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tcp_minisocks.c
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linux-6.19.14/net/ipv4/tcp_minisocks.c
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/tcp_ecn.h> 24#include <net/xfrm.h> 25#include <net/busy_poll.h> 26#include <net/rstreason.h> 27#include <net/psp.h> 28 29static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 30{ 31 if (seq == s_win) 32 return true; 33 if (after(end_seq, s_win) && before(seq, e_win)) 34 return true; 35 return seq == e_win && seq == end_seq; 36} 37 38static enum tcp_tw_status 39tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 40 const struct sk_buff *skb, int mib_idx) 41{ 42 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 43 44 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 45 &tcptw->tw_last_oow_ack_time)) { 46 /* Send ACK. Note, we do not put the bucket, 47 * it will be released by caller. 48 */ 49 return TCP_TW_ACK_OOW; 50 } 51 52 /* We are rate-limiting, so just release the tw sock and drop skb. */ 53 inet_twsk_put(tw); 54 return TCP_TW_SUCCESS; 55} 56 57static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq, 58 u32 rcv_nxt) 59{ 60#ifdef CONFIG_TCP_AO 61 struct tcp_ao_info *ao; 62 63 ao = rcu_dereference(tcptw->ao_info); 64 if (unlikely(ao && seq < rcv_nxt)) 65 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1); 66#endif 67 WRITE_ONCE(tcptw->tw_rcv_nxt, seq); 68} 69 70/* 71 * * Main purpose of TIME-WAIT state is to close connection gracefully, 72 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 73 * (and, probably, tail of data) and one or more our ACKs are lost. 74 * * What is TIME-WAIT timeout? It is associated with maximal packet 75 * lifetime in the internet, which results in wrong conclusion, that 76 * it is set to catch "old duplicate segments" wandering out of their path. 77 * It is not quite correct. This timeout is calculated so that it exceeds 78 * maximal retransmission timeout enough to allow to lose one (or more) 79 * segments sent by peer and our ACKs. This time may be calculated from RTO. 80 * * When TIME-WAIT socket receives RST, it means that another end 81 * finally closed and we are allowed to kill TIME-WAIT too. 82 * * Second purpose of TIME-WAIT is catching old duplicate segments. 83 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 84 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 85 * * If we invented some more clever way to catch duplicates 86 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 87 * 88 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 89 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 90 * from the very beginning. 91 * 92 * NOTE. With recycling (and later with fin-wait-2) TW bucket 93 * is _not_ stateless. It means, that strictly speaking we must 94 * spinlock it. I do not want! Well, probability of misbehaviour 95 * is ridiculously low and, seems, we could use some mb() tricks 96 * to avoid misread sequence numbers, states etc. --ANK 97 * 98 * We don't need to initialize tmp_out.sack_ok as we don't use the results 99 */ 100enum tcp_tw_status 101tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 102 const struct tcphdr *th, u32 *tw_isn, 103 enum skb_drop_reason *drop_reason) 104{ 105 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 106 u32 rcv_nxt = READ_ONCE(tcptw->tw_rcv_nxt); 107 struct tcp_options_received tmp_opt; 108 enum skb_drop_reason psp_drop; 109 bool paws_reject = false; 110 int ts_recent_stamp; 111 112 /* Instead of dropping immediately, wait to see what value is 113 * returned. We will accept a non psp-encapsulated syn in the 114 * case where TCP_TW_SYN is returned. 