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_unreach(struct in_conninfo *inc, tcp_seq th_seq, 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) 726 goto done; 727 728 /* If the port != sc_port, then it's a bogus ICMP msg */ 729 if (port != sc->sc_port) 730 goto done; 731 732 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 733 if (ntohl(th_seq) != sc->sc_iss) 734 goto done; 735 736 /* 737 * If we've rertransmitted 3 times and this is our second error, 738 * we remove the entry. Otherwise, we allow it to continue on. 739 * This prevents us from incorrectly nuking an entry during a 740 * spurious network outage. 741 * 742 * See tcp_notify(). 743 */ 744 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 745 sc->sc_flags |= SCF_UNREACH; 746 goto done; 747 } 748 syncache_drop(sc, sch); 749 TCPSTAT_INC(tcps_sc_unreach); 750 done: 751 SCH_UNLOCK(sch); 752 } 753 754 /* 755 * Build a new TCP socket structure from a syncache entry. 756 * 757 * On success return the newly created socket with its underlying inp locked. 758 */ 759 static struct socket * 760 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 761 { 762 struct inpcb *inp = NULL; 763 struct socket *so; 764 struct tcpcb *tp; 765 int error; 766 char *s; 767 768 NET_EPOCH_ASSERT(); 769 770 /* 771 * Ok, create the full blown connection, and set things up 772 * as they would have been set up if we had created the 773 * connection when the SYN arrived. 774 */ 775 if ((so = solisten_clone(lso)) == NULL) 776 goto allocfail; 777 #ifdef MAC 778 mac_socketpeer_set_from_mbuf(m, so); 779 #endif 780 error = in_pcballoc(so, &V_tcbinfo); 781 if (error) { 782 sodealloc(so); 783 goto allocfail; 784 } 785 inp = sotoinpcb(so); 786 if ((tp = tcp_newtcpcb(inp, sototcpcb(lso))) == NULL) { 787 in_pcbfree(inp); 788 sodealloc(so); 789 goto allocfail; 790 } 791 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 792 #ifdef INET6 793 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 794 inp->inp_vflag &= ~INP_IPV4; 795 inp->inp_vflag |= INP_IPV6; 796 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 797 } else { 798 inp->inp_vflag &= ~INP_IPV6; 799 inp->inp_vflag |= INP_IPV4; 800 #endif 801 inp->inp_ip_ttl = sc->sc_ip_ttl; 802 inp->inp_ip_tos = sc->sc_ip_tos; 803 inp->inp_laddr = sc->sc_inc.inc_laddr; 804 #ifdef INET6 805 } 806 #endif 807 808 /* 809 * If there's an mbuf and it has a flowid, then let's initialise the 810 * inp with that particular flowid. 811 */ 812 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 813 inp->inp_flowid = m->m_pkthdr.flowid; 814 inp->inp_flowtype = M_HASHTYPE_GET(m); 815 #ifdef NUMA 816 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 817 #endif 818 } 819 820 inp->inp_lport = sc->sc_inc.inc_lport; 821 #ifdef INET6 822 if (inp->inp_vflag & INP_IPV6PROTO) { 823 struct inpcb *oinp = sotoinpcb(lso); 824 825 /* 826 * Inherit socket options from the listening socket. 827 * Note that in6p_inputopts are not (and should not be) 828 * copied, since it stores previously received options and is 829 * used to detect if each new option is different than the 830 * previous one and hence should be passed to a user. 831 * If we copied in6p_inputopts, a user would not be able to 832 * receive options just after calling the accept system call. 833 */ 834 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 835 if (oinp->in6p_outputopts) 836 inp->in6p_outputopts = 837 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 838 inp->in6p_hops = oinp->in6p_hops; 839 } 840 841 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 842 struct sockaddr_in6 sin6; 843 844 sin6.sin6_family = AF_INET6; 845 sin6.sin6_len = sizeof(sin6); 846 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 847 sin6.sin6_port = sc->sc_inc.inc_fport; 848 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 849 INP_HASH_WLOCK(&V_tcbinfo); 850 