1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. [2001 McAfee, Inc.] 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD$"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_pcbgroup.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/hash.h> 44 #include <sys/refcount.h> 45 #include <sys/kernel.h> 46 #include <sys/sysctl.h> 47 #include <sys/limits.h> 48 #include <sys/lock.h> 49 #include <sys/mutex.h> 50 #include <sys/malloc.h> 51 #include <sys/mbuf.h> 52 #include <sys/proc.h> /* for proc0 declaration */ 53 #include <sys/random.h> 54 #include <sys/socket.h> 55 #include <sys/socketvar.h> 56 #include <sys/syslog.h> 57 #include <sys/ucred.h> 58 59 #include <sys/md5.h> 60 #include <crypto/siphash/siphash.h> 61 62 #include <vm/uma.h> 63 64 #include <net/if.h> 65 #include <net/if_var.h> 66 #include <net/route.h> 67 #include <net/vnet.h> 68 69 #include <netinet/in.h> 70 #include <netinet/in_systm.h> 71 #include <netinet/ip.h> 72 #include <netinet/in_var.h> 73 #include <netinet/in_pcb.h> 74 #include <netinet/ip_var.h> 75 #include <netinet/ip_options.h> 76 #ifdef INET6 77 #include <netinet/ip6.h> 78 #include <netinet/icmp6.h> 79 #include <netinet6/nd6.h> 80 #include <netinet6/ip6_var.h> 81 #include <netinet6/in6_pcb.h> 82 #endif 83 #include <netinet/tcp.h> 84 #ifdef TCP_RFC7413 85 #include <netinet/tcp_fastopen.h> 86 #endif 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #ifdef INET6 93 #include <netinet6/tcp6_var.h> 94 #endif 95 #ifdef TCP_OFFLOAD 96 #include <netinet/toecore.h> 97 #endif 98 99 #ifdef IPSEC 100 #include <netipsec/ipsec.h> 101 #ifdef INET6 102 #include <netipsec/ipsec6.h> 103 #endif 104 #include <netipsec/key.h> 105 #endif /*IPSEC*/ 106 107 #include <machine/in_cksum.h> 108 109 #include <security/mac/mac_framework.h> 110 111 static VNET_DEFINE(int, tcp_syncookies) = 1; 112 #define V_tcp_syncookies VNET(tcp_syncookies) 113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookies), 0, 115 "Use TCP SYN cookies if the syncache overflows"); 116 117 static VNET_DEFINE(int, tcp_syncookiesonly) = 0; 118 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 120 &VNET_NAME(tcp_syncookiesonly), 0, 121 "Use only TCP SYN cookies"); 122 123 static VNET_DEFINE(int, functions_inherit_listen_socket_stack) = 1; 124 #define V_functions_inherit_listen_socket_stack \ 125 VNET(functions_inherit_listen_socket_stack) 126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 127 CTLFLAG_VNET | CTLFLAG_RW, 128 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 129 "Inherit listen socket's stack"); 130 131 #ifdef TCP_OFFLOAD 132 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 133 #endif 134 135 static void syncache_drop(struct syncache *, struct syncache_head *); 136 static void syncache_free(struct syncache *); 137 static void syncache_insert(struct syncache *, struct syncache_head *); 138 static int syncache_respond(struct syncache *, struct syncache_head *, int, 139 const struct mbuf *); 140 static struct socket *syncache_socket(struct syncache *, struct socket *, 141 struct mbuf *m); 142 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 143 int docallout); 144 static void syncache_timer(void *); 145 146 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 147 uint8_t *, uintptr_t); 148 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 149 static struct syncache 150 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 151 struct syncache *, struct tcphdr *, struct tcpopt *, 152 struct socket *); 153 static void syncookie_reseed(void *); 154 #ifdef INVARIANTS 155 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 156 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 157 struct socket *lso); 158 #endif 159 160 /* 161 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 162 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, 163 * the odds are that the user has given up attempting to connect by then. 164 */ 165 #define SYNCACHE_MAXREXMTS 3 166 167 /* Arbitrary values */ 168 #define TCP_SYNCACHE_HASHSIZE 512 169 #define TCP_SYNCACHE_BUCKETLIMIT 30 170 171 static VNET_DEFINE(struct tcp_syncache, tcp_syncache); 172 #define V_tcp_syncache VNET(tcp_syncache) 173 174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, 175 "TCP SYN cache"); 176 177 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 178 &VNET_NAME(tcp_syncache.bucket_limit), 0, 179 "Per-bucket hash limit for syncache"); 180 181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 182 &VNET_NAME(tcp_syncache.cache_limit), 0, 183 "Overall entry limit for syncache"); 184 185 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 186 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 187 188 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 189 &VNET_NAME(tcp_syncache.hashsize), 0, 190 "Size of TCP syncache hashtable"); 191 192 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW, 193 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 194 "Limit on SYN/ACK retransmissions"); 195 196 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 197 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 198 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 199 "Send reset on socket allocation failure"); 200 201 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 202 203 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 204 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 205 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 206 207 /* 208 * Requires the syncache entry to be already removed from the bucket list. 209 */ 210 static void 211 syncache_free(struct syncache *sc) 212 { 213 214 if (sc->sc_ipopts) 215 (void) m_free(sc->sc_ipopts); 216 if (sc->sc_cred) 217 crfree(sc->sc_cred); 218 #ifdef MAC 219 mac_syncache_destroy(&sc->sc_label); 220 #endif 221 222 uma_zfree(V_tcp_syncache.zone, sc); 223 } 224 225 void 226 syncache_init(void) 227 { 228 int i; 229 230 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 231 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 232 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 233 V_tcp_syncache.hash_secret = arc4random(); 234 235 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 236 &V_tcp_syncache.hashsize); 237 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 238 &V_tcp_syncache.bucket_limit); 239 if (!powerof2(V_tcp_syncache.hashsize) || 240 V_tcp_syncache.hashsize == 0) { 241 printf("WARNING: syncache hash size is not a power of 2.\n"); 242 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 243 } 244 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 245 246 /* Set limits. */ 247 V_tcp_syncache.cache_limit = 248 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 249 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 250 &V_tcp_syncache.cache_limit); 251 252 /* Allocate the hash table. */ 253 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 254 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 255 256 #ifdef VIMAGE 257 V_tcp_syncache.vnet = curvnet; 258 #endif 259 260 /* Initialize the hash buckets. */ 261 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 262 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 263 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 264 NULL, MTX_DEF); 265 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 266 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 267 V_tcp_syncache.hashbase[i].sch_length = 0; 268 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 269 } 270 271 /* Create the syncache entry zone. */ 272 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 273 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 274 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 275 V_tcp_syncache.cache_limit); 276 277 /* Start the SYN cookie reseeder callout. */ 278 callout_init(&V_tcp_syncache.secret.reseed, 1); 279 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 280 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 281 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 282 syncookie_reseed, &V_tcp_syncache); 283 } 284 285 #ifdef VIMAGE 286 void 287 syncache_destroy(void) 288 { 289 struct syncache_head *sch; 290 struct syncache *sc, *nsc; 291 int i; 292 293 /* 294 * Stop the re-seed timer before freeing resources. No need to 295 * possibly schedule it another time. 296 */ 297 callout_drain(&V_tcp_syncache.secret.reseed); 298 299 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 300 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 301 302 sch = &V_tcp_syncache.hashbase[i]; 303 callout_drain(&sch->sch_timer); 304 305 SCH_LOCK(sch); 306 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 307 syncache_drop(sc, sch); 308 SCH_UNLOCK(sch); 309 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 310 ("%s: sch->sch_bucket not empty", __func__)); 311 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 312 __func__, sch->sch_length)); 313 mtx_destroy(&sch->sch_mtx); 314 } 315 316 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 317 ("%s: cache_count not 0", __func__)); 318 319 /* Free the allocated global resources. */ 320 uma_zdestroy(V_tcp_syncache.zone); 321 free(V_tcp_syncache.hashbase, M_SYNCACHE); 322 } 323 #endif 324 325 /* 326 * Inserts a syncache entry into the specified bucket row. 327 * Locks and unlocks the syncache_head autonomously. 