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 * except in the case of 0. Some boxes are known for sending 1075 * broken timestamp replies during the 3whs (and potentially 1076 * during the connection also). 1077 * 1078 * Accept the final ACK of 3whs with reflected timestamp of 0 1079 * instead of sending a RST and deleting the syncache entry. 1080 */ 1081 if ((to->to_flags & TOF_TS) && to->to_tsecr && 1082 to->to_tsecr != sc->sc_ts) { 1083 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1084 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 1085 "segment rejected\n", 1086 s, __func__, to->to_tsecr, sc->sc_ts); 1087 goto failed; 1088 } 1089 1090 *lsop = syncache_socket(sc, *lsop, m); 1091 1092 if (*lsop == NULL) 1093 TCPSTAT_INC(tcps_sc_aborted); 1094 else 1095 TCPSTAT_INC(tcps_sc_completed); 1096 1097 /* how do we find the inp for the new socket? */ 1098 if (sc != &scs) 1099 syncache_free(sc); 1100 return (1); 1101 failed: 1102 if (sc != NULL && sc != &scs) 1103 syncache_free(sc); 1104 if (s != NULL) 1105 free(s, M_TCPLOG); 1106 *lsop = NULL; 1107 return (0); 1108 } 1109 1110 #ifdef TCP_RFC7413 1111 static void 1112 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m, 1113 uint64_t response_cookie) 1114 { 1115 struct inpcb *inp; 1116 struct tcpcb *tp; 1117 unsigned int *pending_counter; 1118 1119 /* 1120 * Global TCP locks are held because we manipulate the PCB lists 1121 * and create a new socket. 1122 */ 1123 INP_INFO_RLOCK_ASSERT(&V_tcbinfo); 1124 1125 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending; 1126 *lsop = syncache_socket(sc, *lsop, m); 1127 if (*lsop == NULL) { 1128 TCPSTAT_INC(tcps_sc_aborted); 1129 atomic_subtract_int(pending_counter, 1); 1130 } else { 1131 inp = sotoinpcb(*lsop); 1132 tp = intotcpcb(inp); 1133 tp->t_flags |= TF_FASTOPEN; 1134 tp->t_tfo_cookie = response_cookie; 1135 tp->snd_max = tp->iss; 1136 tp->snd_nxt = tp->iss; 1137 tp->t_tfo_pending = pending_counter; 1138 TCPSTAT_INC(tcps_sc_completed); 1139 } 1140 } 1141 #endif /* TCP_RFC7413 */ 1142 1143 /* 1144 * Given a LISTEN socket and an inbound SYN request, add 1145 * this to the syn cache, and send back a segment: 1146 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1147 * to the source. 1148 * 1149 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1150 * Doing so would require that we hold onto the data and deliver it 1151 * to the application. However, if we are the target of a SYN-flood 1152 * DoS attack, an attacker could send data which would eventually 1153 * consume all available buffer space if it were ACKed. By not ACKing 1154 * the data, we avoid this DoS scenario. 1155 * 1156 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1157 * cookie is processed and a new socket is created. In this case, any data 1158 * accompanying the SYN will be queued to the socket by tcp_input() and will 1159 * be ACKed either when the application sends response data or the delayed 1160 * ACK timer expires, whichever comes first. 1161 */ 1162 int 1163 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1164 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod, 1165 void *todctx) 1166 { 1167 struct tcpcb *tp; 1168 struct socket *so; 1169 struct syncache *sc = NULL; 1170 struct syncache_head *sch; 1171 struct mbuf *ipopts = NULL; 1172 u_int ltflags; 1173 int win, ip_ttl, ip_tos; 1174 char *s; 1175 int rv = 0; 1176 #ifdef INET6 1177 int autoflowlabel = 0; 1178 #endif 1179 #ifdef MAC 1180 struct label *maclabel; 1181 #endif 1182 struct syncache scs; 1183 struct ucred *cred; 1184 #ifdef TCP_RFC7413 1185 uint64_t tfo_response_cookie; 1186 unsigned int *tfo_pending = NULL; 1187 int tfo_cookie_valid = 0; 1188 int tfo_response_cookie_valid = 0; 1189 #endif 1190 1191 INP_WLOCK_ASSERT(inp); /* listen socket */ 1192 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1193 ("%s: unexpected tcp flags", __func__)); 1194 1195 /* 1196 * Combine all so/tp operations very early to drop the INP lock as 1197 * soon as possible. 1198 */ 1199 so = *lsop; 1200 tp = sototcpcb(so); 1201 cred = crhold(so->so_cred); 1202 1203 #ifdef INET6 1204 if ((inc->inc_flags & INC_ISIPV6) && 1205 (inp->inp_flags & IN6P_AUTOFLOWLABEL)) 1206 autoflowlabel = 1; 1207 #endif 1208 ip_ttl = inp->inp_ip_ttl; 1209 ip_tos = inp->inp_ip_tos; 1210 win = sbspace(&so->so_rcv); 1211 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1212 1213 #ifdef TCP_RFC7413 1214 if (V_tcp_fastopen_enabled && IS_FASTOPEN(tp->t_flags) && 1215 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1216 /* 1217 * Limit the number of pending TFO connections to 1218 * approximately half of the queue limit. This prevents TFO 1219 * SYN floods from starving the service by filling the 1220 * listen queue with bogus TFO connections. 