1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 #include "opt_pcbgroup.h" 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/hash.h> 46 #include <sys/refcount.h> 47 #include <sys/kernel.h> 48 #include <sys/sysctl.h> 49 #include <sys/limits.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/malloc.h> 53 #include <sys/mbuf.h> 54 #include <sys/proc.h> /* for proc0 declaration */ 55 #include <sys/random.h> 56 #include <sys/socket.h> 57 #include <sys/socketvar.h> 58 #include <sys/syslog.h> 59 #include <sys/ucred.h> 60 61 #include <sys/md5.h> 62 #include <crypto/siphash/siphash.h> 63 64 #include <vm/uma.h> 65 66 #include <net/if.h> 67 #include <net/if_var.h> 68 #include <net/route.h> 69 #include <net/vnet.h> 70 71 #include <netinet/in.h> 72 #include <netinet/in_kdtrace.h> 73 #include <netinet/in_systm.h> 74 #include <netinet/ip.h> 75 #include <netinet/in_var.h> 76 #include <netinet/in_pcb.h> 77 #include <netinet/ip_var.h> 78 #include <netinet/ip_options.h> 79 #ifdef INET6 80 #include <netinet/ip6.h> 81 #include <netinet/icmp6.h> 82 #include <netinet6/nd6.h> 83 #include <netinet6/ip6_var.h> 84 #include <netinet6/in6_pcb.h> 85 #endif 86 #include <netinet/tcp.h> 87 #include <netinet/tcp_fastopen.h> 88 #include <netinet/tcp_fsm.h> 89 #include <netinet/tcp_seq.h> 90 #include <netinet/tcp_timer.h> 91 #include <netinet/tcp_var.h> 92 #include <netinet/tcp_syncache.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 100 #include <netipsec/ipsec_support.h> 101 102 #include <machine/in_cksum.h> 103 104 #include <security/mac/mac_framework.h> 105 106 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 107 #define V_tcp_syncookies VNET(tcp_syncookies) 108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 109 &VNET_NAME(tcp_syncookies), 0, 110 "Use TCP SYN cookies if the syncache overflows"); 111 112 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 113 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 115 &VNET_NAME(tcp_syncookiesonly), 0, 116 "Use only TCP SYN cookies"); 117 118 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 119 #define V_functions_inherit_listen_socket_stack \ 120 VNET(functions_inherit_listen_socket_stack) 121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 122 CTLFLAG_VNET | CTLFLAG_RW, 123 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 124 "Inherit listen socket's stack"); 125 126 #ifdef TCP_OFFLOAD 127 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 128 #endif 129 130 static void syncache_drop(struct syncache *, struct syncache_head *); 131 static void syncache_free(struct syncache *); 132 static void syncache_insert(struct syncache *, struct syncache_head *); 133 static int syncache_respond(struct syncache *, struct syncache_head *, int, 134 const struct mbuf *); 135 static struct socket *syncache_socket(struct syncache *, struct socket *, 136 struct mbuf *m); 137 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 138 int docallout); 139 static void syncache_timer(void *); 140 141 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 142 uint8_t *, uintptr_t); 143 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 144 static struct syncache 145 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 146 struct syncache *, struct tcphdr *, struct tcpopt *, 147 struct socket *); 148 static void syncookie_reseed(void *); 149 #ifdef INVARIANTS 150 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 151 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 152 struct socket *lso); 153 #endif 154 155 /* 156 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 157 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 158 * the odds are that the user has given up attempting to connect by then. 159 */ 160 #define SYNCACHE_MAXREXMTS 3 161 162 /* Arbitrary values */ 163 #define TCP_SYNCACHE_HASHSIZE 512 164 #define TCP_SYNCACHE_BUCKETLIMIT 30 165 166 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 167 #define V_tcp_syncache VNET(tcp_syncache) 168 169 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 170 "TCP SYN cache"); 171 172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 173 &VNET_NAME(tcp_syncache.bucket_limit), 0, 174 "Per-bucket hash limit for syncache"); 175 176 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 177 &VNET_NAME(tcp_syncache.cache_limit), 0, 178 "Overall entry limit for syncache"); 179 180 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 181 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 182 183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 184 &VNET_NAME(tcp_syncache.hashsize), 0, 185 "Size of TCP syncache hashtable"); 186 187 static int 188 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 189 { 190 int error; 191 u_int new; 192 193 new = V_tcp_syncache.rexmt_limit; 194 error = sysctl_handle_int(oidp, &new, 0, req); 195 if ((error == 0) && (req->newptr != NULL)) { 196 if (new > TCP_MAXRXTSHIFT) 197 error = EINVAL; 198 else 199 V_tcp_syncache.rexmt_limit = new; 200 } 201 return (error); 202 } 203 204 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 205 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW, 206 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 207 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 208 "Limit on SYN/ACK retransmissions"); 209 210 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 211 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 212 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 213 "Send reset on socket allocation failure"); 214 215 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 216 217 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 218 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 219 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 220 221 /* 222 * Requires the syncache entry to be already removed from the bucket list. 223 */ 224 static void 225 syncache_free(struct syncache *sc) 226 { 227 228 if (sc->sc_ipopts) 229 (void) m_free(sc->sc_ipopts); 230 if (sc->sc_cred) 231 crfree(sc->sc_cred); 232 #ifdef MAC 233 mac_syncache_destroy(&sc->sc_label); 234 #endif 235 236 uma_zfree(V_tcp_syncache.zone, sc); 237 } 238 239 void 240 syncache_init(void) 241 { 242 int i; 243 244 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 245 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 246 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 247 V_tcp_syncache.hash_secret = arc4random(); 248 249 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 250 &V_tcp_syncache.hashsize); 251 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 252 &V_tcp_syncache.bucket_limit); 253 if (!powerof2(V_tcp_syncache.hashsize) || 254 V_tcp_syncache.hashsize == 0) { 255 printf("WARNING: syncache hash size is not a power of 2.\n"); 256 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 257 } 258 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 259 260 /* Set limits. */ 261 V_tcp_syncache.cache_limit = 262 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 263 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 264 &V_tcp_syncache.cache_limit); 265 266 /* Allocate the hash table. */ 267 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 268 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 269 270 #ifdef VIMAGE 271 V_tcp_syncache.vnet = curvnet; 272 #endif 273 274 /* Initialize the hash buckets. */ 275 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 276 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 277 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 278 NULL, MTX_DEF); 279 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 280 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 281 V_tcp_syncache.hashbase[i].sch_length = 0; 282 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 283 V_tcp_syncache.hashbase[i].sch_last_overflow = 284 -(SYNCOOKIE_LIFETIME + 1); 285 } 286 287 /* Create the syncache entry zone. */ 288 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 289 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 290 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 291 V_tcp_syncache.cache_limit); 292 293 /* Start the SYN cookie reseeder callout. */ 294 callout_init(&V_tcp_syncache.secret.reseed, 1); 295 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 296 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 297 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 298 syncookie_reseed, &V_tcp_syncache); 299 } 300 301 #ifdef VIMAGE 302 void 303 syncache_destroy(void) 304 { 305 struct syncache_head *sch; 306 struct syncache *sc, *nsc; 307 int i; 308 309 /* 310 * Stop the re-seed timer before freeing resources. No need to 311 * possibly schedule it another time. 312 */ 313 callout_drain(&V_tcp_syncache.secret.reseed); 314 315 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 316 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 317 318 sch = &V_tcp_syncache.hashbase[i]; 319 callout_drain(&sch->sch_timer); 320 321 SCH_LOCK(sch); 322 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 323 syncache_drop(sc, sch); 324 SCH_UNLOCK(sch); 325 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 326 ("%s: sch->sch_bucket not empty", __func__)); 327 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 328 __func__, sch->sch_length)); 329 mtx_destroy(&sch->sch_mtx); 330 } 331 332 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 333 ("%s: cache_count not 0", __func__)); 334 335 /* Free the allocated global resources. */ 336 uma_zdestroy(V_tcp_syncache.zone); 337 free(V_tcp_syncache.hashbase, M_SYNCACHE); 338 } 339 #endif 340 341 /* 342 * Inserts a syncache entry into the specified bucket row. 343 * Locks and unlocks the syncache_head autonomously. 