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 851 INP_HASH_WUNLOCK(&V_tcbinfo); 852 if (error != 0) 853 goto abort; 854 /* Override flowlabel from in6_pcbconnect. */ 855 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 856 inp->inp_flow |= sc->sc_flowlabel; 857 } 858 #endif /* INET6 */ 859 #if defined(INET) && defined(INET6) 860 else 861 #endif 862 #ifdef INET 863 { 864 struct sockaddr_in sin; 865 866 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 867 868 if (inp->inp_options == NULL) { 869 inp->inp_options = sc->sc_ipopts; 870 sc->sc_ipopts = NULL; 871 } 872 873 sin.sin_family = AF_INET; 874 sin.sin_len = sizeof(sin); 875 sin.sin_addr = sc->sc_inc.inc_faddr; 876 sin.sin_port = sc->sc_inc.inc_fport; 877 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 878 INP_HASH_WLOCK(&V_tcbinfo); 879 error = in_pcbconnect(inp, &sin, thread0.td_ucred); 880 INP_HASH_WUNLOCK(&V_tcbinfo); 881 if (error != 0) 882 goto abort; 883 } 884 #endif /* INET */ 885 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 886 /* Copy old policy into new socket's. */ 887 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 888 printf("syncache_socket: could not copy policy\n"); 889 #endif 890 tp->t_state = TCPS_SYN_RECEIVED; 891 tp->iss = sc->sc_iss; 892 tp->irs = sc->sc_irs; 893 tp->t_port = sc->sc_port; 894 tcp_rcvseqinit(tp); 895 tcp_sendseqinit(tp); 896 tp->snd_wl1 = sc->sc_irs; 897 tp->snd_max = tp->iss + 1; 898 tp->snd_nxt = tp->iss + 1; 899 tp->rcv_up = sc->sc_irs + 1; 900 tp->rcv_wnd = sc->sc_wnd; 901 tp->rcv_adv += tp->rcv_wnd; 902 tp->last_ack_sent = tp->rcv_nxt; 903 904 tp->t_flags = sototcpcb(lso)->t_flags & 905 (TF_LRD|TF_NOPUSH|TF_NODELAY); 906 if (sc->sc_flags & SCF_NOOPT) 907 tp->t_flags |= TF_NOOPT; 908 else { 909 if (sc->sc_flags & SCF_WINSCALE) { 910 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 911 tp->snd_scale = sc->sc_requested_s_scale; 912 tp->request_r_scale = sc->sc_requested_r_scale; 913 } 914 if (sc->sc_flags & SCF_TIMESTAMP) { 915 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 916 tp->ts_recent = sc->sc_tsreflect; 917 tp->ts_recent_age = tcp_ts_getticks(); 918 tp->ts_offset = sc->sc_tsoff; 919 } 920 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 921 if (sc->sc_flags & SCF_SIGNATURE) 922 tp->t_flags |= TF_SIGNATURE; 923 #endif 924 if (sc->sc_flags & SCF_SACK) 925 tp->t_flags |= TF_SACK_PERMIT; 926 } 927 928 tcp_ecn_syncache_socket(tp, sc); 929 930 /* 931 * Set up MSS and get cached values from tcp_hostcache. 932 * This might overwrite some of the defaults we just set. 933 */ 934 tcp_mss(tp, sc->sc_peer_mss); 935 936 /* 937 * If the SYN,ACK was retransmitted, indicate that CWND to be 938 * limited to one segment in cc_conn_init(). 939 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 940 */ 941 if (sc->sc_rxmits > 1) 942 tp->snd_cwnd = 1; 943 944 /* Copy over the challenge ACK state. */ 945 tp->t_challenge_ack_end = sc->sc_challenge_ack_end; 946 tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; 947 948 #ifdef TCP_OFFLOAD 949 /* 950 * Allow a TOE driver to install its hooks. Note that we hold the 951 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 952 * new connection before the TOE driver has done its thing. 953 */ 954 if (ADDED_BY_TOE(sc)) { 955 struct toedev *tod = sc->sc_tod; 956 957 tod->tod_offload_socket(tod, sc->sc_todctx, so); 958 } 959 #endif 960 #ifdef TCP_BLACKBOX 961 /* 962 * Inherit the log state from the listening socket, if 963 * - the log state of the listening socket is not off and 964 * - the listening socket was not auto selected from all sessions and 965 * - a log id is not set on the listening socket. 966 * This avoids inheriting a log state which was automatically set. 967 */ 968 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 969 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 970 (sototcpcb(lso)->t_lib == NULL)) { 971 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 972 } 973 #endif 974 /* 975 * Copy and activate timers. 