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 int 1051 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1052 struct socket **lsop, struct mbuf *m, uint16_t port) 1053 { 1054 struct syncache *sc; 1055 struct syncache_head *sch; 1056 struct syncache scs; 1057 char *s; 1058 bool locked; 1059 1060 NET_EPOCH_ASSERT(); 1061 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1062 ("%s: can handle only ACK", __func__)); 1063 1064 if (syncache_cookiesonly()) { 1065 sc = NULL; 1066 sch = syncache_hashbucket(inc); 1067 locked = false; 1068 } else { 1069 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1070 locked = true; 1071 SCH_LOCK_ASSERT(sch); 1072 } 1073 1074 #ifdef INVARIANTS 1075 /* 1076 * Test code for syncookies comparing the syncache stored 1077 * values with the reconstructed values from the cookie. 1078 */ 1079 if (sc != NULL) 1080 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1081 #endif 1082 1083 if (sc == NULL) { 1084 if (locked) { 1085 /* 1086 * The syncache is currently in use (neither disabled, 1087 * nor paused), but no entry was found. 1088 */ 1089 if (!V_tcp_syncookies) { 1090 /* 1091 * Since no syncookies are used in case of 1092 * a bucket overflow, don't even check for 1093 * a valid syncookie. 1094 */ 1095 SCH_UNLOCK(sch); 1096 TCPSTAT_INC(tcps_sc_spurcookie); 1097 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1098 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1099 "segment rejected " 1100 "(syncookies disabled)\n", 1101 s, __func__); 1102 goto failed; 1103 } 1104 if (sch->sch_last_overflow < 1105 time_uptime - SYNCOOKIE_LIFETIME) { 1106 /* 1107 * Since the bucket did not overflow recently, 1108 * don't even check for a valid syncookie. 1109 */ 1110 SCH_UNLOCK(sch); 1111 TCPSTAT_INC(tcps_sc_spurcookie); 1112 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1113 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1114 "segment rejected " 1115 "(no syncache entry)\n", 1116 s, __func__); 1117 goto failed; 1118 } 1119 SCH_UNLOCK(sch); 1120 } 1121 bzero(&scs, sizeof(scs)); 1122 /* 1123 * Now check, if the syncookie is valid. If it is, create an on 1124 * stack syncache entry. 1125 */ 1126 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1127 sc = &scs; 1128 TCPSTAT_INC(tcps_sc_recvcookie); 1129 } else { 1130 TCPSTAT_INC(tcps_sc_failcookie); 1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1132 log(LOG_DEBUG, "%s; %s: Segment failed " 1133 "SYNCOOKIE authentication, segment rejected " 1134 "(probably spoofed)\n", s, __func__); 1135 goto failed; 1136 } 1137 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1138 /* If received ACK has MD5 signature, check it. */ 1139 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1140 (!TCPMD5_ENABLED() || 1141 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1142 /* Drop the ACK. */ 1143 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1144 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1145 "MD5 signature doesn't match.\n", 1146 s, __func__); 1147 free(s, M_TCPLOG); 1148 } 1149 TCPSTAT_INC(tcps_sig_err_sigopt); 1150 return (-1); /* Do not send RST */ 1151 } 1152 #endif /* TCP_SIGNATURE */ 1153 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1154 } else { 1155 if (sc->sc_port != port) { 1156 SCH_UNLOCK(sch); 1157 return (0); 1158 } 1159 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1160 /* 1161 * If listening socket requested TCP digests, check that 1162 * received ACK has signature and it is correct. 1163 * If not, drop the ACK and leave sc entry in th cache, 1164 * because SYN was received with correct signature. 1165 */ 1166 if (sc->sc_flags & SCF_SIGNATURE) { 1167 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1168 /* No signature */ 1169 TCPSTAT_INC(tcps_sig_err_nosigopt); 1170 SCH_UNLOCK(sch); 1171 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1172 log(LOG_DEBUG, "%s; %s: Segment " 1173 "rejected, MD5 signature wasn't " 1174 "provided.\n", s, __func__); 1175 free(s, M_TCPLOG); 1176 } 1177 return (-1); /* Do not send RST */ 1178 } 1179 if (!TCPMD5_ENABLED() || 1180 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1181 /* Doesn't match or no SA */ 1182 SCH_UNLOCK(sch); 1183 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1184 log(LOG_DEBUG, "%s; %s: Segment " 1185 "rejected, MD5 signature doesn't " 1186 "match.\n", s, __func__); 1187 free(s, M_TCPLOG); 1188 } 1189 return (-1); /* Do not send RST */ 1190 } 1191 } 1192 #endif /* TCP_SIGNATURE */ 1193 1194 /* 1195 * RFC 7323 PAWS: If we have a timestamp on this segment and 1196 * it's less than ts_recent, drop it. 1197 * XXXMT: RFC 7323 also requires to send an ACK. 1198 * In tcp_input.c this is only done for TCP segments 1199 * with user data, so be consistent here and just drop 1200 * the segment. 1201 */ 1202 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1203 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1204 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1205 log(LOG_DEBUG, 1206 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1207 "segment dropped\n", s, __func__, 1208 to->to_tsval, sc->sc_tsreflect); 1209 free(s, M_TCPLOG); 1210 } 1211 SCH_UNLOCK(sch); 1212 return (-1); /* Do not send RST */ 1213 } 1214 1215 /* 1216 * If timestamps were not negotiated during SYN/ACK and a 1217 * segment with a timestamp is received, ignore the 1218 * timestamp and process the packet normally. 1219 * See section 3.2 of RFC 7323. 1220 */ 1221 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1222 (to->to_flags & TOF_TS)) { 1223 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1224 log(LOG_DEBUG, "%s; %s: Timestamp not " 1225 "expected, segment processed normally\n", 1226 s, __func__); 1227 free(s, M_TCPLOG); 1228 s = NULL; 1229 } 1230 } 1231 1232 /* 1233 * If timestamps were negotiated during SYN/ACK and a 1234 * segment without a timestamp is received, silently drop 1235 * the segment, unless the missing timestamps are tolerated. 1236 * See section 3.2 of RFC 7323. 1237 */ 1238 if ((sc->sc_flags & SCF_TIMESTAMP) && 1239 !