115 */ 116 psp_drop = psp_twsk_rx_policy_check(tw, skb); 117 118 tmp_opt.saw_tstamp = 0; 119 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp); 120 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) { 121 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 122 123 if (tmp_opt.saw_tstamp) { 124 if (tmp_opt.rcv_tsecr) 125 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 126 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent); 127 tmp_opt.ts_recent_stamp = ts_recent_stamp; 128 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 129 } 130 } 131 132 if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) { 133 /* Just repeat all the checks of tcp_rcv_state_process() */ 134 135 if (psp_drop) 136 goto out_put; 137 138 /* Out of window, send ACK */ 139 if (paws_reject || 140 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 141 rcv_nxt, 142 rcv_nxt + tcptw->tw_rcv_wnd)) 143 return tcp_timewait_check_oow_rate_limit( 144 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 145 146 if (th->rst) 147 goto kill; 148 149 if (th->syn && !before(TCP_SKB_CB(skb)->seq, rcv_nxt)) 150 return TCP_TW_RST; 151 152 /* Dup ACK? */ 153 if (!th->ack || 154 !after(TCP_SKB_CB(skb)->end_seq, rcv_nxt) || 155 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 156 inet_twsk_put(tw); 157 return TCP_TW_SUCCESS; 158 } 159 160 /* New data or FIN. If new data arrive after half-duplex close, 161 * reset. 162 */ 163 if (!th->fin || 164 TCP_SKB_CB(skb)->end_seq != rcv_nxt + 1) 165 return TCP_TW_RST; 166 167 /* FIN arrived, enter true time-wait state. */ 168 WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT); 169 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq, 170 rcv_nxt); 171 172 if (tmp_opt.saw_tstamp) { 173 u64 ts = tcp_clock_ms(); 174 175 WRITE_ONCE(tw->tw_entry_stamp, ts); 176 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 177 div_u64(ts, MSEC_PER_SEC)); 178 WRITE_ONCE(tcptw->tw_ts_recent, 179 tmp_opt.rcv_tsval); 180 } 181 182 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 183 return TCP_TW_ACK; 184 } 185 186 /* 187 * Now real TIME-WAIT state. 188 * 189 * RFC 1122: 190 * "When a connection is [...] on TIME-WAIT state [...] 191 * [a TCP] MAY accept a new SYN from the remote TCP to 192 * reopen the connection directly, if it: 193 * 194 * (1) assigns its initial sequence number for the new 195 * connection to be larger than the largest sequence 196 * number it used on the previous connection incarnation, 197 * and 198 * 199 * (2) returns to TIME-WAIT state if the SYN turns out 200 * to be an old duplicate". 201 */ 202 203 if (!paws_reject && 204 (TCP_SKB_CB(skb)->seq == rcv_nxt && 205 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 206 /* In window segment, it may be only reset or bare ack. */ 207 208 if (psp_drop) 209 goto out_put; 210 211 if (th->rst) { 212 /* This is TIME_WAIT assassination, in two flavors. 213 * Oh well... nobody has a sufficient solution to this 214 * protocol bug yet. 215 */ 216 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 217kill: 218 inet_twsk_deschedule_put(tw); 219 return TCP_TW_SUCCESS; 220 } 221 } else { 222 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 223 } 224 225 if (tmp_opt.saw_tstamp) { 226 WRITE_ONCE(tcptw->tw_ts_recent, 227 tmp_opt.rcv_tsval); 228 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 229 ktime_get_seconds()); 230 } 231 232 inet_twsk_put(tw); 233 return TCP_TW_SUCCESS; 234 } 235 236 /* Out of window segment. 237 238 All the segments are ACKed immediately. 239 240 The only exception is new SYN. We accept it, if it is 241 not old duplicate and we are not in danger to be killed 242 by delayed old duplicates. RFC check is that it has 243 newer sequence number works at rates <40Mbit/sec. 244 However, if paws works, it is reliable AND even more, 245 we even may relax silly seq space cutoff. 246 247 RED-PEN: we violate main RFC requirement, if this SYN will appear 248 old duplicate (i.e. we receive RST in reply to SYN-ACK), 249 we must return socket to time-wait state. It is not good, 250 but not fatal yet. 251 */ 252 253 if (th->syn && !th->rst && !th->ack && !paws_reject && 254 (after(TCP_SKB_CB(skb)->seq, rcv_nxt) || 255 (tmp_opt.saw_tstamp && 256 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) { 257 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 258 if (isn == 0) 259 isn++; 260 *tw_isn = isn; 261 return TCP_TW_SYN; 262 } 263 264 if (psp_drop) 265 goto out_put; 266 267 if (paws_reject) { 268 *drop_reason = SKB_DROP_REASON_TCP_RFC7323_TW_PAWS; 269 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWS_TW_REJECTED); 270 } 271 272 if (!th->rst) { 273 /* In this case we must reset the TIMEWAIT timer. 