1221 */ 1222 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1223 (so->so_qlimit / 2)) { 1224 int result; 1225 1226 result = tcp_fastopen_check_cookie(inc, 1227 to->to_tfo_cookie, to->to_tfo_len, 1228 &tfo_response_cookie); 1229 tfo_cookie_valid = (result > 0); 1230 tfo_response_cookie_valid = (result >= 0); 1231 } 1232 1233 /* 1234 * Remember the TFO pending counter as it will have to be 1235 * decremented below if we don't make it to syncache_tfo_expand(). 1236 */ 1237 tfo_pending = tp->t_tfo_pending; 1238 } 1239 #endif 1240 1241 /* By the time we drop the lock these should no longer be used. */ 1242 so = NULL; 1243 tp = NULL; 1244 1245 #ifdef MAC 1246 if (mac_syncache_init(&maclabel) != 0) { 1247 INP_WUNLOCK(inp); 1248 goto done; 1249 } else 1250 mac_syncache_create(maclabel, inp); 1251 #endif 1252 #ifdef TCP_RFC7413 1253 if (!tfo_cookie_valid) 1254 #endif 1255 INP_WUNLOCK(inp); 1256 1257 /* 1258 * Remember the IP options, if any. 1259 */ 1260 #ifdef INET6 1261 if (!(inc->inc_flags & INC_ISIPV6)) 1262 #endif 1263 #ifdef INET 1264 ipopts = (m) ? ip_srcroute(m) : NULL; 1265 #else 1266 ipopts = NULL; 1267 #endif 1268 1269 /* 1270 * See if we already have an entry for this connection. 1271 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1272 * 1273 * XXX: should the syncache be re-initialized with the contents 1274 * of the new SYN here (which may have different options?) 1275 * 1276 * XXX: We do not check the sequence number to see if this is a 1277 * real retransmit or a new connection attempt. The question is 1278 * how to handle such a case; either ignore it as spoofed, or 1279 * drop the current entry and create a new one? 1280 */ 1281 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1282 SCH_LOCK_ASSERT(sch); 1283 if (sc != NULL) { 1284 #ifdef TCP_RFC7413 1285 if (tfo_cookie_valid) 1286 INP_WUNLOCK(inp); 1287 #endif 1288 TCPSTAT_INC(tcps_sc_dupsyn); 1289 if (ipopts) { 1290 /* 1291 * If we were remembering a previous source route, 1292 * forget it and use the new one we've been given. 1293 */ 1294 if (sc->sc_ipopts) 1295 (void) m_free(sc->sc_ipopts); 1296 sc->sc_ipopts = ipopts; 1297 } 1298 /* 1299 * Update timestamp if present. 1300 */ 1301 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1302 sc->sc_tsreflect = to->to_tsval; 1303 else 1304 sc->sc_flags &= ~SCF_TIMESTAMP; 1305 #ifdef MAC 1306 /* 1307 * Since we have already unconditionally allocated label 1308 * storage, free it up. The syncache entry will already 1309 * have an initialized label we can use. 1310 */ 1311 mac_syncache_destroy(&maclabel); 1312 #endif 1313 /* Retransmit SYN|ACK and reset retransmit count. */ 1314 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1315 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1316 "resetting timer and retransmitting SYN|ACK\n", 1317 s, __func__); 1318 free(s, M_TCPLOG); 1319 } 1320 if (syncache_respond(sc, sch, 1, m) == 0) { 1321 sc->sc_rxmits = 0; 1322 syncache_timeout(sc, sch, 1); 1323 TCPSTAT_INC(tcps_sndacks); 1324 TCPSTAT_INC(tcps_sndtotal); 1325 } 1326 SCH_UNLOCK(sch); 1327 goto done; 1328 } 1329 1330 #ifdef TCP_RFC7413 1331 if (tfo_cookie_valid) { 1332 bzero(&scs, sizeof(scs)); 1333 sc = &scs; 1334 goto skip_alloc; 1335 } 1336 #endif 1337 1338 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1339 if (sc == NULL) { 1340 /* 1341 * The zone allocator couldn't provide more entries. 1342 * Treat this as if the cache was full; drop the oldest 1343 * entry and insert the new one. 1344 */ 1345 TCPSTAT_INC(tcps_sc_zonefail); 1346 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1347 syncache_drop(sc, sch); 1348 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1349 if (sc == NULL) { 1350 if (V_tcp_syncookies) { 1351 bzero(&scs, sizeof(scs)); 1352 sc = &scs; 1353 } else { 1354 SCH_UNLOCK(sch); 1355 if (ipopts) 1356 (void) m_free(ipopts); 1357 goto done; 1358 } 1359 } 1360 } 1361 1362 #ifdef TCP_RFC7413 1363 skip_alloc: 1364 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1365 sc->sc_tfo_cookie = &tfo_response_cookie; 1366 #endif 1367 1368 /* 1369 * Fill in the syncache values. 