976 */ 977 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 978 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 979 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 980 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 981 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 982 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 983 984 TCPSTAT_INC(tcps_accepts); 985 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 986 987 if (!solisten_enqueue(so, SS_ISCONNECTED)) 988 tp->t_flags |= TF_SONOTCONN; 989 /* Can we inherit anything from the listener? */ 990 if (tp->t_fb->tfb_inherit != NULL) { 991 (*tp->t_fb->tfb_inherit)(tp, sotoinpcb(lso)); 992 } 993 return (so); 994 995 allocfail: 996 /* 997 * Drop the connection; we will either send a RST or have the peer 998 * retransmit its SYN again after its RTO and try again. 999 */ 1000 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1001 log(LOG_DEBUG, "%s; %s: Socket create failed " 1002 "due to limits or memory shortage\n", 1003 s, __func__); 1004 free(s, M_TCPLOG); 1005 } 1006 TCPSTAT_INC(tcps_listendrop); 1007 return (NULL); 1008 1009 abort: 1010 tcp_discardcb(tp); 1011 in_pcbfree(inp); 1012 sodealloc(so); 1013 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1014 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1015 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1016 error); 1017 free(s, M_TCPLOG); 1018 } 1019 TCPSTAT_INC(tcps_listendrop); 1020 return (NULL); 1021 } 1022 1023 /* 1024 * This function gets called when we receive an ACK for a 1025 * socket in the LISTEN state. We look up the connection 1026 * in the syncache, and if its there, we pull it out of 1027 * the cache and turn it into a full-blown connection in 1028 * the SYN-RECEIVED state. 1029 * 1030 * On syncache_socket() success the newly created socket 1031 * has its underlying inp locked. 1032 * 1033 * *lsop is updated, if and only if 1 is returned. 1034 */ 1035 int 1036 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1037 struct socket **lsop, struct mbuf *m, uint16_t port) 1038 { 1039 struct syncache *sc; 1040 struct syncache_head *sch; 1041 struct syncache scs; 1042 char *s; 1043 bool locked; 1044 1045 NET_EPOCH_ASSERT(); 1046 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1047 ("%s: can handle only ACK", __func__)); 1048 1049 if (syncache_cookiesonly()) { 1050 sc = NULL; 1051 sch = syncache_hashbucket(inc); 1052 locked = false; 1053 } else { 1054 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1055 locked = true; 1056 SCH_LOCK_ASSERT(sch); 1057 } 1058 1059 #ifdef INVARIANTS 1060 /* 1061 * Test code for syncookies comparing the syncache stored 1062 * values with the reconstructed values from the cookie. 1063 */ 1064 if (sc != NULL) 1065 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1066 #endif 1067 1068 if (sc == NULL) { 1069 if (locked) { 1070 /* 1071 * The syncache is currently in use (neither disabled, 1072 * nor paused), but no entry was found. 1073 */ 1074 if (!V_tcp_syncookies) { 1075 /* 1076 * Since no syncookies are used in case of 1077 * a bucket overflow, don't even check for 1078 * a valid syncookie. 1079 */ 1080 SCH_UNLOCK(sch); 1081 TCPSTAT_INC(tcps_sc_spurcookie); 1082 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1083 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1084 "segment rejected " 1085 "(syncookies disabled)\n", 1086 s, __func__); 1087 free(s, M_TCPLOG); 1088 } 1089 return (0); 1090 } 1091 if (sch->sch_last_overflow < 1092 time_uptime - SYNCOOKIE_LIFETIME) { 1093 /* 1094 * Since the bucket did not overflow recently, 1095 * don't even check for 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 "(no syncache entry)\n", 1103 s, __func__); 1104 free(s, M_TCPLOG); 1105 } 1106 return (0); 1107 } 1108 SCH_UNLOCK(sch); 1109 } 1110 bzero(&scs, sizeof(scs)); 1111 /* 1112 * Now check, if the syncookie is valid. If it is, create an on 1113 * stack syncache entry. 