1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/hash.h> 43 #include <sys/refcount.h> 44 #include <sys/kernel.h> 45 #include <sys/sysctl.h> 46 #include <sys/limits.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/malloc.h> 50 #include <sys/mbuf.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 #include <sys/ucred.h> 57 58 #include <sys/md5.h> 59 #include <crypto/siphash/siphash.h> 60 61 #include <vm/uma.h> 62 63 #include <net/if.h> 64 #include <net/if_var.h> 65 #include <net/route.h> 66 #include <net/vnet.h> 67 68 #include <netinet/in.h> 69 #include <netinet/in_kdtrace.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 #include <netinet/tcp_fastopen.h> 85 #include <netinet/tcp_fsm.h> 86 #include <netinet/tcp_seq.h> 87 #include <netinet/tcp_timer.h> 88 #include <netinet/tcp_var.h> 89 #include <netinet/tcp_syncache.h> 90 #include <netinet/tcp_ecn.h> 91 #ifdef TCP_BLACKBOX 92 #include <netinet/tcp_log_buf.h> 93 #endif 94 #ifdef TCP_OFFLOAD 95 #include <netinet/toecore.h> 96 #endif 97 #include <netinet/udp.h> 98 99 #include <netipsec/ipsec_support.h> 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 VNET_DEFINE_STATIC(bool, tcp_syncookies) = true; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 108 &VNET_NAME(tcp_syncookies), 0, 109 "Use TCP SYN cookies if the syncache overflows"); 110 111 VNET_DEFINE_STATIC(bool, tcp_syncookiesonly) = false; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 114 &VNET_NAME(tcp_syncookiesonly), 0, 115 "Use only TCP SYN cookies"); 116 117 #ifdef TCP_OFFLOAD 118 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 119 #endif 120 121 static void syncache_drop(struct syncache *, struct syncache_head *); 122 static void syncache_free(struct syncache *); 123 static void syncache_insert(struct syncache *, struct syncache_head *); 124 static int syncache_respond(struct syncache *, const struct mbuf *, int); 125 static void syncache_send_challenge_ack(struct syncache *, struct mbuf *); 126 static struct socket *syncache_socket(struct syncache *, struct socket *, 127 struct mbuf *m); 128 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 129 int docallout); 130 static void syncache_timer(void *); 131 132 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 133 uint8_t *, uintptr_t); 134 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 135 static bool syncookie_expand(struct in_conninfo *, 136 const struct syncache_head *, struct syncache *, 137 struct tcphdr *, struct tcpopt *, struct socket *, 138 uint16_t); 139 static void syncache_pause(struct in_conninfo *); 140 static void syncache_unpause(void *); 141 static void syncookie_reseed(void *); 142 #ifdef INVARIANTS 143 static void syncookie_cmp(struct in_conninfo *, 144 const struct syncache_head *, struct syncache *, 145 struct tcphdr *, struct tcpopt *, struct socket *, 146 uint16_t); 147 #endif 148 149 /* 150 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 151 * 3 retransmits corresponds to a timeout with default values of 152 * tcp_rexmit_initial * ( 1 + 153 * tcp_backoff[1] + 154 * tcp_backoff[2] + 155 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 156 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 157 * the odds are that the user has given up attempting to connect by then. 158 */ 159 #define SYNCACHE_MAXREXMTS 3 160 161 /* Arbitrary values */ 162 #define TCP_SYNCACHE_HASHSIZE 512 163 #define TCP_SYNCACHE_BUCKETLIMIT 30 164 165 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 166 #define V_tcp_syncache VNET(tcp_syncache) 167 168 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 169 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 170 "TCP SYN cache"); 171 172 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 173 &VNET_NAME(tcp_syncache.bucket_limit), 0, 174 "Per-bucket hash limit for syncache"); 175 176 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 177 &VNET_NAME(tcp_syncache.cache_limit), 0, 178 "Overall entry limit for syncache"); 179 180 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 181 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 182 183 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 184 &VNET_NAME(tcp_syncache.hashsize), 0, 185 "Size of TCP syncache hashtable"); 186 187 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 188 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 189 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 190 "and mac(4) checks"); 191 192 static int 193 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 194 { 195 int error; 196 u_int new; 197 198 new = V_tcp_syncache.rexmt_limit; 199 error = sysctl_handle_int(oidp, &new, 0, req); 200 if ((error == 0) && (req->newptr != NULL)) { 201 if (new > TCP_MAXRXTSHIFT) 202 error = EINVAL; 203 else 204 V_tcp_syncache.rexmt_limit = new; 205 } 206 return (error); 207 } 208 209 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 210 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 211 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 212 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "IU", 213 "Limit on SYN/ACK retransmissions"); 214 215 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 216 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 217 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 218 "Send reset on socket allocation failure"); 219 220 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 221 222 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 223 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 224 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 225 226 /* 227 * Requires the syncache entry to be already removed from the bucket list. 228 */ 229 static void 230 syncache_free(struct syncache *sc) 231 { 232 233 if (sc->sc_ipopts) 234 (void)m_free(sc->sc_ipopts); 235 if (sc->sc_cred) 236 crfree(sc->sc_cred); 237 #ifdef MAC 238 mac_syncache_destroy(&sc->sc_label); 239 #endif 240 241 uma_zfree(V_tcp_syncache.zone, sc); 242 } 243 244 void 245 syncache_init(void) 246 { 247 int i; 248 249 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 250 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 251 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 252 V_tcp_syncache.hash_secret = arc4random(); 253 254 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 255 &V_tcp_syncache.hashsize); 256 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 257 &V_tcp_syncache.bucket_limit); 258 if (!powerof2(V_tcp_syncache.hashsize) || 259 V_tcp_syncache.hashsize == 0) { 260 printf("WARNING: syncache hash size is not a power of 2.\n"); 261 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 262 } 263 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 264 265 /* Set limits. */ 266 V_tcp_syncache.cache_limit = 267 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 268 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 269 &V_tcp_syncache.cache_limit); 270 271 /* Allocate the hash table. */ 272 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 273 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 274 275 #ifdef VIMAGE 276 V_tcp_syncache.vnet = curvnet; 277 #endif 278 279 /* Initialize the hash buckets. */ 280 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 281 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 282 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 283 NULL, MTX_DEF); 284 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 285 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 286 V_tcp_syncache.hashbase[i].sch_length = 0; 287 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 288 V_tcp_syncache.hashbase[i].sch_last_overflow = 289 -(SYNCOOKIE_LIFETIME + 1); 290 } 291 292 /* Create the syncache entry zone. */ 293 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 294 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 295 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 296 V_tcp_syncache.cache_limit); 297 298 /* Start the SYN cookie reseeder callout. */ 299 callout_init(&V_tcp_syncache.secret.reseed, 1); 300 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 301 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 302 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 303 syncookie_reseed, &V_tcp_syncache); 304 305 /* Initialize the pause machinery. */ 306 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 307 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 308 0); 309 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 310 V_tcp_syncache.pause_backoff = 0; 311 V_tcp_syncache.paused = false; 312 } 313 314 #ifdef VIMAGE 315 void 316 syncache_destroy(void) 317 { 318 struct syncache_head *sch; 319 struct syncache *sc, *nsc; 320 int i; 321 322 /* 323 * Stop the re-seed timer before freeing resources. No need to 324 * possibly schedule it another time. 325 */ 326 callout_drain(&V_tcp_syncache.secret.reseed); 327 328 /* Stop the SYN cache pause callout. */ 329 mtx_lock(&V_tcp_syncache.pause_mtx); 330 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 331 mtx_unlock(&V_tcp_syncache.pause_mtx); 332 callout_drain(&V_tcp_syncache.pause_co); 333 } else 334 mtx_unlock(&V_tcp_syncache.pause_mtx); 335 336 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 337 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 338 sch = &V_tcp_syncache.hashbase[i]; 339 callout_drain(&sch->sch_timer); 340 341 SCH_LOCK(sch); 342 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 343 syncache_drop(sc, sch); 344 SCH_UNLOCK(sch); 345 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 346 ("%s: sch->sch_bucket not empty", __func__)); 347 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 348 __func__, sch->sch_length)); 349 mtx_destroy(&sch->sch_mtx); 350 } 351 352 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 353 ("%s: cache_count not 0", __func__)); 354 355 /* Free the allocated global resources. */ 356 uma_zdestroy(V_tcp_syncache.zone); 357 free(V_tcp_syncache.hashbase, M_SYNCACHE); 358 mtx_destroy(&V_tcp_syncache.pause_mtx); 359 } 360 #endif 361 362 /* 363 * Inserts a syncache entry into the specified bucket row. 364 * Locks and unlocks the syncache_head autonomously. 