344 */ 345 static void 346 syncache_insert(struct syncache *sc, struct syncache_head *sch) 347 { 348 struct syncache *sc2; 349 350 SCH_LOCK(sch); 351 352 /* 353 * Make sure that we don't overflow the per-bucket limit. 354 * If the bucket is full, toss the oldest element. 355 */ 356 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 357 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 358 ("sch->sch_length incorrect")); 359 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 360 sch->sch_last_overflow = time_uptime; 361 syncache_drop(sc2, sch); 362 TCPSTAT_INC(tcps_sc_bucketoverflow); 363 } 364 365 /* Put it into the bucket. */ 366 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 367 sch->sch_length++; 368 369 #ifdef TCP_OFFLOAD 370 if (ADDED_BY_TOE(sc)) { 371 struct toedev *tod = sc->sc_tod; 372 373 tod->tod_syncache_added(tod, sc->sc_todctx); 374 } 375 #endif 376 377 /* Reinitialize the bucket row's timer. */ 378 if (sch->sch_length == 1) 379 sch->sch_nextc = ticks + INT_MAX; 380 syncache_timeout(sc, sch, 1); 381 382 SCH_UNLOCK(sch); 383 384 TCPSTATES_INC(TCPS_SYN_RECEIVED); 385 TCPSTAT_INC(tcps_sc_added); 386 } 387 388 /* 389 * Remove and free entry from syncache bucket row. 390 * Expects locked syncache head. 391 */ 392 static void 393 syncache_drop(struct syncache *sc, struct syncache_head *sch) 394 { 395 396 SCH_LOCK_ASSERT(sch); 397 398 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 399 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 400 sch->sch_length--; 401 402 #ifdef TCP_OFFLOAD 403 if (ADDED_BY_TOE(sc)) { 404 struct toedev *tod = sc->sc_tod; 405 406 tod->tod_syncache_removed(tod, sc->sc_todctx); 407 } 408 #endif 409 410 syncache_free(sc); 411 } 412 413 /* 414 * Engage/reengage time on bucket row. 415 */ 416 static void 417 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 418 { 419 int rexmt; 420 421 if (sc->sc_rxmits == 0) 422 rexmt = TCPTV_RTOBASE; 423 else 424 TCPT_RANGESET(rexmt, TCPTV_RTOBASE * tcp_syn_backoff[sc->sc_rxmits], 425 tcp_rexmit_min, TCPTV_REXMTMAX); 426 sc->sc_rxttime = ticks + rexmt; 427 sc->sc_rxmits++; 428 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 429 sch->sch_nextc = sc->sc_rxttime; 430 if (docallout) 431 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 432 syncache_timer, (void *)sch); 433 } 434 } 435 436 /* 437 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 438 * If we have retransmitted an entry the maximum number of times, expire it. 439 * One separate timer for each bucket row. 440 */ 441 static void 442 syncache_timer(void *xsch) 443 { 444 struct syncache_head *sch = (struct syncache_head *)xsch; 445 struct syncache *sc, *nsc; 446 int tick = ticks; 447 char *s; 448 449 CURVNET_SET(sch->sch_sc->vnet); 450 451 /* NB: syncache_head has already been locked by the callout. */ 452 SCH_LOCK_ASSERT(sch); 453 454 /* 455 * In the following cycle we may remove some entries and/or 456 * advance some timeouts, so re-initialize the bucket timer. 457 */ 458 sch->sch_nextc = tick + INT_MAX; 459 460 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 461 /* 462 * We do not check if the listen socket still exists 463 * and accept the case where the listen socket may be 464 * gone by the time we resend the SYN/ACK. We do 465 * not expect this to happens often. If it does, 466 * then the RST will be sent by the time the remote 467 * host does the SYN/ACK->ACK. 468 */ 469 if (TSTMP_GT(sc->sc_rxttime, tick)) { 470 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 471 sch->sch_nextc = sc->sc_rxttime; 472 continue; 473 } 474 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 475 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 476 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 477 "giving up and removing syncache entry\n", 478 s, __func__); 479 free(s, M_TCPLOG); 480 } 481 syncache_drop(sc, sch); 482 TCPSTAT_INC(tcps_sc_stale); 483 continue; 484 } 485 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 486 log(LOG_DEBUG, "%s; %s: Response timeout, " 487 "retransmitting (%u) SYN|ACK\n", 488 s, __func__, sc->sc_rxmits); 489 free(s, M_TCPLOG); 490 } 491 492 syncache_respond(sc, sch, 1, NULL); 493 TCPSTAT_INC(tcps_sc_retransmitted); 494 syncache_timeout(sc, sch, 0); 495 } 496 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 497 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 498 syncache_timer, (void *)(sch)); 499 CURVNET_RESTORE(); 500 } 501 502 /* 503 * Find an entry in the syncache. 504 * Returns always with locked syncache_head plus a matching entry or NULL. 505 */ 506 static struct syncache * 507 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 508 { 509 struct syncache *sc; 510 struct syncache_head *sch; 511 uint32_t hash; 512 513 /* 514 * The hash is built on foreign port + local port + foreign address. 515 * We rely on the fact that struct in_conninfo starts with 16 bits 516 * of foreign port, then 16 bits of local port then followed by 128 517 * bits of foreign address. In case of IPv4 address, the first 3 518 * 32-bit words of the address always are zeroes. 519 */ 520 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 521 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 522 523 sch = &V_tcp_syncache.hashbase[hash]; 524 *schp = sch; 525 SCH_LOCK(sch); 526 527 /* Circle through bucket row to find matching entry. */ 528 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 529 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 530 sizeof(struct in_endpoints)) == 0) 531 break; 532 533 return (sc); /* Always returns with locked sch. */ 534 } 535 536 /* 537 * This function is called when we get a RST for a 538 * non-existent connection, so that we can see if the 539 * connection is in the syn cache. If it is, zap it. 540 */ 541 void 542 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 543 { 544 struct syncache *sc; 545 struct syncache_head *sch; 546 char *s = NULL; 547 548 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 549 SCH_LOCK_ASSERT(sch); 550 551 /* 552 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 553 * See RFC 793 page 65, section SEGMENT ARRIVES. 554 */ 555 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 556 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 557 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 558 "FIN flag set, segment ignored\n", s, __func__); 559 TCPSTAT_INC(tcps_badrst); 560 goto done; 561 } 562 563 /* 564 * No corresponding connection was found in syncache. 565 * If syncookies are enabled and possibly exclusively 566 * used, or we are under memory pressure, a valid RST 567 * may not find a syncache entry. In that case we're 568 * done and no SYN|ACK retransmissions will happen. 569 * Otherwise the RST was misdirected or spoofed. 570 */ 571 if (sc == NULL) { 572 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 573 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 574 "syncache entry (possibly syncookie only), " 575 "segment ignored\n", s, __func__); 576 TCPSTAT_INC(tcps_badrst); 577 goto done; 578 } 579 580 /* 581 * If the RST bit is set, check the sequence number to see 582 * if this is a valid reset segment. 583 * RFC 793 page 37: 584 * In all states except SYN-SENT, all reset (RST) segments 585 * are validated by checking their SEQ-fields. A reset is 586 * valid if its sequence number is in the window. 