1370 */ 1371 #ifdef MAC 1372 sc->sc_label = maclabel; 1373 #endif 1374 sc->sc_cred = cred; 1375 cred = NULL; 1376 sc->sc_ipopts = ipopts; 1377 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1378 #ifdef INET6 1379 if (!(inc->inc_flags & INC_ISIPV6)) 1380 #endif 1381 { 1382 sc->sc_ip_tos = ip_tos; 1383 sc->sc_ip_ttl = ip_ttl; 1384 } 1385 #ifdef TCP_OFFLOAD 1386 sc->sc_tod = tod; 1387 sc->sc_todctx = todctx; 1388 #endif 1389 sc->sc_irs = th->th_seq; 1390 sc->sc_iss = arc4random(); 1391 sc->sc_flags = 0; 1392 sc->sc_flowlabel = 0; 1393 1394 /* 1395 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1396 * win was derived from socket earlier in the function. 1397 */ 1398 win = imax(win, 0); 1399 win = imin(win, TCP_MAXWIN); 1400 sc->sc_wnd = win; 1401 1402 if (V_tcp_do_rfc1323) { 1403 /* 1404 * A timestamp received in a SYN makes 1405 * it ok to send timestamp requests and replies. 1406 */ 1407 if (to->to_flags & TOF_TS) { 1408 sc->sc_tsreflect = to->to_tsval; 1409 sc->sc_ts = tcp_ts_getticks(); 1410 sc->sc_flags |= SCF_TIMESTAMP; 1411 } 1412 if (to->to_flags & TOF_SCALE) { 1413 int wscale = 0; 1414 1415 /* 1416 * Pick the smallest possible scaling factor that 1417 * will still allow us to scale up to sb_max, aka 1418 * kern.ipc.maxsockbuf. 1419 * 1420 * We do this because there are broken firewalls that 1421 * will corrupt the window scale option, leading to 1422 * the other endpoint believing that our advertised 1423 * window is unscaled. At scale factors larger than 1424 * 5 the unscaled window will drop below 1500 bytes, 1425 * leading to serious problems when traversing these 1426 * broken firewalls. 1427 * 1428 * With the default maxsockbuf of 256K, a scale factor 1429 * of 3 will be chosen by this algorithm. Those who 1430 * choose a larger maxsockbuf should watch out 1431 * for the compatibility problems mentioned above. 1432 * 1433 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1434 * or <SYN,ACK>) segment itself is never scaled. 1435 */ 1436 while (wscale < TCP_MAX_WINSHIFT && 1437 (TCP_MAXWIN << wscale) < sb_max) 1438 wscale++; 1439 sc->sc_requested_r_scale = wscale; 1440 sc->sc_requested_s_scale = to->to_wscale; 1441 sc->sc_flags |= SCF_WINSCALE; 1442 } 1443 } 1444 #ifdef TCP_SIGNATURE 1445 /* 1446 * If listening socket requested TCP digests, OR received SYN 1447 * contains the option, flag this in the syncache so that 1448 * syncache_respond() will do the right thing with the SYN+ACK. 1449 */ 1450 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1451 sc->sc_flags |= SCF_SIGNATURE; 1452 #endif 1453 if (to->to_flags & TOF_SACKPERM) 1454 sc->sc_flags |= SCF_SACK; 1455 if (to->to_flags & TOF_MSS) 1456 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1457 if (ltflags & TF_NOOPT) 1458 sc->sc_flags |= SCF_NOOPT; 1459 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1460 sc->sc_flags |= SCF_ECN; 1461 1462 if (V_tcp_syncookies) 1463 sc->sc_iss = syncookie_generate(sch, sc); 1464 #ifdef INET6 1465 if (autoflowlabel) { 1466 if (V_tcp_syncookies) 1467 sc->sc_flowlabel = sc->sc_iss; 1468 else 1469 sc->sc_flowlabel = ip6_randomflowlabel(); 1470 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1471 } 1472 #endif 1473 SCH_UNLOCK(sch); 1474 1475 #ifdef TCP_RFC7413 1476 if (tfo_cookie_valid) { 1477 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1478 /* INP_WUNLOCK(inp) will be performed by the caller */ 1479 rv = 1; 1480 goto tfo_expanded; 1481 } 1482 #endif 1483 1484 /* 1485 * Do a standard 3-way handshake. 1486 */ 1487 if (syncache_respond(sc, sch, 0, m) == 0) { 1488 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1489 syncache_free(sc); 1490 else if (sc != &scs) 1491 syncache_insert(sc, sch); /* locks and unlocks sch */ 1492 TCPSTAT_INC(tcps_sndacks); 1493 TCPSTAT_INC(tcps_sndtotal); 1494 } else { 1495 if (sc != &scs) 1496 syncache_free(sc); 1497 TCPSTAT_INC(tcps_sc_dropped); 1498 } 1499 1500 done: 1501 if (m) { 1502 *lsop = NULL; 1503 m_freem(m); 1504 } 1505 #ifdef TCP_RFC7413 1506 /* 1507 * If tfo_pending is not NULL here, then a TFO SYN that did not 1508 * result in a new socket was processed and the associated pending 1509 * counter has not yet been decremented. All such TFO processing paths 1510 * transit this point. 