365 */ 366 static void 367 syncache_insert(struct syncache *sc, struct syncache_head *sch) 368 { 369 struct syncache *sc2; 370 371 SCH_LOCK(sch); 372 373 /* 374 * Make sure that we don't overflow the per-bucket limit. 375 * If the bucket is full, toss the oldest element. 376 */ 377 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 378 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 379 ("sch->sch_length incorrect")); 380 syncache_pause(&sc->sc_inc); 381 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 382 sch->sch_last_overflow = time_uptime; 383 syncache_drop(sc2, sch); 384 } 385 386 /* Put it into the bucket. */ 387 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 388 sch->sch_length++; 389 390 #ifdef TCP_OFFLOAD 391 if (ADDED_BY_TOE(sc)) { 392 struct toedev *tod = sc->sc_tod; 393 394 tod->tod_syncache_added(tod, sc->sc_todctx); 395 } 396 #endif 397 398 /* Reinitialize the bucket row's timer. */ 399 if (sch->sch_length == 1) 400 sch->sch_nextc = ticks + INT_MAX; 401 syncache_timeout(sc, sch, 1); 402 403 SCH_UNLOCK(sch); 404 405 TCPSTATES_INC(TCPS_SYN_RECEIVED); 406 TCPSTAT_INC(tcps_sc_added); 407 } 408 409 /* 410 * Remove and free entry from syncache bucket row. 411 * Expects locked syncache head. 412 */ 413 static void 414 syncache_drop(struct syncache *sc, struct syncache_head *sch) 415 { 416 417 SCH_LOCK_ASSERT(sch); 418 419 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 420 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 421 sch->sch_length--; 422 423 #ifdef TCP_OFFLOAD 424 if (ADDED_BY_TOE(sc)) { 425 struct toedev *tod = sc->sc_tod; 426 427 tod->tod_syncache_removed(tod, sc->sc_todctx); 428 } 429 #endif 430 431 syncache_free(sc); 432 } 433 434 /* 435 * Engage/reengage time on bucket row. 436 */ 437 static void 438 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 439 { 440 int rexmt; 441 442 if (sc->sc_rxmits == 0) 443 rexmt = tcp_rexmit_initial; 444 else 445 TCPT_RANGESET(rexmt, 446 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 447 tcp_rexmit_min, tcp_rexmit_max); 448 sc->sc_rxttime = ticks + rexmt; 449 sc->sc_rxmits++; 450 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 451 sch->sch_nextc = sc->sc_rxttime; 452 if (docallout) 453 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 454 syncache_timer, (void *)sch); 455 } 456 } 457 458 /* 459 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 460 * If we have retransmitted an entry the maximum number of times, expire it. 461 * One separate timer for each bucket row. 462 */ 463 static void 464 syncache_timer(void *xsch) 465 { 466 struct syncache_head *sch = (struct syncache_head *)xsch; 467 struct syncache *sc, *nsc; 468 struct epoch_tracker et; 469 int tick = ticks; 470 char *s; 471 bool paused; 472 473 CURVNET_SET(sch->sch_sc->vnet); 474 475 /* NB: syncache_head has already been locked by the callout. */ 476 SCH_LOCK_ASSERT(sch); 477 478 /* 479 * In the following cycle we may remove some entries and/or 480 * advance some timeouts, so re-initialize the bucket timer. 481 */ 482 sch->sch_nextc = tick + INT_MAX; 483 484 /* 485 * If we have paused processing, unconditionally remove 486 * all syncache entries. 487 */ 488 mtx_lock(&V_tcp_syncache.pause_mtx); 489 paused = V_tcp_syncache.paused; 490 mtx_unlock(&V_tcp_syncache.pause_mtx); 491 492 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 493 if (paused) { 494 syncache_drop(sc, sch); 495 continue; 496 } 497 /* 498 * We do not check if the listen socket still exists 499 * and accept the case where the listen socket may be 500 * gone by the time we resend the SYN/ACK. We do 501 * not expect this to happens often. If it does, 502 * then the RST will be sent by the time the remote 503 * host does the SYN/ACK->ACK. 504 */ 505 if (TSTMP_GT(sc->sc_rxttime, tick)) { 506 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 507 sch->sch_nextc = sc->sc_rxttime; 508 continue; 509 } 510 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 511 sc->sc_flags &= ~SCF_ECN_MASK; 512 } 513 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 514 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 515 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 516 "giving up and removing syncache entry\n", 517 s, __func__); 518 free(s, M_TCPLOG); 519 } 520 syncache_drop(sc, sch); 521 TCPSTAT_INC(tcps_sc_stale); 522 continue; 523 } 524 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 525 log(LOG_DEBUG, "%s; %s: Response timeout, " 526 "retransmitting (%u) SYN|ACK\n", 527 s, __func__, sc->sc_rxmits); 528 free(s, M_TCPLOG); 529 } 530 531 NET_EPOCH_ENTER(et); 532 if (syncache_respond(sc, NULL, TH_SYN|TH_ACK) == 0) { 533 syncache_timeout(sc, sch, 0); 534 TCPSTAT_INC(tcps_sndacks); 535 TCPSTAT_INC(tcps_sndtotal); 536 TCPSTAT_INC(tcps_sc_retransmitted); 537 } else { 538 syncache_drop(sc, sch); 539 TCPSTAT_INC(tcps_sc_dropped); 540 } 541 NET_EPOCH_EXIT(et); 542 } 543 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 544 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 545 syncache_timer, (void *)(sch)); 546 CURVNET_RESTORE(); 547 } 548 549 /* 550 * Returns true if the system is only using cookies at the moment. 551 * This could be due to a sysadmin decision to only use cookies, or it 552 * could be due to the system detecting an attack. 553 */ 554 static inline bool 555 syncache_cookiesonly(void) 556 { 557 return ((V_tcp_syncookies && V_tcp_syncache.paused) || 558 V_tcp_syncookiesonly); 559 } 560 561 /* 562 * Find the hash bucket for the given connection. 563 */ 564 static struct syncache_head * 565 syncache_hashbucket(struct in_conninfo *inc) 566 { 567 uint32_t hash; 568 569 /* 570 * The hash is built on foreign port + local port + foreign address. 571 * We rely on the fact that struct in_conninfo starts with 16 bits 572 * of foreign port, then 16 bits of local port then followed by 128 573 * bits of foreign address. In case of IPv4 address, the first 3 574 * 32-bit words of the address always are zeroes. 575 */ 576 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 577 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 578 579 return (&V_tcp_syncache.hashbase[hash]); 580 } 581 582 /* 583 * Find an entry in the syncache. 584 * Returns always with locked syncache_head plus a matching entry or NULL. 585 */ 586 static struct syncache * 587 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 588 { 589 struct syncache *sc; 590 struct syncache_head *sch; 591 592 *schp = sch = syncache_hashbucket(inc); 593 SCH_LOCK(sch); 594 595 /* Circle through bucket row to find matching entry. */ 596 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 597 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 598 sizeof(struct in_endpoints)) == 0) 599 break; 600 601 return (sc); /* Always returns with locked sch. */ 602 } 603 604 /* 605 * This function is called when we get a RST for a 606 * non-existent connection, so that we can see if the 607 * connection is in the syn cache. If it is, zap it. 608 * If required send a challenge ACK. 609 */ 610 void 611 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 612 uint16_t port) 613 { 614 struct syncache *sc; 615 struct syncache_head *sch; 616 char *s = NULL; 617 618 if (syncache_cookiesonly()) 619 return; 620 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 621 SCH_LOCK_ASSERT(sch); 622 623 /* 624 * No corresponding connection was found in syncache. 625 * If syncookies are enabled and possibly exclusively 626 * used, or we are under memory pressure, a valid RST 627 * may not find a syncache entry. In that case we're 628 * done and no SYN|ACK retransmissions will happen. 629 * Otherwise the RST was misdirected or spoofed. 630 */ 631 if (sc == NULL) { 632 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 633 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 634 "syncache entry (possibly syncookie only), " 635 "segment ignored\n", s, __func__); 636 TCPSTAT_INC(tcps_badrst); 637 goto done; 638 } 639 640 /* The remote UDP encaps port does not match. */ 641 if (sc->sc_port != port) { 642 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 643 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 644 "syncache entry but non-matching UDP encaps port, " 645 "segment ignored\n", s, __func__); 646 TCPSTAT_INC(tcps_badrst); 647 goto done; 648 } 649 650 /* 651 * If the RST bit is set, check the sequence number to see 652 * if this is a valid reset segment. 653 * 654 * RFC 793 page 37: 655 * In all states except SYN-SENT, all reset (RST) segments 656 * are validated by checking their SEQ-fields. A reset is 657 * valid if its sequence number is in the window. 658 * 659 * RFC 793 page 69: 660 * There are four cases for the acceptability test for an incoming 661 * segment: 662 * 663 * Segment Receive Test 664 * Length Window 665 * ------- ------- ------------------------------------------- 666 * 0 0 SEG.SEQ = RCV.NXT 667 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 668 * >0 0 not acceptable 669 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 670 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 671 * 672 * Note that when receiving a SYN segment in the LISTEN state, 673 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 674 * described in RFC 793, page 66. 