587 * 588 * The sequence number in the reset segment is normally an 589 * echo of our outgoing acknowlegement numbers, but some hosts 590 * send a reset with the sequence number at the rightmost edge 591 * of our receive window, and we have to handle this case. 592 */ 593 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 594 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 595 syncache_drop(sc, sch); 596 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 597 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 598 "connection attempt aborted by remote endpoint\n", 599 s, __func__); 600 TCPSTAT_INC(tcps_sc_reset); 601 } else { 602 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 603 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 604 "IRS %u (+WND %u), segment ignored\n", 605 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 606 TCPSTAT_INC(tcps_badrst); 607 } 608 609 done: 610 if (s != NULL) 611 free(s, M_TCPLOG); 612 SCH_UNLOCK(sch); 613 } 614 615 void 616 syncache_badack(struct in_conninfo *inc) 617 { 618 struct syncache *sc; 619 struct syncache_head *sch; 620 621 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 622 SCH_LOCK_ASSERT(sch); 623 if (sc != NULL) { 624 syncache_drop(sc, sch); 625 TCPSTAT_INC(tcps_sc_badack); 626 } 627 SCH_UNLOCK(sch); 628 } 629 630 void 631 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq) 632 { 633 struct syncache *sc; 634 struct syncache_head *sch; 635 636 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 637 SCH_LOCK_ASSERT(sch); 638 if (sc == NULL) 639 goto done; 640 641 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 642 if (ntohl(th_seq) != sc->sc_iss) 643 goto done; 644 645 /* 646 * If we've rertransmitted 3 times and this is our second error, 647 * we remove the entry. Otherwise, we allow it to continue on. 648 * This prevents us from incorrectly nuking an entry during a 649 * spurious network outage. 650 * 651 * See tcp_notify(). 652 */ 653 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 654 sc->sc_flags |= SCF_UNREACH; 655 goto done; 656 } 657 syncache_drop(sc, sch); 658 TCPSTAT_INC(tcps_sc_unreach); 659 done: 660 SCH_UNLOCK(sch); 661 } 662 663 /* 664 * Build a new TCP socket structure from a syncache entry. 665 * 666 * On success return the newly created socket with its underlying inp locked. 667 */ 668 static struct socket * 669 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 670 { 671 struct tcp_function_block *blk; 672 struct inpcb *inp = NULL; 673 struct socket *so; 674 struct tcpcb *tp; 675 int error; 676 char *s; 677 678 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 679 680 /* 681 * Ok, create the full blown connection, and set things up 682 * as they would have been set up if we had created the 683 * connection when the SYN arrived. If we can't create 684 * the connection, abort it. 685 */ 686 so = sonewconn(lso, 0); 687 if (so == NULL) { 688 /* 689 * Drop the connection; we will either send a RST or 690 * have the peer retransmit its SYN again after its 691 * RTO and try again. 692 */ 693 TCPSTAT_INC(tcps_listendrop); 694 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 695 log(LOG_DEBUG, "%s; %s: Socket create failed " 696 "due to limits or memory shortage\n", 697 s, __func__); 698 free(s, M_TCPLOG); 699 } 700 goto abort2; 701 } 702 #ifdef MAC 703 mac_socketpeer_set_from_mbuf(m, so); 704 #endif 705 706 inp = sotoinpcb(so); 707 inp->inp_inc.inc_fibnum = so->so_fibnum; 708 INP_WLOCK(inp); 709 /* 710 * Exclusive pcbinfo lock is not required in syncache socket case even 711 * if two inpcb locks can be acquired simultaneously: 712 * - the inpcb in LISTEN state, 713 * - the newly created inp. 714 * 715 * In this case, an inp cannot be at same time in LISTEN state and 716 * just created by an accept() call. 717 */ 718 INP_HASH_WLOCK(&V_tcbinfo); 719 720 /* Insert new socket into PCB hash list. */ 721 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 722 #ifdef INET6 723 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 724 inp->inp_vflag &= ~INP_IPV4; 725 inp->inp_vflag |= INP_IPV6; 726 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 727 } else { 728 inp->inp_vflag &= ~INP_IPV6; 729 inp->inp_vflag |= INP_IPV4; 730 #endif 731 inp->inp_laddr = sc->sc_inc.inc_laddr; 732 #ifdef INET6 733 } 734 #endif 735 736 /* 737 * If there's an mbuf and it has a flowid, then let's initialise the 738 * inp with that particular flowid. 739 */ 740 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 741 inp->inp_flowid = m->m_pkthdr.flowid; 742 inp->inp_flowtype = M_HASHTYPE_GET(m); 743 } 744 745 /* 746 * Install in the reservation hash table for now, but don't yet 747 * install a connection group since the full 4-tuple isn't yet 748 * configured. 749 */ 750 inp->inp_lport = sc->sc_inc.inc_lport; 751 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 752 /* 753 * Undo the assignments above if we failed to 754 * put the PCB on the hash lists. 755 */ 756 #ifdef INET6 757 if (sc->sc_inc.inc_flags & INC_ISIPV6) 758 inp->in6p_laddr = in6addr_any; 759 else 760 #endif 761 inp->inp_laddr.s_addr = INADDR_ANY; 762 inp->inp_lport = 0; 763 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 764 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 765 "with error %i\n", 766 s, __func__, error); 767 free(s, M_TCPLOG); 768 } 769 INP_HASH_WUNLOCK(&V_tcbinfo); 770 goto abort; 771 } 772 #ifdef INET6 773 if (inp->inp_vflag & INP_IPV6PROTO) { 774 struct inpcb *oinp = sotoinpcb(lso); 775 776 /* 777 * Inherit socket options from the listening socket. 778 * Note that in6p_inputopts are not (and should not be) 779 * copied, since it stores previously received options and is 780 * used to detect if each new option is different than the 781 * previous one and hence should be passed to a user. 782 * If we copied in6p_inputopts, a user would not be able to 783 * receive options just after calling the accept system call. 784 */ 785 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 786 if (oinp->in6p_outputopts) 787 inp->in6p_outputopts = 788 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 789 } 790 791 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 792 struct in6_addr laddr6; 793 struct sockaddr_in6 sin6; 794 795 sin6.sin6_family = AF_INET6; 796 sin6.sin6_len = sizeof(sin6); 797 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 798 sin6.sin6_port = sc->sc_inc.inc_fport; 799 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 800 laddr6 = inp->in6p_laddr; 801 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 802 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 803 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 804 thread0.td_ucred, m)) != 0) { 805 inp->in6p_laddr = laddr6; 806 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 807 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 808 "with error %i\n", 809 s, __func__, error); 810 free(s, M_TCPLOG); 811 } 812 INP_HASH_WUNLOCK(&V_tcbinfo); 813 goto abort; 814 } 815 /* Override flowlabel from in6_pcbconnect. */ 816 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 817 inp->inp_flow |= sc->sc_flowlabel; 818 } 819 #endif /* INET6 */ 820 #if defined(INET) && defined(INET6) 821 else 822 #endif 823 #ifdef INET 824 { 825 struct in_addr laddr; 826 struct sockaddr_in sin; 827 828 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 829 830 if (inp->inp_options == NULL) { 831 inp->inp_options = sc->sc_ipopts; 832 sc->sc_ipopts = NULL; 833 } 834 835 sin.sin_family = AF_INET; 836 sin.sin_len = sizeof(sin); 837 sin.sin_addr = sc->sc_inc.inc_faddr; 838 sin.sin_port = sc->sc_inc.inc_fport; 839 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 840 laddr = inp->inp_laddr; 841 if (inp->inp_laddr.s_addr == INADDR_ANY) 842 inp->inp_laddr = sc->sc_inc.inc_laddr; 843 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 844 thread0.td_ucred, m)) != 0) { 845 inp->inp_laddr = laddr; 846 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 847 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 848 "with error %i\n", 849 s, __func__, error); 850 free(s, M_TCPLOG); 851 } 852 INP_HASH_WUNLOCK(&V_tcbinfo); 853 goto abort; 854 } 855 } 856 #endif /* INET */ 857 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 858 /* Copy old policy into new socket's. */ 859 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 860 printf("syncache_socket: could not copy policy\n"); 861 #endif 862 INP_HASH_WUNLOCK(&V_tcbinfo); 863 tp = intotcpcb(inp); 864 tcp_state_change(tp, TCPS_SYN_RECEIVED); 865 tp->iss = sc->sc_iss; 866 tp->irs = sc->sc_irs; 867 tcp_rcvseqinit(tp); 868 tcp_sendseqinit(tp); 869 blk = sototcpcb(lso)->t_fb; 870 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 871 /* 872 * Our parents t_fb was not the default, 873 * we need to release our ref on tp->t_fb and 874 * pickup one on the new entry. 