274 * 275 * If it is ACKless SYN it may be both old duplicate 276 * and new good SYN with random sequence number <rcv_nxt. 277 * Do not reschedule in the last case. 278 */ 279 if (paws_reject || th->ack) 280 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 281 282 return tcp_timewait_check_oow_rate_limit( 283 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 284 } 285 286out_put: 287 inet_twsk_put(tw); 288 return TCP_TW_SUCCESS; 289} 290EXPORT_IPV6_MOD(tcp_timewait_state_process); 291 292static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 293{ 294#ifdef CONFIG_TCP_MD5SIG 295 const struct tcp_sock *tp = tcp_sk(sk); 296 struct tcp_md5sig_key *key; 297 298 /* 299 * The timewait bucket does not have the key DB from the 300 * sock structure. We just make a quick copy of the 301 * md5 key being used (if indeed we are using one) 302 * so the timewait ack generating code has the key. 303 */ 304 tcptw->tw_md5_key = NULL; 305 if (!static_branch_unlikely(&tcp_md5_needed.key)) 306 return; 307 308 key = tp->af_specific->md5_lookup(sk, sk); 309 if (key) { 310 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 311 if (!tcptw->tw_md5_key) 312 return; 313 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 314 goto out_free; 315 } 316 return; 317out_free: 318 WARN_ON_ONCE(1); 319 kfree(tcptw->tw_md5_key); 320 tcptw->tw_md5_key = NULL; 321#endif 322} 323 324/* 325 * Move a socket to time-wait or dead fin-wait-2 state. 326 */ 327void tcp_time_wait(struct sock *sk, int state, int timeo) 328{ 329 const struct inet_connection_sock *icsk = inet_csk(sk); 330 struct tcp_sock *tp = tcp_sk(sk); 331 struct net *net = sock_net(sk); 332 struct inet_timewait_sock *tw; 333 334 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 335 336 if (tw) { 337 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 338 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 339 340 tw->tw_mark = sk->sk_mark; 341 tw->tw_priority = READ_ONCE(sk->sk_priority); 342 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 343 /* refreshed when we enter true TIME-WAIT state */ 344 tw->tw_entry_stamp = tcp_time_stamp_ms(tp); 345 tcptw->tw_rcv_nxt = tp->rcv_nxt; 346 tcptw->tw_snd_nxt = tp->snd_nxt; 347 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 348 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 349 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 350 tcptw->tw_ts_offset = tp->tsoffset; 351 tw->tw_usec_ts = tp->tcp_usec_ts; 352 tcptw->tw_last_oow_ack_time = 0; 353 tcptw->tw_tx_delay = tp->tcp_tx_delay; 354 tw->tw_txhash = sk->sk_txhash; 355 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping; 356#ifdef CONFIG_SOCK_RX_QUEUE_MAPPING 357 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping; 358#endif 359#if IS_ENABLED(CONFIG_IPV6) 360 if (tw->tw_family == PF_INET6) { 361 struct ipv6_pinfo *np = inet6_sk(sk); 362 363 tw->tw_v6_daddr = sk->sk_v6_daddr; 364 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 365 tw->tw_tclass = np->tclass; 366 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 367 tw->tw_ipv6only = sk->sk_ipv6only; 368 } 369#endif 370 371 tcp_time_wait_init(sk, tcptw); 372 tcp_ao_time_wait(tcptw, tp); 373 374 /* Get the TIME_WAIT timeout firing. */ 375 if (timeo < rto) 376 timeo = rto; 377 378 if (state == TCP_TIME_WAIT) 379 timeo = TCP_TIMEWAIT_LEN; 380 381 /* Linkage updates. 382 * Note that access to tw after this point is illegal. 383 */ 384 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 385 } else { 386 /* Sorry, if we're out of memory, just CLOSE this 387 * socket up. We've got bigger problems than 388 * non-graceful socket closings. 