675 */ 676 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 677 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 678 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 679 if (V_tcp_insecure_rst || 680 th->th_seq == sc->sc_irs + 1) { 681 syncache_drop(sc, sch); 682 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 683 log(LOG_DEBUG, 684 "%s; %s: Our SYN|ACK was rejected, " 685 "connection attempt aborted by remote " 686 "endpoint\n", 687 s, __func__); 688 TCPSTAT_INC(tcps_sc_reset); 689 } else { 690 TCPSTAT_INC(tcps_badrst); 691 /* Send challenge ACK. */ 692 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 693 log(LOG_DEBUG, "%s; %s: RST with invalid " 694 " SEQ %u != NXT %u (+WND %u), " 695 "sending challenge ACK\n", 696 s, __func__, 697 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 698 syncache_send_challenge_ack(sc, m); 699 } 700 } else { 701 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 702 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 703 "NXT %u (+WND %u), segment ignored\n", 704 s, __func__, 705 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 706 TCPSTAT_INC(tcps_badrst); 707 } 708 709 done: 710 if (s != NULL) 711 free(s, M_TCPLOG); 712 SCH_UNLOCK(sch); 713 } 714 715 void 716 syncache_badack(struct in_conninfo *inc, uint16_t port) 717 { 718 struct syncache *sc; 719 struct syncache_head *sch; 720 721 if (syncache_cookiesonly()) 722 return; 723 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 724 SCH_LOCK_ASSERT(sch); 725 if ((sc != NULL) && (sc->sc_port == port)) { 726 syncache_drop(sc, sch); 727 TCPSTAT_INC(tcps_sc_badack); 728 } 729 SCH_UNLOCK(sch); 730 } 731 732 void 733 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 734 { 735 struct syncache *sc; 736 struct syncache_head *sch; 737 738 if (syncache_cookiesonly()) 739 return; 740 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 741 SCH_LOCK_ASSERT(sch); 742 if (sc == NULL) 743 goto done; 744 745 /* If the port != sc_port, then it's a bogus ICMP msg */ 746 if (port != sc->sc_port) 747 goto done; 748 749 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 750 if (ntohl(th_seq) != sc->sc_iss) 751 goto done; 752 753 /* 754 * If we've rertransmitted 3 times and this is our second error, 755 * we remove the entry. Otherwise, we allow it to continue on. 756 * This prevents us from incorrectly nuking an entry during a 757 * spurious network outage. 758 * 759 * See tcp_notify(). 760 */ 761 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 762 sc->sc_flags |= SCF_UNREACH; 763 goto done; 764 } 765 syncache_drop(sc, sch); 766 TCPSTAT_INC(tcps_sc_unreach); 767 done: 768 SCH_UNLOCK(sch); 769 } 770 771 /* 772 * Build a new TCP socket structure from a syncache entry. 773 * 774 * On success return the newly created socket with its underlying inp locked. 775 */ 776 static struct socket * 777 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 778 { 779 struct inpcb *inp = NULL; 780 struct socket *so; 781 struct tcpcb *tp; 782 int error; 783 char *s; 784 785 NET_EPOCH_ASSERT(); 786 787 /* 788 * Ok, create the full blown connection, and set things up 789 * as they would have been set up if we had created the 790 * connection when the SYN arrived. 791 */ 792 if ((so = solisten_clone(lso)) == NULL) 793 goto allocfail; 794 #ifdef MAC 795 mac_socketpeer_set_from_mbuf(m, so); 796 #endif 797 error = in_pcballoc(so, &V_tcbinfo); 798 if (error) { 799 sodealloc(so); 800 goto allocfail; 801 } 802 inp = sotoinpcb(so); 803 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 804 in_pcbfree(inp); 805 sodealloc(so); 806 goto allocfail; 807 } 808 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 809 #ifdef INET6 810 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 811 inp->inp_vflag &= ~INP_IPV4; 812 inp->inp_vflag |= INP_IPV6; 813 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 814 } else { 815 inp->inp_vflag &= ~INP_IPV6; 816 inp->inp_vflag |= INP_IPV4; 817 #endif 818 inp->inp_ip_ttl = sc->sc_ip_ttl; 819 inp->inp_ip_tos = sc->sc_ip_tos; 820 inp->inp_laddr = sc->sc_inc.inc_laddr; 821 #ifdef INET6 822 } 823 #endif 824 825 /* 826 * If there's an mbuf and it has a flowid, then let's initialise the 827 * inp with that particular flowid. 828 */ 829 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 830 inp->inp_flowid = m->m_pkthdr.flowid; 831 inp->inp_flowtype = M_HASHTYPE_GET(m); 832 #ifdef NUMA 833 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 834 #endif 835 } 836 837 inp->inp_lport = sc->sc_inc.inc_lport; 838 #ifdef INET6 839 if (inp->inp_vflag & INP_IPV6PROTO) { 840 struct inpcb *oinp = sotoinpcb(lso); 841 842 /* 843 * Inherit socket options from the listening socket. 844 * Note that in6p_inputopts are not (and should not be) 845 * copied, since it stores previously received options and is 846 * used to detect if each new option is different than the 847 * previous one and hence should be passed to a user. 848 * If we copied in6p_inputopts, a user would not be able to 849 * receive options just after calling the accept system call. 850 */ 851 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 852 if (oinp->in6p_outputopts) 853 inp->in6p_outputopts = 854 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 855 inp->in6p_hops = oinp->in6p_hops; 856 } 857 858 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 859 struct sockaddr_in6 sin6; 860 861 sin6.sin6_family = AF_INET6; 862 sin6.sin6_len = sizeof(sin6); 863 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 864 sin6.sin6_port = sc->sc_inc.inc_fport; 865 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 866 INP_HASH_WLOCK(&V_tcbinfo); 867 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 868 INP_HASH_WUNLOCK(&V_tcbinfo); 869 if (error != 0) 870 goto abort; 871 /* Override flowlabel from in6_pcbconnect. */ 872 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 873 inp->inp_flow |= sc->sc_flowlabel; 874 } 875 #endif /* INET6 */ 876 #if defined(INET) && defined(INET6) 877 else 878 #endif 879 #ifdef INET 880 { 881 struct sockaddr_in sin; 882 883 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 884 885 if (inp->inp_options == NULL) { 886 inp->inp_options = sc->sc_ipopts; 887 sc->sc_ipopts = NULL; 888 } 889 890 sin.sin_family = AF_INET; 891 sin.sin_len = sizeof(sin); 892 sin.sin_addr = sc->sc_inc.inc_faddr; 893 sin.sin_port = sc->sc_inc.inc_fport; 894 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 895 INP_HASH_WLOCK(&V_tcbinfo); 896 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 897 INP_HASH_WUNLOCK(&V_tcbinfo); 898 if (error != 0) 899 goto abort; 900 } 901 #endif /* INET */ 902 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 903 /* Copy old policy into new socket's. */ 904 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 905 printf("syncache_socket: could not copy policy\n"); 906 #endif 907 tp->t_state = TCPS_SYN_RECEIVED; 908 tp->iss = sc->sc_iss; 909 tp->irs = sc->sc_irs; 910 tp->t_port = sc->sc_port; 911 tcp_rcvseqinit(tp); 912 tcp_sendseqinit(tp); 913 tp->snd_wl1 = sc->sc_irs; 914 tp->snd_max = tp->iss + 1; 915 tp->snd_nxt = tp->iss + 1; 916 tp->rcv_up = sc->sc_irs + 1; 917 tp->rcv_wnd = sc->sc_wnd; 918 tp->rcv_adv += tp->rcv_wnd; 919 tp->last_ack_sent = tp->rcv_nxt; 920 921 tp->t_flags = sototcpcb(lso)->t_flags & 922 (TF_LRD|TF_NOPUSH|TF_NODELAY); 923 if (sc->sc_flags & SCF_NOOPT) 924 tp->t_flags |= TF_NOOPT; 925 else { 926 if (sc->sc_flags & SCF_WINSCALE) { 927 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 928 tp->snd_scale = sc->sc_requested_s_scale; 929 tp->request_r_scale = sc->sc_requested_r_scale; 930 } 931 if (sc->sc_flags & SCF_TIMESTAMP) { 932 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 933 tp->ts_recent = sc->sc_tsreflect; 934 tp->ts_recent_age = tcp_ts_getticks(); 935 tp->ts_offset = sc->sc_tsoff; 936 } 937 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 938 if (sc->sc_flags & SCF_SIGNATURE) 939 tp->t_flags |= TF_SIGNATURE; 940 #endif 941 if (sc->sc_flags & SCF_SACK) 942 tp->t_flags |= TF_SACK_PERMIT; 943 } 944 945 tcp_ecn_syncache_socket(tp, sc); 946 947 /* 948 * Set up MSS and get cached values from tcp_hostcache. 949 * This might overwrite some of the defaults we just set. 950 */ 951 tcp_mss(tp, sc->sc_peer_mss); 952 953 /* 954 * If the SYN,ACK was retransmitted, indicate that CWND to be 955 * limited to one segment in cc_conn_init(). 956 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 957 */ 958 if (sc->sc_rxmits > 1) 959 tp->snd_cwnd = 1; 960 961 /* Copy over the challenge ACK state. */ 962 tp->t_challenge_ack_end = sc->sc_challenge_ack_end; 963 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; 964 965 #ifdef TCP_OFFLOAD 966 /* 967 * Allow a TOE driver to install its hooks. Note that we hold the 968 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 969 * new connection before the TOE driver has done its thing. 970 */ 971 if (ADDED_BY_TOE(sc)) { 972 struct toedev *tod = sc->sc_tod; 973 974 tod->tod_offload_socket(tod, sc->sc_todctx, so); 975 } 976 #endif 977 #ifdef TCP_BLACKBOX 978 /* 979 * Inherit the log state from the listening socket, if 980 * - the log state of the listening socket is not off and 981 * - the listening socket was not auto selected from all sessions and 982 * - a log id is not set on the listening socket. 983 * This avoids inheriting a log state which was automatically set. 984 */ 985 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 986 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 987 (sototcpcb(lso)->t_lib == NULL)) { 988 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 989 } 990 #endif 991 /* 992 * Copy and activate timers. 993 */ 994 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 995 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 996 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 997 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 998 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 999 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1000 1001 TCPSTAT_INC(tcps_accepts); 1002 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1003 1004 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1005 tp->t_flags |= TF_SONOTCONN; 1006 /* Can we inherit anything from the listener? */ 1007 if (tp->t_fb->tfb_inherit != NULL) { 1008 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 1009 } 1010 return (so); 1011 1012 allocfail: 1013 /* 1014 * Drop the connection; we will either send a RST or have the peer 1015 * retransmit its SYN again after its RTO and try again. 