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, sb_hiwat, 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 sb_hiwat = so->so_rcv.sb_hiwat; 1212 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1213 1214 #ifdef TCP_RFC7413 1215 if (V_tcp_fastopen_enabled && IS_FASTOPEN(tp->t_flags) && 1216 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) { 1217 /* 1218 * Limit the number of pending TFO connections to 1219 * approximately half of the queue limit. This prevents TFO 1220 * SYN floods from starving the service by filling the 1221 * listen queue with bogus TFO connections. 1222 */ 1223 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1224 (so->so_qlimit / 2)) { 1225 int result; 1226 1227 result = tcp_fastopen_check_cookie(inc, 1228 to->to_tfo_cookie, to->to_tfo_len, 1229 &tfo_response_cookie); 1230 tfo_cookie_valid = (result > 0); 1231 tfo_response_cookie_valid = (result >= 0); 1232 } 1233 1234 /* 1235 * Remember the TFO pending counter as it will have to be 1236 * decremented below if we don't make it to syncache_tfo_expand(). 1237 */ 1238 tfo_pending = tp->t_tfo_pending; 1239 } 1240 #endif 1241 1242 /* By the time we drop the lock these should no longer be used. */ 1243 so = NULL; 1244 tp = NULL; 1245 1246 #ifdef MAC 1247 if (mac_syncache_init(&maclabel) != 0) { 1248 INP_WUNLOCK(inp); 1249 goto done; 1250 } else 1251 mac_syncache_create(maclabel, inp); 1252 #endif 1253 #ifdef TCP_RFC7413 1254 if (!tfo_cookie_valid) 1255 #endif 1256 INP_WUNLOCK(inp); 1257 1258 /* 1259 * Remember the IP options, if any. 1260 */ 1261 #ifdef INET6 1262 if (!(inc->inc_flags & INC_ISIPV6)) 1263 #endif 1264 #ifdef INET 1265 ipopts = (m) ? ip_srcroute(m) : NULL; 1266 #else 1267 ipopts = NULL; 1268 #endif 1269 1270 /* 1271 * See if we already have an entry for this connection. 1272 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1273 * 1274 * XXX: should the syncache be re-initialized with the contents 1275 * of the new SYN here (which may have different options?) 1276 * 1277 * XXX: We do not check the sequence number to see if this is a 1278 * real retransmit or a new connection attempt. The question is 1279 * how to handle such a case; either ignore it as spoofed, or 1280 * drop the current entry and create a new one? 1281 */ 1282 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1283 SCH_LOCK_ASSERT(sch); 1284 if (sc != NULL) { 1285 #ifdef TCP_RFC7413 1286 if (tfo_cookie_valid) 1287 INP_WUNLOCK(inp); 1288 #endif 1289 TCPSTAT_INC(tcps_sc_dupsyn); 1290 if (ipopts) { 1291 /* 1292 * If we were remembering a previous source route, 1293 * forget it and use the new one we've been given. 1294 */ 1295 if (sc->sc_ipopts) 1296 (void) m_free(sc->sc_ipopts); 1297 sc->sc_ipopts = ipopts; 1298 } 1299 /* 1300 * Update timestamp if present. 1301 */ 1302 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1303 sc->sc_tsreflect = to->to_tsval; 1304 else 1305 sc->sc_flags &= ~SCF_TIMESTAMP; 1306 #ifdef MAC 1307 /* 1308 * Since we have already unconditionally allocated label 1309 * storage, free it up. The syncache entry will already 1310 * have an initialized label we can use. 1311 */ 1312 mac_syncache_destroy(&maclabel); 1313 #endif 1314 /* Retransmit SYN|ACK and reset retransmit count. */ 1315 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1316 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1317 "resetting timer and retransmitting SYN|ACK\n", 1318 s, __func__); 1319 free(s, M_TCPLOG); 1320 } 1321 if (syncache_respond(sc, sch, 1, m) == 0) { 1322 sc->sc_rxmits = 0; 1323 syncache_timeout(sc, sch, 1); 1324 TCPSTAT_INC(tcps_sndacks); 1325 TCPSTAT_INC(tcps_sndtotal); 1326 } 1327 SCH_UNLOCK(sch); 1328 goto done; 1329 } 1330 1331 #ifdef TCP_RFC7413 1332 if (tfo_cookie_valid) { 1333 bzero(&scs, sizeof(scs)); 1334 sc = &scs; 1335 goto skip_alloc; 1336 } 1337 #endif 1338 1339 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1340 if (sc == NULL) { 1341 /* 1342 * The zone allocator couldn't provide more entries. 