875 */ 876 struct tcp_function_block *rblk; 877 878 rblk = find_and_ref_tcp_fb(blk); 879 KASSERT(rblk != NULL, 880 ("cannot find blk %p out of syncache?", blk)); 881 if (tp->t_fb->tfb_tcp_fb_fini) 882 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 883 refcount_release(&tp->t_fb->tfb_refcnt); 884 tp->t_fb = rblk; 885 /* 886 * XXXrrs this is quite dangerous, it is possible 887 * for the new function to fail to init. We also 888 * are not asking if the handoff_is_ok though at 889 * the very start thats probalbly ok. 890 */ 891 if (tp->t_fb->tfb_tcp_fb_init) { 892 (*tp->t_fb->tfb_tcp_fb_init)(tp); 893 } 894 } 895 tp->snd_wl1 = sc->sc_irs; 896 tp->snd_max = tp->iss + 1; 897 tp->snd_nxt = tp->iss + 1; 898 tp->rcv_up = sc->sc_irs + 1; 899 tp->rcv_wnd = sc->sc_wnd; 900 tp->rcv_adv += tp->rcv_wnd; 901 tp->last_ack_sent = tp->rcv_nxt; 902 903 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 904 if (sc->sc_flags & SCF_NOOPT) 905 tp->t_flags |= TF_NOOPT; 906 else { 907 if (sc->sc_flags & SCF_WINSCALE) { 908 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 909 tp->snd_scale = sc->sc_requested_s_scale; 910 tp->request_r_scale = sc->sc_requested_r_scale; 911 } 912 if (sc->sc_flags & SCF_TIMESTAMP) { 913 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 914 tp->ts_recent = sc->sc_tsreflect; 915 tp->ts_recent_age = tcp_ts_getticks(); 916 tp->ts_offset = sc->sc_tsoff; 917 } 918 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 919 if (sc->sc_flags & SCF_SIGNATURE) 920 tp->t_flags |= TF_SIGNATURE; 921 #endif 922 if (sc->sc_flags & SCF_SACK) 923 tp->t_flags |= TF_SACK_PERMIT; 924 } 925 926 if (sc->sc_flags & SCF_ECN) 927 tp->t_flags |= TF_ECN_PERMIT; 928 929 /* 930 * Set up MSS and get cached values from tcp_hostcache. 931 * This might overwrite some of the defaults we just set. 932 */ 933 tcp_mss(tp, sc->sc_peer_mss); 934 935 /* 936 * If the SYN,ACK was retransmitted, indicate that CWND to be 937 * limited to one segment in cc_conn_init(). 938 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 939 */ 940 if (sc->sc_rxmits > 1) 941 tp->snd_cwnd = 1; 942 943 #ifdef TCP_OFFLOAD 944 /* 945 * Allow a TOE driver to install its hooks. Note that we hold the 946 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 947 * new connection before the TOE driver has done its thing. 948 */ 949 if (ADDED_BY_TOE(sc)) { 950 struct toedev *tod = sc->sc_tod; 951 952 tod->tod_offload_socket(tod, sc->sc_todctx, so); 953 } 954 #endif 955 /* 956 * Copy and activate timers. 957 */ 958 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 959 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 960 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 961 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 962 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 963 964 TCPSTAT_INC(tcps_accepts); 965 return (so); 966 967 abort: 968 INP_WUNLOCK(inp); 969 abort2: 970 if (so != NULL) 971 soabort(so); 972 return (NULL); 973 } 974 975 /* 976 * This function gets called when we receive an ACK for a 977 * socket in the LISTEN state. We look up the connection 978 * in the syncache, and if its there, we pull it out of 979 * the cache and turn it into a full-blown connection in 980 * the SYN-RECEIVED state. 981 * 982 * On syncache_socket() success the newly created socket 983 * has its underlying inp locked. 984 */ 985 int 986 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 987 struct socket **lsop, struct mbuf *m) 988 { 989 struct syncache *sc; 990 struct syncache_head *sch; 991 struct syncache scs; 992 char *s; 993 994 /* 995 * Global TCP locks are held because we manipulate the PCB lists 996 * and create a new socket. 997 */ 998 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 999 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1000 ("%s: can handle only ACK", __func__)); 1001 1002 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1003 SCH_LOCK_ASSERT(sch); 1004 1005 #ifdef INVARIANTS 1006 /* 1007 * Test code for syncookies comparing the syncache stored 1008 * values with the reconstructed values from the cookie. 1009 */ 1010 if (sc != NULL) 1011 syncookie_cmp(inc, sch, sc, th, to, *lsop); 1012 #endif 1013 1014 if (sc == NULL) { 1015 /* 1016 * There is no syncache entry, so see if this ACK is 1017 * a returning syncookie. To do this, first: 1018 * A. Check if syncookies are used in case of syncache 1019 * overflows 1020 * B. See if this socket has had a syncache entry dropped in 1021 * the recent past. We don't want to accept a bogus 1022 * syncookie if we've never received a SYN or accept it 1023 * twice. 1024 * C. check that the syncookie is valid. If it is, then 1025 * cobble up a fake syncache entry, and return. 1026 */ 1027 if (!V_tcp_syncookies) { 1028 SCH_UNLOCK(sch); 1029 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1030 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1031 "segment rejected (syncookies disabled)\n", 1032 s, __func__); 1033 goto failed; 1034 } 1035 if (!V_tcp_syncookiesonly && 1036 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1037 SCH_UNLOCK(sch); 1038 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1039 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1040 "segment rejected (no syncache entry)\n", 1041 s, __func__); 1042 goto failed; 1043 } 1044 bzero(&scs, sizeof(scs)); 1045 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 1046 SCH_UNLOCK(sch); 1047 if (sc == NULL) { 1048 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1049 log(LOG_DEBUG, "%s; %s: Segment failed " 1050 "SYNCOOKIE authentication, segment rejected " 1051 "(probably spoofed)\n", s, __func__); 1052 goto failed; 1053 } 1054 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1055 /* If received ACK has MD5 signature, check it. */ 1056 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1057 (!TCPMD5_ENABLED() || 1058 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1059 /* Drop the ACK. */ 1060 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1061 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1062 "MD5 signature doesn't match.\n", 1063 s, __func__); 1064 free(s, M_TCPLOG); 1065 } 1066 TCPSTAT_INC(tcps_sig_err_sigopt); 1067 return (-1); /* Do not send RST */ 1068 } 1069 #endif /* TCP_SIGNATURE */ 1070 } else { 1071 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1072 /* 1073 * If listening socket requested TCP digests, check that 1074 * received ACK has signature and it is correct. 1075 * If not, drop the ACK and leave sc entry in th cache, 1076 * because SYN was received with correct signature. 1077 */ 1078 if (sc->sc_flags & SCF_SIGNATURE) { 1079 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1080 /* No signature */ 1081 TCPSTAT_INC(tcps_sig_err_nosigopt); 1082 SCH_UNLOCK(sch); 1083 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1084 log(LOG_DEBUG, "%s; %s: Segment " 1085 "rejected, MD5 signature wasn't " 1086 "provided.\n", s, __func__); 1087 free(s, M_TCPLOG); 1088 } 1089 return (-1); /* Do not send RST */ 1090 } 1091 if (!TCPMD5_ENABLED() || 1092 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1093 /* Doesn't match or no SA */ 1094 SCH_UNLOCK(sch); 1095 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1096 log(LOG_DEBUG, "%s; %s: Segment " 1097 "rejected, MD5 signature doesn't " 1098 "match.\n", s, __func__); 1099 free(s, M_TCPLOG); 1100 } 1101 return (-1); /* Do not send RST */ 1102 } 1103 } 1104 #endif /* TCP_SIGNATURE */ 1105 /* 1106 * Pull out the entry to unlock the bucket row. 1107 * 1108 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1109 * tcp_state_change(). The tcpcb is not existent at this 1110 * moment. A new one will be allocated via syncache_socket-> 1111 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1112 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1113 */ 1114 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1115 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1116 sch->sch_length--; 1117 #ifdef TCP_OFFLOAD 1118 if (ADDED_BY_TOE(sc)) { 1119 struct toedev *tod = sc->sc_tod; 1120 1121 tod->tod_syncache_removed(tod, sc->sc_todctx); 1122 } 1123 #endif 1124 SCH_UNLOCK(sch); 1125 } 1126 1127 /* 1128 * Segment validation: 1129 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1130 */ 1131 if (th->th_ack != sc->sc_iss + 1) { 1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1133 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1134 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1135 goto failed; 1136 } 1137 1138 /* 1139 * The SEQ must fall in the window starting at the received 1140 * initial receive sequence number + 1 (the SYN). 1141 */ 1142 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1143 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1144 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1145 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1146 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1147 goto failed; 1148 } 1149 1150 /* 1151 * If timestamps were not negotiated during SYN/ACK they 1152 * must not appear on any segment during this session. 1153 */ 1154 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1155 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1156 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1157 "segment rejected\n", s, __func__); 1158 goto failed; 1159 } 1160 1161 /* 1162 * If timestamps were negotiated during SYN/ACK they should 1163 * appear on every segment during this session. 1164 * XXXAO: This is only informal as there have been unverified 1165 * reports of non-compliants stacks. 