328 */ 329 static void 330 syncache_insert(struct syncache *sc, struct syncache_head *sch) 331 { 332 struct syncache *sc2; 333 334 SCH_LOCK(sch); 335 336 /* 337 * Make sure that we don't overflow the per-bucket limit. 338 * If the bucket is full, toss the oldest element. 339 */ 340 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 341 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 342 ("sch->sch_length incorrect")); 343 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 344 syncache_drop(sc2, sch); 345 TCPSTAT_INC(tcps_sc_bucketoverflow); 346 } 347 348 /* Put it into the bucket. */ 349 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 350 sch->sch_length++; 351 352 #ifdef TCP_OFFLOAD 353 if (ADDED_BY_TOE(sc)) { 354 struct toedev *tod = sc->sc_tod; 355 356 tod->tod_syncache_added(tod, sc->sc_todctx); 357 } 358 #endif 359 360 /* Reinitialize the bucket row's timer. */ 361 if (sch->sch_length == 1) 362 sch->sch_nextc = ticks + INT_MAX; 363 syncache_timeout(sc, sch, 1); 364 365 SCH_UNLOCK(sch); 366 367 TCPSTATES_INC(TCPS_SYN_RECEIVED); 368 TCPSTAT_INC(tcps_sc_added); 369 } 370 371 /* 372 * Remove and free entry from syncache bucket row. 373 * Expects locked syncache head. 374 */ 375 static void 376 syncache_drop(struct syncache *sc, struct syncache_head *sch) 377 { 378 379 SCH_LOCK_ASSERT(sch); 380 381 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 382 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 383 sch->sch_length--; 384 385 #ifdef TCP_OFFLOAD 386 if (ADDED_BY_TOE(sc)) { 387 struct toedev *tod = sc->sc_tod; 388 389 tod->tod_syncache_removed(tod, sc->sc_todctx); 390 } 391 #endif 392 393 syncache_free(sc); 394 } 395 396 /* 397 * Engage/reengage time on bucket row. 398 */ 399 static void 400 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 401 { 402 sc->sc_rxttime = ticks + 403 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]); 404 sc->sc_rxmits++; 405 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 406 sch->sch_nextc = sc->sc_rxttime; 407 if (docallout) 408 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 409 syncache_timer, (void *)sch); 410 } 411 } 412 413 /* 414 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 415 * If we have retransmitted an entry the maximum number of times, expire it. 416 * One separate timer for each bucket row. 417 */ 418 static void 419 syncache_timer(void *xsch) 420 { 421 struct syncache_head *sch = (struct syncache_head *)xsch; 422 struct syncache *sc, *nsc; 423 int tick = ticks; 424 char *s; 425 426 CURVNET_SET(sch->sch_sc->vnet); 427 428 /* NB: syncache_head has already been locked by the callout. */ 429 SCH_LOCK_ASSERT(sch); 430 431 /* 432 * In the following cycle we may remove some entries and/or 433 * advance some timeouts, so re-initialize the bucket timer. 434 */ 435 sch->sch_nextc = tick + INT_MAX; 436 437 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 438 /* 439 * We do not check if the listen socket still exists 440 * and accept the case where the listen socket may be 441 * gone by the time we resend the SYN/ACK. We do 442 * not expect this to happens often. If it does, 443 * then the RST will be sent by the time the remote 444 * host does the SYN/ACK->ACK. 445 */ 446 if (TSTMP_GT(sc->sc_rxttime, tick)) { 447 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 448 sch->sch_nextc = sc->sc_rxttime; 449 continue; 450 } 451 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 452 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 453 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 454 "giving up and removing syncache entry\n", 455 s, __func__); 456 free(s, M_TCPLOG); 457 } 458 syncache_drop(sc, sch); 459 TCPSTAT_INC(tcps_sc_stale); 460 continue; 461 } 462 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 463 log(LOG_DEBUG, "%s; %s: Response timeout, " 464 "retransmitting (%u) SYN|ACK\n", 465 s, __func__, sc->sc_rxmits); 466 free(s, M_TCPLOG); 467 } 468 469 syncache_respond(sc, sch, 1, NULL); 470 TCPSTAT_INC(tcps_sc_retransmitted); 471 syncache_timeout(sc, sch, 0); 472 } 473 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 474 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 475 syncache_timer, (void *)(sch)); 476 CURVNET_RESTORE(); 477 } 478 479 /* 480 * Find an entry in the syncache. 481 * Returns always with locked syncache_head plus a matching entry or NULL. 482 */ 483 static struct syncache * 484 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 485 { 486 struct syncache *sc; 487 struct syncache_head *sch; 488 uint32_t hash; 489 490 /* 491 * The hash is built on foreign port + local port + foreign address. 492 * We rely on the fact that struct in_conninfo starts with 16 bits 493 * of foreign port, then 16 bits of local port then followed by 128 494 * bits of foreign address. In case of IPv4 address, the first 3 495 * 32-bit words of the address always are zeroes. 496 */ 497 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 498 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 499 500 sch = &V_tcp_syncache.hashbase[hash]; 501 *schp = sch; 502 SCH_LOCK(sch); 503 504 /* Circle through bucket row to find matching entry. */ 505 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 506 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 507 sizeof(struct in_endpoints)) == 0) 508 break; 509 510 return (sc); /* Always returns with locked sch. */ 511 } 512 513 /* 514 * This function is called when we get a RST for a 515 * non-existent connection, so that we can see if the 516 * connection is in the syn cache. If it is, zap it. 517 */ 518 void 519 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 520 { 521 struct syncache *sc; 522 struct syncache_head *sch; 523 char *s = NULL; 524 525 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 526 SCH_LOCK_ASSERT(sch); 527 528 /* 529 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 530 * See RFC 793 page 65, section SEGMENT ARRIVES. 531 */ 532 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 533 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 534 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 535 "FIN flag set, segment ignored\n", s, __func__); 536 TCPSTAT_INC(tcps_badrst); 537 goto done; 538 } 539 540 /* 541 * No corresponding connection was found in syncache. 542 * If syncookies are enabled and possibly exclusively 543 * used, or we are under memory pressure, a valid RST 544 * may not find a syncache entry. In that case we're 545 * done and no SYN|ACK retransmissions will happen. 546 * Otherwise the RST was misdirected or spoofed. 547 */ 548 if (sc == NULL) { 549 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 550 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 551 "syncache entry (possibly syncookie only), " 552 "segment ignored\n", s, __func__); 553 TCPSTAT_INC(tcps_badrst); 554 goto done; 555 } 556 557 /* 558 * If the RST bit is set, check the sequence number to see 559 * if this is a valid reset segment. 560 * RFC 793 page 37: 561 * In all states except SYN-SENT, all reset (RST) segments 562 * are validated by checking their SEQ-fields. A reset is 563 * valid if its sequence number is in the window. 