389 */ 390 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 391 } 392 393 tcp_update_metrics(sk); 394 tcp_done(sk); 395} 396EXPORT_SYMBOL(tcp_time_wait); 397 398void tcp_twsk_destructor(struct sock *sk) 399{ 400#ifdef CONFIG_TCP_MD5SIG 401 if (static_branch_unlikely(&tcp_md5_needed.key)) { 402 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 403 404 if (twsk->tw_md5_key) { 405 kfree(twsk->tw_md5_key); 406 static_branch_slow_dec_deferred(&tcp_md5_needed); 407 } 408 } 409#endif 410 tcp_ao_destroy_sock(sk, true); 411 psp_twsk_assoc_free(inet_twsk(sk)); 412} 413 414void tcp_twsk_purge(struct list_head *net_exit_list) 415{ 416 bool purged_once = false; 417 struct net *net; 418 419 list_for_each_entry(net, net_exit_list, exit_list) { 420 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 421 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 422 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 423 } else if (!purged_once) { 424 inet_twsk_purge(&tcp_hashinfo); 425 purged_once = true; 426 } 427 } 428} 429 430/* Warning : This function is called without sk_listener being locked. 431 * Be sure to read socket fields once, as their value could change under us. 432 */ 433void tcp_openreq_init_rwin(struct request_sock *req, 434 const struct sock *sk_listener, 435 const struct dst_entry *dst) 436{ 437 struct inet_request_sock *ireq = inet_rsk(req); 438 const struct tcp_sock *tp = tcp_sk(sk_listener); 439 int full_space = tcp_full_space(sk_listener); 440 u32 window_clamp; 441 __u8 rcv_wscale; 442 u32 rcv_wnd; 443 int mss; 444 445 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 446 window_clamp = READ_ONCE(tp->window_clamp); 447 /* Set this up on the first call only */ 448 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 449 450 /* limit the window selection if the user enforce a smaller rx buffer */ 451 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 452 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 453 req->rsk_window_clamp = full_space; 454 455 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 456 if (rcv_wnd == 0) 457 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 458 else if (full_space < rcv_wnd * mss) 459 full_space = rcv_wnd * mss; 460 461 /* tcp_full_space because it is guaranteed to be the first packet */ 462 tcp_select_initial_window(sk_listener, full_space, 463 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 464 &req->rsk_rcv_wnd, 465 &req->rsk_window_clamp, 466 ireq->wscale_ok, 467 &rcv_wscale, 468 rcv_wnd); 469 ireq->rcv_wscale = rcv_wscale; 470} 471 472static void tcp_ecn_openreq_child(struct sock *sk, 473 const struct request_sock *req, 474 const struct sk_buff *skb) 475{ 476 const struct tcp_request_sock *treq = tcp_rsk(req); 477 struct tcp_sock *tp = tcp_sk(sk); 478 479 if (treq->accecn_ok) { 480 tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN); 481 tp->syn_ect_snt = treq->syn_ect_snt; 482 tcp_accecn_third_ack(sk, skb, treq->syn_ect_snt); 483 tp->saw_accecn_opt = treq->saw_accecn_opt; 484 tp->prev_ecnfield = treq->syn_ect_rcv; 485 tp->accecn_opt_demand = 1; 486 tcp_ecn_received_counters_payload(sk, skb); 487 } else { 488 if (inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk)) 489 tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168); 490 else 491 tcp_ecn_mode_set(tp, TCP_ECN_DISABLED); 492 } 493} 494 495void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 496{ 497 struct inet_connection_sock *icsk = inet_csk(sk); 498 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 499 bool ca_got_dst = false; 500 501 if (ca_key != TCP_CA_UNSPEC) { 502 const struct tcp_congestion_ops *ca; 503 504 rcu_read_lock(); 505 ca = tcp_ca_find_key(ca_key); 506 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 507 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 508 icsk->icsk_ca_ops = ca; 509 ca_got_dst = true; 510 } 511 rcu_read_unlock(); 512 } 513 514 /* If no valid choice made yet, assign current system default ca. */ 515 if (!ca_got_dst && 516 (!icsk->icsk_ca_setsockopt || 517 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 518 tcp_assign_congestion_control(sk); 519 520 tcp_set_ca_state(sk, TCP_CA_Open); 521} 522EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child); 