1166 */ 1167 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1168 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1169 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1170 "no action\n", s, __func__); 1171 free(s, M_TCPLOG); 1172 s = NULL; 1173 } 1174 } 1175 1176 *lsop = syncache_socket(sc, *lsop, m); 1177 1178 if (*lsop == NULL) 1179 TCPSTAT_INC(tcps_sc_aborted); 1180 else 1181 TCPSTAT_INC(tcps_sc_completed); 1182 1183 /* how do we find the inp for the new socket? */ 1184 if (sc != &scs) 1185 syncache_free(sc); 1186 return (1); 1187 failed: 1188 if (sc != NULL && sc != &scs) 1189 syncache_free(sc); 1190 if (s != NULL) 1191 free(s, M_TCPLOG); 1192 *lsop = NULL; 1193 return (0); 1194 } 1195 1196 static void 1197 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1198 uint64_t response_cookie) 1199 { 1200 struct inpcb *inp; 1201 struct tcpcb *tp; 1202 unsigned int *pending_counter; 1203 1204 /* 1205 * Global TCP locks are held because we manipulate the PCB lists 1206 * and create a new socket. 1207 */ 1208 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1209 1210 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1211 *lsop = syncache_socket(sc, *lsop, m); 1212 if (*lsop == NULL) { 1213 TCPSTAT_INC(tcps_sc_aborted); 1214 atomic_subtract_int(pending_counter, 1); 1215 } else { 1216 soisconnected(*lsop); 1217 inp = sotoinpcb(*lsop); 1218 tp = intotcpcb(inp); 1219 tp->t_flags |= TF_FASTOPEN; 1220 tp->t_tfo_cookie.server = response_cookie; 1221 tp->snd_max = tp->iss; 1222 tp->snd_nxt = tp->iss; 1223 tp->t_tfo_pending = pending_counter; 1224 TCPSTAT_INC(tcps_sc_completed); 1225 } 1226 } 1227 1228 /* 1229 * Given a LISTEN socket and an inbound SYN request, add 1230 * this to the syn cache, and send back a segment: 1231 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1232 * to the source. 1233 * 1234 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1235 * Doing so would require that we hold onto the data and deliver it 1236 * to the application. However, if we are the target of a SYN-flood 1237 * DoS attack, an attacker could send data which would eventually 1238 * consume all available buffer space if it were ACKed. By not ACKing 1239 * the data, we avoid this DoS scenario. 1240 * 1241 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1242 * cookie is processed and a new socket is created. In this case, any data 1243 * accompanying the SYN will be queued to the socket by tcp_input() and will 1244 * be ACKed either when the application sends response data or the delayed 1245 * ACK timer expires, whichever comes first. 1246 */ 1247 int 1248 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1249 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1250 void *todctx) 1251 { 1252 struct tcpcb *tp; 1253 struct socket *so; 1254 struct syncache *sc = NULL; 1255 struct syncache_head *sch; 1256 struct mbuf *ipopts = NULL; 1257 u_int ltflags; 1258 int win, ip_ttl, ip_tos; 1259 char *s; 1260 int rv = 0; 1261 #ifdef INET6 1262 int autoflowlabel = 0; 1263 #endif 1264 #ifdef MAC 1265 struct label *maclabel; 1266 #endif 1267 struct syncache scs; 1268 struct ucred *cred; 1269 uint64_t tfo_response_cookie; 1270 unsigned int *tfo_pending = NULL; 1271 int tfo_cookie_valid = 0; 1272 int tfo_response_cookie_valid = 0; 1273 1274 INP_WLOCK_ASSERT(inp); /* listen socket */ 1275 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1276 ("%s: unexpected tcp flags", __func__)); 1277 1278 /* 1279 * Combine all so/tp operations very early to drop the INP lock as 1280 * soon as possible. 1281 */ 1282 so = *lsop; 1283 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1284 tp = sototcpcb(so); 1285 cred = crhold(so->so_cred); 1286 1287 #ifdef INET6 1288 if ((inc->inc_flags & INC_ISIPV6) && 1289 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1290 autoflowlabel = 1; 1291 #endif 1292 ip_ttl = inp->inp_ip_ttl; 1293 ip_tos = inp->inp_ip_tos; 1294 win = so->sol_sbrcv_hiwat; 1295 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1296 1297 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1298 (tp->t_tfo_pending != NULL) && 1299 (to->to_flags & TOF_FASTOPEN)) { 1300 /* 1301 * Limit the number of pending TFO connections to 1302 * approximately half of the queue limit. This prevents TFO 1303 * SYN floods from starving the service by filling the 1304 * listen queue with bogus TFO connections. 1305 */ 1306 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1307 (so->sol_qlimit / 2)) { 1308 int result; 1309 1310 result = tcp_fastopen_check_cookie(inc, 1311 to->to_tfo_cookie, to->to_tfo_len, 1312 &tfo_response_cookie); 1313 tfo_cookie_valid = (result > 0); 1314 tfo_response_cookie_valid = (result >= 0); 1315 } 1316 1317 /* 1318 * Remember the TFO pending counter as it will have to be 1319 * decremented below if we don't make it to syncache_tfo_expand(). 1320 */ 1321 tfo_pending = tp->t_tfo_pending; 1322 } 1323 1324 /* By the time we drop the lock these should no longer be used. */ 1325 so = NULL; 1326 tp = NULL; 1327 1328 #ifdef MAC 1329 if (mac_syncache_init(&maclabel) != 0) { 1330 INP_WUNLOCK(inp); 1331 goto done; 1332 } else 1333 mac_syncache_create(maclabel, inp); 1334 #endif 1335 if (!tfo_cookie_valid) 1336 INP_WUNLOCK(inp); 1337 1338 /* 1339 * Remember the IP options, if any. 1340 */ 1341 #ifdef INET6 1342 if (!(inc->inc_flags & INC_ISIPV6)) 1343 #endif 1344 #ifdef INET 1345 ipopts = (m) ? ip_srcroute(m) : NULL; 1346 #else 1347 ipopts = NULL; 1348 #endif 1349 1350 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1351 /* 1352 * If listening socket requested TCP digests, check that received 1353 * SYN has signature and it is correct. If signature doesn't match 1354 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1355 */ 1356 if (ltflags & TF_SIGNATURE) { 1357 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1358 TCPSTAT_INC(tcps_sig_err_nosigopt); 1359 goto done; 1360 } 1361 if (!TCPMD5_ENABLED() || 1362 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1363 goto done; 1364 } 1365 #endif /* TCP_SIGNATURE */ 1366 /* 1367 * See if we already have an entry for this connection. 1368 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1369 * 1370 * XXX: should the syncache be re-initialized with the contents 1371 * of the new SYN here (which may have different options?) 1372 * 1373 * XXX: We do not check the sequence number to see if this is a 1374 * real retransmit or a new connection attempt. The question is 1375 * how to handle such a case; either ignore it as spoofed, or 1376 * drop the current entry and create a new one? 1377 */ 1378 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1379 SCH_LOCK_ASSERT(sch); 1380 if (sc != NULL) { 1381 if (tfo_cookie_valid) 1382 INP_WUNLOCK(inp); 1383 TCPSTAT_INC(tcps_sc_dupsyn); 1384 if (ipopts) { 1385 /* 1386 * If we were remembering a previous source route, 1387 * forget it and use the new one we've been given. 1388 */ 1389 if (sc->sc_ipopts) 1390 (void) m_free(sc->sc_ipopts); 1391 sc->sc_ipopts = ipopts; 1392 } 1393 /* 1394 * Update timestamp if present. 1395 */ 1396 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1397 sc->sc_tsreflect = to->to_tsval; 1398 else 1399 sc->sc_flags &= ~SCF_TIMESTAMP; 1400 #ifdef MAC 1401 /* 1402 * Since we have already unconditionally allocated label 1403 * storage, free it up. The syncache entry will already 1404 * have an initialized label we can use. 1405 */ 1406 mac_syncache_destroy(&maclabel); 1407 #endif 1408 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1409 /* Retransmit SYN|ACK and reset retransmit count. */ 1410 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1411 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1412 "resetting timer and retransmitting SYN|ACK\n", 1413 s, __func__); 1414 free(s, M_TCPLOG); 1415 } 1416 if (syncache_respond(sc, sch, 1, m) == 0) { 1417 sc->sc_rxmits = 0; 1418 syncache_timeout(sc, sch, 1); 1419 TCPSTAT_INC(tcps_sndacks); 1420 TCPSTAT_INC(tcps_sndtotal); 1421 } 1422 SCH_UNLOCK(sch); 1423 goto donenoprobe; 1424 } 1425 1426 if (tfo_cookie_valid) { 1427 bzero(&scs, sizeof(scs)); 1428 sc = &scs; 1429 goto skip_alloc; 1430 } 1431 1432 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1433 if (sc == NULL) { 1434 /* 1435 * The zone allocator couldn't provide more entries. 1436 * Treat this as if the cache was full; drop the oldest 1437 * entry and insert the new one. 1438 */ 1439 TCPSTAT_INC(tcps_sc_zonefail); 1440 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1441 sch->sch_last_overflow = time_uptime; 1442 syncache_drop(sc, sch); 1443 } 1444 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1445 if (sc == NULL) { 1446 if (V_tcp_syncookies) { 1447 bzero(&scs, sizeof(scs)); 1448 sc = &scs; 1449 } else { 1450 SCH_UNLOCK(sch); 1451 if (ipopts) 1452 (void) m_free(ipopts); 1453 goto done; 1454 } 1455 } 1456 } 1457 1458 skip_alloc: 1459 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1460 sc->sc_tfo_cookie = &tfo_response_cookie; 1461 1462 /* 1463 * Fill in the syncache values. 