564 * 565 * The sequence number in the reset segment is normally an 566 * echo of our outgoing acknowlegement numbers, but some hosts 567 * send a reset with the sequence number at the rightmost edge 568 * of our receive window, and we have to handle this case. 569 */ 570 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 571 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 572 syncache_drop(sc, sch); 573 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 574 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 575 "connection attempt aborted by remote endpoint\n", 576 s, __func__); 577 TCPSTAT_INC(tcps_sc_reset); 578 } else { 579 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 580 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 581 "IRS %u (+WND %u), segment ignored\n", 582 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 583 TCPSTAT_INC(tcps_badrst); 584 } 585 586 done: 587 if (s != NULL) 588 free(s, M_TCPLOG); 589 SCH_UNLOCK(sch); 590 } 591 592 void 593 syncache_badack(struct in_conninfo *inc) 594 { 595 struct syncache *sc; 596 struct syncache_head *sch; 597 598 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 599 SCH_LOCK_ASSERT(sch); 600 if (sc != NULL) { 601 syncache_drop(sc, sch); 602 TCPSTAT_INC(tcps_sc_badack); 603 } 604 SCH_UNLOCK(sch); 605 } 606 607 void 608 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 609 { 610 struct syncache *sc; 611 struct syncache_head *sch; 612 613 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 614 SCH_LOCK_ASSERT(sch); 615 if (sc == NULL) 616 goto done; 617 618 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 619 if (ntohl(th->th_seq) != sc->sc_iss) 620 goto done; 621 622 /* 623 * If we've rertransmitted 3 times and this is our second error, 624 * we remove the entry. Otherwise, we allow it to continue on. 625 * This prevents us from incorrectly nuking an entry during a 626 * spurious network outage. 627 * 628 * See tcp_notify(). 629 */ 630 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 631 sc->sc_flags |= SCF_UNREACH; 632 goto done; 633 } 634 syncache_drop(sc, sch); 635 TCPSTAT_INC(tcps_sc_unreach); 636 done: 637 SCH_UNLOCK(sch); 638 } 639 640 /* 641 * Build a new TCP socket structure from a syncache entry. 642 * 643 * On success return the newly created socket with its underlying inp locked. 644 */ 645 static struct socket * 646 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 647 { 648 struct tcp_function_block *blk; 649 struct inpcb *inp = NULL; 650 struct socket *so; 651 struct tcpcb *tp; 652 int error; 653 char *s; 654 655 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 656 657 /* 658 * Ok, create the full blown connection, and set things up 659 * as they would have been set up if we had created the 660 * connection when the SYN arrived. If we can't create 661 * the connection, abort it. 662 */ 663 so = sonewconn(lso, 0); 664 if (so == NULL) { 665 /* 666 * Drop the connection; we will either send a RST or 667 * have the peer retransmit its SYN again after its 668 * RTO and try again. 669 */ 670 TCPSTAT_INC(tcps_listendrop); 671 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 672 log(LOG_DEBUG, "%s; %s: Socket create failed " 673 "due to limits or memory shortage\n", 674 s, __func__); 675 free(s, M_TCPLOG); 676 } 677 goto abort2; 678 } 679 #ifdef MAC 680 mac_socketpeer_set_from_mbuf(m, so); 681 #endif 682 683 inp = sotoinpcb(so); 684 inp->inp_inc.inc_fibnum = so->so_fibnum; 685 INP_WLOCK(inp); 686 /* 687 * Exclusive pcbinfo lock is not required in syncache socket case even 688 * if two inpcb locks can be acquired simultaneously: 689 * - the inpcb in LISTEN state, 690 * - the newly created inp. 691 * 692 * In this case, an inp cannot be at same time in LISTEN state and 693 * just created by an accept() call. 694 */ 695 INP_HASH_WLOCK(&V_tcbinfo); 696 697 /* Insert new socket into PCB hash list. */ 698 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 699 #ifdef INET6 700 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 701 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 702 } else { 703 inp->inp_vflag &= ~INP_IPV6; 704 inp->inp_vflag |= INP_IPV4; 705 #endif 706 inp->inp_laddr = sc->sc_inc.inc_laddr; 707 #ifdef INET6 708 } 709 #endif 710 711 /* 712 * If there's an mbuf and it has a flowid, then let's initialise the 713 * inp with that particular flowid. 714 */ 715 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 716 inp->inp_flowid = m->m_pkthdr.flowid; 717 inp->inp_flowtype = M_HASHTYPE_GET(m); 718 } 719 720 /* 721 * Install in the reservation hash table for now, but don't yet 722 * install a connection group since the full 4-tuple isn't yet 723 * configured. 724 */ 725 inp->inp_lport = sc->sc_inc.inc_lport; 726 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) { 727 /* 728 * Undo the assignments above if we failed to 729 * put the PCB on the hash lists. 730 */ 731 #ifdef INET6 732 if (sc->sc_inc.inc_flags & INC_ISIPV6) 733 inp->in6p_laddr = in6addr_any; 734 else 735 #endif 736 inp->inp_laddr.s_addr = INADDR_ANY; 737 inp->inp_lport = 0; 738 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 739 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed " 740 "with error %i\n", 741 s, __func__, error); 742 free(s, M_TCPLOG); 743 } 744 INP_HASH_WUNLOCK(&V_tcbinfo); 745 goto abort; 746 } 747 #ifdef IPSEC 748 /* Copy old policy into new socket's. */ 749 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 750 printf("syncache_socket: could not copy policy\n"); 751 #endif 752 #ifdef INET6 753 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 754 struct inpcb *oinp = sotoinpcb(lso); 755 struct in6_addr laddr6; 756 struct sockaddr_in6 sin6; 757 /* 758 * Inherit socket options from the listening socket. 759 * Note that in6p_inputopts are not (and should not be) 760 * copied, since it stores previously received options and is 761 * used to detect if each new option is different than the 762 * previous one and hence should be passed to a user. 763 * If we copied in6p_inputopts, a user would not be able to 764 * receive options just after calling the accept system call. 765 */ 766 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 767 if (oinp->in6p_outputopts) 768 inp->in6p_outputopts = 769 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 770 771 sin6.sin6_family = AF_INET6; 772 sin6.sin6_len = sizeof(sin6); 773 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 774 sin6.sin6_port = sc->sc_inc.inc_fport; 775 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 776 laddr6 = inp->in6p_laddr; 777 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 778 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 779 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 780 thread0.td_ucred, m)) != 0) { 781 inp->in6p_laddr = laddr6; 782 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 783 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 784 "with error %i\n", 785 s, __func__, error); 786 free(s, M_TCPLOG); 787 } 788 INP_HASH_WUNLOCK(&V_tcbinfo); 789 goto abort; 790 } 791 /* Override flowlabel from in6_pcbconnect. */ 792 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 793 inp->inp_flow |= sc->sc_flowlabel; 794 } 795 #endif /* INET6 */ 796 #if defined(INET) && defined(INET6) 797 else 798 #endif 799 #ifdef INET 800 { 801 struct in_addr laddr; 802 struct sockaddr_in sin; 803 804 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 805 806 if (inp->inp_options == NULL) { 807 inp->inp_options = sc->sc_ipopts; 808 sc->sc_ipopts = NULL; 809 } 810 811 sin.sin_family = AF_INET; 812 sin.sin_len = sizeof(sin); 813 sin.sin_addr = sc->sc_inc.inc_faddr; 814 sin.sin_port = sc->sc_inc.inc_fport; 815 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 816 laddr = inp->inp_laddr; 817 if (inp->inp_laddr.s_addr == INADDR_ANY) 818 inp->inp_laddr = sc->sc_inc.inc_laddr; 819 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 820 thread0.td_ucred, m)) != 0) { 821 inp->inp_laddr = laddr; 822 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 823 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 824 "with error %i\n", 825 s, __func__, error); 826 free(s, M_TCPLOG); 827 } 828 INP_HASH_WUNLOCK(&V_tcbinfo); 829 goto abort; 830 } 831 } 832 #endif /* INET */ 833 INP_HASH_WUNLOCK(&V_tcbinfo); 834 tp = intotcpcb(inp); 835 tcp_state_change(tp, TCPS_SYN_RECEIVED); 836 tp->iss = sc->sc_iss; 837 tp->irs = sc->sc_irs; 838 tcp_rcvseqinit(tp); 839 tcp_sendseqinit(tp); 840 blk = sototcpcb(lso)->t_fb; 841 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 842 /* 843 * Our parents t_fb was not the default, 844 * we need to release our ref on tp->t_fb and 845 * pickup one on the new entry. 