1343 * Treat this as if the cache was full; drop the oldest 1344 * entry and insert the new one. 1345 */ 1346 TCPSTAT_INC(tcps_sc_zonefail); 1347 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1348 syncache_drop(sc, sch); 1349 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1350 if (sc == NULL) { 1351 if (V_tcp_syncookies) { 1352 bzero(&scs, sizeof(scs)); 1353 sc = &scs; 1354 } else { 1355 SCH_UNLOCK(sch); 1356 if (ipopts) 1357 (void) m_free(ipopts); 1358 goto done; 1359 } 1360 } 1361 } 1362 1363 #ifdef TCP_RFC7413 1364 skip_alloc: 1365 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1366 sc->sc_tfo_cookie = &tfo_response_cookie; 1367 #endif 1368 1369 /* 1370 * Fill in the syncache values. 1371 */ 1372 #ifdef MAC 1373 sc->sc_label = maclabel; 1374 #endif 1375 sc->sc_cred = cred; 1376 cred = NULL; 1377 sc->sc_ipopts = ipopts; 1378 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1379 #ifdef INET6 1380 if (!(inc->inc_flags & INC_ISIPV6)) 1381 #endif 1382 { 1383 sc->sc_ip_tos = ip_tos; 1384 sc->sc_ip_ttl = ip_ttl; 1385 } 1386 #ifdef TCP_OFFLOAD 1387 sc->sc_tod = tod; 1388 sc->sc_todctx = todctx; 1389 #endif 1390 sc->sc_irs = th->th_seq; 1391 sc->sc_iss = arc4random(); 1392 sc->sc_flags = 0; 1393 sc->sc_flowlabel = 0; 1394 1395 /* 1396 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1397 * win was derived from socket earlier in the function. 1398 */ 1399 win = imax(win, 0); 1400 win = imin(win, TCP_MAXWIN); 1401 sc->sc_wnd = win; 1402 1403 if (V_tcp_do_rfc1323) { 1404 /* 1405 * A timestamp received in a SYN makes 1406 * it ok to send timestamp requests and replies. 1407 */ 1408 if (to->to_flags & TOF_TS) { 1409 sc->sc_tsreflect = to->to_tsval; 1410 sc->sc_ts = tcp_ts_getticks(); 1411 sc->sc_flags |= SCF_TIMESTAMP; 1412 } 1413 if (to->to_flags & TOF_SCALE) { 1414 int wscale = 0; 1415 1416 /* 1417 * Pick the smallest possible scaling factor that 1418 * will still allow us to scale up to sb_max, aka 1419 * kern.ipc.maxsockbuf. 1420 * 1421 * We do this because there are broken firewalls that 1422 * will corrupt the window scale option, leading to 1423 * the other endpoint believing that our advertised 1424 * window is unscaled. At scale factors larger than 1425 * 5 the unscaled window will drop below 1500 bytes, 1426 * leading to serious problems when traversing these 1427 * broken firewalls. 1428 * 1429 * With the default maxsockbuf of 256K, a scale factor 1430 * of 3 will be chosen by this algorithm. Those who 1431 * choose a larger maxsockbuf should watch out 1432 * for the compatibility problems mentioned above. 1433 * 1434 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1435 * or <SYN,ACK>) segment itself is never scaled. 1436 */ 1437 while (wscale < TCP_MAX_WINSHIFT && 1438 (TCP_MAXWIN << wscale) < sb_max) 1439 wscale++; 1440 sc->sc_requested_r_scale = wscale; 1441 sc->sc_requested_s_scale = to->to_wscale; 1442 sc->sc_flags |= SCF_WINSCALE; 1443 } 1444 } 1445 #ifdef TCP_SIGNATURE 1446 /* 1447 * If listening socket requested TCP digests, OR received SYN 1448 * contains the option, flag this in the syncache so that 1449 * syncache_respond() will do the right thing with the SYN+ACK. 1450 */ 1451 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE) 1452 sc->sc_flags |= SCF_SIGNATURE; 1453 #endif 1454 if (to->to_flags & TOF_SACKPERM) 1455 sc->sc_flags |= SCF_SACK; 1456 if (to->to_flags & TOF_MSS) 1457 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1458 if (ltflags & TF_NOOPT) 1459 sc->sc_flags |= SCF_NOOPT; 1460 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn) 1461 sc->sc_flags |= SCF_ECN; 1462 1463 if (V_tcp_syncookies) 1464 sc->sc_iss = syncookie_generate(sch, sc); 1465 #ifdef INET6 1466 if (autoflowlabel) { 1467 if (V_tcp_syncookies) 1468 sc->sc_flowlabel = sc->sc_iss; 1469 else 1470 sc->sc_flowlabel = ip6_randomflowlabel(); 1471 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1472 } 1473 #endif 1474 SCH_UNLOCK(sch); 1475 1476 #ifdef TCP_RFC7413 1477 if (tfo_cookie_valid) { 1478 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie); 1479 /* INP_WUNLOCK(inp) will be performed by the caller */ 1480 rv = 1; 1481 goto tfo_expanded; 1482 } 1483 #endif 1484 1485 /* 1486 * Do a standard 3-way handshake. 