1464 */ 1465 #ifdef MAC 1466 sc->sc_label = maclabel; 1467 #endif 1468 sc->sc_cred = cred; 1469 cred = NULL; 1470 sc->sc_ipopts = ipopts; 1471 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1472 #ifdef INET6 1473 if (!(inc->inc_flags & INC_ISIPV6)) 1474 #endif 1475 { 1476 sc->sc_ip_tos = ip_tos; 1477 sc->sc_ip_ttl = ip_ttl; 1478 } 1479 #ifdef TCP_OFFLOAD 1480 sc->sc_tod = tod; 1481 sc->sc_todctx = todctx; 1482 #endif 1483 sc->sc_irs = th->th_seq; 1484 sc->sc_iss = arc4random(); 1485 sc->sc_flags = 0; 1486 sc->sc_flowlabel = 0; 1487 1488 /* 1489 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1490 * win was derived from socket earlier in the function. 1491 */ 1492 win = imax(win, 0); 1493 win = imin(win, TCP_MAXWIN); 1494 sc->sc_wnd = win; 1495 1496 if (V_tcp_do_rfc1323) { 1497 /* 1498 * A timestamp received in a SYN makes 1499 * it ok to send timestamp requests and replies. 1500 */ 1501 if (to->to_flags & TOF_TS) { 1502 sc->sc_tsreflect = to->to_tsval; 1503 sc->sc_flags |= SCF_TIMESTAMP; 1504 sc->sc_tsoff = tcp_new_ts_offset(inc); 1505 } 1506 if (to->to_flags & TOF_SCALE) { 1507 int wscale = 0; 1508 1509 /* 1510 * Pick the smallest possible scaling factor that 1511 * will still allow us to scale up to sb_max, aka 1512 * kern.ipc.maxsockbuf. 1513 * 1514 * We do this because there are broken firewalls that 1515 * will corrupt the window scale option, leading to 1516 * the other endpoint believing that our advertised 1517 * window is unscaled. At scale factors larger than 1518 * 5 the unscaled window will drop below 1500 bytes, 1519 * leading to serious problems when traversing these 1520 * broken firewalls. 1521 * 1522 * With the default maxsockbuf of 256K, a scale factor 1523 * of 3 will be chosen by this algorithm. Those who 1524 * choose a larger maxsockbuf should watch out 1525 * for the compatibility problems mentioned above. 1526 * 1527 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1528 * or <SYN,ACK>) segment itself is never scaled. 1529 */ 1530 while (wscale < TCP_MAX_WINSHIFT && 1531 (TCP_MAXWIN << wscale) < sb_max) 1532 wscale++; 1533 sc->sc_requested_r_scale = wscale; 1534 sc->sc_requested_s_scale = to->to_wscale; 1535 sc->sc_flags |= SCF_WINSCALE; 1536 } 1537 } 1538 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1539 /* 1540 * If listening socket requested TCP digests, flag this in the 1541 * syncache so that syncache_respond() will do the right thing 1542 * with the SYN+ACK. 1543 */ 1544 if (ltflags & TF_SIGNATURE) 1545 sc->sc_flags |= SCF_SIGNATURE; 1546 #endif /* TCP_SIGNATURE */ 1547 if (to->to_flags & TOF_SACKPERM) 1548 sc->sc_flags |= SCF_SACK; 1549 if (to->to_flags & TOF_MSS) 1550 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1551 if (ltflags & TF_NOOPT) 1552 sc->sc_flags |= SCF_NOOPT; 1553 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1554 sc->sc_flags |= SCF_ECN; 1555 1556 if (V_tcp_syncookies) 1557 sc->sc_iss = syncookie_generate(sch, sc); 1558 #ifdef INET6 1559 if (autoflowlabel) { 1560 if (V_tcp_syncookies) 1561 sc->sc_flowlabel = sc->sc_iss; 1562 else 1563 sc->sc_flowlabel = ip6_randomflowlabel(); 1564 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1565 } 1566 #endif 1567 SCH_UNLOCK(sch); 1568 1569 if (tfo_cookie_valid) { 1570 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1571 /* INP_WUNLOCK(inp) will be performed by the caller */ 1572 rv = 1; 1573 goto tfo_expanded; 1574 } 1575 1576 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1577 /* 1578 * Do a standard 3-way handshake. 1579 */ 1580 if (syncache_respond(sc, sch, 0, m) == 0) { 1581 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1582 syncache_free(sc); 1583 else if (sc != &scs) 1584 syncache_insert(sc, sch); /* locks and unlocks sch */ 1585 TCPSTAT_INC(tcps_sndacks); 1586 TCPSTAT_INC(tcps_sndtotal); 1587 } else { 1588 if (sc != &scs) 1589 syncache_free(sc); 1590 TCPSTAT_INC(tcps_sc_dropped); 1591 } 1592 goto donenoprobe; 1593 1594 done: 1595 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1596 donenoprobe: 1597 if (m) { 1598 *lsop = NULL; 1599 m_freem(m); 1600 } 1601 /* 1602 * If tfo_pending is not NULL here, then a TFO SYN that did not 1603 * result in a new socket was processed and the associated pending 1604 * counter has not yet been decremented. All such TFO processing paths 1605 * transit this point. 1606 */ 1607 if (tfo_pending != NULL) 1608 tcp_fastopen_decrement_counter(tfo_pending); 1609 1610 tfo_expanded: 1611 if (cred != NULL) 1612 crfree(cred); 1613 #ifdef MAC 1614 if (sc == &scs) 1615 mac_syncache_destroy(&maclabel); 1616 #endif 1617 return (rv); 1618 } 1619 1620 /* 1621 * Send SYN|ACK to the peer. Either in response to the peer's SYN, 1622 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1623 */ 1624 static int 1625 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked, 1626 const struct mbuf *m0) 1627 { 1628 struct ip *ip = NULL; 1629 struct mbuf *m; 1630 struct tcphdr *th = NULL; 1631 int optlen, error = 0; /* Make compiler happy */ 1632 u_int16_t hlen, tlen, mssopt; 1633 struct tcpopt to; 1634 #ifdef INET6 1635 struct ip6_hdr *ip6 = NULL; 1636 #endif 1637 hlen = 1638 #ifdef INET6 1639 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1640 #endif 1641 sizeof(struct ip); 1642 tlen = hlen + sizeof(struct tcphdr); 1643 1644 /* Determine MSS we advertize to other end of connection. */ 1645 mssopt = max(tcp_mssopt(&sc->sc_inc), V_tcp_minmss); 1646 1647 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1648 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1649 ("syncache: mbuf too small")); 1650 1651 /* Create the IP+TCP header from scratch. */ 1652 m = m_gethdr(M_NOWAIT, MT_DATA); 1653 if (m == NULL) 1654 return (ENOBUFS); 1655 #ifdef MAC 1656 mac_syncache_create_mbuf(sc->sc_label, m); 1657 #endif 1658 m->m_data += max_linkhdr; 1659 m->m_len = tlen; 1660 m->m_pkthdr.len = tlen; 1661 m->m_pkthdr.rcvif = NULL; 1662 1663 #ifdef INET6 1664 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1665 ip6 = mtod(m, struct ip6_hdr *); 1666 ip6->ip6_vfc = IPV6_VERSION; 1667 ip6->ip6_nxt = IPPROTO_TCP; 1668 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1669 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1670 ip6->ip6_plen = htons(tlen - hlen); 1671 /* ip6_hlim is set after checksum */ 1672 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1673 ip6->ip6_flow |= sc->sc_flowlabel; 1674 1675 th = (struct tcphdr *)(ip6 + 1); 1676 } 1677 #endif 1678 #if defined(INET6) && defined(INET) 1679 else 1680 #endif 1681 #ifdef INET 1682 { 1683 ip = mtod(m, struct ip *); 1684 ip->ip_v = IPVERSION; 1685 ip->ip_hl = sizeof(struct ip) >> 2; 1686 ip->ip_len = htons(tlen); 1687 ip->ip_id = 0; 1688 ip->ip_off = 0; 1689 ip->ip_sum = 0; 1690 ip->ip_p = IPPROTO_TCP; 1691 ip->ip_src = sc->sc_inc.inc_laddr; 1692 ip->ip_dst = sc->sc_inc.inc_faddr; 1693 ip->ip_ttl = sc->sc_ip_ttl; 1694 ip->ip_tos = sc->sc_ip_tos; 1695 1696 /* 1697 * See if we should do MTU discovery. Route lookups are 1698 * expensive, so we will only unset the DF bit if: 1699 * 1700 * 1) path_mtu_discovery is disabled 1701 * 2) the SCF_UNREACH flag has been set 1702 */ 1703 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1704 ip->ip_off |= htons(IP_DF); 1705 1706 th = (struct tcphdr *)(ip + 1); 1707 } 1708 #endif /* INET */ 1709 th->th_sport = sc->sc_inc.inc_lport; 1710 th->th_dport = sc->sc_inc.inc_fport; 1711 1712 th->th_seq = htonl(sc->sc_iss); 1713 th->th_ack = htonl(sc->sc_irs + 1); 1714 th->th_off = sizeof(struct tcphdr) >> 2; 1715 th->th_x2 = 0; 1716 th->th_flags = TH_SYN|TH_ACK; 1717 th->th_win = htons(sc->sc_wnd); 1718 th->th_urp = 0; 1719 1720 if (sc->sc_flags & SCF_ECN) { 1721 th->th_flags |= TH_ECE; 1722 TCPSTAT_INC(tcps_ecn_shs); 1723 } 1724 1725 /* Tack on the TCP options. */ 1726 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1727 to.to_flags = 0; 1728 1729 to.to_mss = mssopt; 1730 to.to_flags = TOF_MSS; 1731 if (sc->sc_flags & SCF_WINSCALE) { 1732 to.to_wscale = sc->sc_requested_r_scale; 1733 to.to_flags |= TOF_SCALE; 1734 } 1735 if (sc->sc_flags & SCF_TIMESTAMP) { 1736 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1737 to.to_tsecr = sc->sc_tsreflect; 1738 to.to_flags |= TOF_TS; 1739 } 1740 if (sc->sc_flags & SCF_SACK) 1741 to.to_flags |= TOF_SACKPERM; 1742 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1743 if (sc->sc_flags & SCF_SIGNATURE) 1744 to.to_flags |= TOF_SIGNATURE; 1745 #endif 1746 if (sc->sc_tfo_cookie) { 1747 to.to_flags |= TOF_FASTOPEN; 1748 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1749 to.to_tfo_cookie = sc->sc_tfo_cookie; 1750 /* don't send cookie again when retransmitting response */ 1751 sc->sc_tfo_cookie = NULL; 1752 } 1753 