846 */ 847 struct tcp_function_block *rblk; 848 849 rblk = find_and_ref_tcp_fb(blk); 850 KASSERT(rblk != NULL, 851 ("cannot find blk %p out of syncache?", blk)); 852 if (tp->t_fb->tfb_tcp_fb_fini) 853 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 854 refcount_release(&tp->t_fb->tfb_refcnt); 855 tp->t_fb = rblk; 856 if (tp->t_fb->tfb_tcp_fb_init) { 857 (*tp->t_fb->tfb_tcp_fb_init)(tp); 858 } 859 } 860 tp->snd_wl1 = sc->sc_irs; 861 tp->snd_max = tp->iss + 1; 862 tp->snd_nxt = tp->iss + 1; 863 tp->rcv_up = sc->sc_irs + 1; 864 tp->rcv_wnd = sc->sc_wnd; 865 tp->rcv_adv += tp->rcv_wnd; 866 tp->last_ack_sent = tp->rcv_nxt; 867 868 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 869 if (sc->sc_flags & SCF_NOOPT) 870 tp->t_flags |= TF_NOOPT; 871 else { 872 if (sc->sc_flags & SCF_WINSCALE) { 873 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 874 tp->snd_scale = sc->sc_requested_s_scale; 875 tp->request_r_scale = sc->sc_requested_r_scale; 876 } 877 if (sc->sc_flags & SCF_TIMESTAMP) { 878 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 879 tp->ts_recent = sc->sc_tsreflect; 880 tp->ts_recent_age = tcp_ts_getticks(); 881 tp->ts_offset = sc->sc_tsoff; 882 } 883 #ifdef TCP_SIGNATURE 884 if (sc->sc_flags & SCF_SIGNATURE) 885 tp->t_flags |= TF_SIGNATURE; 886 #endif 887 if (sc->sc_flags & SCF_SACK) 888 tp->t_flags |= TF_SACK_PERMIT; 889 } 890 891 if (sc->sc_flags & SCF_ECN) 892 tp->t_flags |= TF_ECN_PERMIT; 893 894 /* 895 * Set up MSS and get cached values from tcp_hostcache. 896 * This might overwrite some of the defaults we just set. 897 */ 898 tcp_mss(tp, sc->sc_peer_mss); 899 900 /* 901 * If the SYN,ACK was retransmitted, indicate that CWND to be 902 * limited to one segment in cc_conn_init(). 903 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 904 */ 905 if (sc->sc_rxmits > 1) 906 tp->snd_cwnd = 1; 907 908 #ifdef TCP_OFFLOAD 909 /* 910 * Allow a TOE driver to install its hooks. Note that we hold the 911 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 912 * new connection before the TOE driver has done its thing. 913 */ 914 if (ADDED_BY_TOE(sc)) { 915 struct toedev *tod = sc->sc_tod; 916 917 tod->tod_offload_socket(tod, sc->sc_todctx, so); 918 } 919 #endif 920 /* 921 * Copy and activate timers. 922 */ 923 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 924 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 925 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 926 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 927 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 928 929 TCPSTAT_INC(tcps_accepts); 930 return (so); 931 932 abort: 933 INP_WUNLOCK(inp); 934 abort2: 935 if (so != NULL) 936 soabort(so); 937 return (NULL); 938 } 939 940 /* 941 * This function gets called when we receive an ACK for a 942 * socket in the LISTEN state. We look up the connection 943 * in the syncache, and if its there, we pull it out of 944 * the cache and turn it into a full-blown connection in 945 * the SYN-RECEIVED state. 946 * 947 * On syncache_socket() success the newly created socket 948 * has its underlying inp locked. 949 */ 950 int 951 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 952 struct socket **lsop, struct mbuf *m) 953 { 954 struct syncache *sc; 955 struct syncache_head *sch; 956 struct syncache scs; 957 char *s; 958 959 /* 960 * Global TCP locks are held because we manipulate the PCB lists 961 * and create a new socket. 962 */ 963 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 964 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 965 ("%s: can handle only ACK", __func__)); 966 967 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 968 SCH_LOCK_ASSERT(sch); 969 970 #ifdef INVARIANTS 971 /* 972 * Test code for syncookies comparing the syncache stored 973 * values with the reconstructed values from the cookie. 974 */ 975 if (sc != NULL) 976 syncookie_cmp(inc, sch, sc, th, to, *lsop); 977 #endif 978 979 if (sc == NULL) { 980 /* 981 * There is no syncache entry, so see if this ACK is 982 * a returning syncookie. To do this, first: 983 * A. See if this socket has had a syncache entry dropped in 984 * the past. We don't want to accept a bogus syncookie 985 * if we've never received a SYN. 986 * B. check that the syncookie is valid. If it is, then 987 * cobble up a fake syncache entry, and return. 988 */ 989 if (!V_tcp_syncookies) { 990 SCH_UNLOCK(sch); 991 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 992 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 993 "segment rejected (syncookies disabled)\n", 994 s, __func__); 995 goto failed; 996 } 997 bzero(&scs, sizeof(scs)); 998 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop); 999 SCH_UNLOCK(sch); 1000 if (sc == NULL) { 1001 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1002 log(LOG_DEBUG, "%s; %s: Segment failed " 1003 "SYNCOOKIE authentication, segment rejected " 1004 "(probably spoofed)\n", s, __func__); 1005 goto failed; 1006 } 1007 } else { 1008 /* 1009 * Pull out the entry to unlock the bucket row. 1010 * 1011 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1012 * tcp_state_change(). The tcpcb is not existent at this 1013 * moment. A new one will be allocated via syncache_socket-> 1014 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1015 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1016 */ 1017 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1018 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1019 sch->sch_length--; 1020 #ifdef TCP_OFFLOAD 1021 if (ADDED_BY_TOE(sc)) { 1022 struct toedev *tod = sc->sc_tod; 1023 1024 tod->tod_syncache_removed(tod, sc->sc_todctx); 1025 } 1026 #endif 1027 SCH_UNLOCK(sch); 1028 } 1029 1030 /* 1031 * Segment validation: 1032 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1033 */ 1034 if (th->th_ack != sc->sc_iss + 1) { 1035 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1036 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1037 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1038 goto failed; 1039 } 1040 1041 /* 1042 * The SEQ must fall in the window starting at the received 1043 * initial receive sequence number + 1 (the SYN). 1044 */ 1045 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1046 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1047 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1048 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1049 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1050 goto failed; 1051 } 1052 1053 /* 1054 * If timestamps were not negotiated during SYN/ACK they 1055 * must not appear on any segment during this session. 1056 */ 1057 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 1058 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1059 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 1060 "segment rejected\n", s, __func__); 1061 goto failed; 1062 } 1063 1064 /* 1065 * If timestamps were negotiated during SYN/ACK they should 1066 * appear on every segment during this session. 1067 * XXXAO: This is only informal as there have been unverified 1068 * reports of non-compliants stacks. 1069 */ 1070 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 1071 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1072 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 1073 "no action\n", s, __func__); 1074 free(s, M_TCPLOG); 1075 s = NULL; 1076 } 1077 } 1078 1079 /* 1080 * If timestamps were negotiated, the reflected timestamp 1081 * must be equal to what we actually sent in the SYN|ACK 1082 * except in the case of 0. Some boxes are known for sending 1083 * broken timestamp replies during the 3whs (and potentially 1084 * during the connection also). 1085 * 1086 * Accept the final ACK of 3whs with reflected timestamp of 0 1087 * instead of sending a RST and deleting the syncache entry. 1088 */ 1089 if ((to->to_flags & TOF_TS) && to->to_tsecr && 1090 to->to_tsecr != sc->sc_ts) { 1091 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1092 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1093 "segment rejected\n", 1094 s, __func__, to->to_tsecr, sc->sc_ts); 1095 goto failed; 1096 } 1097 1098 *lsop = syncache_socket(sc, *lsop, m); 1099 1100 if (*lsop == NULL) 1101 TCPSTAT_INC(tcps_sc_aborted); 1102 else 1103 TCPSTAT_INC(tcps_sc_completed); 1104 1105 /* how do we find the inp for the new socket? */ 1106 if (sc != &scs) 1107 syncache_free(sc); 1108 return (1); 1109 failed: 1110 if (sc != NULL && sc != &scs) 1111 syncache_free(sc); 1112 if (s != NULL) 1113 free(s, M_TCPLOG); 1114 *lsop = NULL; 1115 return (0); 1116 } 1117 1118 #ifdef TCP_RFC7413 1119 static void 1120 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1121 uint64_t response_cookie) 1122 { 1123 struct inpcb *inp; 1124 struct tcpcb *tp; 1125 unsigned int *pending_counter; 1126 1127 /* 1128 * Global TCP locks are held because we manipulate the PCB lists 1129 * and create a new socket. 