523 524static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 525 struct request_sock *req, 526 struct tcp_sock *newtp) 527{ 528#if IS_ENABLED(CONFIG_SMC) 529 struct inet_request_sock *ireq; 530 531 if (static_branch_unlikely(&tcp_have_smc)) { 532 ireq = inet_rsk(req); 533 if (oldtp->syn_smc && !ireq->smc_ok) 534 newtp->syn_smc = 0; 535 } 536#endif 537} 538 539/* This is not only more efficient than what we used to do, it eliminates 540 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 541 * 542 * Actually, we could lots of memory writes here. tp of listening 543 * socket contains all necessary default parameters. 544 */ 545struct sock *tcp_create_openreq_child(const struct sock *sk, 546 struct request_sock *req, 547 struct sk_buff *skb) 548{ 549 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 550 const struct inet_request_sock *ireq = inet_rsk(req); 551 struct tcp_request_sock *treq = tcp_rsk(req); 552 struct inet_connection_sock *newicsk; 553 const struct tcp_sock *oldtp; 554 struct tcp_sock *newtp; 555 u32 seq; 556 557 if (!newsk) 558 return NULL; 559 560 newicsk = inet_csk(newsk); 561 newtp = tcp_sk(newsk); 562 oldtp = tcp_sk(sk); 563 564 smc_check_reset_syn_req(oldtp, req, newtp); 565 566 /* Now setup tcp_sock */ 567 newtp->pred_flags = 0; 568 569 seq = treq->rcv_isn + 1; 570 newtp->rcv_wup = seq; 571 WRITE_ONCE(newtp->copied_seq, seq); 572 WRITE_ONCE(newtp->rcv_nxt, seq); 573 newtp->segs_in = 1; 574 575 seq = treq->snt_isn + 1; 576 newtp->snd_sml = newtp->snd_una = seq; 577 WRITE_ONCE(newtp->snd_nxt, seq); 578 newtp->snd_up = seq; 579 580 INIT_LIST_HEAD(&newtp->tsq_node); 581 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 582 583 tcp_init_wl(newtp, treq->rcv_isn); 584 585 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 586 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 587 588 newtp->lsndtime = tcp_jiffies32; 589 newsk->sk_txhash = READ_ONCE(treq->txhash); 590 newtp->total_retrans = req->num_retrans; 591 592 tcp_init_xmit_timers(newsk); 593 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 594 595 if (sock_flag(newsk, SOCK_KEEPOPEN)) 596 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 597 598 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 599 newtp->rx_opt.sack_ok = ireq->sack_ok; 600 newtp->window_clamp = req->rsk_window_clamp; 601 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 602 newtp->rcv_wnd = req->rsk_rcv_wnd; 603 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 604 if (newtp->rx_opt.wscale_ok) { 605 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 606 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 607 } else { 608 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 609 newtp->window_clamp = min(newtp->window_clamp, 65535U); 610 } 611 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 612 newtp->max_window = newtp->snd_wnd; 613 614 if (newtp->rx_opt.tstamp_ok) { 615 newtp->tcp_usec_ts = treq->req_usec_ts; 616 newtp->rx_opt.ts_recent = req->ts_recent; 617 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 618 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 619 } else { 620 newtp->tcp_usec_ts = 0; 621 newtp->rx_opt.ts_recent_stamp = 0; 622 newtp->tcp_header_len = sizeof(struct tcphdr); 623 } 624 if (req->num_timeout) { 625 newtp->total_rto = req->num_timeout; 626 newtp->undo_marker = treq->snt_isn; 627 if (newtp->tcp_usec_ts) { 628 newtp->retrans_stamp = treq->snt_synack; 629 newtp->total_rto_time = (u32)(tcp_clock_us() - 630 newtp->retrans_stamp) / USEC_PER_MSEC; 631 } else { 632 newtp->retrans_stamp = div_u64(treq->snt_synack, 633 USEC_PER_SEC / TCP_TS_HZ); 634 newtp->total_rto_time = tcp_clock_ms() - 635 newtp->retrans_stamp; 636 } 637 newtp->total_rto_recoveries = 1; 638 } 639 newtp->tsoffset = treq->ts_off; 640#ifdef CONFIG_TCP_MD5SIG 641 newtp->md5sig_info = NULL; /*XXX*/ 642#endif 643#ifdef CONFIG_TCP_AO 644 newtp->ao_info = NULL; 645 646 if (tcp_rsk_used_ao(req)) { 647 struct tcp_ao_key *ao_key; 648 649 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 650 if (ao_key) 651 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 652 } 653 #endif 654 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 655 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 656 newtp->rx_opt.mss_clamp = req->mss; 657 tcp_ecn_openreq_child(newsk, req, skb); 658 newtp->fastopen_req = NULL; 659 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 660 661 newtp->bpf_chg_cc_inprogress = 0; 662 tcp_bpf_clone(sk, newsk); 663 664 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 665 666 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 667 668 return newsk; 669} 670EXPORT_SYMBOL(tcp_create_openreq_child); 671 672/* 673 * Process an incoming packet for SYN_RECV sockets represented as a 674 * request_sock. Normally sk is the listener socket but for TFO it 675 * points to the child socket. 676 * 677 * XXX (TFO) - The current impl contains a special check for ack 678 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 679 * 680 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 681 * 682 * Note: If @fastopen is true, this can be called from process context. 683 * Otherwise, this is from BH context. 684 */ 685 686struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 687 struct request_sock *req, 688 bool fastopen, bool *req_stolen, 689 enum skb_drop_reason *drop_reason) 690{ 691 struct tcp_options_received tmp_opt; 692 struct sock *child; 693 const struct tcphdr *th = tcp_hdr(skb); 694 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 695 bool tsecr_reject = false; 696 bool paws_reject = false; 697 bool own_req; 698 699 tmp_opt.saw_tstamp = 0; 700 tmp_opt.accecn = 0; 701 if (th->doff > (sizeof(struct tcphdr)>>2)) { 702 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 703 704 if (tmp_opt.saw_tstamp) { 705 tmp_opt.ts_recent = req->ts_recent; 706 if (tmp_opt.rcv_tsecr) { 707 if (inet_rsk(req)->tstamp_ok && !fastopen) 708 tsecr_reject = !between(tmp_opt.rcv_tsecr, 709 tcp_rsk(req)->snt_tsval_first, 710 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 711 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 712 } 713 /* We do not store true stamp, but it is not required, 714 * it can be estimated (approximately) 715 * from another data. 716 */ 717 tmp_opt.ts_recent_stamp = ktime_get_seconds() - 718 tcp_reqsk_timeout(req) / HZ; 719 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 720 } 721 } 722 723 /* Check for pure retransmitted SYN. */ 724 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 725 flg == TCP_FLAG_SYN && 726 !paws_reject) { 727 /* 728 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 729 * this case on figure 6 and figure 8, but formal 730 * protocol description says NOTHING. 731 * To be more exact, it says that we should send ACK, 732 * because this segment (at least, if it has no data) 733 * is out of window. 734 * 735 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 736 * describe SYN-RECV state. All the description 737 * is wrong, we cannot believe to it and should 738 * rely only on common sense and implementation 739 * experience. 740 * 741 * Enforce "SYN-ACK" according to figure 8, figure 6 742 * of RFC793, fixed by RFC1122. 743 * 744 * Note that even if there is new data in the SYN packet 745 * they will be thrown away too. 746 * 747 * Reset timer after retransmitting SYNACK, similar to 748 * the idea of fast retransmit in recovery. 749 */ 750 if (!tcp_oow_rate_limited(sock_net(sk), skb, 751 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 752 &tcp_rsk(req)->last_oow_ack_time) && 753 754 !tcp_rtx_synack(sk, req)) { 755 unsigned long expires = jiffies; 756 757 expires += tcp_reqsk_timeout(req); 758 if (!fastopen) 759 mod_timer_pending(&req->rsk_timer, expires); 760 else 761 req->rsk_timer.expires = expires; 762 } 763 return NULL; 764 } 765 766 /* Further reproduces section "SEGMENT ARRIVES" 767 for state SYN-RECEIVED of RFC793. 768 It is broken, however, it does not work only 769 when SYNs are crossed. 