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1754 1755 /* Adjust headers by option size. */ 1756 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1757 m->m_len += optlen; 1758 m->m_pkthdr.len += optlen; 1759 #ifdef INET6 1760 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1761 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1762 else 1763 #endif 1764 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1765 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1766 if (sc->sc_flags & SCF_SIGNATURE) { 1767 KASSERT(to.to_flags & TOF_SIGNATURE, 1768 ("tcp_addoptions() didn't set tcp_signature")); 1769 1770 /* NOTE: to.to_signature is inside of mbuf */ 1771 if (!TCPMD5_ENABLED() || 1772 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1773 m_freem(m); 1774 return (EACCES); 1775 } 1776 } 1777 #endif 1778 } else 1779 optlen = 0; 1780 1781 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1782 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1783 /* 1784 * If we have peer's SYN and it has a flowid, then let's assign it to 1785 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1786 * to SYN|ACK due to lack of inp here. 1787 */ 1788 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1789 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1790 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1791 } 1792 #ifdef INET6 1793 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1794 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1795 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1796 IPPROTO_TCP, 0); 1797 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1798 #ifdef TCP_OFFLOAD 1799 if (ADDED_BY_TOE(sc)) { 1800 struct toedev *tod = sc->sc_tod; 1801 1802 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1803 1804 return (error); 1805 } 1806 #endif 1807 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 1808 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1809 } 1810 #endif 1811 #if defined(INET6) && defined(INET) 1812 else 1813 #endif 1814 #ifdef INET 1815 { 1816 m->m_pkthdr.csum_flags = CSUM_TCP; 1817 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1818 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1819 #ifdef TCP_OFFLOAD 1820 if (ADDED_BY_TOE(sc)) { 1821 struct toedev *tod = sc->sc_tod; 1822 1823 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1824 1825 return (error); 1826 } 1827 #endif 1828 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 1829 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1830 } 1831 #endif 1832 return (error); 1833 } 1834 1835 /* 1836 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1837 * that exceed the capacity of the syncache by avoiding the storage of any 1838 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1839 * attacks where the attacker does not have access to our responses. 1840 * 1841 * Syncookies encode and include all necessary information about the 1842 * connection setup within the SYN|ACK that we send back. That way we 1843 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1844 * (if ever). Normally the syncache and syncookies are running in parallel 1845 * with the latter taking over when the former is exhausted. When matching 1846 * syncache entry is found the syncookie is ignored. 1847 * 1848 * The only reliable information persisting the 3WHS is our initial sequence 1849 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1850 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1851 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1852 * returns and signifies a legitimate connection if it matches the ACK. 1853 * 1854 * The available space of 32 bits to store the hash and to encode the SYN 1855 * option information is very tight and we should have at least 24 bits for 1856 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1857 * 1858 * SYN option information we have to encode to fully restore a connection: 1859 * MSS: is imporant to chose an optimal segment size to avoid IP level 1860 * fragmentation along the path. The common MSS values can be encoded 1861 * in a 3-bit table. Uncommon values are captured by the next lower value 1862 * in the table leading to a slight increase in packetization overhead. 1863 * WSCALE: is necessary to allow large windows to be used for high delay- 1864 * bandwidth product links. Not scaling the window when it was initially 1865 * negotiated is bad for performance as lack of scaling further decreases 1866 * the apparent available send window. We only need to encode the WSCALE 1867 * we received from the remote end. Our end can be recalculated at any 1868 * time. The common WSCALE values can be encoded in a 3-bit table. 1869 * Uncommon values are captured by the next lower value in the table 1870 * making us under-estimate the available window size halving our 1871 * theoretically possible maximum throughput for that connection. 1872 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1873 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1874 * that are included in all segments on a connection. We enable them when 1875 * the ACK has them. 1876 * 1877 * Security of syncookies and attack vectors: 1878 * 1879 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1880 * together with the gloabl secret to make it unique per connection attempt. 1881 * Thus any change of any of those parameters results in a different MAC output 1882 * in an unpredictable way unless a collision is encountered. 24 bits of the 1883 * MAC are embedded into the ISS. 1884 * 1885 * To prevent replay attacks two rotating global secrets are updated with a 1886 * new random value every 15 seconds. The life-time of a syncookie is thus 1887 * 15-30 seconds. 1888 * 1889 * Vector 1: Attacking the secret. This requires finding a weakness in the 1890 * MAC itself or the way it is used here. The attacker can do a chosen plain 1891 * text attack by varying and testing the all parameters under his control. 1892 * The strength depends on the size and randomness of the secret, and the 1893 * cryptographic security of the MAC function. Due to the constant updating 1894 * of the secret the attacker has at most 29.999 seconds to find the secret 1895 * and launch spoofed connections. After that he has to start all over again. 1896 * 1897 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1898 * size an average of 4,823 attempts are required for a 50% chance of success 1899 * to spoof a single syncookie (birthday collision paradox). However the 1900 * attacker is blind and doesn't know if one of his attempts succeeded unless 1901 * he has a side channel to interfere success from. A single connection setup 1902 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1903 * This many attempts are required for each one blind spoofed connection. For 1904 * every additional spoofed connection he has to launch another N attempts. 1905 * Thus for a sustained rate 100 spoofed connections per second approximately 1906 * 1,800,000 packets per second would have to be sent. 1907 * 1908 * NB: The MAC function should be fast so that it doesn't become a CPU 1909 * exhaustion attack vector itself. 1910 * 1911 * References: 1912 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1913 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1914 * http://cr.yp.to/syncookies.html (overview) 1915 * http://cr.yp.to/syncookies/archive (details) 1916 * 1917 * 1918 * Schematic construction of a syncookie enabled Initial Sequence Number: 1919 * 0 1 2 3 1920 * 12345678901234567890123456789012 1921 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1922 * 1923 * x 24 MAC (truncated) 1924 * W 3 Send Window Scale index 1925 * M 3 MSS index 1926 * S 1 SACK permitted 1927 * P 1 Odd/even secret 1928 */ 1929 1930 /* 1931 * Distribution and probability of certain MSS values. Those in between are 1932 * rounded down to the next lower one. 1933 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1934 * .2% .3% 5% 7% 7% 20% 15% 45% 1935 */ 1936 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1937 1938 /* 1939 * Distribution and probability of certain WSCALE values. We have to map the 1940 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1941 * bits based on prevalence of certain values. Where we don't have an exact 1942 * match for are rounded down to the next lower one letting us under-estimate 1943 * the true available window. At the moment this would happen only for the 1944 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1945 * and window size). The absence of the WSCALE option (no scaling in either 1946 * direction) is encoded with index zero. 1947 * [WSCALE values histograms, Allman, 2012] 1948 * X 10 10 35 5 6 14 10% by host 1949 * X 11 4 5 5 18 49 3% by connections 1950 */ 1951 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1952 1953 /* 1954 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1955 * and good cryptographic properties. 