1130 */ 1131 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1132 1133 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1134 *lsop = syncache_socket(sc, *lsop, m); 1135 if (*lsop == NULL) { 1136 TCPSTAT_INC(tcps_sc_aborted); 1137 atomic_subtract_int(pending_counter, 1); 1138 } else { 1139 inp = sotoinpcb(*lsop); 1140 tp = intotcpcb(inp); 1141 tp->t_flags |= TF_FASTOPEN; 1142 tp->t_tfo_cookie = response_cookie; 1143 tp->snd_max = tp->iss; 1144 tp->snd_nxt = tp->iss; 1145 tp->t_tfo_pending = pending_counter; 1146 TCPSTAT_INC(tcps_sc_completed); 1147 } 1148 } 1149 #endif /* TCP_RFC7413 */ 1150 1151 /* 1152 * Given a LISTEN socket and an inbound SYN request, add 1153 * this to the syn cache, and send back a segment: 1154 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1155 * to the source. 1156 * 1157 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1158 * Doing so would require that we hold onto the data and deliver it 1159 * to the application. However, if we are the target of a SYN-flood 1160 * DoS attack, an attacker could send data which would eventually 1161 * consume all available buffer space if it were ACKed. By not ACKing 1162 * the data, we avoid this DoS scenario. 1163 * 1164 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1165 * cookie is processed and a new socket is created. In this case, any data 1166 * accompanying the SYN will be queued to the socket by tcp_input() and will 1167 * be ACKed either when the application sends response data or the delayed 1168 * ACK timer expires, whichever comes first. 1169 */ 1170 int 1171 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1172 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1173 void *todctx) 1174 { 1175 struct tcpcb *tp; 1176 struct socket *so; 1177 struct syncache *sc = NULL; 1178 struct syncache_head *sch; 1179 struct mbuf *ipopts = NULL; 1180 u_int ltflags; 1181 int win, ip_ttl, ip_tos; 1182 char *s; 1183 int rv = 0; 1184 #ifdef INET6 1185 int autoflowlabel = 0; 1186 #endif 1187 #ifdef MAC 1188 struct label *maclabel; 1189 #endif 1190 struct syncache scs; 1191 struct ucred *cred; 1192 #ifdef TCP_RFC7413 1193 uint64_t tfo_response_cookie; 1194 unsigned int *tfo_pending = NULL; 1195 int tfo_cookie_valid = 0; 1196 int tfo_response_cookie_valid = 0; 1197 #endif 1198 1199 INP_WLOCK_ASSERT(inp); /* listen socket */ 1200 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1201 ("%s: unexpected tcp flags", __func__)); 1202 1203 /* 1204 * Combine all so/tp operations very early to drop the INP lock as 1205 * soon as possible. 1206 */ 1207 so = *lsop; 1208 tp = sototcpcb(so); 1209 cred = crhold(so->so_cred); 1210 1211 #ifdef INET6 1212 if ((inc->inc_flags & INC_ISIPV6) && 1213 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1214 autoflowlabel = 1; 1215 #endif 1216 ip_ttl = inp->inp_ip_ttl; 1217 ip_tos = inp->inp_ip_tos; 1218 win = sbspace(&so->so_rcv); 1219 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1220 1221 #ifdef TCP_RFC7413 1222 if (V_tcp_fastopen_enabled && IS_FASTOPEN(tp->t_flags) && 1223 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1224 /* 1225 * Limit the number of pending TFO connections to 1226 * approximately half of the queue limit. This prevents TFO 1227 * SYN floods from starving the service by filling the 1228 * listen queue with bogus TFO connections. 1229 */ 1230 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1231 (so->so_qlimit / 2)) { 1232 int result; 1233 1234 result = tcp_fastopen_check_cookie(inc, 1235 to->to_tfo_cookie, to->to_tfo_len, 1236 &tfo_response_cookie); 1237 tfo_cookie_valid = (result > 0); 1238 tfo_response_cookie_valid = (result >= 0); 1239 } 1240 1241 /* 1242 * Remember the TFO pending counter as it will have to be 1243 * decremented below if we don't make it to syncache_tfo_expand(). 1244 */ 1245 tfo_pending = tp->t_tfo_pending; 1246 } 1247 #endif 1248 1249 /* By the time we drop the lock these should no longer be used. */ 1250 so = NULL; 1251 tp = NULL; 1252 1253 #ifdef MAC 1254 if (mac_syncache_init(&maclabel) != 0) { 1255 INP_WUNLOCK(inp); 1256 goto done; 1257 } else 1258 mac_syncache_create(maclabel, inp); 1259 #endif 1260 #ifdef TCP_RFC7413 1261 if (!tfo_cookie_valid) 1262 #endif 1263 INP_WUNLOCK(inp); 1264 1265 /* 1266 * Remember the IP options, if any. 1267 */ 1268 #ifdef INET6 1269 if (!(inc->inc_flags & INC_ISIPV6)) 1270 #endif 1271 #ifdef INET 1272 ipopts = (m) ? ip_srcroute(m) : NULL; 1273 #else 1274 ipopts = NULL; 1275 #endif 1276 1277 /* 1278 * See if we already have an entry for this connection. 1279 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1280 * 1281 * XXX: should the syncache be re-initialized with the contents 1282 * of the new SYN here (which may have different options?) 1283 * 1284 * XXX: We do not check the sequence number to see if this is a 1285 * real retransmit or a new connection attempt. The question is 1286 * how to handle such a case; either ignore it as spoofed, or 1287 * drop the current entry and create a new one? 1288 */ 1289 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1290 SCH_LOCK_ASSERT(sch); 1291 if (sc != NULL) { 1292 #ifdef TCP_RFC7413 1293 if (tfo_cookie_valid) 1294 INP_WUNLOCK(inp); 1295 #endif 1296 TCPSTAT_INC(tcps_sc_dupsyn); 1297 if (ipopts) { 1298 /* 1299 * If we were remembering a previous source route, 1300 * forget it and use the new one we've been given. 1301 */ 1302 if (sc->sc_ipopts) 1303 (void) m_free(sc->sc_ipopts); 1304 sc->sc_ipopts = ipopts; 1305 } 1306 /* 1307 * Update timestamp if present. 1308 */ 1309 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1310 sc->sc_tsreflect = to->to_tsval; 1311 else 1312 sc->sc_flags &= ~SCF_TIMESTAMP; 1313 #ifdef MAC 1314 /* 1315 * Since we have already unconditionally allocated label 1316 * storage, free it up. The syncache entry will already 1317 * have an initialized label we can use. 1318 */ 1319 mac_syncache_destroy(&maclabel); 1320 #endif 1321 /* Retransmit SYN|ACK and reset retransmit count. */ 1322 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1323 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1324 "resetting timer and retransmitting SYN|ACK\n", 1325 s, __func__); 1326 free(s, M_TCPLOG); 1327 } 1328 if (syncache_respond(sc, sch, 1, m) == 0) { 1329 sc->sc_rxmits = 0; 1330 syncache_timeout(sc, sch, 1); 1331 TCPSTAT_INC(tcps_sndacks); 1332 TCPSTAT_INC(tcps_sndtotal); 1333 } 1334 SCH_UNLOCK(sch); 1335 goto done; 1336 } 1337 1338 #ifdef TCP_RFC7413 1339 if (tfo_cookie_valid) { 1340 bzero(&scs, sizeof(scs)); 1341 sc = &scs; 1342 goto skip_alloc; 1343 } 1344 #endif 1345 1346 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1347 if (sc == NULL) { 1348 /* 1349 * The zone allocator couldn't provide more entries. 1350 * Treat this as if the cache was full; drop the oldest 1351 * entry and insert the new one. 1352 */ 1353 TCPSTAT_INC(tcps_sc_zonefail); 1354 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1355 syncache_drop(sc, sch); 1356 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1357 if (sc == NULL) { 1358 if (V_tcp_syncookies) { 1359 bzero(&scs, sizeof(scs)); 1360 sc = &scs; 1361 } else { 1362 SCH_UNLOCK(sch); 1363 if (ipopts) 1364 (void) m_free(ipopts); 1365 goto done; 1366 } 1367 } 1368 } 1369 1370 #ifdef TCP_RFC7413 1371 skip_alloc: 1372 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1373 sc->sc_tfo_cookie = &tfo_response_cookie; 1374 #endif 1375 1376 /* 1377 * Fill in the syncache values. 1378 */ 1379 #ifdef MAC 1380 sc->sc_label = maclabel; 1381 #endif 1382 sc->sc_cred = cred; 1383 cred = NULL; 1384 sc->sc_ipopts = ipopts; 1385 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1386 #ifdef INET6 1387 if (!(inc->inc_flags & INC_ISIPV6)) 1388 #endif 1389 { 1390 sc->sc_ip_tos = ip_tos; 1391 sc->sc_ip_ttl = ip_ttl; 1392 } 1393 #ifdef TCP_OFFLOAD 1394 sc->sc_tod = tod; 1395 sc->sc_todctx = todctx; 1396 #endif 1397 sc->sc_irs = th->th_seq; 1398 sc->sc_iss = arc4random(); 1399 sc->sc_flags = 0; 1400 sc->sc_flowlabel = 0; 1401 1402 /* 1403 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1404 * win was derived from socket earlier in the function. 1405 */ 1406 win = imax(win, 0); 1407 win = imin(win, TCP_MAXWIN); 1408 sc->sc_wnd = win; 1409 1410 if (V_tcp_do_rfc1323) { 1411 /* 1412 * A timestamp received in a SYN makes 1413 * it ok to send timestamp requests and replies. 1414 */ 1415 if (to->to_flags & TOF_TS) { 1416 sc->sc_tsreflect = to->to_tsval; 1417 sc->sc_ts = tcp_ts_getticks(); 1418 sc->sc_flags |= SCF_TIMESTAMP; 1419 } 1420 if (to->to_flags & TOF_SCALE) { 1421 int wscale = 0; 1422 1423 /* 1424 * Pick the smallest possible scaling factor that 1425 * will still allow us to scale up to sb_max, aka 1426 * kern.ipc.maxsockbuf. 