1114 */ 1115 if (syncookie_expand(inc, sch, &scs, th, to, *lsop, port)) { 1116 sc = &scs; 1117 TCPSTAT_INC(tcps_sc_recvcookie); 1118 } else { 1119 TCPSTAT_INC(tcps_sc_failcookie); 1120 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1121 log(LOG_DEBUG, "%s; %s: Segment failed " 1122 "SYNCOOKIE authentication, segment rejected " 1123 "(probably spoofed)\n", s, __func__); 1124 free(s, M_TCPLOG); 1125 } 1126 return (0); 1127 } 1128 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1129 /* If received ACK has MD5 signature, check it. */ 1130 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1131 (!TCPMD5_ENABLED() || 1132 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1133 /* Drop the ACK. */ 1134 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1135 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1136 "MD5 signature doesn't match.\n", 1137 s, __func__); 1138 free(s, M_TCPLOG); 1139 } 1140 TCPSTAT_INC(tcps_sig_err_sigopt); 1141 return (-1); /* Do not send RST */ 1142 } 1143 #endif /* TCP_SIGNATURE */ 1144 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1145 } else { 1146 if (sc->sc_port != port) { 1147 SCH_UNLOCK(sch); 1148 return (0); 1149 } 1150 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1151 /* 1152 * If listening socket requested TCP digests, check that 1153 * received ACK has signature and it is correct. 1154 * If not, drop the ACK and leave sc entry in the cache, 1155 * because SYN was received with correct signature. 1156 */ 1157 if (sc->sc_flags & SCF_SIGNATURE) { 1158 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1159 /* No signature */ 1160 TCPSTAT_INC(tcps_sig_err_nosigopt); 1161 SCH_UNLOCK(sch); 1162 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1163 log(LOG_DEBUG, "%s; %s: Segment " 1164 "rejected, MD5 signature wasn't " 1165 "provided.\n", s, __func__); 1166 free(s, M_TCPLOG); 1167 } 1168 return (-1); /* Do not send RST */ 1169 } 1170 if (!TCPMD5_ENABLED() || 1171 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1172 /* Doesn't match or no SA */ 1173 SCH_UNLOCK(sch); 1174 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1175 log(LOG_DEBUG, "%s; %s: Segment " 1176 "rejected, MD5 signature doesn't " 1177 "match.\n", s, __func__); 1178 free(s, M_TCPLOG); 1179 } 1180 return (-1); /* Do not send RST */ 1181 } 1182 } 1183 #endif /* TCP_SIGNATURE */ 1184 1185 /* 1186 * RFC 7323 PAWS: If we have a timestamp on this segment and 1187 * it's less than ts_recent, drop it. 1188 * XXXMT: RFC 7323 also requires to send an ACK. 1189 * In tcp_input.c this is only done for TCP segments 1190 * with user data, so be consistent here and just drop 1191 * the segment. 1192 */ 1193 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1194 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1195 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1196 log(LOG_DEBUG, 1197 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1198 "segment dropped\n", s, __func__, 1199 to->to_tsval, sc->sc_tsreflect); 1200 } 1201 SCH_UNLOCK(sch); 1202 free(s, M_TCPLOG); 1203 return (-1); /* Do not send RST */ 1204 } 1205 1206 /* 1207 * If timestamps were not negotiated during SYN/ACK and a 1208 * segment with a timestamp is received, ignore the 1209 * timestamp and process the packet normally. 1210 * See section 3.2 of RFC 7323. 1211 */ 1212 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1213 (to->to_flags & TOF_TS)) { 1214 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1215 log(LOG_DEBUG, "%s; %s: Timestamp not " 1216 "expected, segment processed normally\n", 1217 s, __func__); 1218 free(s, M_TCPLOG); 1219 } 1220 } 1221 1222 /* 1223 * If timestamps were negotiated during SYN/ACK and a 1224 * segment without a timestamp is received, silently drop 1225 * the segment, unless the missing timestamps are tolerated. 