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