sequence, PAWS is OK. */ 753 754 /* TODO: We probably should defer ts_recent change once 755 * we take ownership of @req. 756 */ 757 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 758 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 759 760 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 761 /* Truncate SYN, it is out of window starting 762 at tcp_rsk(req)->rcv_isn + 1. */ 763 flg &= ~TCP_FLAG_SYN; 764 } 765 766 /* RFC793: "second check the RST bit" and 767 * "fourth, check the SYN bit" 768 */ 769 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 770 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 771 goto embryonic_reset; 772 } 773 774 /* ACK sequence verified above, just make sure ACK is 775 * set. If ACK not set, just silently drop the packet. 776 * 777 * XXX (TFO) - if we ever allow "data after SYN", the 778 * following check needs to be removed. 779 */ 780 if (!(flg & TCP_FLAG_ACK)) 781 return NULL; 782 783 /* For Fast Open no more processing is needed (sk is the 784 * child socket). 785 */ 786 if (fastopen) 787 return sk; 788 789 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 790 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 791 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 792 inet_rsk(req)->acked = 1; 793 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 794 return NULL; 795 } 796 797 /* OK, ACK is valid, create big socket and 798 * feed this segment to it. It will repeat all 799 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 800 * ESTABLISHED STATE. If it will be dropped after 801 * socket is created, wait for troubles. 802 */ 803 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 804 req, &own_req); 805 if (!child) 806 goto listen_overflow; 807 808 if (own_req && rsk_drop_req(req)) { 809 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 810 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 811 return child; 812 } 813 814 sock_rps_save_rxhash(child, skb); 815 tcp_synack_rtt_meas(child, req); 816 *req_stolen = !own_req; 817 return inet_csk_complete_hashdance(sk, child, req, own_req); 818 819listen_overflow: 820 if (sk != req->rsk_listener) 821 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 822 823 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 824 inet_rsk(req)->acked = 1; 825 return NULL; 826 } 827 828embryonic_reset: 829 if (!(flg & TCP_FLAG_RST)) { 830 /* Received a bad SYN pkt - for TFO We try not to reset 831 * the local connection unless it's really necessary to 832 * avoid becoming vulnerable to outside attack aiming at 833 * resetting legit local connections. 834 */ 835 req->rsk_ops->send_reset(sk, skb); 836 } else if (fastopen) { /* received a valid RST pkt */ 837 reqsk_fastopen_remove(sk, req, true); 838 tcp_reset(sk, skb); 839 } 840 if (!fastopen) { 841 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 842 843 if (unlinked) 844 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 845 *req_stolen = !unlinked; 846 } 847 return NULL; 848} 849EXPORT_SYMBOL(tcp_check_req); 850 851/* 852 * Queue segment on the new socket if the new socket is active, 853 * otherwise we just shortcircuit this and continue with 854 * the new socket. 855 * 856 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 857 * when entering. But other states are possible due to a race condition 858 * where after __inet_lookup_established() fails but before the listener 859 * locked is obtained, other packets cause the same connection to 860 * be created. 861 */ 862 863int tcp_child_process(struct sock *parent, struct sock *child, 864 struct sk_buff *skb) 865 __releases(&((child)->sk_lock.slock)) 866{ 867 int ret = 0; 868 int state = child->sk_state; 869 870 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 871 sk_mark_napi_id_set(child, skb); 872 873 tcp_segs_in(tcp_sk(child), skb); 874 if (!sock_owned_by_user(child)) { 875 ret = tcp_rcv_state_process(child, skb); 876 /* Wakeup parent, send SIGIO */ 877 if (state == TCP_SYN_RECV && child->sk_state != state) 878 parent->sk_data_ready(parent); 879 } else { 880 /* Alas, it is possible again, because we do lookup 881 * in main socket hash table and lock on listening 882 * socket does not protect us more. 883 */ 884 __sk_add_backlog(child, skb); 885 } 886 887 bh_unlock_sock(child); 888 sock_put(child); 889 return ret; 890} 891EXPORT_SYMBOL(tcp_child_process); 892