1016 */ 1017 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1018 log(LOG_DEBUG, "%s; %s: Socket create failed " 1019 "due to limits or memory shortage\n", 1020 s, __func__); 1021 free(s, M_TCPLOG); 1022 } 1023 TCPSTAT_INC(tcps_listendrop); 1024 return (NULL); 1025 1026 abort: 1027 tcp_discardcb(tp); 1028 in_pcbfree(inp); 1029 sodealloc(so); 1030 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1031 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1032 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1033 error); 1034 free(s, M_TCPLOG); 1035 } 1036 TCPSTAT_INC(tcps_listendrop); 1037 return (NULL); 1038 } 1039 1040 /* 1041 * This function gets called when we receive an ACK for a 1042 * socket in the LISTEN state. We look up the connection 1043 * in the syncache, and if its there, we pull it out of 1044 * the cache and turn it into a full-blown connection in 1045 * the SYN-RECEIVED state. 1046 * 1047 * On syncache_socket() success the newly created socket 1048 * has its underlying inp locked. 1049 * 1050 * *lsop is updated, if and only if 1 is returned. 1051 */ 1052 int 1053 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1054 struct socket **lsop, struct mbuf *m, uint16_t port) 1055 { 1056 struct syncache *sc; 1057 struct syncache_head *sch; 1058 struct syncache scs; 1059 char *s; 1060 bool locked; 1061 1062 NET_EPOCH_ASSERT(); 1063 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1064 ("%s: can handle only ACK", __func__)); 1065 1066 if (syncache_cookiesonly()) { 1067 sc = NULL; 1068 sch = syncache_hashbucket(inc); 1069 locked = false; 1070 } else { 1071 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1072 locked = true; 1073 SCH_LOCK_ASSERT(sch); 1074 } 1075 1076 #ifdef INVARIANTS 1077 /* 1078 * Test code for syncookies comparing the syncache stored 1079 * values with the reconstructed values from the cookie. 1080 */ 1081 if (sc != NULL) 1082 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1083 #endif 1084 1085 if (sc == NULL) { 1086 if (locked) { 1087 /* 1088 * The syncache is currently in use (neither disabled, 1089 * nor paused), but no entry was found. 1090 */ 1091 if (!V_tcp_syncookies) { 1092 /* 1093 * Since no syncookies are used in case of 1094 * a bucket overflow, don't even check for 1095 * a valid syncookie. 1096 */ 1097 SCH_UNLOCK(sch); 1098 TCPSTAT_INC(tcps_sc_spurcookie); 1099 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1100 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1101 "segment rejected " 1102 "(syncookies disabled)\n", 1103 s, __func__); 1104 free(s, M_TCPLOG); 1105 } 1106 return (0); 1107 } 1108 if (sch->sch_last_overflow < 1109 time_uptime - SYNCOOKIE_LIFETIME) { 1110 /* 1111 * Since the bucket did not overflow recently, 1112 * don't even check for a valid syncookie. 1113 */ 1114 SCH_UNLOCK(sch); 1115 TCPSTAT_INC(tcps_sc_spurcookie); 1116 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1117 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1118 "segment rejected " 1119 "(no syncache entry)\n", 1120 s, __func__); 1121 free(s, M_TCPLOG); 1122 } 1123 return (0); 1124 } 1125 SCH_UNLOCK(sch); 1126 } 1127 bzero(&scs, sizeof(scs)); 1128 /* 1129 * Now check, if the syncookie is valid. If it is, create an on 1130 * stack syncache entry. 1131 */ 1132 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1133 sc = &scs; 1134 TCPSTAT_INC(tcps_sc_recvcookie); 1135 } else { 1136 TCPSTAT_INC(tcps_sc_failcookie); 1137 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1138 log(LOG_DEBUG, "%s; %s: Segment failed " 1139 "SYNCOOKIE authentication, segment rejected " 1140 "(probably spoofed)\n", s, __func__); 1141 free(s, M_TCPLOG); 1142 } 1143 return (0); 1144 } 1145 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1146 /* If received ACK has MD5 signature, check it. */ 1147 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1148 (!TCPMD5_ENABLED() || 1149 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1150 /* Drop the ACK. */ 1151 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1152 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1153 "MD5 signature doesn't match.\n", 1154 s, __func__); 1155 free(s, M_TCPLOG); 1156 } 1157 TCPSTAT_INC(tcps_sig_err_sigopt); 1158 return (-1); /* Do not send RST */ 1159 } 1160 #endif /* TCP_SIGNATURE */ 1161 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1162 } else { 1163 if (sc->sc_port != port) { 1164 SCH_UNLOCK(sch); 1165 return (0); 1166 } 1167 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1168 /* 1169 * If listening socket requested TCP digests, check that 1170 * received ACK has signature and it is correct. 1171 * If not, drop the ACK and leave sc entry in th cache, 1172 * because SYN was received with correct signature. 1173 */ 1174 if (sc->sc_flags & SCF_SIGNATURE) { 1175 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1176 /* No signature */ 1177 TCPSTAT_INC(tcps_sig_err_nosigopt); 1178 SCH_UNLOCK(sch); 1179 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1180 log(LOG_DEBUG, "%s; %s: Segment " 1181 "rejected, MD5 signature wasn't " 1182 "provided.\n", s, __func__); 1183 free(s, M_TCPLOG); 1184 } 1185 return (-1); /* Do not send RST */ 1186 } 1187 if (!TCPMD5_ENABLED() || 1188 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1189 /* Doesn't match or no SA */ 1190 SCH_UNLOCK(sch); 1191 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1192 log(LOG_DEBUG, "%s; %s: Segment " 1193 "rejected, MD5 signature doesn't " 1194 "match.\n", s, __func__); 1195 free(s, M_TCPLOG); 1196 } 1197 return (-1); /* Do not send RST */ 1198 } 1199 } 1200 #endif /* TCP_SIGNATURE */ 1201 1202 /* 1203 * RFC 7323 PAWS: If we have a timestamp on this segment and 1204 * it's less than ts_recent, drop it. 1205 * XXXMT: RFC 7323 also requires to send an ACK. 1206 * In tcp_input.c this is only done for TCP segments 1207 * with user data, so be consistent here and just drop 1208 * the segment. 1209 */ 1210 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1211 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1212 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1213 log(LOG_DEBUG, 1214 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1215 "segment dropped\n", s, __func__, 1216 to->to_tsval, sc->sc_tsreflect); 1217 } 1218 SCH_UNLOCK(sch); 1219 free(s, M_TCPLOG); 1220 return (-1); /* Do not send RST */ 1221 } 1222 1223 /* 1224 * If timestamps were not negotiated during SYN/ACK and a 1225 * segment with a timestamp is received, ignore the 1226 * timestamp and process the packet normally. 1227 * See section 3.2 of RFC 7323. 1228 */ 1229 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1230 (to->to_flags & TOF_TS)) { 1231 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1232 log(LOG_DEBUG, "%s; %s: Timestamp not " 1233 "expected, segment processed normally\n", 1234 s, __func__); 1235 free(s, M_TCPLOG); 1236 } 1237 } 1238 1239 /* 1240 * If timestamps were negotiated during SYN/ACK and a 1241 * segment without a timestamp is received, silently drop 1242 * the segment, unless the missing timestamps are tolerated. 1243 * See section 3.2 of RFC 7323. 1244 */ 1245 if ((sc->sc_flags & SCF_TIMESTAMP) && 1246 !(to->to_flags & TOF_TS)) { 1247 if (V_tcp_tolerate_missing_ts) { 1248 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1249 log(LOG_DEBUG, 1250 "%s; %s: Timestamp missing, " 1251 "segment processed normally\n", 1252 s, __func__); 1253 free(s, M_TCPLOG); 1254 } 1255 } else { 1256 SCH_UNLOCK(sch); 1257 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1258 log(LOG_DEBUG, 1259 "%s; %s: Timestamp missing, " 1260 "segment silently dropped\n", 1261 s, __func__); 1262 free(s, M_TCPLOG); 1263 } 1264 return (-1); /* Do not send RST */ 1265 } 1266 } 1267 1268 /* 1269 * SEG.SEQ validation: 1270 * The SEG.SEQ must be in the window starting at our 1271 * initial receive sequence number + 1. 1272 */ 1273 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1274 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1275 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1276 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1277 "sending challenge ACK\n", 1278 s, __func__, th->th_seq, sc->sc_irs + 1); 1279 syncache_send_challenge_ack(sc, m); 1280 SCH_UNLOCK(sch); 1281 free(s, M_TCPLOG); 1282 return (-1); /* Do not send RST */ 1283 } 1284 1285 /* 1286 * SEG.ACK validation: 1287 * SEG.ACK must match our initial send sequence number + 1. 1288 */ 1289 if (th->th_ack != sc->sc_iss + 1) { 1290 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1291 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1292 "segment rejected\n", 1293 s, __func__, th->th_ack, sc->sc_iss + 1); 1294 SCH_UNLOCK(sch); 1295 free(s, M_TCPLOG); 1296 return (0); /* Do send RST, do not free sc. */ 1297 } 1298 1299 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1300 sch->sch_length--; 1301 #ifdef TCP_OFFLOAD 1302 if (ADDED_BY_TOE(sc)) { 1303 struct toedev *tod = sc->sc_tod; 1304 1305 tod->tod_syncache_removed(tod, sc->sc_todctx); 1306 } 1307 #endif 1308 SCH_UNLOCK(sch); 1309 } 1310 1311 *lsop = syncache_socket(sc, *lsop, m); 1312 1313 if (__predict_false(*lsop == NULL)) { 1314 TCPSTAT_INC(tcps_sc_aborted); 1315 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1316 } else if (sc != &scs) 1317 TCPSTAT_INC(tcps_sc_completed); 1318 1319 if (sc != &scs) 1320 syncache_free(sc); 1321 return (1); 1322 } 1323 1324 static struct socket * 1325 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1326 uint64_t response_cookie) 1327 { 1328 struct inpcb *inp; 1329 struct tcpcb *tp; 1330 unsigned int *pending_counter; 1331 struct socket *so; 1332 1333 NET_EPOCH_ASSERT(); 1334 1335 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1336 so = syncache_socket(sc, lso, m); 1337 if (so == NULL) { 1338 TCPSTAT_INC(tcps_sc_aborted); 1339 atomic_subtract_int(pending_counter, 1); 1340 } else { 1341 soisconnected(so); 1342 inp = sotoinpcb(so); 1343 tp = intotcpcb(inp); 1344 tp->t_flags |= TF_FASTOPEN; 1345 tp->t_tfo_cookie.server = response_cookie; 1346 tp->snd_max = tp->iss; 1347 tp->snd_nxt = tp->iss; 1348 tp->t_tfo_pending = pending_counter; 1349 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1350 TCPSTAT_INC(tcps_sc_completed); 1351 } 1352 1353 return (so); 1354 } 1355 1356 /* 1357 * Given a LISTEN socket and an inbound SYN request, add 1358 * this to the syn cache, and send back a segment: 1359 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1360 * to the source. 