1511 */ 1512 if (tfo_pending != NULL) 1513 tcp_fastopen_decrement_counter(tfo_pending); 1514 1515 tfo_expanded: 1516 #endif 1517 if (cred != NULL) 1518 crfree(cred); 1519 #ifdef MAC 1520 if (sc == &scs) 1521 mac_syncache_destroy(&maclabel); 1522 #endif 1523 return (rv); 1524 } 1525 1526 /* 1527 * Send SYN|ACK to the peer. Either in response to the peer's SYN, 1528 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1529 */ 1530 static int 1531 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked, 1532 const struct mbuf *m0) 1533 { 1534 struct ip *ip = NULL; 1535 struct mbuf *m; 1536 struct tcphdr *th = NULL; 1537 int optlen, error = 0; /* Make compiler happy */ 1538 u_int16_t hlen, tlen, mssopt; 1539 struct tcpopt to; 1540 #ifdef INET6 1541 struct ip6_hdr *ip6 = NULL; 1542 #endif 1543 #ifdef TCP_SIGNATURE 1544 struct secasvar *sav; 1545 #endif 1546 1547 hlen = 1548 #ifdef INET6 1549 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1550 #endif 1551 sizeof(struct ip); 1552 tlen = hlen + sizeof(struct tcphdr); 1553 1554 /* Determine MSS we advertize to other end of connection. */ 1555 mssopt = tcp_mssopt(&sc->sc_inc); 1556 if (sc->sc_peer_mss) 1557 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1558 1559 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1560 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1561 ("syncache: mbuf too small")); 1562 1563 /* Create the IP+TCP header from scratch. */ 1564 m = m_gethdr(M_NOWAIT, MT_DATA); 1565 if (m == NULL) 1566 return (ENOBUFS); 1567 #ifdef MAC 1568 mac_syncache_create_mbuf(sc->sc_label, m); 1569 #endif 1570 m->m_data += max_linkhdr; 1571 m->m_len = tlen; 1572 m->m_pkthdr.len = tlen; 1573 m->m_pkthdr.rcvif = NULL; 1574 1575 #ifdef INET6 1576 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1577 ip6 = mtod(m, struct ip6_hdr *); 1578 ip6->ip6_vfc = IPV6_VERSION; 1579 ip6->ip6_nxt = IPPROTO_TCP; 1580 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1581 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1582 ip6->ip6_plen = htons(tlen - hlen); 1583 /* ip6_hlim is set after checksum */ 1584 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1585 ip6->ip6_flow |= sc->sc_flowlabel; 1586 1587 th = (struct tcphdr *)(ip6 + 1); 1588 } 1589 #endif 1590 #if defined(INET6) && defined(INET) 1591 else 1592 #endif 1593 #ifdef INET 1594 { 1595 ip = mtod(m, struct ip *); 1596 ip->ip_v = IPVERSION; 1597 ip->ip_hl = sizeof(struct ip) >> 2; 1598 ip->ip_len = htons(tlen); 1599 ip->ip_id = 0; 1600 ip->ip_off = 0; 1601 ip->ip_sum = 0; 1602 ip->ip_p = IPPROTO_TCP; 1603 ip->ip_src = sc->sc_inc.inc_laddr; 1604 ip->ip_dst = sc->sc_inc.inc_faddr; 1605 ip->ip_ttl = sc->sc_ip_ttl; 1606 ip->ip_tos = sc->sc_ip_tos; 1607 1608 /* 1609 * See if we should do MTU discovery. Route lookups are 1610 * expensive, so we will only unset the DF bit if: 1611 * 1612 * 1) path_mtu_discovery is disabled 1613 * 2) the SCF_UNREACH flag has been set 1614 */ 1615 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1616 ip->ip_off |= htons(IP_DF); 1617 1618 th = (struct tcphdr *)(ip + 1); 1619 } 1620 #endif /* INET */ 1621 th->th_sport = sc->sc_inc.inc_lport; 1622 th->th_dport = sc->sc_inc.inc_fport; 1623 1624 th->th_seq = htonl(sc->sc_iss); 1625 th->th_ack = htonl(sc->sc_irs + 1); 1626 th->th_off = sizeof(struct tcphdr) >> 2; 1627 th->th_x2 = 0; 1628 th->th_flags = TH_SYN|TH_ACK; 1629 th->th_win = htons(sc->sc_wnd); 1630 th->th_urp = 0; 1631 1632 if (sc->sc_flags & SCF_ECN) { 1633 th->th_flags |= TH_ECE; 1634 TCPSTAT_INC(tcps_ecn_shs); 1635 } 1636 1637 /* Tack on the TCP options. */ 1638 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1639 to.to_flags = 0; 1640 1641 to.to_mss = mssopt; 1642 to.to_flags = TOF_MSS; 1643 if (sc->sc_flags & SCF_WINSCALE) { 1644 to.to_wscale = sc->sc_requested_r_scale; 1645 to.to_flags |= TOF_SCALE; 1646 } 1647 if (sc->sc_flags & SCF_TIMESTAMP) { 1648 /* Virgin timestamp or TCP cookie enhanced one. */ 1649 to.to_tsval = sc->sc_ts; 1650 to.to_tsecr = sc->sc_tsreflect; 1651 to.to_flags |= TOF_TS; 1652 } 1653 if (sc->sc_flags & SCF_SACK) 1654 to.to_flags |= TOF_SACKPERM; 1655 #ifdef TCP_SIGNATURE 1656 sav = NULL; 1657 if (sc->sc_flags & SCF_SIGNATURE) { 1658 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1659 if (sav != NULL) 1660 to.to_flags |= TOF_SIGNATURE; 1661 else { 1662 1663 /* 1664 * We've got SCF_SIGNATURE flag 1665 * inherited from listening socket, 1666 * but no SADB key for given source 1667 * address. Assume signature is not 1668 * required and remove signature flag 1669 * instead of silently dropping 1670 * connection. 