1226 * See section 3.2 of RFC 7323. 1227 */ 1228 if ((sc->sc_flags & SCF_TIMESTAMP) && 1229 !(to->to_flags & TOF_TS)) { 1230 if (V_tcp_tolerate_missing_ts) { 1231 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1232 log(LOG_DEBUG, 1233 "%s; %s: Timestamp missing, " 1234 "segment processed normally\n", 1235 s, __func__); 1236 free(s, M_TCPLOG); 1237 } 1238 } else { 1239 SCH_UNLOCK(sch); 1240 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1241 log(LOG_DEBUG, 1242 "%s; %s: Timestamp missing, " 1243 "segment silently dropped\n", 1244 s, __func__); 1245 free(s, M_TCPLOG); 1246 } 1247 return (-1); /* Do not send RST */ 1248 } 1249 } 1250 1251 /* 1252 * SEG.SEQ validation: 1253 * The SEG.SEQ must be in the window starting at our 1254 * initial receive sequence number + 1. 1255 */ 1256 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1257 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1258 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1259 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, " 1260 "sending challenge ACK\n", 1261 s, __func__, th->th_seq, sc->sc_irs + 1); 1262 syncache_send_challenge_ack(sc, m); 1263 SCH_UNLOCK(sch); 1264 free(s, M_TCPLOG); 1265 return (-1); /* Do not send RST */ 1266 } 1267 1268 /* 1269 * SEG.ACK validation: 1270 * SEG.ACK must match our initial send sequence number + 1. 1271 */ 1272 if (th->th_ack != sc->sc_iss + 1) { 1273 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1274 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, " 1275 "segment rejected\n", 1276 s, __func__, th->th_ack, sc->sc_iss + 1); 1277 SCH_UNLOCK(sch); 1278 free(s, M_TCPLOG); 1279 return (0); /* Do send RST, do not free sc. */ 1280 } 1281 1282 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1283 sch->sch_length--; 1284 #ifdef TCP_OFFLOAD 1285 if (ADDED_BY_TOE(sc)) { 1286 struct toedev *tod = sc->sc_tod; 1287 1288 tod->tod_syncache_removed(tod, sc->sc_todctx); 1289 } 1290 #endif 1291 SCH_UNLOCK(sch); 1292 } 1293 1294 *lsop = syncache_socket(sc, *lsop, m); 1295 1296 if (__predict_false(*lsop == NULL)) { 1297 TCPSTAT_INC(tcps_sc_aborted); 1298 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1299 } else if (sc != &scs) 1300 TCPSTAT_INC(tcps_sc_completed); 1301 1302 if (sc != &scs) 1303 syncache_free(sc); 1304 return (1); 1305 } 1306 1307 static struct socket * 1308 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1309 uint64_t response_cookie) 1310 { 1311 struct inpcb *inp; 1312 struct tcpcb *tp; 1313 unsigned int *pending_counter; 1314 struct socket *so; 1315 1316 NET_EPOCH_ASSERT(); 1317 1318 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1319 so = syncache_socket(sc, lso, m); 1320 if (so == NULL) { 1321 TCPSTAT_INC(tcps_sc_aborted); 1322 atomic_subtract_int(pending_counter, 1); 1323 } else { 1324 soisconnected(so); 1325 inp = sotoinpcb(so); 1326 tp = intotcpcb(inp); 1327 tp->t_flags |= TF_FASTOPEN; 1328 tp->t_tfo_cookie.server = response_cookie; 1329 tp->snd_max = tp->iss; 1330 tp->snd_nxt = tp->iss; 1331 tp->t_tfo_pending = pending_counter; 1332 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1333 TCPSTAT_INC(tcps_sc_completed); 1334 } 1335 1336 return (so); 1337 } 1338 1339 /* 1340 * Given a LISTEN socket and an inbound SYN request, add 1341 * this to the syn cache, and send back a segment: 1342 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1343 * to the source. 1344 * 1345 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1346 * Doing so would require that we hold onto the data and deliver it 1347 * to the application. However, if we are the target of a SYN-flood 1348 * DoS attack, an attacker could send data which would eventually 1349 * consume all available buffer space if it were ACKed. By not ACKing 1350 * the data, we avoid this DoS scenario. 