1361 * 1362 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1363 * Doing so would require that we hold onto the data and deliver it 1364 * to the application. However, if we are the target of a SYN-flood 1365 * DoS attack, an attacker could send data which would eventually 1366 * consume all available buffer space if it were ACKed. By not ACKing 1367 * the data, we avoid this DoS scenario. 1368 * 1369 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1370 * cookie is processed and a new socket is created. In this case, any data 1371 * accompanying the SYN will be queued to the socket by tcp_input() and will 1372 * be ACKed either when the application sends response data or the delayed 1373 * ACK timer expires, whichever comes first. 1374 */ 1375 struct socket * 1376 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1377 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1378 void *todctx, uint8_t iptos, uint16_t port) 1379 { 1380 struct tcpcb *tp; 1381 struct socket *rv = NULL; 1382 struct syncache *sc = NULL; 1383 struct syncache_head *sch; 1384 struct mbuf *ipopts = NULL; 1385 u_int ltflags; 1386 int win, ip_ttl, ip_tos; 1387 char *s; 1388 #ifdef INET6 1389 int autoflowlabel = 0; 1390 #endif 1391 #ifdef MAC 1392 struct label *maclabel = NULL; 1393 #endif 1394 struct syncache scs; 1395 uint64_t tfo_response_cookie; 1396 unsigned int *tfo_pending = NULL; 1397 int tfo_cookie_valid = 0; 1398 int tfo_response_cookie_valid = 0; 1399 bool locked; 1400 1401 INP_RLOCK_ASSERT(inp); /* listen socket */ 1402 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1403 ("%s: unexpected tcp flags", __func__)); 1404 1405 /* 1406 * Combine all so/tp operations very early to drop the INP lock as 1407 * soon as possible. 1408 */ 1409 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1410 tp = sototcpcb(so); 1411 1412 #ifdef INET6 1413 if (inc->inc_flags & INC_ISIPV6) { 1414 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1415 autoflowlabel = 1; 1416 } 1417 ip_ttl = in6_selecthlim(inp, NULL); 1418 if ((inp->in6p_outputopts == NULL) || 1419 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1420 ip_tos = 0; 1421 } else { 1422 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1423 } 1424 } 1425 #endif 1426 #if defined(INET6) && defined(INET) 1427 else 1428 #endif 1429 #ifdef INET 1430 { 1431 ip_ttl = inp->inp_ip_ttl; 1432 ip_tos = inp->inp_ip_tos; 1433 } 1434 #endif 1435 win = so->sol_sbrcv_hiwat; 1436 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1437 1438 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1439 (tp->t_tfo_pending != NULL) && 1440 (to->to_flags & TOF_FASTOPEN)) { 1441 /* 1442 * Limit the number of pending TFO connections to 1443 * approximately half of the queue limit. This prevents TFO 1444 * SYN floods from starving the service by filling the 1445 * listen queue with bogus TFO connections. 1446 */ 1447 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1448 (so->sol_qlimit / 2)) { 1449 int result; 1450 1451 result = tcp_fastopen_check_cookie(inc, 1452 to->to_tfo_cookie, to->to_tfo_len, 1453 &tfo_response_cookie); 1454 tfo_cookie_valid = (result > 0); 1455 tfo_response_cookie_valid = (result >= 0); 1456 } 1457 1458 /* 1459 * Remember the TFO pending counter as it will have to be 1460 * decremented below if we don't make it to syncache_tfo_expand(). 1461 */ 1462 tfo_pending = tp->t_tfo_pending; 1463 } 1464 1465 #ifdef MAC 1466 if (mac_syncache_init(&maclabel) != 0) { 1467 INP_RUNLOCK(inp); 1468 goto done; 1469 } else 1470 mac_syncache_create(maclabel, inp); 1471 #endif 1472 if (!tfo_cookie_valid) 1473 INP_RUNLOCK(inp); 1474 1475 /* 1476 * Remember the IP options, if any. 1477 */ 1478 #ifdef INET6 1479 if (!(inc->inc_flags & INC_ISIPV6)) 1480 #endif 1481 #ifdef INET 1482 ipopts = (m) ? ip_srcroute(m) : NULL; 1483 #else 1484 ipopts = NULL; 1485 #endif 1486 1487 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1488 /* 1489 * When the socket is TCP-MD5 enabled check that, 1490 * - a signed packet is valid 1491 * - a non-signed packet does not have a security association 1492 * 1493 * If a signed packet fails validation or a non-signed packet has a 1494 * security association, the packet will be dropped. 1495 */ 1496 if (ltflags & TF_SIGNATURE) { 1497 if (to->to_flags & TOF_SIGNATURE) { 1498 if (!TCPMD5_ENABLED() || 1499 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1500 goto done; 1501 } else { 1502 if (TCPMD5_ENABLED() && 1503 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1504 goto done; 1505 } 1506 } else if (to->to_flags & TOF_SIGNATURE) 1507 goto done; 1508 #endif /* TCP_SIGNATURE */ 1509 /* 1510 * See if we already have an entry for this connection. 1511 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1512 * 1513 * XXX: should the syncache be re-initialized with the contents 1514 * of the new SYN here (which may have different options?) 1515 * 1516 * XXX: We do not check the sequence number to see if this is a 1517 * real retransmit or a new connection attempt. The question is 1518 * how to handle such a case; either ignore it as spoofed, or 1519 * drop the current entry and create a new one? 1520 */ 1521 if (syncache_cookiesonly()) { 1522 sc = NULL; 1523 sch = syncache_hashbucket(inc); 1524 locked = false; 1525 } else { 1526 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1527 locked = true; 1528 SCH_LOCK_ASSERT(sch); 1529 } 1530 if (sc != NULL) { 1531 if (tfo_cookie_valid) 1532 INP_RUNLOCK(inp); 1533 TCPSTAT_INC(tcps_sc_dupsyn); 1534 if (ipopts) { 1535 /* 1536 * If we were remembering a previous source route, 1537 * forget it and use the new one we've been given. 1538 */ 1539 if (sc->sc_ipopts) 1540 (void)m_free(sc->sc_ipopts); 1541 sc->sc_ipopts = ipopts; 1542 } 1543 /* 1544 * Update timestamp if present. 1545 */ 1546 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1547 sc->sc_tsreflect = to->to_tsval; 1548 else 1549 sc->sc_flags &= ~SCF_TIMESTAMP; 1550 /* 1551 * Adjust ECN response if needed, e.g. different 1552 * IP ECN field, or a fallback by the remote host. 1553 */ 1554 if (sc->sc_flags & SCF_ECN_MASK) { 1555 sc->sc_flags &= ~SCF_ECN_MASK; 1556 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1557 } 1558 #ifdef MAC 1559 /* 1560 * Since we have already unconditionally allocated label 1561 * storage, free it up. The syncache entry will already 1562 * have an initialized label we can use. 1563 */ 1564 mac_syncache_destroy(&maclabel); 1565 #endif 1566 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1567 /* Retransmit SYN|ACK and reset retransmit count. */ 1568 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1569 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1570 "resetting timer and retransmitting SYN|ACK\n", 1571 s, __func__); 1572 free(s, M_TCPLOG); 1573 } 1574 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1575 sc->sc_rxmits = 0; 1576 syncache_timeout(sc, sch, 1); 1577 TCPSTAT_INC(tcps_sndacks); 1578 TCPSTAT_INC(tcps_sndtotal); 1579 } else { 1580 syncache_drop(sc, sch); 1581 TCPSTAT_INC(tcps_sc_dropped); 1582 } 1583 SCH_UNLOCK(sch); 1584 goto donenoprobe; 1585 } 1586 1587 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1588 /* 1589 * Skip allocating a syncache entry if we are just going to discard 1590 * it later. 1591 */ 1592 if (!locked || tfo_cookie_valid) { 1593 bzero(&scs, sizeof(scs)); 1594 sc = &scs; 1595 } else { 1596 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1597 if (sc == NULL) { 1598 /* 1599 * The zone allocator couldn't provide more entries. 1600 * Treat this as if the cache was full; drop the oldest 1601 * entry and insert the new one. 1602 */ 1603 TCPSTAT_INC(tcps_sc_zonefail); 1604 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1605 if (sc != NULL) { 1606 sch->sch_last_overflow = time_uptime; 1607 syncache_drop(sc, sch); 1608 syncache_pause(inc); 1609 } 1610 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1611 if (sc == NULL) { 1612 if (V_tcp_syncookies) { 1613 bzero(&scs, sizeof(scs)); 1614 sc = &scs; 1615 } else { 1616 KASSERT(locked, 1617 ("%s: bucket unexpectedly unlocked", 1618 __func__)); 1619 SCH_UNLOCK(sch); 1620 goto done; 1621 } 1622 } 1623 } 1624 } 1625 1626 KASSERT(sc != NULL, ("sc == NULL")); 1627 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1628 sc->sc_tfo_cookie = &tfo_response_cookie; 1629 1630 /* 1631 * Fill in the syncache values. 1632 */ 1633 #ifdef MAC 1634 sc->sc_label = maclabel; 1635 #endif 1636 /* 1637 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1638 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1639 * Therefore, store the credentials and take a reference count only 1640 * when needed: 1641 * - sc is allocated from the zone and not using the on stack instance. 1642 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1643 * The reference count is decremented when a zone allocated sc is 1644 * freed in syncache_free(). 1645 */ 1646 if (sc != &scs && !V_tcp_syncache.see_other) 1647 sc->sc_cred = crhold(so->so_cred); 1648 else 1649 sc->sc_cred = NULL; 1650 sc->sc_port = port; 1651 sc->sc_ipopts = ipopts; 1652 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1653 sc->sc_ip_tos = ip_tos; 1654 sc->sc_ip_ttl = ip_ttl; 1655 #ifdef TCP_OFFLOAD 1656 sc->sc_tod = tod; 1657 sc->sc_todctx = todctx; 1658 #endif 1659 sc->sc_irs = th->th_seq; 1660 sc->sc_flags = 0; 1661 sc->sc_flowlabel = 0; 1662 1663 /* 1664 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1665 * win was derived from socket earlier in the function. 1666 */ 1667 win = imax(win, 0); 1668 win = imin(win, TCP_MAXWIN); 1669 sc->sc_wnd = win; 1670 1671 if (V_tcp_do_rfc1323 && 1672 !(ltflags & TF_NOOPT)) { 1673 /* 1674 * A timestamp received in a SYN makes 1675 * it ok to send timestamp requests and replies. 1676 */ 1677 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1678 sc->sc_tsreflect = to->to_tsval; 1679 sc->sc_flags |= SCF_TIMESTAMP; 1680 sc->sc_tsoff = tcp_new_ts_offset(inc); 1681 } 1682 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1683 u_int wscale = 0; 1684 1685 /* 1686 * Pick the smallest possible scaling factor that 1687 * will still allow us to scale up to sb_max, aka 1688 * kern.ipc.maxsockbuf. 