1671 */ 1672 if (locked == 0) 1673 SCH_LOCK(sch); 1674 sc->sc_flags &= ~SCF_SIGNATURE; 1675 if (locked == 0) 1676 SCH_UNLOCK(sch); 1677 } 1678 } 1679 #endif 1680 1681 #ifdef TCP_RFC7413 1682 if (sc->sc_tfo_cookie) { 1683 to.to_flags |= TOF_FASTOPEN; 1684 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1685 to.to_tfo_cookie = sc->sc_tfo_cookie; 1686 /* don't send cookie again when retransmitting response */ 1687 sc->sc_tfo_cookie = NULL; 1688 } 1689 #endif 1690 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1691 1692 /* Adjust headers by option size. */ 1693 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1694 m->m_len += optlen; 1695 m->m_pkthdr.len += optlen; 1696 1697 #ifdef TCP_SIGNATURE 1698 if (sc->sc_flags & SCF_SIGNATURE) 1699 tcp_signature_do_compute(m, 0, optlen, 1700 to.to_signature, sav); 1701 #endif 1702 #ifdef INET6 1703 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1704 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1705 else 1706 #endif 1707 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1708 } else 1709 optlen = 0; 1710 1711 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1712 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1713 /* 1714 * If we have peer's SYN and it has a flowid, then let's assign it to 1715 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1716 * to SYN|ACK due to lack of inp here. 1717 */ 1718 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1719 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1720 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1721 } 1722 #ifdef INET6 1723 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1724 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1725 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1726 IPPROTO_TCP, 0); 1727 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1728 #ifdef TCP_OFFLOAD 1729 if (ADDED_BY_TOE(sc)) { 1730 struct toedev *tod = sc->sc_tod; 1731 1732 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1733 1734 return (error); 1735 } 1736 #endif 1737 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1738 } 1739 #endif 1740 #if defined(INET6) && defined(INET) 1741 else 1742 #endif 1743 #ifdef INET 1744 { 1745 m->m_pkthdr.csum_flags = CSUM_TCP; 1746 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1747 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1748 #ifdef TCP_OFFLOAD 1749 if (ADDED_BY_TOE(sc)) { 1750 struct toedev *tod = sc->sc_tod; 1751 1752 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1753 1754 return (error); 1755 } 1756 #endif 1757 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1758 } 1759 #endif 1760 return (error); 1761 } 1762 1763 /* 1764 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1765 * that exceed the capacity of the syncache by avoiding the storage of any 1766 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1767 * attacks where the attacker does not have access to our responses. 1768 * 1769 * Syncookies encode and include all necessary information about the 1770 * connection setup within the SYN|ACK that we send back. That way we 1771 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1772 * (if ever). Normally the syncache and syncookies are running in parallel 1773 * with the latter taking over when the former is exhausted. When matching 1774 * syncache entry is found the syncookie is ignored. 1775 * 1776 * The only reliable information persisting the 3WHS is our initial sequence 1777 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1778 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1779 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1780 * returns and signifies a legitimate connection if it matches the ACK. 1781 * 1782 * The available space of 32 bits to store the hash and to encode the SYN 1783 * option information is very tight and we should have at least 24 bits for 1784 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1785 * 1786 * SYN option information we have to encode to fully restore a connection: 1787 * MSS: is imporant to chose an optimal segment size to avoid IP level 1788 * fragmentation along the path. The common MSS values can be encoded 1789 * in a 3-bit table. Uncommon values are captured by the next lower value 1790 * in the table leading to a slight increase in packetization overhead. 1791 * WSCALE: is necessary to allow large windows to be used for high delay- 1792 * bandwidth product links. Not scaling the window when it was initially 1793 * negotiated is bad for performance as lack of scaling further decreases 1794 * the apparent available send window. We only need to encode the WSCALE 1795 * we received from the remote end. Our end can be recalculated at any 1796 * time. The common WSCALE values can be encoded in a 3-bit table. 