1487 */ 1488 if (syncache_respond(sc, sch, 0, m) == 0) { 1489 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1490 syncache_free(sc); 1491 else if (sc != &scs) 1492 syncache_insert(sc, sch); /* locks and unlocks sch */ 1493 TCPSTAT_INC(tcps_sndacks); 1494 TCPSTAT_INC(tcps_sndtotal); 1495 } else { 1496 if (sc != &scs) 1497 syncache_free(sc); 1498 TCPSTAT_INC(tcps_sc_dropped); 1499 } 1500 1501 done: 1502 if (m) { 1503 *lsop = NULL; 1504 m_freem(m); 1505 } 1506 #ifdef TCP_RFC7413 1507 /* 1508 * If tfo_pending is not NULL here, then a TFO SYN that did not 1509 * result in a new socket was processed and the associated pending 1510 * counter has not yet been decremented. All such TFO processing paths 1511 * transit this point. 1512 */ 1513 if (tfo_pending != NULL) 1514 tcp_fastopen_decrement_counter(tfo_pending); 1515 1516 tfo_expanded: 1517 #endif 1518 if (cred != NULL) 1519 crfree(cred); 1520 #ifdef MAC 1521 if (sc == &scs) 1522 mac_syncache_destroy(&maclabel); 1523 #endif 1524 return (rv); 1525 } 1526 1527 /* 1528 * Send SYN|ACK to the peer. Either in response to the peer's SYN, 1529 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1530 */ 1531 static int 1532 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked, 1533 const struct mbuf *m0) 1534 { 1535 struct ip *ip = NULL; 1536 struct mbuf *m; 1537 struct tcphdr *th = NULL; 1538 int optlen, error = 0; /* Make compiler happy */ 1539 u_int16_t hlen, tlen, mssopt; 1540 struct tcpopt to; 1541 #ifdef INET6 1542 struct ip6_hdr *ip6 = NULL; 1543 #endif 1544 #ifdef TCP_SIGNATURE 1545 struct secasvar *sav; 1546 #endif 1547 1548 hlen = 1549 #ifdef INET6 1550 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1551 #endif 1552 sizeof(struct ip); 1553 tlen = hlen + sizeof(struct tcphdr); 1554 1555 /* Determine MSS we advertize to other end of connection. */ 1556 mssopt = tcp_mssopt(&sc->sc_inc); 1557 if (sc->sc_peer_mss) 1558 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss); 1559 1560 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1561 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1562 ("syncache: mbuf too small")); 1563 1564 /* Create the IP+TCP header from scratch. */ 1565 m = m_gethdr(M_NOWAIT, MT_DATA); 1566 if (m == NULL) 1567 return (ENOBUFS); 1568 #ifdef MAC 1569 mac_syncache_create_mbuf(sc->sc_label, m); 1570 #endif 1571 m->m_data += max_linkhdr; 1572 m->m_len = tlen; 1573 m->m_pkthdr.len = tlen; 1574 m->m_pkthdr.rcvif = NULL; 1575 1576 #ifdef INET6 1577 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1578 ip6 = mtod(m, struct ip6_hdr *); 1579 ip6->ip6_vfc = IPV6_VERSION; 1580 ip6->ip6_nxt = IPPROTO_TCP; 1581 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1582 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1583 ip6->ip6_plen = htons(tlen - hlen); 1584 /* ip6_hlim is set after checksum */ 1585 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1586 ip6->ip6_flow |= sc->sc_flowlabel; 1587 1588 th = (struct tcphdr *)(ip6 + 1); 1589 } 1590 #endif 1591 #if defined(INET6) && defined(INET) 1592 else 1593 #endif 1594 #ifdef INET 1595 { 1596 ip = mtod(m, struct ip *); 1597 ip->ip_v = IPVERSION; 1598 ip->ip_hl = sizeof(struct ip) >> 2; 1599 ip->ip_len = htons(tlen); 1600 ip->ip_id = 0; 1601 ip->ip_off = 0; 1602 ip->ip_sum = 0; 1603 ip->ip_p = IPPROTO_TCP; 1604 ip->ip_src = sc->sc_inc.inc_laddr; 1605 ip->ip_dst = sc->sc_inc.inc_faddr; 1606 ip->ip_ttl = sc->sc_ip_ttl; 1607 ip->ip_tos = sc->sc_ip_tos; 1608 1609 /* 1610 * See if we should do MTU discovery. Route lookups are 1611 * expensive, so we will only unset the DF bit if: 1612 * 1613 * 1) path_mtu_discovery is disabled 1614 * 2) the SCF_UNREACH flag has been set 1615 */ 1616 