1689 * 1690 * We do this because there are broken firewalls that 1691 * will corrupt the window scale option, leading to 1692 * the other endpoint believing that our advertised 1693 * window is unscaled. At scale factors larger than 1694 * 5 the unscaled window will drop below 1500 bytes, 1695 * leading to serious problems when traversing these 1696 * broken firewalls. 1697 * 1698 * With the default maxsockbuf of 256K, a scale factor 1699 * of 3 will be chosen by this algorithm. Those who 1700 * choose a larger maxsockbuf should watch out 1701 * for the compatibility problems mentioned above. 1702 * 1703 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1704 * or <SYN,ACK>) segment itself is never scaled. 1705 */ 1706 while (wscale < TCP_MAX_WINSHIFT && 1707 (TCP_MAXWIN << wscale) < sb_max) 1708 wscale++; 1709 sc->sc_requested_r_scale = wscale; 1710 sc->sc_requested_s_scale = to->to_wscale; 1711 sc->sc_flags |= SCF_WINSCALE; 1712 } 1713 } 1714 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1715 /* 1716 * If incoming packet has an MD5 signature, flag this in the 1717 * syncache so that syncache_respond() will do the right thing 1718 * with the SYN+ACK. 1719 */ 1720 if (to->to_flags & TOF_SIGNATURE) 1721 sc->sc_flags |= SCF_SIGNATURE; 1722 #endif /* TCP_SIGNATURE */ 1723 if (to->to_flags & TOF_SACKPERM) 1724 sc->sc_flags |= SCF_SACK; 1725 if (to->to_flags & TOF_MSS) 1726 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1727 if (ltflags & TF_NOOPT) 1728 sc->sc_flags |= SCF_NOOPT; 1729 /* ECN Handshake */ 1730 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1731 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1732 1733 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1734 sc->sc_iss = syncookie_generate(sch, sc); 1735 else 1736 sc->sc_iss = arc4random(); 1737 #ifdef INET6 1738 if (autoflowlabel) { 1739 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1740 sc->sc_flowlabel = sc->sc_iss; 1741 else 1742 sc->sc_flowlabel = ip6_randomflowlabel(); 1743 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1744 } 1745 #endif 1746 if (locked) 1747 SCH_UNLOCK(sch); 1748 1749 if (tfo_cookie_valid) { 1750 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1751 /* INP_RUNLOCK(inp) will be performed by the caller */ 1752 goto tfo_expanded; 1753 } 1754 1755 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1756 /* 1757 * Do a standard 3-way handshake. 1758 */ 1759 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1760 if (sc != &scs) 1761 syncache_insert(sc, sch); /* locks and unlocks sch */ 1762 TCPSTAT_INC(tcps_sndacks); 1763 TCPSTAT_INC(tcps_sndtotal); 1764 } else { 1765 if (sc != &scs) 1766 syncache_free(sc); 1767 TCPSTAT_INC(tcps_sc_dropped); 1768 } 1769 goto donenoprobe; 1770 1771 done: 1772 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1773 donenoprobe: 1774 if (m) 1775 m_freem(m); 1776 /* 1777 * If tfo_pending is not NULL here, then a TFO SYN that did not 1778 * result in a new socket was processed and the associated pending 1779 * counter has not yet been decremented. All such TFO processing paths 1780 * transit this point. 1781 */ 1782 if (tfo_pending != NULL) 1783 tcp_fastopen_decrement_counter(tfo_pending); 1784 1785 tfo_expanded: 1786 if (sc == NULL || sc == &scs) { 1787 #ifdef MAC 1788 mac_syncache_destroy(&maclabel); 1789 #endif 1790 if (ipopts) 1791 (void)m_free(ipopts); 1792 } 1793 return (rv); 1794 } 1795 1796 /* 1797 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1798 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1799 */ 1800 static int 1801 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1802 { 1803 struct ip *ip = NULL; 1804 struct mbuf *m; 1805 struct tcphdr *th = NULL; 1806 struct udphdr *udp = NULL; 1807 int optlen, error = 0; /* Make compiler happy */ 1808 u_int16_t hlen, tlen, mssopt, ulen; 1809 struct tcpopt to; 1810 #ifdef INET6 1811 struct ip6_hdr *ip6 = NULL; 1812 #endif 1813 1814 NET_EPOCH_ASSERT(); 1815 1816 hlen = 1817 #ifdef INET6 1818 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1819 #endif 1820 sizeof(struct ip); 1821 tlen = hlen + sizeof(struct tcphdr); 1822 if (sc->sc_port) { 1823 tlen += sizeof(struct udphdr); 1824 } 1825 /* Determine MSS we advertize to other end of connection. */ 1826 mssopt = tcp_mssopt(&sc->sc_inc); 1827 if (sc->sc_port) 1828 mssopt -= V_tcp_udp_tunneling_overhead; 1829 mssopt = max(mssopt, V_tcp_minmss); 1830 1831 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1832 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1833 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1834 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1835 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1836 1837 /* Create the IP+TCP header from scratch. */ 1838 m = m_gethdr(M_NOWAIT, MT_DATA); 1839 if (m == NULL) 1840 return (ENOBUFS); 1841 #ifdef MAC 1842 mac_syncache_create_mbuf(sc->sc_label, m); 1843 #endif 1844 m->m_data += max_linkhdr; 1845 m->m_len = tlen; 1846 m->m_pkthdr.len = tlen; 1847 m->m_pkthdr.rcvif = NULL; 1848 1849 #ifdef INET6 1850 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1851 ip6 = mtod(m, struct ip6_hdr *); 1852 ip6->ip6_vfc = IPV6_VERSION; 1853 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1854 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1855 ip6->ip6_plen = htons(tlen - hlen); 1856 /* ip6_hlim is set after checksum */ 1857 /* Zero out traffic class and flow label. */ 1858 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1859 ip6->ip6_flow |= sc->sc_flowlabel; 1860 if (sc->sc_port != 0) { 1861 ip6->ip6_nxt = IPPROTO_UDP; 1862 udp = (struct udphdr *)(ip6 + 1); 1863 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1864 udp->uh_dport = sc->sc_port; 1865 ulen = (tlen - sizeof(struct ip6_hdr)); 1866 th = (struct tcphdr *)(udp + 1); 1867 } else { 1868 ip6->ip6_nxt = IPPROTO_TCP; 1869 th = (struct tcphdr *)(ip6 + 1); 1870 } 1871 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1872 } 1873 #endif 1874 #if defined(INET6) && defined(INET) 1875 else 1876 #endif 1877 #ifdef INET 1878 { 1879 ip = mtod(m, struct ip *); 1880 ip->ip_v = IPVERSION; 1881 ip->ip_hl = sizeof(struct ip) >> 2; 1882 ip->ip_len = htons(tlen); 1883 ip->ip_id = 0; 1884 ip->ip_off = 0; 1885 ip->ip_sum = 0; 1886 ip->ip_src = sc->sc_inc.inc_laddr; 1887 ip->ip_dst = sc->sc_inc.inc_faddr; 1888 ip->ip_ttl = sc->sc_ip_ttl; 1889 ip->ip_tos = sc->sc_ip_tos; 1890 1891 /* 1892 * See if we should do MTU discovery. Route lookups are 1893 * expensive, so we will only unset the DF bit if: 1894 * 1895 * 1) path_mtu_discovery is disabled 1896 * 2) the SCF_UNREACH flag has been set 1897 */ 1898 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1899 ip->ip_off |= htons(IP_DF); 1900 if (sc->sc_port == 0) { 1901 ip->ip_p = IPPROTO_TCP; 1902 th = (struct tcphdr *)(ip + 1); 1903 } else { 1904 ip->ip_p = IPPROTO_UDP; 1905 udp = (struct udphdr *)(ip + 1); 1906 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1907 udp->uh_dport = sc->sc_port; 1908 ulen = (tlen - sizeof(struct ip)); 1909 th = (struct tcphdr *)(udp + 1); 1910 } 1911 } 1912 #endif /* INET */ 1913 th->th_sport = sc->sc_inc.inc_lport; 1914 th->th_dport = sc->sc_inc.inc_fport; 1915 1916 if (flags & TH_SYN) 1917 th->th_seq = htonl(sc->sc_iss); 1918 else 1919 th->th_seq = htonl(sc->sc_iss + 1); 1920 th->th_ack = htonl(sc->sc_irs + 1); 1921 th->th_off = sizeof(struct tcphdr) >> 2; 1922 th->th_win = htons(sc->sc_wnd); 1923 th->th_urp = 0; 1924 1925 flags = tcp_ecn_syncache_respond(flags, sc); 1926 tcp_set_flags(th, flags); 1927 1928 /* Tack on the TCP options. */ 1929 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1930 to.to_flags = 0; 1931 1932 if (flags & TH_SYN) { 1933 to.to_mss = mssopt; 1934 to.to_flags = TOF_MSS; 1935 if (sc->sc_flags & SCF_WINSCALE) { 1936 to.to_wscale = sc->sc_requested_r_scale; 1937 to.to_flags |= TOF_SCALE; 1938 } 1939 if (sc->sc_flags & SCF_SACK) 1940 to.to_flags |= TOF_SACKPERM; 1941 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1942 if (sc->sc_flags & SCF_SIGNATURE) 1943 to.to_flags |= TOF_SIGNATURE; 1944 #endif 1945 if (sc->sc_tfo_cookie) { 1946 to.to_flags |= TOF_FASTOPEN; 1947 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1948 to.to_tfo_cookie = sc->sc_tfo_cookie; 1949 /* don't send cookie again when retransmitting response */ 1950 sc->sc_tfo_cookie = NULL; 1951 } 1952 } 1953 if (sc->sc_flags & SCF_TIMESTAMP) { 1954 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1955 to.to_tsecr = sc->sc_tsreflect; 1956 to.to_flags |= TOF_TS; 1957 } 1958 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1959 1960 /* Adjust headers by option size. */ 1961 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1962 m->m_len += optlen; 1963 m->m_pkthdr.len += optlen; 1964 #ifdef INET6 1965 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1966 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1967 else 1968 #endif 1969 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1970 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1971 if (sc->sc_flags & SCF_SIGNATURE) { 1972 KASSERT(to.to_flags & TOF_SIGNATURE, 1973 ("tcp_addoptions() didn't set tcp_signature")); 1974 1975 /* NOTE: to.to_signature is inside of mbuf */ 1976 if (!TCPMD5_ENABLED() || 1977 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1978 m_freem(m); 1979 return (EACCES); 1980 } 1981 } 1982 #endif 1983 } else 1984 optlen = 0; 1985 1986 if (udp) { 1987 ulen += optlen; 1988 udp->uh_ulen = htons(ulen); 1989 } 1990 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1991 /* 1992 * If we have peer's SYN and it has a flowid, then let's assign it to 1993 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1994 * to SYN|ACK due to lack of inp here. 1995 */ 1996 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1997 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1998 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1999 } 2000 #ifdef INET6 2001 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2002 if (sc->sc_port) { 2003 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2004 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2005 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2006 