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