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1617 ip->ip_off |= htons(IP_DF); 1618 1619 th = (struct tcphdr *)(ip + 1); 1620 } 1621 #endif /* INET */ 1622 th->th_sport = sc->sc_inc.inc_lport; 1623 th->th_dport = sc->sc_inc.inc_fport; 1624 1625 th->th_seq = htonl(sc->sc_iss); 1626 th->th_ack = htonl(sc->sc_irs + 1); 1627 th->th_off = sizeof(struct tcphdr) >> 2; 1628 th->th_x2 = 0; 1629 th->th_flags = TH_SYN|TH_ACK; 1630 th->th_win = htons(sc->sc_wnd); 1631 th->th_urp = 0; 1632 1633 if (sc->sc_flags & SCF_ECN) { 1634 th->th_flags |= TH_ECE; 1635 TCPSTAT_INC(tcps_ecn_shs); 1636 } 1637 1638 /* Tack on the TCP options. */ 1639 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1640 to.to_flags = 0; 1641 1642 to.to_mss = mssopt; 1643 to.to_flags = TOF_MSS; 1644 if (sc->sc_flags & SCF_WINSCALE) { 1645 to.to_wscale = sc->sc_requested_r_scale; 1646 to.to_flags |= TOF_SCALE; 1647 } 1648 if (sc->sc_flags & SCF_TIMESTAMP) { 1649 /* Virgin timestamp or TCP cookie enhanced one. */ 1650 to.to_tsval = sc->sc_ts; 1651 to.to_tsecr = sc->sc_tsreflect; 1652 to.to_flags |= TOF_TS; 1653 } 1654 if (sc->sc_flags & SCF_SACK) 1655 to.to_flags |= TOF_SACKPERM; 1656 #ifdef TCP_SIGNATURE 1657 sav = NULL; 1658 if (sc->sc_flags & SCF_SIGNATURE) { 1659 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND); 1660 if (sav != NULL) 1661 to.to_flags |= TOF_SIGNATURE; 1662 else { 1663 1664 /* 1665 * We've got SCF_SIGNATURE flag 1666 * inherited from listening socket, 1667 * but no SADB key for given source 1668 * address. Assume signature is not 1669 * required and remove signature flag 1670 * instead of silently dropping 1671 * connection. 1672 */ 1673 if (locked == 0) 1674 SCH_LOCK(sch); 1675 sc->sc_flags &= ~SCF_SIGNATURE; 1676 if (locked == 0) 1677 SCH_UNLOCK(sch); 1678 } 1679 } 1680 #endif 1681 1682 #ifdef TCP_RFC7413 1683 if (sc->sc_tfo_cookie) { 1684 to.to_flags |= TOF_FASTOPEN; 1685 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1686 to.to_tfo_cookie = sc->sc_tfo_cookie; 1687 /* don't send cookie again when retransmitting response */ 1688 sc->sc_tfo_cookie = NULL; 1689 } 1690 #endif 1691 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1692 1693 /* Adjust headers by option size. */ 1694 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1695 m->m_len += optlen; 1696 m->m_pkthdr.len += optlen; 1697 1698 #ifdef TCP_SIGNATURE 1699 if (sc->sc_flags & SCF_SIGNATURE) 1700 tcp_signature_do_compute(m, 0, optlen, 1701 to.to_signature, sav); 1702 #endif 1703 #ifdef INET6 1704 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1705 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1706 else 1707 #endif 1708 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1709 } else 1710 optlen = 0; 1711 1712 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1713 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1714 /* 1715 * If we have peer's SYN and it has a flowid, then let's assign it to 1716 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1717 * to SYN|ACK due to lack of inp here. 1718 */ 1719 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1720 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1721 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1722 } 1723 #ifdef INET6 1724 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1725 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1726 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1727 IPPROTO_TCP, 0); 1728 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1729 #ifdef TCP_OFFLOAD 1730 if (ADDED_BY_TOE(sc)) { 1731 struct toedev *tod = sc->sc_tod; 1732 1733 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1734 1735 return (error); 1736 } 1737 #endif 1738 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1739 } 1740 #endif 1741 #if defined(INET6) && defined(INET) 1742 else 1743 #endif 1744 #ifdef INET 1745 { 1746 m->m_pkthdr.csum_flags = CSUM_TCP; 1747 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1748 