1351 * 1352 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1353 * cookie is processed and a new socket is created. In this case, any data 1354 * accompanying the SYN will be queued to the socket by tcp_input() and will 1355 * be ACKed either when the application sends response data or the delayed 1356 * ACK timer expires, whichever comes first. 1357 */ 1358 struct socket * 1359 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1360 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1361 void *todctx, uint8_t iptos, uint16_t port) 1362 { 1363 struct tcpcb *tp; 1364 struct socket *rv = NULL; 1365 struct syncache *sc = NULL; 1366 struct ucred *cred; 1367 struct syncache_head *sch; 1368 struct mbuf *ipopts = NULL; 1369 u_int ltflags; 1370 int win, ip_ttl, ip_tos; 1371 char *s; 1372 #ifdef INET6 1373 int autoflowlabel = 0; 1374 #endif 1375 #ifdef MAC 1376 struct label *maclabel = NULL; 1377 #endif 1378 struct syncache scs; 1379 uint64_t tfo_response_cookie; 1380 unsigned int *tfo_pending = NULL; 1381 int tfo_cookie_valid = 0; 1382 int tfo_response_cookie_valid = 0; 1383 bool locked; 1384 1385 INP_RLOCK_ASSERT(inp); /* listen socket */ 1386 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1387 ("%s: unexpected tcp flags", __func__)); 1388 1389 /* 1390 * Combine all so/tp operations very early to drop the INP lock as 1391 * soon as possible. 1392 */ 1393 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1394 tp = sototcpcb(so); 1395 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1396 1397 #ifdef INET6 1398 if (inc->inc_flags & INC_ISIPV6) { 1399 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1400 autoflowlabel = 1; 1401 } 1402 ip_ttl = in6_selecthlim(inp, NULL); 1403 if ((inp->in6p_outputopts == NULL) || 1404 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1405 ip_tos = 0; 1406 } else { 1407 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1408 } 1409 } 1410 #endif 1411 #if defined(INET6) && defined(INET) 1412 else 1413 #endif 1414 #ifdef INET 1415 { 1416 ip_ttl = inp->inp_ip_ttl; 1417 ip_tos = inp->inp_ip_tos; 1418 } 1419 #endif 1420 win = so->sol_sbrcv_hiwat; 1421 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1422 1423 if (V_tcp_fastopen_server_enable && (tp->t_flags & TF_FASTOPEN) && 1424 (tp->t_tfo_pending != NULL) && 1425 (to->to_flags & TOF_FASTOPEN)) { 1426 /* 1427 * Limit the number of pending TFO connections to 1428 * approximately half of the queue limit. This prevents TFO 1429 * SYN floods from starving the service by filling the 1430 * listen queue with bogus TFO connections. 1431 */ 1432 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1433 (so->sol_qlimit / 2)) { 1434 int result; 1435 1436 result = tcp_fastopen_check_cookie(inc, 1437 to->to_tfo_cookie, to->to_tfo_len, 1438 &tfo_response_cookie); 1439 tfo_cookie_valid = (result > 0); 1440 tfo_response_cookie_valid = (result >= 0); 1441 } 1442 1443 /* 1444 * Remember the TFO pending counter as it will have to be 1445 * decremented below if we don't make it to syncache_tfo_expand(). 1446 */ 1447 tfo_pending = tp->t_tfo_pending; 1448 } 1449 1450 #ifdef MAC 1451 if (mac_syncache_init(&maclabel) != 0) { 1452 INP_RUNLOCK(inp); 1453 goto done; 1454 } else 1455 mac_syncache_create(maclabel, inp); 1456 #endif 1457 if (!tfo_cookie_valid) 1458 INP_RUNLOCK(inp); 1459 1460 /* 1461 * Remember the IP options, if any. 1462 */ 1463 #ifdef INET6 1464 if (!(inc->inc_flags & INC_ISIPV6)) 1465 #endif 1466 #ifdef INET 1467 ipopts = (m) ? ip_srcroute(m) : NULL; 1468 #else 1469 ipopts = NULL; 1470 #endif 1471 1472 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1473 /* 1474 * When the socket is TCP-MD5 enabled check that, 1475 * - a signed packet is valid 1476 * - a non-signed packet does not have a security association 1477 * 1478 * If a signed packet fails validation or a non-signed packet has a 1479 * security association, the packet will be dropped. 