1797 * Uncommon values are captured by the next lower value in the table 1798 * making us under-estimate the available window size halving our 1799 * theoretically possible maximum throughput for that connection. 1800 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1801 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1802 * that are included in all segments on a connection. We enable them when 1803 * the ACK has them. 1804 * 1805 * Security of syncookies and attack vectors: 1806 * 1807 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1808 * together with the gloabl secret to make it unique per connection attempt. 1809 * Thus any change of any of those parameters results in a different MAC output 1810 * in an unpredictable way unless a collision is encountered. 24 bits of the 1811 * MAC are embedded into the ISS. 1812 * 1813 * To prevent replay attacks two rotating global secrets are updated with a 1814 * new random value every 15 seconds. The life-time of a syncookie is thus 1815 * 15-30 seconds. 1816 * 1817 * Vector 1: Attacking the secret. This requires finding a weakness in the 1818 * MAC itself or the way it is used here. The attacker can do a chosen plain 1819 * text attack by varying and testing the all parameters under his control. 1820 * The strength depends on the size and randomness of the secret, and the 1821 * cryptographic security of the MAC function. Due to the constant updating 1822 * of the secret the attacker has at most 29.999 seconds to find the secret 1823 * and launch spoofed connections. After that he has to start all over again. 1824 * 1825 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1826 * size an average of 4,823 attempts are required for a 50% chance of success 1827 * to spoof a single syncookie (birthday collision paradox). However the 1828 * attacker is blind and doesn't know if one of his attempts succeeded unless 1829 * he has a side channel to interfere success from. A single connection setup 1830 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1831 * This many attempts are required for each one blind spoofed connection. For 1832 * every additional spoofed connection he has to launch another N attempts. 1833 * Thus for a sustained rate 100 spoofed connections per second approximately 1834 * 1,800,000 packets per second would have to be sent. 1835 * 1836 * NB: The MAC function should be fast so that it doesn't become a CPU 1837 * exhaustion attack vector itself. 1838 * 1839 * References: 1840 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1841 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1842 * http://cr.yp.to/syncookies.html (overview) 1843 * http://cr.yp.to/syncookies/archive (details) 1844 * 1845 * 1846 * Schematic construction of a syncookie enabled Initial Sequence Number: 1847 * 0 1 2 3 1848 * 12345678901234567890123456789012 1849 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1850 * 1851 * x 24 MAC (truncated) 1852 * W 3 Send Window Scale index 1853 * M 3 MSS index 1854 * S 1 SACK permitted 1855 * P 1 Odd/even secret 1856 */ 1857 1858 /* 1859 * Distribution and probability of certain MSS values. Those in between are 1860 * rounded down to the next lower one. 1861 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1862 * .2% .3% 5% 7% 7% 20% 15% 45% 1863 */ 1864 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1865 1866 /* 1867 * Distribution and probability of certain WSCALE values. We have to map the 1868 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1869 * bits based on prevalence of certain values. Where we don't have an exact 1870 * match for are rounded down to the next lower one letting us under-estimate 1871 * the true available window. At the moment this would happen only for the 1872 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1873 * and window size). The absence of the WSCALE option (no scaling in either 1874 * direction) is encoded with index zero. 1875 * [WSCALE values histograms, Allman, 2012] 1876 * X 10 10 35 5 6 14 10% by host 1877 * X 11 4 5 5 18 49 3% by connections 1878 */ 1879 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1880 1881 /* 1882 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1883 * and good cryptographic properties. 