1427 * 1428 * We do this because there are broken firewalls that 1429 * will corrupt the window scale option, leading to 1430 * the other endpoint believing that our advertised 1431 * window is unscaled. At scale factors larger than 1432 * 5 the unscaled window will drop below 1500 bytes, 1433 * leading to serious problems when traversing these 1434 * broken firewalls. 1435 * 1436 * With the default maxsockbuf of 256K, a scale factor 1437 * of 3 will be chosen by this algorithm. Those who 1438 * choose a larger maxsockbuf should watch out 1439 * for the compatibility problems mentioned above. 1440 * 1441 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1442 * or <SYN,ACK>) segment itself is never scaled. 1443 */ 1444 while (wscale < TCP_MAX_WINSHIFT && 1445 (TCP_MAXWIN << wscale) < sb_max) 1446 wscale++; 1447 sc->sc_requested_r_scale = wscale; 1448 sc->sc_requested_s_scale = to->to_wscale; 1449 sc->sc_flags |= SCF_WINSCALE; 1450 } 1451 } 1452 #ifdef TCP_SIGNATURE 1453 /* 1454 * If listening socket requested TCP digests, OR received SYN 1455 * contains the option, flag this in the syncache so that 1456 * syncache_respond() will do the right thing with the SYN+ACK. 1457 */ 1458 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1459 sc->sc_flags |= SCF_SIGNATURE; 1460 #endif 1461 if (to->to_flags & TOF_SACKPERM) 1462 sc->sc_flags |= SCF_SACK; 1463 if (to->to_flags & TOF_MSS) 1464 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1465 if (ltflags & TF_NOOPT) 1466 sc->sc_flags |= SCF_NOOPT; 1467 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1468 sc->sc_flags |= SCF_ECN; 1469 1470 if (V_tcp_syncookies) 1471 sc->sc_iss = syncookie_generate(sch, sc); 1472 #ifdef INET6 1473 if (autoflowlabel) { 1474 if (V_tcp_syncookies) 1475 sc->sc_flowlabel = sc->sc_iss; 1476 else 1477 sc->sc_flowlabel = ip6_randomflowlabel(); 1478 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1479 } 1480 #endif 1481 SCH_UNLOCK(sch); 1482 1483 #ifdef TCP_RFC7413 1484 if (tfo_cookie_valid) { 1485 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1486 /* INP_WUNLOCK(inp) will be performed by the caller */ 1487 rv = 1; 1488 goto tfo_expanded; 1489 } 1490 #endif 1491 1492 /* 1493 * Do a standard 3-way handshake. 1494 */ 1495 if (syncache_respond(sc, sch, 0, m) == 0) { 1496 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1497 syncache_free(sc); 1498 else if (sc != &scs) 1499 syncache_insert(sc, sch); /* locks and unlocks sch */ 1500 TCPSTAT_INC(tcps_sndacks); 1501 TCPSTAT_INC(tcps_sndtotal); 1502 } else { 1503 if (sc != &scs) 1504 syncache_free(sc); 1505 TCPSTAT_INC(tcps_sc_dropped); 1506 } 1507 1508 done: 1509 if (m) { 1510 *lsop = NULL; 1511 m_freem(m); 1512 } 1513 #ifdef TCP_RFC7413 1514 /* 1515 * If tfo_pending is not NULL here, then a TFO SYN that did not 1516 * result in a new socket was processed and the associated pending 1517 * counter has not yet been decremented. All such TFO processing paths 1518 * transit this point. 1519 */ 1520 if (tfo_pending != NULL) 1521 tcp_fastopen_decrement_counter(tfo_pending); 1522 1523 tfo_expanded: 1524 #endif 1525 if (cred != NULL) 1526 crfree(cred); 1527 #ifdef MAC 1528 if (sc == &scs) 1529 mac_syncache_destroy(&maclabel); 1530 #endif 1531 return (rv); 1532 } 1533 1534 /* 1535 * Send SYN|ACK to the peer. Either in response to the peer's SYN, 1536 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1537 */ 1538 static int 1539 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked, 1540 const struct mbuf *m0) 1541 { 1542 struct ip *ip = NULL; 1543 struct mbuf *m; 1544 struct tcphdr *th = NULL; 1545 int optlen, error = 0; /* Make compiler happy */ 1546 u_int16_t hlen, tlen, mssopt; 1547 struct tcpopt to; 1548 #ifdef INET6 1549 struct ip6_hdr *ip6 = NULL; 1550 #endif 1551 #ifdef TCP_SIGNATURE 1552 struct secasvar *sav; 1553 #endif 1554 1555 hlen = 1556 #ifdef INET6 1557 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1558 #endif 1559 sizeof(struct ip); 1560 tlen = hlen + sizeof(struct tcphdr); 1561 1562 /* Determine MSS we advertize to other end of connection. */ 1563 mssopt = tcp_mssopt(&sc->sc_inc); 1564 if (sc->sc_peer_mss) 1565 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1566 1567 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1568 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1569 ("syncache: mbuf too small")); 1570 1571 /* Create the IP+TCP header from scratch. */ 1572 m = m_gethdr(M_NOWAIT, MT_DATA); 1573 if (m == NULL) 1574 return (ENOBUFS); 1575 #ifdef MAC 1576 mac_syncache_create_mbuf(sc->sc_label, m); 1577 #endif 1578 m->m_data += max_linkhdr; 1579 m->m_len = tlen; 1580 m->m_pkthdr.len = tlen; 1581 m->m_pkthdr.rcvif = NULL; 1582 1583 #ifdef INET6 1584 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1585 ip6 = mtod(m, struct ip6_hdr *); 1586 ip6->ip6_vfc = IPV6_VERSION; 1587 ip6->ip6_nxt = IPPROTO_TCP; 1588 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1589 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1590 ip6->ip6_plen = htons(tlen - hlen); 1591 /* ip6_hlim is set after checksum */ 1592 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1593 ip6->ip6_flow |= sc->sc_flowlabel; 1594 1595 th = (struct tcphdr *)(ip6 + 1); 1596 } 1597 #endif 1598 #if defined(INET6) && defined(INET) 1599 else 1600 #endif 1601 #ifdef INET 1602 { 1603 ip = mtod(m, struct ip *); 1604 ip->ip_v = IPVERSION; 1605 ip->ip_hl = sizeof(struct ip) >> 2; 1606 ip->ip_len = htons(tlen); 1607 ip->ip_id = 0; 1608 ip->ip_off = 0; 1609 ip->ip_sum = 0; 1610 ip->ip_p = IPPROTO_TCP; 1611 ip->ip_src = sc->sc_inc.inc_laddr; 1612 ip->ip_dst = sc->sc_inc.inc_faddr; 1613 ip->ip_ttl = sc->sc_ip_ttl; 1614 ip->ip_tos = sc->sc_ip_tos; 1615 1616 /* 1617 * See if we should do MTU discovery. Route lookups are 1618 * expensive, so we will only unset the DF bit if: 1619 * 1620 * 1) path_mtu_discovery is disabled 1621 * 2) the SCF_UNREACH flag has been set 1622 */ 1623 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1624 ip->ip_off |= htons(IP_DF); 1625 1626 th = (struct tcphdr *)(ip + 1); 1627 } 1628 #endif /* INET */ 1629 th->th_sport = sc->sc_inc.inc_lport; 1630 th->th_dport = sc->sc_inc.inc_fport; 1631 1632 th->th_seq = htonl(sc->sc_iss); 1633 th->th_ack = htonl(sc->sc_irs + 1); 1634 th->th_off = sizeof(struct tcphdr) >> 2; 1635 th->th_x2 = 0; 1636 th->th_flags = TH_SYN|TH_ACK; 1637 th->th_win = htons(sc->sc_wnd); 1638 th->th_urp = 0; 1639 1640 if (sc->sc_flags & SCF_ECN) { 1641 th->th_flags |= TH_ECE; 1642 TCPSTAT_INC(tcps_ecn_shs); 1643 } 1644 1645 /* Tack on the TCP options. */ 1646 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1647 to.to_flags = 0; 1648 1649 to.to_mss = mssopt; 1650 to.to_flags = TOF_MSS; 1651 if (sc->sc_flags & SCF_WINSCALE) { 1652 to.to_wscale = sc->sc_requested_r_scale; 1653 to.to_flags |= TOF_SCALE; 1654 } 1655 if (sc->sc_flags & SCF_TIMESTAMP) { 1656 /* Virgin timestamp or TCP cookie enhanced one. */ 1657 to.to_tsval = sc->sc_ts; 1658 to.to_tsecr = sc->sc_tsreflect; 1659 to.to_flags |= TOF_TS; 1660 } 1661 if (sc->sc_flags & SCF_SACK) 1662 to.to_flags |= TOF_SACKPERM; 1663 #ifdef TCP_SIGNATURE 1664 sav = NULL; 1665 if (sc->sc_flags & SCF_SIGNATURE) { 1666 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1667 if (sav != NULL) 1668 to.to_flags |= TOF_SIGNATURE; 1669 else { 1670 1671 /* 1672 * We've got SCF_SIGNATURE flag 1673 * inherited from listening socket, 1674 * but no SADB key for given source 1675 * address. Assume signature is not 1676 * required and remove signature flag 1677 * instead of silently dropping 1678 * connection. 