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1749 #ifdef TCP_OFFLOAD 1750 if (ADDED_BY_TOE(sc)) { 1751 struct toedev *tod = sc->sc_tod; 1752 1753 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 1754 1755 return (error); 1756 } 1757 #endif 1758 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1759 } 1760 #endif 1761 return (error); 1762 } 1763 1764 /* 1765 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 1766 * that exceed the capacity of the syncache by avoiding the storage of any 1767 * of the SYNs we receive. Syncookies defend against blind SYN flooding 1768 * attacks where the attacker does not have access to our responses. 1769 * 1770 * Syncookies encode and include all necessary information about the 1771 * connection setup within the SYN|ACK that we send back. That way we 1772 * can avoid keeping any local state until the ACK to our SYN|ACK returns 1773 * (if ever). Normally the syncache and syncookies are running in parallel 1774 * with the latter taking over when the former is exhausted. When matching 1775 * syncache entry is found the syncookie is ignored. 1776 * 1777 * The only reliable information persisting the 3WHS is our initial sequence 1778 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 1779 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 1780 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 1781 * returns and signifies a legitimate connection if it matches the ACK. 1782 * 1783 * The available space of 32 bits to store the hash and to encode the SYN 1784 * option information is very tight and we should have at least 24 bits for 1785 * the MAC to keep the number of guesses by blind spoofing reasonably high. 1786 * 1787 * SYN option information we have to encode to fully restore a connection: 1788 * MSS: is imporant to chose an optimal segment size to avoid IP level 1789 * fragmentation along the path. The common MSS values can be encoded 1790 * in a 3-bit table. Uncommon values are captured by the next lower value 1791 * in the table leading to a slight increase in packetization overhead. 1792 * WSCALE: is necessary to allow large windows to be used for high delay- 1793 * bandwidth product links. Not scaling the window when it was initially 1794 * negotiated is bad for performance as lack of scaling further decreases 1795 * the apparent available send window. We only need to encode the WSCALE 1796 * we received from the remote end. Our end can be recalculated at any 1797 * time. The common WSCALE values can be encoded in a 3-bit table. 1798 * Uncommon values are captured by the next lower value in the table 1799 * making us under-estimate the available window size halving our 1800 * theoretically possible maximum throughput for that connection. 1801 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 1802 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 1803 * that are included in all segments on a connection. We enable them when 1804 * the ACK has them. 1805 * 1806 * Security of syncookies and attack vectors: 1807 * 1808 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 1809 * together with the gloabl secret to make it unique per connection attempt. 1810 * Thus any change of any of those parameters results in a different MAC output 1811 * in an unpredictable way unless a collision is encountered. 24 bits of the 1812 * MAC are embedded into the ISS. 1813 * 1814 * To prevent replay attacks two rotating global secrets are updated with a 1815 * new random value every 15 seconds. The life-time of a syncookie is thus 1816 * 15-30 seconds. 1817 * 1818 * Vector 1: Attacking the secret. This requires finding a weakness in the 1819 * MAC itself or the way it is used here. The attacker can do a chosen plain 1820 * text attack by varying and testing the all parameters under his control. 1821 * The strength depends on the size and randomness of the secret, and the 1822 * cryptographic security of the MAC function. Due to the constant updating 1823 * of the secret the attacker has at most 29.999 seconds to find the secret 1824 * and launch spoofed connections. After that he has to start all over again. 