1884 */ 1885 static uint32_t 1886 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1887 uint8_t *secbits, uintptr_t secmod) 1888 { 1889 SIPHASH_CTX ctx; 1890 uint32_t siphash[2]; 1891 1892 SipHash24_Init(&ctx); 1893 SipHash_SetKey(&ctx, secbits); 1894 switch (inc->inc_flags & INC_ISIPV6) { 1895 #ifdef INET 1896 case 0: 1897 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1898 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1899 break; 1900 #endif 1901 #ifdef INET6 1902 case INC_ISIPV6: 1903 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1904 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1905 break; 1906 #endif 1907 } 1908 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1909 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1910 SipHash_Update(&ctx, &irs, sizeof(irs)); 1911 SipHash_Update(&ctx, &flags, sizeof(flags)); 1912 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1913 SipHash_Final((u_int8_t *)&siphash, &ctx); 1914 1915 return (siphash[0] ^ siphash[1]); 1916 } 1917 1918 static tcp_seq 1919 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1920 { 1921 u_int i, mss, secbit, wscale; 1922 uint32_t iss, hash; 1923 uint8_t *secbits; 1924 union syncookie cookie; 1925 1926 SCH_LOCK_ASSERT(sch); 1927 1928 cookie.cookie = 0; 1929 1930 /* Map our computed MSS into the 3-bit index. */ 1931 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1932 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0; 1933 i--) 1934 ; 1935 cookie.flags.mss_idx = i; 1936 1937 /* 1938 * Map the send window scale into the 3-bit index but only if 1939 * the wscale option was received. 1940 */ 1941 if (sc->sc_flags & SCF_WINSCALE) { 1942 wscale = sc->sc_requested_s_scale; 1943 for (i = nitems(tcp_sc_wstab) - 1; 1944 tcp_sc_wstab[i] > wscale && i > 0; 1945 i--) 1946 ; 1947 cookie.flags.wscale_idx = i; 1948 } 1949 1950 /* Can we do SACK? */ 1951 if (sc->sc_flags & SCF_SACK) 1952 cookie.flags.sack_ok = 1; 1953 1954 /* Which of the two secrets to use. */ 1955 secbit = sch->sch_sc->secret.oddeven & 0x1; 1956 cookie.flags.odd_even = secbit; 1957 1958 secbits = sch->sch_sc->secret.key[secbit]; 1959 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1960 (uintptr_t)sch); 1961 1962 /* 1963 * Put the flags into the hash and XOR them to get better ISS number 1964 * variance. This doesn't enhance the cryptographic strength and is 1965 * done to prevent the 8 cookie bits from showing up directly on the 1966 * wire. 1967 */ 1968 iss = hash & ~0xff; 1969 iss |= cookie.cookie ^ (hash >> 24); 1970 1971 /* Randomize the timestamp. */ 1972 if (sc->sc_flags & SCF_TIMESTAMP) { 1973 sc->sc_ts = arc4random(); 1974 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1975 } 1976 1977 TCPSTAT_INC(tcps_sc_sendcookie); 1978 return (iss); 1979 } 1980 1981 static struct syncache * 1982 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1983 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1984 struct socket *lso) 1985 { 1986 uint32_t hash; 1987 uint8_t *secbits; 1988 tcp_seq ack, seq; 1989 int wnd, wscale = 0; 1990 union syncookie cookie; 1991 1992 SCH_LOCK_ASSERT(sch); 1993 1994 /* 1995 * Pull information out of SYN-ACK/ACK and revert sequence number 1996 * advances. 1997 */ 1998 ack = th->th_ack - 1; 1999 seq = th->th_seq - 1; 2000 2001 /* 2002 * Unpack the flags containing enough information to restore the 2003 * connection. 2004 */ 2005 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2006 2007 /* Which of the two secrets to use. */ 2008 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 2009 2010 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2011 2012 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2013 if ((ack & ~0xff) != (hash & ~0xff)) 2014 return (NULL); 2015 2016 /* Fill in the syncache values. */ 2017 sc->sc_flags = 0; 2018 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2019 sc->sc_ipopts = NULL; 2020 2021 sc->sc_irs = seq; 2022 sc->sc_iss = ack; 2023 2024 switch (inc->inc_flags & INC_ISIPV6) { 2025 #ifdef INET 2026 case 0: 2027 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2028 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2029 break; 2030 #endif 2031 #ifdef INET6 2032 case INC_ISIPV6: 2033 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2034 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2035 break; 2036 #endif 2037 } 2038 2039 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2040 2041 /* We can simply recompute receive window scale we sent earlier. */ 2042 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2043 wscale++; 2044 