(to->to_flags & TOF_TS)) { 1240 if (V_tcp_tolerate_missing_ts) { 1241 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1242 log(LOG_DEBUG, 1243 "%s; %s: Timestamp missing, " 1244 "segment processed normally\n", 1245 s, __func__); 1246 free(s, M_TCPLOG); 1247 } 1248 } else { 1249 SCH_UNLOCK(sch); 1250 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1251 log(LOG_DEBUG, 1252 "%s; %s: Timestamp missing, " 1253 "segment silently dropped\n", 1254 s, __func__); 1255 free(s, M_TCPLOG); 1256 } 1257 return (-1); /* Do not send RST */ 1258 } 1259 } 1260 1261 /* 1262 * SEG.SEQ validation: 1263 * The SEG.SEQ must be in the window starting at our 1264 * initial receive sequence number + 1. 1265 */ 1266 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1267 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1268 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1269 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1270 "sending challenge ACK\n", 1271 s, __func__, th->th_seq, sc->sc_irs + 1); 1272 syncache_send_challenge_ack(sc, m); 1273 SCH_UNLOCK(sch); 1274 free(s, M_TCPLOG); 1275 return (-1); /* Do not send RST */ 1276 } 1277 1278 /* 1279 * SEG.ACK validation: 1280 * SEG.ACK must match our initial send sequence number + 1. 1281 */ 1282 if (th->th_ack != sc->sc_iss + 1) { 1283 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1284 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1285 "segment rejected\n", 1286 s, __func__, th->th_ack, sc->sc_iss + 1); 1287 SCH_UNLOCK(sch); 1288 free(s, M_TCPLOG); 1289 return (0); /* Do send RST, do not free sc. */ 1290 } 1291 1292 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1293 sch->sch_length--; 1294 #ifdef TCP_OFFLOAD 1295 if (ADDED_BY_TOE(sc)) { 1296 struct toedev *tod = sc->sc_tod; 1297 1298 tod->tod_syncache_removed(tod, sc->sc_todctx); 1299 } 1300 #endif 1301 SCH_UNLOCK(sch); 1302 } 1303 1304 *lsop = syncache_socket(sc, *lsop, m); 1305 1306 if (__predict_false(*lsop == NULL)) { 1307 TCPSTAT_INC(tcps_sc_aborted); 1308 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1309 } else if (sc != &scs) 1310 TCPSTAT_INC(tcps_sc_completed); 1311 1312 if (sc != &scs) 1313 syncache_free(sc); 1314 return (1); 1315 failed: 1316 if (sc != NULL) { 1317 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1318 if (sc != &scs) 1319 syncache_free(sc); 1320 } 1321 if (s != NULL) 1322 free(s, M_TCPLOG); 1323 *lsop = NULL; 1324 return (0); 1325 } 1326 1327 static struct socket * 1328 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1329 uint64_t response_cookie) 1330 { 1331 struct inpcb *inp; 1332 struct tcpcb *tp; 1333 unsigned int *pending_counter; 1334 struct socket *so; 1335 1336 NET_EPOCH_ASSERT(); 1337 1338 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1339 so = syncache_socket(sc, lso, m); 1340 if (so == NULL) { 1341 TCPSTAT_INC(tcps_sc_aborted); 1342 atomic_subtract_int(pending_counter, 1); 1343 } else { 1344 soisconnected(so); 1345 inp = sotoinpcb(so); 1346 tp = intotcpcb(inp); 1347 tp->t_flags |= TF_FASTOPEN; 1348 tp->t_tfo_cookie.server = response_cookie; 1349 tp->snd_max = tp->iss; 1350 tp->snd_nxt = tp->iss; 1351 tp->t_tfo_pending = pending_counter; 1352 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1353 TCPSTAT_INC(tcps_sc_completed); 1354 } 1355 1356 return (so); 1357 } 1358 1359 /* 1360 * Given a LISTEN socket and an inbound SYN request, add 1361 * this to the syn cache, and send back a segment: 1362 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1363 * to the source. 1364 * 1365 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1366 * Doing so would require that we hold onto the data and deliver it 1367 * to the application. However, if we are the target of a SYN-flood 1368 * DoS attack, an attacker could send data which would eventually 1369 * consume all available buffer space if it were ACKed. By not ACKing 1370 * the data, we avoid this DoS scenario. 1371 * 1372 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1373 * cookie is processed and a new socket is created. In this case, any data 1374 * accompanying the SYN will be queued to the socket by tcp_input() and will 1375 * be ACKed either when the application sends response data or the delayed 1376 * ACK timer expires, whichever comes first. 1377 */ 1378 struct socket * 1379 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1380 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1381 void *todctx, uint8_t iptos, uint16_t port) 1382 { 1383 struct tcpcb *tp; 1384 struct socket *rv = NULL; 1385 struct syncache *sc = NULL; 1386 struct syncache_head *sch; 1387 struct mbuf *ipopts = NULL; 1388 u_int ltflags; 1389 int win, ip_ttl, ip_tos; 1390 char *s; 1391 #ifdef INET6 1392 int autoflowlabel = 0; 1393 #endif 1394 #ifdef MAC 1395 struct label *maclabel = NULL; 1396 #endif 1397 struct syncache scs; 1398 uint64_t tfo_response_cookie; 1399 unsigned int *tfo_pending = NULL; 1400 int tfo_cookie_valid = 0; 1401 int tfo_response_cookie_valid = 0; 1402 bool locked; 1403 1404 INP_RLOCK_ASSERT(inp); /* listen socket */ 1405 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1406 ("%s: unexpected tcp flags", __func__)); 1407 1408 /* 1409 * Combine all so/tp operations very early to drop the INP lock as 1410 * soon as possible. 1411 */ 1412 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1413 tp = sototcpcb(so); 1414 1415 #ifdef INET6 1416 if (inc->inc_flags & INC_ISIPV6) { 1417 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1418 autoflowlabel = 1; 1419 } 1420 ip_ttl = in6_selecthlim(inp, NULL); 1421 if ((inp->in6p_outputopts == NULL) || 1422 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1423 ip_tos = 0; 1424 } else { 1425 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1426 } 1427 } 1428 #endif 1429 #if defined(INET6) && defined(INET) 1430 else 1431 #endif 1432 #ifdef INET 1433 { 1434 ip_ttl = inp->inp_ip_ttl; 1435 ip_tos = inp->inp_ip_tos; 1436 } 1437 #endif 1438 win = so->sol_sbrcv_hiwat; 1439 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1440 1441 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1442 (tp->t_tfo_pending != NULL) && 1443 (to->to_flags & TOF_FASTOPEN)) { 1444 /* 1445 * Limit the number of pending TFO connections to 1446 * approximately half of the queue limit. This prevents TFO 1447 * SYN floods from starving the service by filling the 1448 * listen queue with bogus TFO connections. 