770 771 You would think that SYN crossing is impossible here, since 772 we should have a SYN_SENT socket (from connect()) on our end, 773 but this is not true if the crossed SYNs were sent to both 774 ends by a malicious third party. We must defend against this, 775 and to do that we first verify the ACK (as per RFC793, page 776 36) and reset if it is invalid. Is this a true full defense? 777 To convince ourselves, let us consider a way in which the ACK 778 test can still pass in this 'malicious crossed SYNs' case. 779 Malicious sender sends identical SYNs (and thus identical sequence 780 numbers) to both A and B: 781 782 A: gets SYN, seq=7 783 B: gets SYN, seq=7 784 785 By our good fortune, both A and B select the same initial 786 send sequence number of seven :-) 787 788 A: sends SYN|ACK, seq=7, ack_seq=8 789 B: sends SYN|ACK, seq=7, ack_seq=8 790 791 So we are now A eating this SYN|ACK, ACK test passes. So 792 does sequence test, SYN is truncated, and thus we consider 793 it a bare ACK. 794 795 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 796 bare ACK. Otherwise, we create an established connection. Both 797 ends (listening sockets) accept the new incoming connection and try 798 to talk to each other. 8-) 799 800 Note: This case is both harmless, and rare. Possibility is about the 801 same as us discovering intelligent life on another plant tomorrow. 802 803 But generally, we should (RFC lies!) to accept ACK 804 from SYNACK both here and in tcp_rcv_state_process(). 805 tcp_rcv_state_process() does not, hence, we do not too. 806 807 Note that the case is absolutely generic: 808 we cannot optimize anything here without 809 violating protocol. All the checks must be made 810 before attempt to create socket. 811 */ 812 813 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 814 * and the incoming segment acknowledges something not yet 815 * sent (the segment carries an unacceptable ACK) ... 816 * a reset is sent." 817 * 818 * Invalid ACK: reset will be sent by listening socket. 819 * Note that the ACK validity check for a Fast Open socket is done 820 * elsewhere and is checked directly against the child socket rather 821 * than req because user data may have been sent out. 822 */ 823 if ((flg & TCP_FLAG_ACK) && !fastopen && 824 (TCP_SKB_CB(skb)->ack_seq != 825 tcp_rsk(req)->snt_isn + 1)) 826 return sk; 827 828 /* RFC793: "first check sequence number". */ 829 830 if (paws_reject || tsecr_reject || 831 !tcp_in_window(TCP_SKB_CB(skb)->seq, 832 TCP_SKB_CB(skb)->end_seq, 833 tcp_rsk(req)->rcv_nxt, 834 tcp_rsk(req)->rcv_nxt + 835 tcp_synack_window(req))) { 836 /* Out of window: send ACK and drop. */ 837 if (!(flg & TCP_FLAG_RST) && 838 !tcp_oow_rate_limited(sock_net(sk), skb, 839 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 840 &tcp_rsk(req)->last_oow_ack_time)) 841 req->rsk_ops->send_ack(sk, skb, req); 842 if (paws_reject) { 843 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 844 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 845 } else if (tsecr_reject) { 846 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 847 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 848 } else { 849 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 850 } 851 return NULL; 852 } 853 854 /* In sequence, PAWS is OK. */ 855 856 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 857 /* Truncate SYN, it is out of window starting 858 at tcp_rsk(req)->rcv_isn + 1. */ 859 flg &= ~TCP_FLAG_SYN; 860 } 861 862 /* RFC793: "second check the RST bit" and 863 * "fourth, check the SYN bit" 864 */ 865 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 866 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 867 goto embryonic_reset; 868 } 869 870 /* ACK sequence verified above, just make sure ACK is 871 * set. If ACK not set, just silently drop the packet. 872 * 873 * XXX (TFO) - if we ever allow "data after SYN", the 874 * following check needs to be removed. 875 */ 876 if (!