IPPROTO_UDP, 0); 2007 th->th_sum = htons(0); 2008 } else { 2009 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2010 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2011 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2012 IPPROTO_TCP, 0); 2013 } 2014 ip6->ip6_hlim = sc->sc_ip_ttl; 2015 #ifdef TCP_OFFLOAD 2016 if (ADDED_BY_TOE(sc)) { 2017 struct toedev *tod = sc->sc_tod; 2018 2019 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2020 2021 return (error); 2022 } 2023 #endif 2024 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2025 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2026 } 2027 #endif 2028 #if defined(INET6) && defined(INET) 2029 else 2030 #endif 2031 #ifdef INET 2032 { 2033 if (sc->sc_port) { 2034 m->m_pkthdr.csum_flags = CSUM_UDP; 2035 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2036 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2037 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2038 th->th_sum = htons(0); 2039 } else { 2040 m->m_pkthdr.csum_flags = CSUM_TCP; 2041 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2042 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2043 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2044 } 2045 #ifdef TCP_OFFLOAD 2046 if (ADDED_BY_TOE(sc)) { 2047 struct toedev *tod = sc->sc_tod; 2048 2049 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2050 2051 return (error); 2052 } 2053 #endif 2054 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2055 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2056 } 2057 #endif 2058 return (error); 2059 } 2060 2061 static void 2062 syncache_send_challenge_ack(struct syncache *sc, struct mbuf *m) 2063 { 2064 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2065 &sc->sc_challenge_ack_cnt)) { 2066 if (syncache_respond(sc, m, TH_ACK) == 0) { 2067 TCPSTAT_INC(tcps_sndacks); 2068 TCPSTAT_INC(tcps_sndtotal); 2069 } 2070 } 2071 } 2072 2073 /* 2074 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2075 * that exceed the capacity of the syncache by avoiding the storage of any 2076 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2077 * attacks where the attacker does not have access to our responses. 2078 * 2079 * Syncookies encode and include all necessary information about the 2080 * connection setup within the SYN|ACK that we send back. That way we 2081 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2082 * (if ever). Normally the syncache and syncookies are running in parallel 2083 * with the latter taking over when the former is exhausted. When matching 2084 * syncache entry is found the syncookie is ignored. 2085 * 2086 * The only reliable information persisting the 3WHS is our initial sequence 2087 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2088 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2089 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2090 * returns and signifies a legitimate connection if it matches the ACK. 2091 * 2092 * The available space of 32 bits to store the hash and to encode the SYN 2093 * option information is very tight and we should have at least 24 bits for 2094 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2095 * 2096 * SYN option information we have to encode to fully restore a connection: 2097 * MSS: is imporant to chose an optimal segment size to avoid IP level 2098 * fragmentation along the path. The common MSS values can be encoded 2099 * in a 3-bit table. Uncommon values are captured by the next lower value 2100 * in the table leading to a slight increase in packetization overhead. 2101 * WSCALE: is necessary to allow large windows to be used for high delay- 2102 * bandwidth product links. Not scaling the window when it was initially 2103 * negotiated is bad for performance as lack of scaling further decreases 2104 * the apparent available send window. We only need to encode the WSCALE 2105 * we received from the remote end. Our end can be recalculated at any 2106 * time. The common WSCALE values can be encoded in a 3-bit table. 2107 * Uncommon values are captured by the next lower value in the table 2108 * making us under-estimate the available window size halving our 2109 * theoretically possible maximum throughput for that connection. 2110 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2111 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2112 * that are included in all segments on a connection. We enable them when 2113 * the ACK has them. 2114 * 2115 * Security of syncookies and attack vectors: 2116 * 2117 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2118 * together with the gloabl secret to make it unique per connection attempt. 2119 * Thus any change of any of those parameters results in a different MAC output 2120 * in an unpredictable way unless a collision is encountered. 24 bits of the 2121 * MAC are embedded into the ISS. 2122 * 2123 * To prevent replay attacks two rotating global secrets are updated with a 2124 * new random value every 15 seconds. The life-time of a syncookie is thus 2125 * 15-30 seconds. 2126 * 2127 * Vector 1: Attacking the secret. This requires finding a weakness in the 2128 * MAC itself or the way it is used here. The attacker can do a chosen plain 2129 * text attack by varying and testing the all parameters under his control. 2130 * The strength depends on the size and randomness of the secret, and the 2131 * cryptographic security of the MAC function. Due to the constant updating 2132 * of the secret the attacker has at most 29.999 seconds to find the secret 2133 * and launch spoofed connections. After that he has to start all over again. 2134 * 2135 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2136 * size an average of 4,823 attempts are required for a 50% chance of success 2137 * to spoof a single syncookie (birthday collision paradox). However the 2138 * attacker is blind and doesn't know if one of his attempts succeeded unless 2139 * he has a side channel to interfere success from. A single connection setup 2140 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2141 * This many attempts are required for each one blind spoofed connection. For 2142 * every additional spoofed connection he has to launch another N attempts. 2143 * Thus for a sustained rate 100 spoofed connections per second approximately 2144 * 1,800,000 packets per second would have to be sent. 2145 * 2146 * NB: The MAC function should be fast so that it doesn't become a CPU 2147 * exhaustion attack vector itself. 2148 * 2149 * References: 2150 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2151 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2152 * http://cr.yp.to/syncookies.html (overview) 2153 * http://cr.yp.to/syncookies/archive (details) 2154 * 2155 * 2156 * Schematic construction of a syncookie enabled Initial Sequence Number: 2157 * 0 1 2 3 2158 * 12345678901234567890123456789012 2159 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2160 * 2161 * x 24 MAC (truncated) 2162 * W 3 Send Window Scale index 2163 * M 3 MSS index 2164 * S 1 SACK permitted 2165 * P 1 Odd/even secret 2166 */ 2167 2168 /* 2169 * Distribution and probability of certain MSS values. Those in between are 2170 * rounded down to the next lower one. 2171 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2172 * .2% .3% 5% 7% 7% 20% 15% 45% 2173 */ 2174 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2175 2176 /* 2177 * Distribution and probability of certain WSCALE values. We have to map the 2178 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2179 * bits based on prevalence of certain values. Where we don't have an exact 2180 * match for are rounded down to the next lower one letting us under-estimate 2181 * the true available window. At the moment this would happen only for the 2182 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2183 * and window size). The absence of the WSCALE option (no scaling in either 2184 * direction) is encoded with index zero. 2185 * [WSCALE values histograms, Allman, 2012] 2186 * X 10 10 35 5 6 14 10% by host 2187 * X 11 4 5 5 18 49 3% by connections 2188 */ 2189 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2190 2191 /* 2192 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2193 * and good cryptographic properties. 2194 */ 2195 static uint32_t 2196 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2197 uint8_t *secbits, uintptr_t secmod) 2198 { 2199 SIPHASH_CTX ctx; 2200 uint32_t siphash[2]; 2201 2202 SipHash24_Init(&ctx); 2203 SipHash_SetKey(&ctx, secbits); 2204 switch (inc->inc_flags & INC_ISIPV6) { 2205 #ifdef INET 2206 case 0: 2207 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2208 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2209 break; 2210 #endif 2211 #ifdef INET6 2212 case INC_ISIPV6: 2213 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2214 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2215 break; 2216 #endif 2217 } 2218 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2219 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2220 SipHash_Update(&ctx, &irs, sizeof(irs)); 2221 SipHash_Update(&ctx, &flags, sizeof(flags)); 2222 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2223 SipHash_Final((u_int8_t *)&siphash, &ctx); 2224 2225 return (siphash[0] ^ siphash[1]); 2226 } 2227 2228 static tcp_seq 2229 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2230 { 2231 u_int i, secbit, wscale; 2232 uint32_t iss, hash; 2233 uint8_t *secbits; 2234 union syncookie cookie; 2235 2236 cookie.cookie = 0; 2237 2238 /* Map our computed MSS into the 3-bit index. */ 2239 for (i = nitems(tcp_sc_msstab) - 1; 2240 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2241 i--) 2242 ; 2243 cookie.flags.mss_idx = i; 2244 2245 /* 2246 * Map the send window scale into the 3-bit index but only if 2247 * the wscale option was received. 