1679 */ 1680 if (locked == 0) 1681 SCH_LOCK(sch); 1682 sc->sc_flags &= ~SCF_SIGNATURE; 1683 if (locked == 0) 1684 SCH_UNLOCK(sch); 1685 } 1686 } 1687 #endif 1688 1689 #ifdef TCP_RFC7413 1690 if (sc->sc_tfo_cookie) { 1691 to.to_flags |= TOF_FASTOPEN; 1692 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1693 to.to_tfo_cookie = sc->sc_tfo_cookie; 1694 /* don't send cookie again when retransmitting response */ 1695 sc->sc_tfo_cookie = NULL; 1696 } 1697 #endif 1698 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1699 1700 /* Adjust headers by option size. */ 1701 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1702 m->m_len += optlen; 1703 m->m_pkthdr.len += optlen; 1704 1705 #ifdef TCP_SIGNATURE 1706 if (sc->sc_flags & SCF_SIGNATURE) 1707 tcp_signature_do_compute(m, 0, optlen, 1708 to.to_signature, sav); 1709 #endif 1710 #ifdef INET6 1711 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1712 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1713 else 1714 #endif 1715 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1716 } else 1717 optlen = 0; 1718 1719 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1720 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1721 /* 1722 * If we have peer's SYN and it has a flowid, then let's assign it to 1723 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1724 * to SYN|ACK due to lack of inp here. 1725 */ 1726 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1727 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1728 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1729 } 1730 #ifdef INET6 1731 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1732 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1733 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1734 IPPROTO_TCP, 0); 1735 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1736 #ifdef TCP_OFFLOAD 1737 if (ADDED_BY_TOE(sc)) { 1738 struct toedev *tod = sc->sc_tod; 1739 1740 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1741 1742 return (error); 1743 } 1744 #endif 1745 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1746 } 1747 #endif 1748 #if defined(INET6) && defined(INET) 1749 else 1750 #endif 1751 #ifdef INET 1752 { 1753 m->m_pkthdr.csum_flags = CSUM_TCP; 1754 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1755 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1756 #ifdef TCP_OFFLOAD 1757 if (ADDED_BY_TOE(sc)) { 1758 struct toedev *tod = sc->sc_tod; 1759 1760 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1761 1762 return (error); 1763 } 1764 #endif 1765 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1766 } 1767 #endif 1768 return (error); 1769 } 1770 1771 /* 1772 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1773 * that exceed the capacity of the syncache by avoiding the storage of any 1774 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1775 * attacks where the attacker does not have access to our responses. 1776 * 1777 * Syncookies encode and include all necessary information about the 1778 * connection setup within the SYN|ACK that we send back. That way we 1779 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1780 * (if ever). Normally the syncache and syncookies are running in parallel 1781 * with the latter taking over when the former is exhausted. When matching 1782 * syncache entry is found the syncookie is ignored. 1783 * 1784 * The only reliable information persisting the 3WHS is our initial sequence 1785 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1786 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1787 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1788 * returns and signifies a legitimate connection if it matches the ACK. 1789 * 1790 * The available space of 32 bits to store the hash and to encode the SYN 1791 * option information is very tight and we should have at least 24 bits for 1792 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1793 * 1794 * SYN option information we have to encode to fully restore a connection: 1795 * MSS: is imporant to chose an optimal segment size to avoid IP level 1796 * fragmentation along the path. The common MSS values can be encoded 1797 * in a 3-bit table. Uncommon values are captured by the next lower value 1798 * in the table leading to a slight increase in packetization overhead. 1799 * WSCALE: is necessary to allow large windows to be used for high delay- 1800 * bandwidth product links. Not scaling the window when it was initially 1801 * negotiated is bad for performance as lack of scaling further decreases 1802 * the apparent available send window. We only need to encode the WSCALE 1803 * we received from the remote end. Our end can be recalculated at any 1804 * time. The common WSCALE values can be encoded in a 3-bit table. 1805 * Uncommon values are captured by the next lower value in the table 1806 * making us under-estimate the available window size halving our 1807 * theoretically possible maximum throughput for that connection. 1808 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1809 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1810 * that are included in all segments on a connection. We enable them when 1811 * the ACK has them. 1812 * 1813 * Security of syncookies and attack vectors: 1814 * 1815 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1816 * together with the gloabl secret to make it unique per connection attempt. 1817 * Thus any change of any of those parameters results in a different MAC output 1818 * in an unpredictable way unless a collision is encountered. 24 bits of the 1819 * MAC are embedded into the ISS. 1820 * 1821 * To prevent replay attacks two rotating global secrets are updated with a 1822 * new random value every 15 seconds. The life-time of a syncookie is thus 1823 * 15-30 seconds. 1824 * 1825 * Vector 1: Attacking the secret. This requires finding a weakness in the 1826 * MAC itself or the way it is used here. The attacker can do a chosen plain 1827 * text attack by varying and testing the all parameters under his control. 1828 * The strength depends on the size and randomness of the secret, and the 1829 * cryptographic security of the MAC function. Due to the constant updating 1830 * of the secret the attacker has at most 29.999 seconds to find the secret 1831 * and launch spoofed connections. After that he has to start all over again. 1832 * 1833 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1834 * size an average of 4,823 attempts are required for a 50% chance of success 1835 * to spoof a single syncookie (birthday collision paradox). However the 1836 * attacker is blind and doesn't know if one of his attempts succeeded unless 1837 * he has a side channel to interfere success from. A single connection setup 1838 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1839 * This many attempts are required for each one blind spoofed connection. For 1840 * every additional spoofed connection he has to launch another N attempts. 1841 * Thus for a sustained rate 100 spoofed connections per second approximately 1842 * 1,800,000 packets per second would have to be sent. 1843 * 1844 * NB: The MAC function should be fast so that it doesn't become a CPU 1845 * exhaustion attack vector itself. 1846 * 1847 * References: 1848 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1849 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1850 * http://cr.yp.to/syncookies.html (overview) 1851 * http://cr.yp.to/syncookies/archive (details) 1852 * 1853 * 1854 * Schematic construction of a syncookie enabled Initial Sequence Number: 1855 * 0 1 2 3 1856 * 12345678901234567890123456789012 1857 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1858 * 1859 * x 24 MAC (truncated) 1860 * W 3 Send Window Scale index 1861 * M 3 MSS index 1862 * S 1 SACK permitted 1863 * P 1 Odd/even secret 1864 */ 1865 1866 /* 1867 * Distribution and probability of certain MSS values. Those in between are 1868 * rounded down to the next lower one. 1869 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1870 * .2% .3% 5% 7% 7% 20% 15% 45% 1871 */ 1872 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1873 1874 /* 1875 * Distribution and probability of certain WSCALE values. We have to map the 1876 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1877 * bits based on prevalence of certain values. Where we don't have an exact 1878 * match for are rounded down to the next lower one letting us under-estimate 1879 * the true available window. At the moment this would happen only for the 1880 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1881 * and window size). The absence of the WSCALE option (no scaling in either 1882 * direction) is encoded with index zero. 1883 * [WSCALE values histograms, Allman, 2012] 1884 * X 10 10 35 5 6 14 10% by host 1885 * X 11 4 5 5 18 49 3% by connections 1886 */ 1887 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1888 1889 /* 1890 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1891 * and good cryptographic properties. 