1449 */ 1450 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1451 (so->sol_qlimit / 2)) { 1452 int result; 1453 1454 result = tcp_fastopen_check_cookie(inc, 1455 to->to_tfo_cookie, to->to_tfo_len, 1456 &tfo_response_cookie); 1457 tfo_cookie_valid = (result > 0); 1458 tfo_response_cookie_valid = (result >= 0); 1459 } 1460 1461 /* 1462 * Remember the TFO pending counter as it will have to be 1463 * decremented below if we don't make it to syncache_tfo_expand(). 1464 */ 1465 tfo_pending = tp->t_tfo_pending; 1466 } 1467 1468 #ifdef MAC 1469 if (mac_syncache_init(&maclabel) != 0) { 1470 INP_RUNLOCK(inp); 1471 goto done; 1472 } else 1473 mac_syncache_create(maclabel, inp); 1474 #endif 1475 if (!tfo_cookie_valid) 1476 INP_RUNLOCK(inp); 1477 1478 /* 1479 * Remember the IP options, if any. 1480 */ 1481 #ifdef INET6 1482 if (!(inc->inc_flags & INC_ISIPV6)) 1483 #endif 1484 #ifdef INET 1485 ipopts = (m) ? ip_srcroute(m) : NULL; 1486 #else 1487 ipopts = NULL; 1488 #endif 1489 1490 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1491 /* 1492 * When the socket is TCP-MD5 enabled check that, 1493 * - a signed packet is valid 1494 * - a non-signed packet does not have a security association 1495 * 1496 * If a signed packet fails validation or a non-signed packet has a 1497 * security association, the packet will be dropped. 1498 */ 1499 if (ltflags & TF_SIGNATURE) { 1500 if (to->to_flags & TOF_SIGNATURE) { 1501 if (!TCPMD5_ENABLED() || 1502 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1503 goto done; 1504 } else { 1505 if (TCPMD5_ENABLED() && 1506 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1507 goto done; 1508 } 1509 } else if (to->to_flags & TOF_SIGNATURE) 1510 goto done; 1511 #endif /* TCP_SIGNATURE */ 1512 /* 1513 * See if we already have an entry for this connection. 1514 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1515 * 1516 * XXX: should the syncache be re-initialized with the contents 1517 * of the new SYN here (which may have different options?) 1518 * 1519 * XXX: We do not check the sequence number to see if this is a 1520 * real retransmit or a new connection attempt. The question is 1521 * how to handle such a case; either ignore it as spoofed, or 1522 * drop the current entry and create a new one? 1523 */ 1524 if (syncache_cookiesonly()) { 1525 sc = NULL; 1526 sch = syncache_hashbucket(inc); 1527 locked = false; 1528 } else { 1529 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1530 locked = true; 1531 SCH_LOCK_ASSERT(sch); 1532 } 1533 if (sc != NULL) { 1534 if (tfo_cookie_valid) 1535 INP_RUNLOCK(inp); 1536 TCPSTAT_INC(tcps_sc_dupsyn); 1537 if (ipopts) { 1538 /* 1539 * If we were remembering a previous source route, 1540 * forget it and use the new one we've been given. 1541 */ 1542 if (sc->sc_ipopts) 1543 (void)m_free(sc->sc_ipopts); 1544 sc->sc_ipopts = ipopts; 1545 } 1546 /* 1547 * Update timestamp if present. 1548 */ 1549 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1550 sc->sc_tsreflect = to->to_tsval; 1551 else 1552 sc->sc_flags &= ~SCF_TIMESTAMP; 1553 /* 1554 * Adjust ECN response if needed, e.g. different 1555 * IP ECN field, or a fallback by the remote host. 1556 */ 1557 if (sc->sc_flags & SCF_ECN_MASK) { 1558 sc->sc_flags &= ~SCF_ECN_MASK; 1559 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1560 } 1561 #ifdef MAC 1562 /* 1563 * Since we have already unconditionally allocated label 1564 * storage, free it up. The syncache entry will already 1565 * have an initialized label we can use. 1566 */ 1567 mac_syncache_destroy(&maclabel); 1568 #endif 1569 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1570 /* Retransmit SYN|ACK and reset retransmit count. */ 1571 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1572 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1573 "resetting timer and retransmitting SYN|ACK\n", 1574 s, __func__); 1575 free(s, M_TCPLOG); 1576 } 1577 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1578 sc->sc_rxmits = 0; 1579 syncache_timeout(sc, sch, 1); 1580 TCPSTAT_INC(tcps_sndacks); 1581 TCPSTAT_INC(tcps_sndtotal); 1582 } else { 1583 syncache_drop(sc, sch); 1584 TCPSTAT_INC(tcps_sc_dropped); 1585 } 1586 SCH_UNLOCK(sch); 1587 goto donenoprobe; 1588 } 1589 1590 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1591 /* 1592 * Skip allocating a syncache entry if we are just going to discard 1593 * it later. 1594 */ 1595 if (!locked || tfo_cookie_valid) { 1596 bzero(&scs, sizeof(scs)); 1597 sc = &scs; 1598 } else { 1599 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1600 if (sc == NULL) { 1601 /* 1602 * The zone allocator couldn't provide more entries. 1603 * Treat this as if the cache was full; drop the oldest 1604 * entry and insert the new one. 1605 */ 1606 TCPSTAT_INC(tcps_sc_zonefail); 1607 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1608 if (sc != NULL) { 1609 sch->sch_last_overflow = time_uptime; 1610 syncache_drop(sc, sch); 1611 syncache_pause(inc); 1612 } 1613 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1614 if (sc == NULL) { 1615 if (V_tcp_syncookies) { 1616 bzero(&scs, sizeof(scs)); 1617 sc = &scs; 1618 } else { 1619 KASSERT(locked, 1620 ("%s: bucket unexpectedly unlocked", 1621 __func__)); 1622 SCH_UNLOCK(sch); 1623 goto done; 1624 } 1625 } 1626 } 1627 } 1628 1629 KASSERT(sc != NULL, ("sc == NULL")); 1630 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1631 sc->sc_tfo_cookie = &tfo_response_cookie; 1632 1633 /* 1634 * Fill in the syncache values. 1635 */ 1636 #ifdef MAC 1637 sc->sc_label = maclabel; 1638 #endif 1639 /* 1640 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1641 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1642 * Therefore, store the credentials and take a reference count only 1643 * when needed: 1644 * - sc is allocated from the zone and not using the on stack instance. 1645 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1646 * The reference count is decremented when a zone allocated sc is 1647 * freed in syncache_free(). 1648 */ 1649 if (sc != &scs && !V_tcp_syncache.see_other) 1650 sc->sc_cred = crhold(so->so_cred); 1651 else 1652 sc->sc_cred = NULL; 1653 sc->sc_port = port; 1654 sc->sc_ipopts = ipopts; 1655 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1656 sc->sc_ip_tos = ip_tos; 1657 sc->sc_ip_ttl = ip_ttl; 1658 #ifdef TCP_OFFLOAD 1659 sc->sc_tod = tod; 1660 sc->sc_todctx = todctx; 1661 #endif 1662 sc->sc_irs = th->th_seq; 1663 sc->sc_flags = 0; 1664 sc->sc_flowlabel = 0; 1665 1666 /* 1667 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1668 * win was derived from socket earlier in the function. 