2248 */ 2249 if (sc->sc_flags & SCF_WINSCALE) { 2250 wscale = sc->sc_requested_s_scale; 2251 for (i = nitems(tcp_sc_wstab) - 1; 2252 tcp_sc_wstab[i] > wscale && i > 0; 2253 i--) 2254 ; 2255 cookie.flags.wscale_idx = i; 2256 } 2257 2258 /* Can we do SACK? */ 2259 if (sc->sc_flags & SCF_SACK) 2260 cookie.flags.sack_ok = 1; 2261 2262 /* Which of the two secrets to use. */ 2263 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2264 cookie.flags.odd_even = secbit; 2265 2266 secbits = V_tcp_syncache.secret.key[secbit]; 2267 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2268 (uintptr_t)sch); 2269 2270 /* 2271 * Put the flags into the hash and XOR them to get better ISS number 2272 * variance. This doesn't enhance the cryptographic strength and is 2273 * done to prevent the 8 cookie bits from showing up directly on the 2274 * wire. 2275 */ 2276 iss = hash & ~0xff; 2277 iss |= cookie.cookie ^ (hash >> 24); 2278 2279 TCPSTAT_INC(tcps_sc_sendcookie); 2280 return (iss); 2281 } 2282 2283 static bool 2284 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2285 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2286 struct socket *lso, uint16_t port) 2287 { 2288 uint32_t hash; 2289 uint8_t *secbits; 2290 tcp_seq ack, seq; 2291 int wnd; 2292 union syncookie cookie; 2293 2294 /* 2295 * Pull information out of SYN-ACK/ACK and revert sequence number 2296 * advances. 2297 */ 2298 ack = th->th_ack - 1; 2299 seq = th->th_seq - 1; 2300 2301 /* 2302 * Unpack the flags containing enough information to restore the 2303 * connection. 2304 */ 2305 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2306 2307 /* Which of the two secrets to use. */ 2308 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2309 2310 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2311 2312 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2313 if ((ack & ~0xff) != (hash & ~0xff)) 2314 return (false); 2315 2316 /* Fill in the syncache values. */ 2317 sc->sc_flags = 0; 2318 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2319 sc->sc_ipopts = NULL; 2320 2321 sc->sc_irs = seq; 2322 sc->sc_iss = ack; 2323 2324 switch (inc->inc_flags & INC_ISIPV6) { 2325 #ifdef INET 2326 case 0: 2327 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2328 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2329 break; 2330 #endif 2331 #ifdef INET6 2332 case INC_ISIPV6: 2333 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2334 sc->sc_flowlabel = 2335 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2336 break; 2337 #endif 2338 } 2339 2340 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2341 2342 /* Only use wscale if it was enabled in the orignal SYN. */ 2343 if (cookie.flags.wscale_idx > 0) { 2344 u_int wscale = 0; 2345 2346 /* Recompute the receive window scale that was sent earlier. */ 2347 while (wscale < TCP_MAX_WINSHIFT && 2348 (TCP_MAXWIN << wscale) < sb_max) 2349 wscale++; 2350 sc->sc_requested_r_scale = wscale; 2351 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2352 sc->sc_flags |= SCF_WINSCALE; 2353 } 2354 2355 wnd = lso->sol_sbrcv_hiwat; 2356 wnd = imax(wnd, 0); 2357 wnd = imin(wnd, TCP_MAXWIN); 2358 sc->sc_wnd = wnd; 2359 2360 if (cookie.flags.sack_ok) 2361 sc->sc_flags |= SCF_SACK; 2362 2363 if (to->to_flags & TOF_TS) { 2364 sc->sc_flags |= SCF_TIMESTAMP; 2365 sc->sc_tsreflect = to->to_tsval; 2366 sc->sc_tsoff = tcp_new_ts_offset(inc); 2367 } 2368 2369 if (to->to_flags & TOF_SIGNATURE) 2370 sc->sc_flags |= SCF_SIGNATURE; 2371 2372 sc->sc_rxmits = 0; 2373 2374 sc->sc_port = port; 2375 2376 return (true); 2377 } 2378 2379 #ifdef INVARIANTS 2380 static void 2381 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2382 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2383 struct socket *lso, uint16_t port) 2384 { 2385 struct syncache scs; 2386 char *s; 2387 2388 bzero(&scs, sizeof(scs)); 2389 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2390 (sc->sc_peer_mss != scs.sc_peer_mss || 2391 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2392 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2393 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2394 2395 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2396 return; 2397 2398 if (sc->sc_peer_mss != scs.sc_peer_mss) 2399 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2400 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2401 2402 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2403 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2404 s, __func__, sc->sc_requested_r_scale, 2405 scs.sc_requested_r_scale); 2406 2407 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2408 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2409 s, __func__, sc->sc_requested_s_scale, 2410 scs.sc_requested_s_scale); 2411 2412 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2413 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2414 2415 free(s, M_TCPLOG); 2416 } 2417 } 2418 #endif /* INVARIANTS */ 2419 2420 static void 2421 syncookie_reseed(void *arg) 2422 { 2423 struct tcp_syncache *sc = arg; 2424 uint8_t *secbits; 2425 int secbit; 2426 2427 /* 2428 * Reseeding the secret doesn't have to be protected by a lock. 2429 * It only must be ensured that the new random values are visible 2430 * to all CPUs in a SMP environment. The atomic with release 2431 * semantics ensures that. 2432 */ 2433 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2434 secbits = sc->secret.key[secbit]; 2435 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2436 atomic_add_rel_int(&sc->secret.oddeven, 1); 2437 2438 /* Reschedule ourself. */ 2439 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2440 } 2441 2442 /* 2443 * We have overflowed a bucket. Let's pause dealing with the syncache. 2444 * This function will increment the bucketoverflow statistics appropriately 2445 * (once per pause when pausing is enabled; otherwise, once per overflow). 2446 */ 2447 static void 2448 syncache_pause(struct in_conninfo *inc) 2449 { 2450 time_t delta; 2451 const char *s; 2452 2453 /* XXX: 2454 * 2. Add sysctl read here so we don't get the benefit of this 2455 * change without the new sysctl. 2456 */ 2457 2458 /* 2459 * Try an unlocked read. If we already know that another thread 2460 * has activated the feature, there is no need to proceed. 2461 */ 2462 if (V_tcp_syncache.paused) 2463 return; 2464 2465 /* Are cookied enabled? If not, we can't pause. */ 2466 if (!V_tcp_syncookies) { 2467 TCPSTAT_INC(tcps_sc_bucketoverflow); 2468 return; 2469 } 2470 2471 /* 2472 * We may be the first thread to find an overflow. Get the lock 2473 * and evaluate if we need to take action. 2474 */ 2475 mtx_lock(&V_tcp_syncache.pause_mtx); 2476 if (V_tcp_syncache.paused) { 2477 mtx_unlock(&V_tcp_syncache.pause_mtx); 2478 return; 2479 } 2480 2481 /* Activate protection. */ 2482 V_tcp_syncache.paused = true; 2483 TCPSTAT_INC(tcps_sc_bucketoverflow); 2484 2485 /* 2486 * Determine the last backoff time. If we are seeing a re-newed 2487 * attack within that same time after last reactivating the syncache, 2488 * consider it an extension of the same attack. 2489 */ 2490 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2491 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2492 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2493 delta <<= 1; 2494 V_tcp_syncache.pause_backoff++; 2495 } 2496 } else { 2497 delta = TCP_SYNCACHE_PAUSE_TIME; 2498 V_tcp_syncache.pause_backoff = 0; 2499 } 2500 2501 /* Log a warning, including IP addresses, if able. */ 2502 if (inc != NULL) 2503 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2504 else 2505 s = (const char *)NULL; 2506 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2507 "the next %lld seconds%s%s%s\n", (long long)delta, 2508 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2509 (s != NULL) ? ")" : ""); 2510 free(__DECONST(void *, s), M_TCPLOG); 2511 2512 /* Use the calculated delta to set a new pause time. */ 2513 V_tcp_syncache.pause_until = time_uptime + delta; 2514 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2515 &V_tcp_syncache); 2516 mtx_unlock(&V_tcp_syncache.pause_mtx); 2517 } 2518 2519 /* Evaluate whether we need to unpause. */ 2520 static void 2521 syncache_unpause(void *arg) 2522 { 2523 struct tcp_syncache *sc; 2524 time_t delta; 2525 2526 sc = arg; 2527 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2528 callout_deactivate(&sc->pause_co); 2529 2530 /* 2531 * Check to make sure we are not running early. If the pause 2532 * time has expired, then deactivate the protection. 2533 */ 2534 if ((delta = sc->pause_until - time_uptime) > 0) 2535 callout_schedule(&sc->pause_co, delta * hz); 2536 else 2537 sc->paused = false; 2538 } 2539 2540 /* 2541 * Exports the syncache entries to userland so that netstat can display 2542 * them alongside the other sockets. This function is intended to be 2543 * called only from tcp_pcblist. 2544 * 2545 * Due to concurrency on an active system, the number of pcbs exported 2546 * may have no relation to max_pcbs. max_pcbs merely indicates the 2547 * amount of space the caller allocated for this function to use. 2548 */ 2549 int 2550 syncache_pcblist(struct sysctl_req *req) 2551 { 2552 struct xtcpcb xt; 2553 struct syncache *sc; 2554 struct syncache_head *sch; 2555 int error, i; 2556 2557 bzero(&xt, sizeof(xt)); 2558 xt.xt_len = sizeof(xt); 2559 xt.t_state = TCPS_SYN_RECEIVED; 2560 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2561 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2562 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2563 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2564 2565 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2566 sch = &V_tcp_syncache.hashbase[i]; 2567 SCH_LOCK(sch); 2568 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2569 if (sc->sc_cred != NULL && 2570 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2571 continue; 2572 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2573 xt.xt_inp.inp_vflag = INP_IPV6; 2574 else 2575 xt.xt_inp.inp_vflag = INP_IPV4; 2576 xt.xt_encaps_port = sc->sc_port; 2577 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2578 sizeof (struct in_conninfo)); 2579 error = SYSCTL_OUT(req, &xt, sizeof xt); 2580 if (error) { 2581 SCH_UNLOCK(sch); 2582 return (0); 2583 } 2584 } 2585 SCH_UNLOCK(sch); 2586 } 2587 2588 return (0); 2589 } 2590