2045 /* Only use wscale if it was enabled in the orignal SYN. */ 2046 if (cookie.flags.wscale_idx > 0) { 2047 sc->sc_requested_r_scale = wscale; 2048 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2049 sc->sc_flags |= SCF_WINSCALE; 2050 } 2051 2052 wnd = sbspace(&lso->so_rcv); 2053 wnd = imax(wnd, 0); 2054 wnd = imin(wnd, TCP_MAXWIN); 2055 sc->sc_wnd = wnd; 2056 2057 if (cookie.flags.sack_ok) 2058 sc->sc_flags |= SCF_SACK; 2059 2060 if (to->to_flags & TOF_TS) { 2061 sc->sc_flags |= SCF_TIMESTAMP; 2062 sc->sc_tsreflect = to->to_tsval; 2063 sc->sc_ts = to->to_tsecr; 2064 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 2065 } 2066 2067 if (to->to_flags & TOF_SIGNATURE) 2068 sc->sc_flags |= SCF_SIGNATURE; 2069 2070 sc->sc_rxmits = 0; 2071 2072 TCPSTAT_INC(tcps_sc_recvcookie); 2073 return (sc); 2074 } 2075 2076 #ifdef INVARIANTS 2077 static int 2078 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2079 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2080 struct socket *lso) 2081 { 2082 struct syncache scs, *scx; 2083 char *s; 2084 2085 bzero(&scs, sizeof(scs)); 2086 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2087 2088 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2089 return (0); 2090 2091 if (scx != NULL) { 2092 if (sc->sc_peer_mss != scx->sc_peer_mss) 2093 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2094 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2095 2096 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2097 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2098 s, __func__, sc->sc_requested_r_scale, 2099 scx->sc_requested_r_scale); 2100 2101 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2102 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2103 s, __func__, sc->sc_requested_s_scale, 2104 scx->sc_requested_s_scale); 2105 2106 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2107 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2108 } 2109 2110 if (s != NULL) 2111 free(s, M_TCPLOG); 2112 return (0); 2113 } 2114 #endif /* INVARIANTS */ 2115 2116 static void 2117 syncookie_reseed(void *arg) 2118 { 2119 struct tcp_syncache *sc = arg; 2120 uint8_t *secbits; 2121 int secbit; 2122 2123 /* 2124 * Reseeding the secret doesn't have to be protected by a lock. 2125 * It only must be ensured that the new random values are visible 2126 * to all CPUs in a SMP environment. The atomic with release 2127 * semantics ensures that. 2128 */ 2129 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2130 secbits = sc->secret.key[secbit]; 2131 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2132 atomic_add_rel_int(&sc->secret.oddeven, 1); 2133 2134 /* Reschedule ourself. */ 2135 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2136 } 2137 2138 /* 2139 * Exports the syncache entries to userland so that netstat can display 2140 * them alongside the other sockets. This function is intended to be 2141 * called only from tcp_pcblist. 2142 * 2143 * Due to concurrency on an active system, the number of pcbs exported 2144 * may have no relation to max_pcbs. max_pcbs merely indicates the 2145 * amount of space the caller allocated for this function to use. 2146 */ 2147 int 2148 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2149 { 2150 struct xtcpcb xt; 2151 struct syncache *sc; 2152 struct syncache_head *sch; 2153 int count, error, i; 2154 2155 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2156 sch = &V_tcp_syncache.hashbase[i]; 2157 SCH_LOCK(sch); 2158 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2159 if (count >= max_pcbs) { 2160 SCH_UNLOCK(sch); 2161 goto exit; 2162 } 2163 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2164 continue; 2165 bzero(&xt, sizeof(xt)); 2166 xt.xt_len = sizeof(xt); 2167 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2168 xt.xt_inp.inp_vflag = INP_IPV6; 2169 else 2170 xt.xt_inp.inp_vflag = INP_IPV4; 2171 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2172 xt.xt_tp.t_inpcb = &xt.xt_inp; 2173 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2174 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2175 xt.xt_socket.xso_len = sizeof (struct xsocket); 2176 xt.xt_socket.so_type = SOCK_STREAM; 2177 xt.xt_socket.so_state = SS_ISCONNECTING; 2178 error = SYSCTL_OUT(req, &xt, sizeof xt); 2179 if (error) { 2180 SCH_UNLOCK(sch); 2181 goto exit; 2182 } 2183 count++; 2184 } 2185 SCH_UNLOCK(sch); 2186 } 2187 exit: 2188 *pcbs_exported = count; 2189 return error; 2190 } 2191