1956 */ 1957 static uint32_t 1958 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1959 uint8_t *secbits, uintptr_t secmod) 1960 { 1961 SIPHASH_CTX ctx; 1962 uint32_t siphash[2]; 1963 1964 SipHash24_Init(&ctx); 1965 SipHash_SetKey(&ctx, secbits); 1966 switch (inc->inc_flags & INC_ISIPV6) { 1967 #ifdef INET 1968 case 0: 1969 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1970 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1971 break; 1972 #endif 1973 #ifdef INET6 1974 case INC_ISIPV6: 1975 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1976 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1977 break; 1978 #endif 1979 } 1980 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1981 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1982 SipHash_Update(&ctx, &irs, sizeof(irs)); 1983 SipHash_Update(&ctx, &flags, sizeof(flags)); 1984 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1985 SipHash_Final((u_int8_t *)&siphash, &ctx); 1986 1987 return (siphash[0] ^ siphash[1]); 1988 } 1989 1990 static tcp_seq 1991 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1992 { 1993 u_int i, secbit, wscale; 1994 uint32_t iss, hash; 1995 uint8_t *secbits; 1996 union syncookie cookie; 1997 1998 SCH_LOCK_ASSERT(sch); 1999 2000 cookie.cookie = 0; 2001 2002 /* Map our computed MSS into the 3-bit index. */ 2003 for (i = nitems(tcp_sc_msstab) - 1; 2004 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2005 i--) 2006 ; 2007 cookie.flags.mss_idx = i; 2008 2009 /* 2010 * Map the send window scale into the 3-bit index but only if 2011 * the wscale option was received. 2012 */ 2013 if (sc->sc_flags & SCF_WINSCALE) { 2014 wscale = sc->sc_requested_s_scale; 2015 for (i = nitems(tcp_sc_wstab) - 1; 2016 tcp_sc_wstab[i] > wscale && i > 0; 2017 i--) 2018 ; 2019 cookie.flags.wscale_idx = i; 2020 } 2021 2022 /* Can we do SACK? */ 2023 if (sc->sc_flags & SCF_SACK) 2024 cookie.flags.sack_ok = 1; 2025 2026 /* Which of the two secrets to use. */ 2027 secbit = sch->sch_sc->secret.oddeven & 0x1; 2028 cookie.flags.odd_even = secbit; 2029 2030 secbits = sch->sch_sc->secret.key[secbit]; 2031 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2032 (uintptr_t)sch); 2033 2034 /* 2035 * Put the flags into the hash and XOR them to get better ISS number 2036 * variance. This doesn't enhance the cryptographic strength and is 2037 * done to prevent the 8 cookie bits from showing up directly on the 2038 * wire. 2039 */ 2040 iss = hash & ~0xff; 2041 iss |= cookie.cookie ^ (hash >> 24); 2042 2043 TCPSTAT_INC(tcps_sc_sendcookie); 2044 return (iss); 2045 } 2046 2047 static struct syncache * 2048 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2049 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2050 struct socket *lso) 2051 { 2052 uint32_t hash; 2053 uint8_t *secbits; 2054 tcp_seq ack, seq; 2055 int wnd, wscale = 0; 2056 union syncookie cookie; 2057 2058 SCH_LOCK_ASSERT(sch); 2059 2060 /* 2061 * Pull information out of SYN-ACK/ACK and revert sequence number 2062 * advances. 2063 */ 2064 ack = th->th_ack - 1; 2065 seq = th->th_seq - 1; 2066 2067 /* 2068 * Unpack the flags containing enough information to restore the 2069 * connection. 2070 */ 2071 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2072 2073 /* Which of the two secrets to use. */ 2074 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 2075 2076 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2077 2078 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2079 if ((ack & ~0xff) != (hash & ~0xff)) 2080 return (NULL); 2081 2082 /* Fill in the syncache values. */ 2083 sc->sc_flags = 0; 2084 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2085 sc->sc_ipopts = NULL; 2086 2087 sc->sc_irs = seq; 2088 sc->sc_iss = ack; 2089 2090 switch (inc->inc_flags & INC_ISIPV6) { 2091 #ifdef INET 2092 case 0: 2093 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2094 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2095 break; 2096 #endif 2097 #ifdef INET6 2098 case INC_ISIPV6: 2099 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2100 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2101 break; 2102 #endif 2103 } 2104 2105 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2106 2107 /* We can simply recompute receive window scale we sent earlier. */ 2108 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2109 wscale++; 2110 2111 /* Only use wscale if it was enabled in the orignal SYN. */ 2112 if (cookie.flags.wscale_idx > 0) { 2113 sc->sc_requested_r_scale = wscale; 2114 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2115 sc->sc_flags |= SCF_WINSCALE; 2116 } 2117 2118 wnd = lso->sol_sbrcv_hiwat; 2119 wnd = imax(wnd, 0); 2120 wnd = imin(wnd, TCP_MAXWIN); 2121 sc->sc_wnd = wnd; 2122 2123 if (cookie.flags.sack_ok) 2124 sc->sc_flags |= SCF_SACK; 2125 2126 if (to->to_flags & TOF_TS) { 2127 sc->sc_flags |= SCF_TIMESTAMP; 2128 sc->sc_tsreflect = to->to_tsval; 2129 sc->sc_tsoff = tcp_new_ts_offset(inc); 2130 } 2131 2132 if (to->to_flags & TOF_SIGNATURE) 2133 sc->sc_flags |= SCF_SIGNATURE; 2134 2135 sc->sc_rxmits = 0; 2136 2137 TCPSTAT_INC(tcps_sc_recvcookie); 2138 return (sc); 2139 } 2140 2141 #ifdef INVARIANTS 2142 static int 2143 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2144 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2145 struct socket *lso) 2146 { 2147 struct syncache scs, *scx; 2148 char *s; 2149 2150 bzero(&scs, sizeof(scs)); 2151 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2152 2153 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2154 return (0); 2155 2156 if (scx != NULL) { 2157 if (sc->sc_peer_mss != scx->sc_peer_mss) 2158 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2159 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2160 2161 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2162 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2163 s, __func__, sc->sc_requested_r_scale, 2164 scx->sc_requested_r_scale); 2165 2166 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2167 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2168 s, __func__, sc->sc_requested_s_scale, 2169 scx->sc_requested_s_scale); 2170 2171 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2172 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2173 } 2174 2175 if (s != NULL) 2176 free(s, M_TCPLOG); 2177 return (0); 2178 } 2179 #endif /* INVARIANTS */ 2180 2181 static void 2182 syncookie_reseed(void *arg) 2183 { 2184 struct tcp_syncache *sc = arg; 2185 uint8_t *secbits; 2186 int secbit; 2187 2188 /* 2189 * Reseeding the secret doesn't have to be protected by a lock. 2190 * It only must be ensured that the new random values are visible 2191 * to all CPUs in a SMP environment. The atomic with release 2192 * semantics ensures that. 2193 */ 2194 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2195 secbits = sc->secret.key[secbit]; 2196 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2197 atomic_add_rel_int(&sc->secret.oddeven, 1); 2198 2199 /* Reschedule ourself. */ 2200 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2201 } 2202 2203 /* 2204 * Exports the syncache entries to userland so that netstat can display 2205 * them alongside the other sockets. This function is intended to be 2206 * called only from tcp_pcblist. 2207 * 2208 * Due to concurrency on an active system, the number of pcbs exported 2209 * may have no relation to max_pcbs. max_pcbs merely indicates the 2210 * amount of space the caller allocated for this function to use. 2211 */ 2212 int 2213 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2214 { 2215 struct xtcpcb xt; 2216 struct syncache *sc; 2217 struct syncache_head *sch; 2218 int count, error, i; 2219 2220 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2221 sch = &V_tcp_syncache.hashbase[i]; 2222 SCH_LOCK(sch); 2223 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2224 if (count >= max_pcbs) { 2225 SCH_UNLOCK(sch); 2226 goto exit; 2227 } 2228 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2229 continue; 2230 bzero(&xt, sizeof(xt)); 2231 xt.xt_len = sizeof(xt); 2232 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2233 xt.xt_inp.inp_vflag = INP_IPV6; 2234 else 2235 xt.xt_inp.inp_vflag = INP_IPV4; 2236 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2237 sizeof (struct in_conninfo)); 2238 xt.t_state = TCPS_SYN_RECEIVED; 2239 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2240 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2241 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2242 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2243 error = SYSCTL_OUT(req, &xt, sizeof xt); 2244 if (error) { 2245 SCH_UNLOCK(sch); 2246 goto exit; 2247 } 2248 count++; 2249 } 2250 SCH_UNLOCK(sch); 2251 } 2252 exit: 2253 *pcbs_exported = count; 2254 return error; 2255 } 2256