1825 * 1826 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 1827 * size an average of 4,823 attempts are required for a 50% chance of success 1828 * to spoof a single syncookie (birthday collision paradox). However the 1829 * attacker is blind and doesn't know if one of his attempts succeeded unless 1830 * he has a side channel to interfere success from. A single connection setup 1831 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 1832 * This many attempts are required for each one blind spoofed connection. For 1833 * every additional spoofed connection he has to launch another N attempts. 1834 * Thus for a sustained rate 100 spoofed connections per second approximately 1835 * 1,800,000 packets per second would have to be sent. 1836 * 1837 * NB: The MAC function should be fast so that it doesn't become a CPU 1838 * exhaustion attack vector itself. 1839 * 1840 * References: 1841 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 1842 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 1843 * http://cr.yp.to/syncookies.html (overview) 1844 * http://cr.yp.to/syncookies/archive (details) 1845 * 1846 * 1847 * Schematic construction of a syncookie enabled Initial Sequence Number: 1848 * 0 1 2 3 1849 * 12345678901234567890123456789012 1850 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 1851 * 1852 * x 24 MAC (truncated) 1853 * W 3 Send Window Scale index 1854 * M 3 MSS index 1855 * S 1 SACK permitted 1856 * P 1 Odd/even secret 1857 */ 1858 1859 /* 1860 * Distribution and probability of certain MSS values. Those in between are 1861 * rounded down to the next lower one. 1862 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 1863 * .2% .3% 5% 7% 7% 20% 15% 45% 1864 */ 1865 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 1866 1867 /* 1868 * Distribution and probability of certain WSCALE values. We have to map the 1869 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 1870 * bits based on prevalence of certain values. Where we don't have an exact 1871 * match for are rounded down to the next lower one letting us under-estimate 1872 * the true available window. At the moment this would happen only for the 1873 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 1874 * and window size). The absence of the WSCALE option (no scaling in either 1875 * direction) is encoded with index zero. 1876 * [WSCALE values histograms, Allman, 2012] 1877 * X 10 10 35 5 6 14 10% by host 1878 * X 11 4 5 5 18 49 3% by connections 1879 */ 1880 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 1881 1882 /* 1883 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 1884 * and good cryptographic properties. 1885 */ 1886 static uint32_t 1887 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 1888 uint8_t *secbits, uintptr_t secmod) 1889 { 1890 SIPHASH_CTX ctx; 1891 uint32_t siphash[2]; 1892 1893 SipHash24_Init(&ctx); 1894 SipHash_SetKey(&ctx, secbits); 1895 switch (inc->inc_flags & INC_ISIPV6) { 1896 #ifdef INET 1897 case 0: 1898 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 1899 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 1900 break; 1901 #endif 1902 #ifdef INET6 1903 case INC_ISIPV6: 1904 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 1905 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 1906 break; 1907 #endif 1908 } 1909 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 1910 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 1911 SipHash_Update(&ctx, &irs, sizeof(irs)); 1912 SipHash_Update(&ctx, &flags, sizeof(flags)); 1913 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 1914 SipHash_Final((u_int8_t *)&siphash, &ctx); 1915 1916 return (siphash[0] ^ siphash[1]); 1917 } 1918 1919 static tcp_seq 1920 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 1921 { 1922 u_int i, mss, secbit, wscale; 1923 uint32_t iss, hash; 1924 uint8_t *secbits; 1925 union syncookie cookie; 1926 1927 SCH_LOCK_ASSERT(sch); 1928 1929 cookie.cookie = 0; 1930 1931 /* Map our computed MSS into the 3-bit index. */ 1932 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss)); 1933 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0; 1934 i--) 1935 ; 1936 cookie.flags.mss_idx = i; 1937 1938 /* 1939 * Map the send window scale into the 3-bit index but only if 1940 * the wscale option was received. 