1669 */ 1670 win = imax(win, 0); 1671 win = imin(win, TCP_MAXWIN); 1672 sc->sc_wnd = win; 1673 1674 if (V_tcp_do_rfc1323 && 1675 !(ltflags & TF_NOOPT)) { 1676 /* 1677 * A timestamp received in a SYN makes 1678 * it ok to send timestamp requests and replies. 1679 */ 1680 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1681 sc->sc_tsreflect = to->to_tsval; 1682 sc->sc_flags |= SCF_TIMESTAMP; 1683 sc->sc_tsoff = tcp_new_ts_offset(inc); 1684 } 1685 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1686 u_int wscale = 0; 1687 1688 /* 1689 * Pick the smallest possible scaling factor that 1690 * will still allow us to scale up to sb_max, aka 1691 * kern.ipc.maxsockbuf. 1692 * 1693 * We do this because there are broken firewalls that 1694 * will corrupt the window scale option, leading to 1695 * the other endpoint believing that our advertised 1696 * window is unscaled. At scale factors larger than 1697 * 5 the unscaled window will drop below 1500 bytes, 1698 * leading to serious problems when traversing these 1699 * broken firewalls. 1700 * 1701 * With the default maxsockbuf of 256K, a scale factor 1702 * of 3 will be chosen by this algorithm. Those who 1703 * choose a larger maxsockbuf should watch out 1704 * for the compatibility problems mentioned above. 1705 * 1706 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1707 * or <SYN,ACK>) segment itself is never scaled. 1708 */ 1709 while (wscale < TCP_MAX_WINSHIFT && 1710 (TCP_MAXWIN << wscale) < sb_max) 1711 wscale++; 1712 sc->sc_requested_r_scale = wscale; 1713 sc->sc_requested_s_scale = to->to_wscale; 1714 sc->sc_flags |= SCF_WINSCALE; 1715 } 1716 } 1717 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1718 /* 1719 * If incoming packet has an MD5 signature, flag this in the 1720 * syncache so that syncache_respond() will do the right thing 1721 * with the SYN+ACK. 1722 */ 1723 if (to->to_flags & TOF_SIGNATURE) 1724 sc->sc_flags |= SCF_SIGNATURE; 1725 #endif /* TCP_SIGNATURE */ 1726 if (to->to_flags & TOF_SACKPERM) 1727 sc->sc_flags |= SCF_SACK; 1728 if (to->to_flags & TOF_MSS) 1729 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1730 if (ltflags & TF_NOOPT) 1731 sc->sc_flags |= SCF_NOOPT; 1732 /* ECN Handshake */ 1733 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1734 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1735 1736 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1737 sc->sc_iss = syncookie_generate(sch, sc); 1738 else 1739 sc->sc_iss = arc4random(); 1740 #ifdef INET6 1741 if (autoflowlabel) { 1742 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1743 sc->sc_flowlabel = sc->sc_iss; 1744 else 1745 sc->sc_flowlabel = ip6_randomflowlabel(); 1746 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1747 } 1748 #endif 1749 if (locked) 1750 SCH_UNLOCK(sch); 1751 1752 if (tfo_cookie_valid) { 1753 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1754 /* INP_RUNLOCK(inp) will be performed by the caller */ 1755 goto tfo_expanded; 1756 } 1757 1758 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1759 /* 1760 * Do a standard 3-way handshake. 1761 */ 1762 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1763 if (sc != &scs) 1764 syncache_insert(sc, sch); /* locks and unlocks sch */ 1765 TCPSTAT_INC(tcps_sndacks); 1766 TCPSTAT_INC(tcps_sndtotal); 1767 } else { 1768 if (sc != &scs) 1769 syncache_free(sc); 1770 TCPSTAT_INC(tcps_sc_dropped); 1771 } 1772 goto donenoprobe; 1773 1774 done: 1775 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1776 donenoprobe: 1777 if (m) 1778 m_freem(m); 1779 /* 1780 * If tfo_pending is not NULL here, then a TFO SYN that did not 1781 * result in a new socket was processed and the associated pending 1782 * counter has not yet been decremented. All such TFO processing paths 1783 * transit this point. 1784 */ 1785 if (tfo_pending != NULL) 1786 tcp_fastopen_decrement_counter(tfo_pending); 1787 1788 tfo_expanded: 1789 if (sc == NULL || sc == &scs) { 1790 #ifdef MAC 1791 mac_syncache_destroy(&maclabel); 1792 #endif 1793 if (ipopts) 1794 (void)m_free(ipopts); 1795 } 1796 return (rv); 1797 } 1798 1799 /* 1800 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1801 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1802 */ 1803 static int 1804 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1805 { 1806 struct ip *ip = NULL; 1807 struct mbuf *m; 1808 struct tcphdr *th = NULL; 1809 struct udphdr *udp = NULL; 1810 int optlen, error = 0; /* Make compiler happy */ 1811 u_int16_t hlen, tlen, mssopt, ulen; 1812 struct tcpopt to; 1813 #ifdef INET6 1814 struct ip6_hdr *ip6 = NULL; 1815 #endif 1816 1817 NET_EPOCH_ASSERT(); 1818 1819 hlen = 1820 #ifdef INET6 1821 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1822 #endif 1823 sizeof(struct ip); 1824 tlen = hlen + sizeof(struct tcphdr); 1825 if (sc->sc_port) { 1826 tlen += sizeof(struct udphdr); 1827 } 1828 /* Determine MSS we advertize to other end of connection. */ 1829 mssopt = tcp_mssopt(&sc->sc_inc); 1830 if (sc->sc_port) 1831 mssopt -= V_tcp_udp_tunneling_overhead; 1832 mssopt = max(mssopt, V_tcp_minmss); 1833 1834 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1835 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1836 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1837 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1838 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1839 1840 /* Create the IP+TCP header from scratch. */ 1841 m = m_gethdr(M_NOWAIT, MT_DATA); 1842 if (m == NULL) 1843 return (ENOBUFS); 1844 #ifdef MAC 1845 mac_syncache_create_mbuf(sc->sc_label, m); 1846 #endif 1847 m->m_data += max_linkhdr; 1848 m->m_len = tlen; 1849 m->m_pkthdr.len = tlen; 1850 m->m_pkthdr.rcvif = NULL; 1851 1852 #ifdef INET6 1853 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1854 ip6 = mtod(m, struct ip6_hdr *); 1855 ip6->ip6_vfc = IPV6_VERSION; 1856 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1857 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1858 ip6->ip6_plen = htons(tlen - hlen); 1859 /* ip6_hlim is set after checksum */ 1860 /* Zero out traffic class and flow label. */ 1861 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1862 ip6->ip6_flow |= sc->sc_flowlabel; 1863 if (sc->sc_port != 0) { 1864 ip6->ip6_nxt = IPPROTO_UDP; 1865 udp = (struct udphdr *)(ip6 + 1); 1866 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1867 udp->uh_dport = sc->sc_port; 1868 ulen = (tlen - sizeof(struct ip6_hdr)); 1869 th = (struct tcphdr *)(udp + 1); 1870 } else { 1871 ip6->ip6_nxt = IPPROTO_TCP; 1872 th = (struct tcphdr *)(ip6 + 1); 1873 } 1874 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1875 } 1876 #endif 1877 #if defined(INET6) && defined(INET) 1878 else 1879 #endif 1880 #ifdef INET 1881 { 1882 ip = mtod(m, struct ip *); 1883 ip->ip_v = IPVERSION; 1884 ip->ip_hl = sizeof(struct ip) >> 2; 1885 ip->ip_len = htons(tlen); 1886 ip->ip_id = 0; 1887 ip->ip_off = 0; 1888 ip->ip_sum = 0; 1889 ip->ip_src = sc->sc_inc.inc_laddr; 1890 ip->ip_dst = sc->sc_inc.inc_faddr; 1891 ip->ip_ttl = sc->sc_ip_ttl; 1892 ip->ip_tos = sc->sc_ip_tos; 1893 1894 /* 1895 * See if we should do MTU discovery. Route lookups are 1896 * expensive, so we will only unset the DF bit if: 1897 * 1898 * 1) path_mtu_discovery is disabled 1899 * 2) the SCF_UNREACH flag has been set 1900 */ 1901 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1902 ip->ip_off |= htons(IP_DF); 1903 if (sc->sc_port == 0) { 1904 ip->ip_p = IPPROTO_TCP; 1905 th = (struct tcphdr *)(ip + 1); 1906 } else { 1907 ip->ip_p = IPPROTO_UDP; 1908 udp = (struct udphdr *)(ip + 1); 1909 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1910 udp->uh_dport = sc->sc_port; 1911 ulen = (tlen - sizeof(struct ip)); 1912 th = (struct tcphdr *)(udp + 1); 1913 } 1914 } 1915 #endif /* INET */ 1916 th->th_sport = sc->sc_inc.inc_lport; 1917 th->th_dport = sc->sc_inc.inc_fport; 1918 1919 if (flags & TH_SYN) 1920 th->th_seq = htonl(sc->sc_iss); 1921 else 1922 th->th_seq = htonl(sc->sc_iss + 1); 1923 th->th_ack = htonl(sc->sc_irs + 1); 1924 th->th_off = sizeof(struct tcphdr) >> 2; 1925 th->th_win = htons(sc->sc_wnd); 1926 th->th_urp = 0; 1927 1928 flags = tcp_ecn_syncache_respond(flags, sc); 1929 tcp_set_flags(th, flags); 1930 1931 /* Tack on the TCP options. */ 1932 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1933 to.to_flags = 0; 1934 1935 if (flags & TH_SYN) { 1936 to.to_mss = mssopt; 1937 to.to_flags = TOF_MSS; 1938 if (sc->sc_flags & SCF_WINSCALE) { 1939 to.to_wscale = sc->sc_requested_r_scale; 1940 to.to_flags |= TOF_SCALE; 1941 } 1942 if (sc->sc_flags & SCF_SACK) 1943 to.to_flags |= TOF_SACKPERM; 1944 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1945 if (sc->sc_flags & SCF_SIGNATURE) 1946 to.to_flags |= TOF_SIGNATURE; 1947 #endif 1948 if (sc->sc_tfo_cookie) { 1949 to.to_flags |= TOF_FASTOPEN; 1950 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1951 to.to_tfo_cookie = sc->sc_tfo_cookie; 1952 /* don't send cookie again when retransmitting response */ 1953 sc->sc_tfo_cookie = NULL; 1954 } 1955 } 1956 if (sc->sc_flags & SCF_TIMESTAMP) { 1957 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1958 to.to_tsecr = sc->sc_tsreflect; 1959 to.to_flags |= TOF_TS; 1960 } 1961 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1962 1963 /* Adjust headers by option size. */ 1964 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1965 m->m_len += optlen; 1966 m->m_pkthdr.len += optlen; 1967 #ifdef INET6 1968 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1969 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1970 else 1971 #endif 1972 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1973 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1974 if (sc->sc_flags & SCF_SIGNATURE) { 1975 KASSERT(to.to_flags & TOF_SIGNATURE, 1976 ("tcp_addoptions() didn't set tcp_signature")); 1977 1978 /* NOTE: to.to_signature is inside of mbuf */ 1979 if (!TCPMD5_ENABLED() || 1980 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1981 m_freem(m); 1982 return (EACCES); 1983 } 1984 } 1985 #endif 1986 } else 1987 optlen = 0; 1988 1989 if (udp) { 1990 ulen += optlen; 1991 udp->uh_ulen = htons(ulen); 1992 } 1993 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1994 /* 1995 * If we have peer's SYN and it has a flowid, then let's assign it to 1996 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1997 * to SYN|ACK due to lack of inp here. 1998 */ 1999 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2000 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2001 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2002 } 2003 #ifdef INET6 2004 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2005 if (sc->sc_port) { 2006 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2007 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2008 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2009 IPPROTO_UDP, 0); 2010 th->th_sum = htons(0); 2011 } else { 2012 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2013 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2014 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2015 IPPROTO_TCP, 0); 2016 } 2017 ip6->ip6_hlim = sc->sc_ip_ttl; 2018 #ifdef TCP_OFFLOAD 2019 if (ADDED_BY_TOE(sc)) { 2020 struct toedev *tod = sc->sc_tod; 2021 2022 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2023 2024 return (error); 2025 } 2026 #endif 2027 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2028 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2029 } 2030 #endif 2031 #if defined(INET6) && defined(INET) 2032 else 2033 #endif 2034 #ifdef INET 2035 { 2036 if (sc->sc_port) { 2037 m->m_pkthdr.csum_flags = CSUM_UDP; 2038 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2039 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2040 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2041 th->th_sum = htons(0); 2042 } else { 2043 m->m_pkthdr.csum_flags = CSUM_TCP; 2044 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2045 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2046 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2047 } 2048 #ifdef TCP_OFFLOAD 2049 if (ADDED_BY_TOE(sc)) { 2050 struct toedev *tod = sc->sc_tod; 2051 2052 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2053 2054 return (error); 2055 } 2056 #endif 2057 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2058 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2059 } 2060 #endif 2061 return (error); 2062 } 2063 2064 static void 2065 syncache_send_challenge_ack(struct syncache *sc, struct mbuf *m) 2066 { 2067 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2068 &sc->sc_challenge_ack_cnt)) { 2069 if (syncache_respond(sc, m, TH_ACK) == 0) { 2070 TCPSTAT_INC(tcps_sndacks); 2071 TCPSTAT_INC(tcps_sndtotal); 2072 } 2073 } 2074 } 2075 2076 /* 2077 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2078 * that exceed the capacity of the syncache by avoiding the storage of any 2079 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2080 * attacks where the attacker does not have access to our responses. 