(flg & TCP_FLAG_ACK)) 877 return NULL; 878 879 if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn && 880 tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) { 881 u8 saw_opt = tcp_accecn_option_init(skb, tmp_opt.accecn); 882 883 tcp_rsk(req)->saw_accecn_opt = saw_opt; 884 if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) { 885 u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV; 886 887 tcp_rsk(req)->accecn_fail_mode |= fail_mode; 888 } 889 } 890 891 /* For Fast Open no more processing is needed (sk is the 892 * child socket). 893 */ 894 if (fastopen) 895 return sk; 896 897 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 898 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 899 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 900 inet_rsk(req)->acked = 1; 901 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 902 return NULL; 903 } 904 905 /* OK, ACK is valid, create big socket and 906 * feed this segment to it. It will repeat all 907 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 908 * ESTABLISHED STATE. If it will be dropped after 909 * socket is created, wait for troubles. 910 */ 911 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 912 req, &own_req, NULL); 913 if (!child) 914 goto listen_overflow; 915 916 if (own_req && tmp_opt.saw_tstamp && 917 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 918 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 919 920 if (own_req && rsk_drop_req(req)) { 921 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 922 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 923 return child; 924 } 925 926 sock_rps_save_rxhash(child, skb); 927 tcp_synack_rtt_meas(child, req); 928 *req_stolen = !own_req; 929 return inet_csk_complete_hashdance(sk, child, req, own_req); 930 931listen_overflow: 932 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 933 if (sk != req->rsk_listener) 934 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 935 936 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 937 inet_rsk(req)->acked = 1; 938 return NULL; 939 } 940 941embryonic_reset: 942 if (!(flg & TCP_FLAG_RST)) { 943 /* Received a bad SYN pkt - for TFO We try not to reset 944 * the local connection unless it's really necessary to 945 * avoid becoming vulnerable to outside attack aiming at 946 * resetting legit local connections. 947 */ 948 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 949 } else if (fastopen) { /* received a valid RST pkt */ 950 reqsk_fastopen_remove(sk, req, true); 951 tcp_reset(sk, skb); 952 } 953 if (!fastopen) { 954 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 955 956 if (unlinked) 957 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 958 *req_stolen = !unlinked; 959 } 960 return NULL; 961} 962EXPORT_IPV6_MOD(tcp_check_req); 963 964/* 965 * Queue segment on the new socket if the new socket is active, 966 * otherwise we just shortcircuit this and continue with 967 * the new socket. 968 * 969 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 970 * when entering. But other states are possible due to a race condition 971 * where after __inet_lookup_established() fails but before the listener 972 * locked is obtained, other packets cause the same connection to 973 * be created. 974 */ 975 976enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 977 struct sk_buff *skb) 978 __releases(&((child)->sk_lock.slock)) 979{ 980 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 981 int state = child->sk_state; 982 983 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 984 sk_mark_napi_id_set(child, skb); 985 986 tcp_segs_in(tcp_sk(child), skb); 987 if (!sock_owned_by_user(child)) { 988 reason = tcp_rcv_state_process(child, skb); 989 /* Wakeup parent, send SIGIO */ 990 if (state == TCP_SYN_RECV && child->sk_state != state) 991 READ_ONCE(parent->sk_data_ready)(parent); 992 } else { 993 /* Alas, it is possible again, because we do lookup 994 * in main socket hash table and lock on listening 995 * socket does not protect us more. 996 */ 997 __sk_add_backlog(child, skb); 998 } 999 1000 bh_unlock_sock(child); 1001 sock_put(child); 1002 return reason; 1003} 1004EXPORT_IPV6_MOD(tcp_child_process);
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