1941 */ 1942 if (sc->sc_flags & SCF_WINSCALE) { 1943 wscale = sc->sc_requested_s_scale; 1944 for (i = nitems(tcp_sc_wstab) - 1; 1945 tcp_sc_wstab[i] > wscale && i > 0; 1946 i--) 1947 ; 1948 cookie.flags.wscale_idx = i; 1949 } 1950 1951 /* Can we do SACK? */ 1952 if (sc->sc_flags & SCF_SACK) 1953 cookie.flags.sack_ok = 1; 1954 1955 /* Which of the two secrets to use. */ 1956 secbit = sch->sch_sc->secret.oddeven & 0x1; 1957 cookie.flags.odd_even = secbit; 1958 1959 secbits = sch->sch_sc->secret.key[secbit]; 1960 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 1961 (uintptr_t)sch); 1962 1963 /* 1964 * Put the flags into the hash and XOR them to get better ISS number 1965 * variance. This doesn't enhance the cryptographic strength and is 1966 * done to prevent the 8 cookie bits from showing up directly on the 1967 * wire. 1968 */ 1969 iss = hash & ~0xff; 1970 iss |= cookie.cookie ^ (hash >> 24); 1971 1972 /* Randomize the timestamp. */ 1973 if (sc->sc_flags & SCF_TIMESTAMP) { 1974 sc->sc_ts = arc4random(); 1975 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks(); 1976 } 1977 1978 TCPSTAT_INC(tcps_sc_sendcookie); 1979 return (iss); 1980 } 1981 1982 static struct syncache * 1983 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1984 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 1985 struct socket *lso) 1986 { 1987 uint32_t hash; 1988 uint8_t *secbits; 1989 tcp_seq ack, seq; 1990 int wnd, wscale = 0; 1991 union syncookie cookie; 1992 1993 SCH_LOCK_ASSERT(sch); 1994 1995 /* 1996 * Pull information out of SYN-ACK/ACK and revert sequence number 1997 * advances. 1998 */ 1999 ack = th->th_ack - 1; 2000 seq = th->th_seq - 1; 2001 2002 /* 2003 * Unpack the flags containing enough information to restore the 2004 * connection. 2005 */ 2006 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2007 2008 /* Which of the two secrets to use. */ 2009 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even]; 2010 2011 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2012 2013 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2014 if ((ack & ~0xff) != (hash & ~0xff)) 2015 return (NULL); 2016 2017 /* Fill in the syncache values. */ 2018 sc->sc_flags = 0; 2019 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2020 sc->sc_ipopts = NULL; 2021 2022 sc->sc_irs = seq; 2023 sc->sc_iss = ack; 2024 2025 switch (inc->inc_flags & INC_ISIPV6) { 2026 #ifdef INET 2027 case 0: 2028 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2029 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2030 break; 2031 #endif 2032 #ifdef INET6 2033 case INC_ISIPV6: 2034 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2035 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK; 2036 break; 2037 #endif 2038 } 2039 2040 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2041 2042 /* We can simply recompute receive window scale we sent earlier. */ 2043 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2044 wscale++; 2045 2046 /* Only use wscale if it was enabled in the orignal SYN. */ 2047 if (cookie.flags.wscale_idx > 0) { 2048 sc->sc_requested_r_scale = wscale; 2049 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2050 sc->sc_flags |= SCF_WINSCALE; 2051 } 2052 2053 wnd = sbspace(&lso->so_rcv); 2054 wnd = imax(wnd, 0); 2055 wnd = imin(wnd, TCP_MAXWIN); 2056 sc->sc_wnd = wnd; 2057 2058 if (cookie.flags.sack_ok) 2059 sc->sc_flags |= SCF_SACK; 2060 2061 if (to->to_flags & TOF_TS) { 2062 sc->sc_flags |= SCF_TIMESTAMP; 