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