1892 */ 1893 static uint32_t 1894 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1895 uint8_t *secbits, uintptr_t secmod) 1896 { 1897 SIPHASH_CTX ctx; 1898 uint32_t siphash[2]; 1899 1900 SipHash24_Init(&ctx); 1901 SipHash_SetKey(&ctx, secbits); 1902 switch (inc->inc_flags & INC_ISIPV6) { 1903 #ifdef INET 1904 case 0: 1905 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1906 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1907 break; 1908 #endif 1909 #ifdef INET6 1910 case INC_ISIPV6: 1911 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1912 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1913 break; 1914 #endif 1915 } 1916 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1917 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1918 SipHash_Update(&ctx, &irs, sizeof(irs)); 1919 SipHash_Update(&ctx, &flags, sizeof(flags)); 1920 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1921 SipHash_Final((u_int8_t *)&siphash, &ctx); 1922 1923 return (siphash[0] ^ siphash[1]); 1924 } 1925 1926 static tcp_seq 1927 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1928 { 1929 u_int i, mss, secbit, wscale; 1930 uint32_t iss, hash; 1931 uint8_t *secbits; 1932 union syncookie cookie; 1933 1934 SCH_LOCK_ASSERT(sch); 1935 1936 cookie.cookie = 0; 1937 1938 /* Map our computed MSS into the 3-bit index. */ 1939 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1940 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0; 1941 i--) 1942 ; 1943 cookie.flags.mss_idx = i; 1944 1945 /* 1946 * Map the send window scale into the 3-bit index but only if 1947 * the wscale option was received. 1948 */ 1949 if (sc->sc_flags & SCF_WINSCALE) { 1950 wscale = sc->sc_requested_s_scale; 1951 for (i = nitems(tcp_sc_wstab) - 1; 1952 tcp_sc_wstab[i] > wscale && i > 0; 1953 i--) 1954 ; 1955 cookie.flags.wscale_idx = i; 1956 } 1957 1958 /* Can we do SACK? */ 1959 if (sc->sc_flags & SCF_SACK) 1960 cookie.flags.sack_ok = 1; 1961 1962 /* Which of the two secrets to use. */ 1963 secbit = sch->sch_sc->secret.oddeven & 0x1; 1964 cookie.flags.odd_even = secbit; 1965 1966 secbits = sch->sch_sc->secret.key[secbit]; 1967 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1968 (uintptr_t)sch); 1969 1970 /* 1971 * Put the flags into the hash and XOR them to get better ISS number 1972 * variance. This doesn't enhance the cryptographic strength and is 1973 * done to prevent the 8 cookie bits from showing up directly on the 1974 * wire. 1975 */ 1976 iss = hash & ~0xff; 1977 iss |= cookie.cookie ^ (hash >> 24); 1978 1979 /* Randomize the timestamp. */ 1980 if (sc->sc_flags & SCF_TIMESTAMP) { 1981 sc->sc_ts = arc4random(); 1982 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1983 } 1984 1985 TCPSTAT_INC(tcps_sc_sendcookie); 1986 return (iss); 1987 } 1988 1989 static struct syncache * 1990 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1991 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1992 struct socket *lso) 1993 { 1994 uint32_t hash; 1995 uint8_t *secbits; 1996 tcp_seq ack, seq; 1997 int wnd, wscale = 0; 1998 union syncookie cookie; 1999 2000 SCH_LOCK_ASSERT(sch); 2001 2002 /* 2003 * Pull information out of SYN-ACK/ACK and revert sequence number 2004 * advances. 2005 */ 2006 ack = th->th_ack - 1; 2007 seq = th->th_seq - 1; 2008 2009 /* 2010 * Unpack the flags containing enough information to restore the 2011 * connection. 2012 */ 2013 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2014 2015 /* Which of the two secrets to use. */ 2016 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 2017 2018 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2019 2020 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2021 if ((ack & ~0xff) != (hash & ~0xff)) 2022 return (NULL); 2023 2024 /* Fill in the syncache values. */ 2025 sc->sc_flags = 0; 2026 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2027 sc->sc_ipopts = NULL; 2028 2029 sc->sc_irs = seq; 2030 sc->sc_iss = ack; 2031 2032 switch (inc->inc_flags & INC_ISIPV6) { 2033 #ifdef INET 2034 case 0: 2035 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2036 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2037 break; 2038 #endif 2039 #ifdef INET6 2040 case INC_ISIPV6: 2041 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2042 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2043 break; 2044 #endif 2045 } 2046 2047 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2048 2049 /* We can simply recompute receive window scale we sent earlier. */ 2050 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2051 wscale++; 2052 2053 /* Only use wscale if it was enabled in the orignal SYN. */ 2054 if (cookie.flags.wscale_idx > 0) { 2055 sc->sc_requested_r_scale = wscale; 2056 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2057 sc->sc_flags |= SCF_WINSCALE; 2058 } 2059 2060 wnd = sbspace(&lso->so_rcv); 2061 wnd = imax(wnd, 0); 2062 wnd = imin(wnd, TCP_MAXWIN); 2063 sc->sc_wnd = wnd; 2064 2065 if (cookie.flags.sack_ok) 2066 sc->sc_flags |= SCF_SACK; 2067 2068 if (to->to_flags & TOF_TS) { 2069 sc->sc_flags |= SCF_TIMESTAMP; 2070 sc->sc_tsreflect = to->to_tsval; 2071 sc->sc_ts = to->to_tsecr; 2072 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 2073 } 2074 2075 if (to->to_flags & TOF_SIGNATURE) 2076 sc->sc_flags |= SCF_SIGNATURE; 2077 2078 sc->sc_rxmits = 0; 2079 2080 TCPSTAT_INC(tcps_sc_recvcookie); 2081 return (sc); 2082 } 2083 2084 #ifdef INVARIANTS 2085 static int 2086 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2087 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2088 struct socket *lso) 2089 { 2090 struct syncache scs, *scx; 2091 char *s; 2092 2093 bzero(&scs, sizeof(scs)); 2094 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2095 2096 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2097 return (0); 2098 2099 if (scx != NULL) { 2100 if (sc->sc_peer_mss != scx->sc_peer_mss) 2101 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2102 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2103 2104 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2105 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2106 s, __func__, sc->sc_requested_r_scale, 2107 scx->sc_requested_r_scale); 2108 2109 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2110 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2111 s, __func__, sc->sc_requested_s_scale, 2112 scx->sc_requested_s_scale); 2113 2114 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2115 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2116 } 2117 2118 if (s != NULL) 2119 free(s, M_TCPLOG); 2120 return (0); 2121 } 2122 #endif /* INVARIANTS */ 2123 2124 static void 2125 syncookie_reseed(void *arg) 2126 { 2127 struct tcp_syncache *sc = arg; 2128 uint8_t *secbits; 2129 int secbit; 2130 2131 /* 2132 * Reseeding the secret doesn't have to be protected by a lock. 2133 * It only must be ensured that the new random values are visible 2134 * to all CPUs in a SMP environment. The atomic with release 2135 * semantics ensures that. 2136 */ 2137 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2138 secbits = sc->secret.key[secbit]; 2139 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2140 atomic_add_rel_int(&sc->secret.oddeven, 1); 2141 2142 /* Reschedule ourself. */ 2143 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2144 } 2145 2146 /* 2147 * Exports the syncache entries to userland so that netstat can display 2148 * them alongside the other sockets. This function is intended to be 2149 * called only from tcp_pcblist. 2150 * 2151 * Due to concurrency on an active system, the number of pcbs exported 2152 * may have no relation to max_pcbs. max_pcbs merely indicates the 2153 * amount of space the caller allocated for this function to use. 2154 */ 2155 int 2156 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2157 { 2158 struct xtcpcb xt; 2159 struct syncache *sc; 2160 struct syncache_head *sch; 2161 int count, error, i; 2162 2163 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2164 sch = &V_tcp_syncache.hashbase[i]; 2165 SCH_LOCK(sch); 2166 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2167 if (count >= max_pcbs) { 2168 SCH_UNLOCK(sch); 2169 goto exit; 2170 } 2171 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2172 continue; 2173 bzero(&xt, sizeof(xt)); 2174 xt.xt_len = sizeof(xt); 2175 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2176 xt.xt_inp.inp_vflag = INP_IPV6; 2177 else 2178 xt.xt_inp.inp_vflag = INP_IPV4; 2179 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2180 xt.xt_tp.t_inpcb = &xt.xt_inp; 2181 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2182 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2183 xt.xt_socket.xso_len = sizeof (struct xsocket); 2184 xt.xt_socket.so_type = SOCK_STREAM; 2185 xt.xt_socket.so_state = SS_ISCONNECTING; 2186 error = SYSCTL_OUT(req, &xt, sizeof xt); 2187 if (error) { 2188 SCH_UNLOCK(sch); 2189 goto exit; 2190 } 2191 count++; 2192 } 2193 SCH_UNLOCK(sch); 2194 } 2195 exit: 2196 *pcbs_exported = count; 2197 return error; 2198 } 2199