2063 sc->sc_tsreflect = to->to_tsval; 2064 sc->sc_ts = to->to_tsecr; 2065 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks(); 2066 } 2067 2068 if (to->to_flags & TOF_SIGNATURE) 2069 sc->sc_flags |= SCF_SIGNATURE; 2070 2071 sc->sc_rxmits = 0; 2072 2073 TCPSTAT_INC(tcps_sc_recvcookie); 2074 return (sc); 2075 } 2076 2077 #ifdef INVARIANTS 2078 static int 2079 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2080 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2081 struct socket *lso) 2082 { 2083 struct syncache scs, *scx; 2084 char *s; 2085 2086 bzero(&scs, sizeof(scs)); 2087 scx = syncookie_lookup(inc, sch, &scs, th, to, lso); 2088 2089 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2090 return (0); 2091 2092 if (scx != NULL) { 2093 if (sc->sc_peer_mss != scx->sc_peer_mss) 2094 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2095 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2096 2097 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2098 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2099 s, __func__, sc->sc_requested_r_scale, 2100 scx->sc_requested_r_scale); 2101 2102 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2103 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2104 s, __func__, sc->sc_requested_s_scale, 2105 scx->sc_requested_s_scale); 2106 2107 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2108 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2109 } 2110 2111 if (s != NULL) 2112 free(s, M_TCPLOG); 2113 return (0); 2114 } 2115 #endif /* INVARIANTS */ 2116 2117 static void 2118 syncookie_reseed(void *arg) 2119 { 2120 struct tcp_syncache *sc = arg; 2121 uint8_t *secbits; 2122 int secbit; 2123 2124 /* 2125 * Reseeding the secret doesn't have to be protected by a lock. 2126 * It only must be ensured that the new random values are visible 2127 * to all CPUs in a SMP environment. The atomic with release 2128 * semantics ensures that. 2129 */ 2130 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2131 secbits = sc->secret.key[secbit]; 2132 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2133 atomic_add_rel_int(&sc->secret.oddeven, 1); 2134 2135 /* Reschedule ourself. */ 2136 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2137 } 2138 2139 /* 2140 * Exports the syncache entries to userland so that netstat can display 2141 * them alongside the other sockets. This function is intended to be 2142 * called only from tcp_pcblist. 2143 * 2144 * Due to concurrency on an active system, the number of pcbs exported 2145 * may have no relation to max_pcbs. max_pcbs merely indicates the 2146 * amount of space the caller allocated for this function to use. 2147 */ 2148 int 2149 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 2150 { 2151 struct xtcpcb xt; 2152 struct syncache *sc; 2153 struct syncache_head *sch; 2154 int count, error, i; 2155 2156 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) { 2157 sch = &V_tcp_syncache.hashbase[i]; 2158 SCH_LOCK(sch); 2159 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2160 if (count >= max_pcbs) { 2161 SCH_UNLOCK(sch); 2162 goto exit; 2163 } 2164 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2165 continue; 2166 bzero(&xt, sizeof(xt)); 2167 xt.xt_len = sizeof(xt); 2168 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2169 xt.xt_inp.inp_vflag = INP_IPV6; 2170 else 2171 xt.xt_inp.inp_vflag = INP_IPV4; 2172 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 2173 xt.xt_tp.t_inpcb = &xt.xt_inp; 2174 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 2175 xt.xt_socket.xso_protocol = IPPROTO_TCP; 2176 xt.xt_socket.xso_len = sizeof (struct xsocket); 2177 xt.xt_socket.so_type = SOCK_STREAM; 2178 xt.xt_socket.so_state = SS_ISCONNECTING; 2179 error = SYSCTL_OUT(req, &xt, sizeof xt); 2180 if (error) { 2181 SCH_UNLOCK(sch); 2182 goto exit; 2183 } 2184 count++; 2185 } 2186 SCH_UNLOCK(sch); 2187 } 2188 exit: 2189 *pcbs_exported = count; 2190 return error; 2191 } 2192