2081 * 2082 * Syncookies encode and include all necessary information about the 2083 * connection setup within the SYN|ACK that we send back. That way we 2084 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2085 * (if ever). Normally the syncache and syncookies are running in parallel 2086 * with the latter taking over when the former is exhausted. When matching 2087 * syncache entry is found the syncookie is ignored. 2088 * 2089 * The only reliable information persisting the 3WHS is our initial sequence 2090 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2091 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2092 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2093 * returns and signifies a legitimate connection if it matches the ACK. 2094 * 2095 * The available space of 32 bits to store the hash and to encode the SYN 2096 * option information is very tight and we should have at least 24 bits for 2097 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2098 * 2099 * SYN option information we have to encode to fully restore a connection: 2100 * MSS: is imporant to chose an optimal segment size to avoid IP level 2101 * fragmentation along the path. The common MSS values can be encoded 2102 * in a 3-bit table. Uncommon values are captured by the next lower value 2103 * in the table leading to a slight increase in packetization overhead. 2104 * WSCALE: is necessary to allow large windows to be used for high delay- 2105 * bandwidth product links. Not scaling the window when it was initially 2106 * negotiated is bad for performance as lack of scaling further decreases 2107 * the apparent available send window. We only need to encode the WSCALE 2108 * we received from the remote end. Our end can be recalculated at any 2109 * time. The common WSCALE values can be encoded in a 3-bit table. 2110 * Uncommon values are captured by the next lower value in the table 2111 * making us under-estimate the available window size halving our 2112 * theoretically possible maximum throughput for that connection. 2113 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2114 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2115 * that are included in all segments on a connection. We enable them when 2116 * the ACK has them. 2117 * 2118 * Security of syncookies and attack vectors: 2119 * 2120 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2121 * together with the gloabl secret to make it unique per connection attempt. 2122 * Thus any change of any of those parameters results in a different MAC output 2123 * in an unpredictable way unless a collision is encountered. 24 bits of the 2124 * MAC are embedded into the ISS. 2125 * 2126 * To prevent replay attacks two rotating global secrets are updated with a 2127 * new random value every 15 seconds. The life-time of a syncookie is thus 2128 * 15-30 seconds. 2129 * 2130 * Vector 1: Attacking the secret. This requires finding a weakness in the 2131 * MAC itself or the way it is used here. The attacker can do a chosen plain 2132 * text attack by varying and testing the all parameters under his control. 2133 * The strength depends on the size and randomness of the secret, and the 2134 * cryptographic security of the MAC function. Due to the constant updating 2135 * of the secret the attacker has at most 29.999 seconds to find the secret 2136 * and launch spoofed connections. After that he has to start all over again. 2137 * 2138 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2139 * size an average of 4,823 attempts are required for a 50% chance of success 2140 * to spoof a single syncookie (birthday collision paradox). However the 2141 * attacker is blind and doesn't know if one of his attempts succeeded unless 2142 * he has a side channel to interfere success from. A single connection setup 2143 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2144 * This many attempts are required for each one blind spoofed connection. For 2145 * every additional spoofed connection he has to launch another N attempts. 2146 * Thus for a sustained rate 100 spoofed connections per second approximately 2147 * 1,800,000 packets per second would have to be sent. 2148 * 2149 * NB: The MAC function should be fast so that it doesn't become a CPU 2150 * exhaustion attack vector itself. 2151 * 2152 * References: 2153 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2154 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2155 * http://cr.yp.to/syncookies.html (overview) 2156 * http://cr.yp.to/syncookies/archive (details) 2157 * 2158 * 2159 * Schematic construction of a syncookie enabled Initial Sequence Number: 2160 * 0 1 2 3 2161 * 12345678901234567890123456789012 2162 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2163 * 2164 * x 24 MAC (truncated) 2165 * W 3 Send Window Scale index 2166 * M 3 MSS index 2167 * S 1 SACK permitted 2168 * P 1 Odd/even secret 2169 */ 2170 2171 /* 2172 * Distribution and probability of certain MSS values. Those in between are 2173 * rounded down to the next lower one. 2174 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2175 * .2% .3% 5% 7% 7% 20% 15% 45% 2176 */ 2177 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2178 2179 /* 2180 * Distribution and probability of certain WSCALE values. We have to map the 2181 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2182 * bits based on prevalence of certain values. Where we don't have an exact 2183 * match for are rounded down to the next lower one letting us under-estimate 2184 * the true available window. At the moment this would happen only for the 2185 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2186 * and window size). The absence of the WSCALE option (no scaling in either 2187 * direction) is encoded with index zero. 2188 * [WSCALE values histograms, Allman, 2012] 2189 * X 10 10 35 5 6 14 10% by host 2190 * X 11 4 5 5 18 49 3% by connections 2191 */ 2192 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2193 2194 /* 2195 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2196 * and good cryptographic properties. 2197 */ 2198 static uint32_t 2199 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2200 uint8_t *secbits, uintptr_t secmod) 2201 { 2202 SIPHASH_CTX ctx; 2203 uint32_t siphash[2]; 2204 2205 SipHash24_Init(&ctx); 2206 SipHash_SetKey(&ctx, secbits); 2207 switch (inc->inc_flags & INC_ISIPV6) { 2208 #ifdef INET 2209 case 0: 2210 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2211 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2212 break; 2213 #endif 2214 #ifdef INET6 2215 case INC_ISIPV6: 2216 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2217 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2218 break; 2219 #endif 2220 } 2221 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2222 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2223 SipHash_Update(&ctx, &irs, sizeof(irs)); 2224 SipHash_Update(&ctx, &flags, sizeof(flags)); 2225 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2226 SipHash_Final((u_int8_t *)&siphash, &ctx); 2227 2228 return (siphash[0] ^ siphash[1]); 2229 } 2230 2231 static tcp_seq 2232 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2233 { 2234 u_int i, secbit, wscale; 2235 uint32_t iss, hash; 2236 uint8_t *secbits; 2237 union syncookie cookie; 2238 2239 cookie.cookie = 0; 2240 2241 /* Map our computed MSS into the 3-bit index. */ 2242 for (i = nitems(tcp_sc_msstab) - 1; 2243 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2244 i--) 2245 ; 2246 cookie.flags.mss_idx = i; 2247 2248 /* 2249 * Map the send window scale into the 3-bit index but only if 2250 * the wscale option was received. 2251 */ 2252 if (sc->sc_flags & SCF_WINSCALE) { 2253 wscale = sc->sc_requested_s_scale; 2254 for (i = nitems(tcp_sc_wstab) - 1; 2255 tcp_sc_wstab[i] > wscale && i > 0; 2256 i--) 2257 ; 2258 cookie.flags.wscale_idx = i; 2259 } 2260 2261 /* Can we do SACK? */ 2262 if (sc->sc_flags & SCF_SACK) 2263 cookie.flags.sack_ok = 1; 2264 2265 /* Which of the two secrets to use. */ 2266 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2267 cookie.flags.odd_even = secbit; 2268 2269 secbits = V_tcp_syncache.secret.key[secbit]; 2270 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2271 (uintptr_t)sch); 2272 2273 /* 2274 * Put the flags into the hash and XOR them to get better ISS number 2275 * variance. This doesn't enhance the cryptographic strength and is 2276 * done to prevent the 8 cookie bits from showing up directly on the 2277 * wire. 2278 */ 2279 iss = hash & ~0xff; 2280 iss |= cookie.cookie ^ (hash >> 24); 2281 2282 TCPSTAT_INC(tcps_sc_sendcookie); 2283 return (iss); 2284 } 2285 2286 static bool 2287 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2288 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2289 struct socket *lso, uint16_t port) 2290 { 2291 uint32_t hash; 2292 uint8_t *secbits; 2293 tcp_seq ack, seq; 2294 int wnd; 2295 union syncookie cookie; 2296 2297 /* 2298 * Pull information out of SYN-ACK/ACK and revert sequence number 2299 * advances. 2300 */ 2301 ack = th->th_ack - 1; 2302 seq = th->th_seq - 1; 2303 2304 /* 2305 * Unpack the flags containing enough information to restore the 2306 * connection. 2307 */ 2308 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2309 2310 /* Which of the two secrets to use. */ 2311 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2312 2313 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2314 2315 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2316 if ((ack & ~0xff) != (hash & ~0xff)) 2317 return (false); 2318 2319 /* Fill in the syncache values. */ 2320 sc->sc_flags = 0; 2321 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2322 sc->sc_ipopts = NULL; 2323 2324 sc->sc_irs = seq; 2325 sc->sc_iss = ack; 2326 2327 switch (inc->inc_flags & INC_ISIPV6) { 2328 #ifdef INET 2329 case 0: 2330 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2331 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2332 break; 2333 #endif 2334 #ifdef INET6 2335 case INC_ISIPV6: 2336 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2337 sc->sc_flowlabel = 2338 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2339 break; 2340 #endif 2341 } 2342 2343 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2344 2345 /* Only use wscale if it was enabled in the orignal SYN. */ 2346 if (cookie.flags.wscale_idx > 0) { 2347 u_int wscale = 0; 2348 2349 /* Recompute the receive window scale that was sent earlier. */ 2350 while (wscale < TCP_MAX_WINSHIFT && 2351 (TCP_MAXWIN << wscale) < sb_max) 2352 wscale++; 2353 sc->sc_requested_r_scale = wscale; 2354 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2355 sc->sc_flags |= SCF_WINSCALE; 2356 } 2357 2358 wnd = lso->sol_sbrcv_hiwat; 2359 wnd = imax(wnd, 0); 2360 wnd = imin(wnd, TCP_MAXWIN); 2361 sc->sc_wnd = wnd; 2362 2363 if (cookie.flags.sack_ok) 2364 sc->sc_flags |= SCF_SACK; 2365 2366 if (to->to_flags & TOF_TS) { 2367 sc->sc_flags |= SCF_TIMESTAMP; 2368 sc->sc_tsreflect = to->to_tsval; 2369 sc->sc_tsoff = tcp_new_ts_offset(inc); 2370 } 2371 2372 if (to->to_flags & TOF_SIGNATURE) 2373 sc->sc_flags |= SCF_SIGNATURE; 2374 2375 sc->sc_rxmits = 0; 2376 2377 sc->sc_port = port; 2378 2379 return (true); 2380 } 2381 2382 #ifdef INVARIANTS 2383 static void 2384 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2385 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2386 struct socket *lso, uint16_t port) 2387 { 2388 struct syncache scs; 2389 char *s; 2390 2391 bzero(&scs, sizeof(scs)); 2392 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2393 (sc->sc_peer_mss != scs.sc_peer_mss || 2394 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2395 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2396 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2397 2398 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2399 return; 2400 2401 if (sc->sc_peer_mss != scs.sc_peer_mss) 2402 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2403 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2404 2405 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2406 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2407 s, __func__, sc->sc_requested_r_scale, 2408 scs.sc_requested_r_scale); 2409 2410 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2411 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2412 s, __func__, sc->sc_requested_s_scale, 2413 scs.sc_requested_s_scale); 2414 2415 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2416 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2417 2418 free(s, M_TCPLOG); 2419 } 2420 } 2421 #endif /* INVARIANTS */ 2422 2423 static void 2424 syncookie_reseed(void *arg) 2425 { 2426 struct tcp_syncache *sc = arg; 2427 uint8_t *secbits; 2428 int secbit; 2429 2430 /* 2431 * Reseeding the secret doesn't have to be protected by a lock. 2432 * It only must be ensured that the new random values are visible 2433 * to all CPUs in a SMP environment. The atomic with release 2434 * semantics ensures that. 2435 */ 2436 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2437 secbits = sc->secret.key[secbit]; 2438 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2439 atomic_add_rel_int(&sc->secret.oddeven, 1); 2440 2441 /* Reschedule ourself. */ 2442 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2443 } 2444 2445 /* 2446 * We have overflowed a bucket. Let's pause dealing with the syncache. 2447 * This function will increment the bucketoverflow statistics appropriately 2448 * (once per pause when pausing is enabled; otherwise, once per overflow). 2449 */ 2450 static void 2451 syncache_pause(struct in_conninfo *inc) 2452 { 2453 time_t delta; 2454 const char *s; 2455 2456 /* XXX: 2457 * 2. Add sysctl read here so we don't get the benefit of this 2458 * change without the new sysctl. 2459 */ 2460 2461 /* 2462 * Try an unlocked read. If we already know that another thread 2463 * has activated the feature, there is no need to proceed. 2464 */ 2465 if (V_tcp_syncache.paused) 2466 return; 2467 2468 /* Are cookied enabled? If not, we can't pause. */ 2469 if (!V_tcp_syncookies) { 2470 TCPSTAT_INC(tcps_sc_bucketoverflow); 2471 return; 2472 } 2473 2474 /* 2475 * We may be the first thread to find an overflow. Get the lock 2476 * and evaluate if we need to take action. 2477 */ 2478 mtx_lock(&V_tcp_syncache.pause_mtx); 2479 if (V_tcp_syncache.paused) { 2480 mtx_unlock(&V_tcp_syncache.pause_mtx); 2481 return; 2482 } 2483 2484 /* Activate protection. */ 2485 V_tcp_syncache.paused = true; 2486 TCPSTAT_INC(tcps_sc_bucketoverflow); 2487 2488 /* 2489 * Determine the last backoff time. If we are seeing a re-newed 2490 * attack within that same time after last reactivating the syncache, 2491 * consider it an extension of the same attack. 2492 */ 2493 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2494 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2495 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2496 delta <<= 1; 2497 V_tcp_syncache.pause_backoff++; 2498 } 2499 } else { 2500 delta = TCP_SYNCACHE_PAUSE_TIME; 2501 V_tcp_syncache.pause_backoff = 0; 2502 } 2503 2504 /* Log a warning, including IP addresses, if able. */ 2505 if (inc != NULL) 2506 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2507 else 2508 s = (const char *)NULL; 2509 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2510 "the next %lld seconds%s%s%s\n", (long long)delta, 2511 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2512 (s != NULL) ? ")" : ""); 2513 free(__DECONST(void *, s), M_TCPLOG); 2514 2515 /* Use the calculated delta to set a new pause time. */ 2516 V_tcp_syncache.pause_until = time_uptime + delta; 2517 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2518 &V_tcp_syncache); 2519 mtx_unlock(&V_tcp_syncache.pause_mtx); 2520 } 2521 2522 /* Evaluate whether we need to unpause. */ 2523 static void 2524 syncache_unpause(void *arg) 2525 { 2526 struct tcp_syncache *sc; 2527 time_t delta; 2528 2529 sc = arg; 2530 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2531 callout_deactivate(&sc->pause_co); 2532 2533 /* 2534 * Check to make sure we are not running early. If the pause 2535 * time has expired, then deactivate the protection. 2536 */ 2537 if ((delta = sc->pause_until - time_uptime) > 0) 2538 callout_schedule(&sc->pause_co, delta * hz); 2539 else 2540 sc->paused = false; 2541 } 2542 2543 /* 2544 * Exports the syncache entries to userland so that netstat can display 2545 * them alongside the other sockets. This function is intended to be 2546 * called only from tcp_pcblist. 2547 * 2548 * Due to concurrency on an active system, the number of pcbs exported 2549 * may have no relation to max_pcbs. max_pcbs merely indicates the 2550 * amount of space the caller allocated for this function to use. 2551 */ 2552 int 2553 syncache_pcblist(struct sysctl_req *req) 2554 { 2555 struct xtcpcb xt; 2556 struct syncache *sc; 2557 struct syncache_head *sch; 2558 int error, i; 2559 2560 bzero(&xt, sizeof(xt)); 2561 xt.xt_len = sizeof(xt); 2562 xt.t_state = TCPS_SYN_RECEIVED; 2563 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2564 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2565 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2566 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2567 2568 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2569 sch = &V_tcp_syncache.hashbase[i]; 2570 SCH_LOCK(sch); 2571 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2572 if (sc->sc_cred != NULL && 2573 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2574 continue; 2575 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2576 xt.xt_inp.inp_vflag = INP_IPV6; 2577 else 2578 xt.xt_inp.inp_vflag = INP_IPV4; 2579 xt.xt_encaps_port = sc->sc_port; 2580 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2581 sizeof (struct in_conninfo)); 2582 error = SYSCTL_OUT(req, &xt, sizeof xt); 2583 if (error) { 2584 SCH_UNLOCK(sch); 2585 return (0); 2586 } 2587 } 2588 SCH_UNLOCK(sch); 2589 } 2590 2591 return (0); 2592 } 2593