1480 */ 1481 if (ltflags & TF_SIGNATURE) { 1482 if (to->to_flags & TOF_SIGNATURE) { 1483 if (!TCPMD5_ENABLED() || 1484 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1485 goto done; 1486 } else { 1487 if (TCPMD5_ENABLED() && 1488 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1489 goto done; 1490 } 1491 } else if (to->to_flags & TOF_SIGNATURE) 1492 goto done; 1493 #endif /* TCP_SIGNATURE */ 1494 /* 1495 * See if we already have an entry for this connection. 1496 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1497 * 1498 * XXX: should the syncache be re-initialized with the contents 1499 * of the new SYN here (which may have different options?) 1500 * 1501 * XXX: We do not check the sequence number to see if this is a 1502 * real retransmit or a new connection attempt. The question is 1503 * how to handle such a case; either ignore it as spoofed, or 1504 * drop the current entry and create a new one? 1505 */ 1506 if (syncache_cookiesonly()) { 1507 sc = NULL; 1508 sch = syncache_hashbucket(inc); 1509 locked = false; 1510 } else { 1511 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1512 locked = true; 1513 SCH_LOCK_ASSERT(sch); 1514 } 1515 if (sc != NULL) { 1516 if (tfo_cookie_valid) 1517 INP_RUNLOCK(inp); 1518 TCPSTAT_INC(tcps_sc_dupsyn); 1519 if (ipopts) { 1520 /* 1521 * If we were remembering a previous source route, 1522 * forget it and use the new one we've been given. 1523 */ 1524 if (sc->sc_ipopts) 1525 (void)m_free(sc->sc_ipopts); 1526 sc->sc_ipopts = ipopts; 1527 } 1528 /* 1529 * Update timestamp if present. 1530 */ 1531 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1532 sc->sc_tsreflect = to->to_tsval; 1533 else 1534 sc->sc_flags &= ~SCF_TIMESTAMP; 1535 /* 1536 * Adjust ECN response if needed, e.g. different 1537 * IP ECN field, or a fallback by the remote host. 1538 */ 1539 if (sc->sc_flags & SCF_ECN_MASK) { 1540 sc->sc_flags &= ~SCF_ECN_MASK; 1541 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1542 } 1543 #ifdef MAC 1544 /* 1545 * Since we have already unconditionally allocated label 1546 * storage, free it up. The syncache entry will already 1547 * have an initialized label we can use. 1548 */ 1549 mac_syncache_destroy(&maclabel); 1550 #endif 1551 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1552 /* Retransmit SYN|ACK and reset retransmit count. */ 1553 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1554 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1555 "resetting timer and retransmitting SYN|ACK\n", 1556 s, __func__); 1557 free(s, M_TCPLOG); 1558 } 1559 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1560 sc->sc_rxmits = 0; 1561 syncache_timeout(sc, sch, 1); 1562 TCPSTAT_INC(tcps_sndacks); 1563 TCPSTAT_INC(tcps_sndtotal); 1564 } else { 1565 syncache_drop(sc, sch); 1566 TCPSTAT_INC(tcps_sc_dropped); 1567 } 1568 SCH_UNLOCK(sch); 1569 goto donenoprobe; 1570 } 1571 1572 KASSERT(sc == NULL, ("sc(%p) != NULL", sc)); 1573 /* 1574 * Skip allocating a syncache entry if we are just going to discard 1575 * it later. 1576 */ 1577 if (!locked || tfo_cookie_valid) { 1578 bzero(&scs, sizeof(scs)); 1579 sc = &scs; 1580 } else { 1581 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1582 if (sc == NULL) { 1583 /* 1584 * The zone allocator couldn't provide more entries. 1585 * Treat this as if the cache was full; drop the oldest 1586 * entry and insert the new one. 1587 */ 1588 TCPSTAT_INC(tcps_sc_zonefail); 1589 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 1590 if (sc != NULL) { 1591 sch->sch_last_overflow = time_uptime; 1592 syncache_drop(sc, sch); 1593 syncache_pause(inc); 1594 } 1595 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1596 if (sc == NULL) { 1597 if (V_tcp_syncookies) { 1598 bzero(&scs, sizeof(scs)); 1599 sc = &scs; 1600 } else { 1601 KASSERT(locked, 1602 ("%s: bucket unexpectedly unlocked", 1603 __func__)); 1604 SCH_UNLOCK(sch); 1605 goto done; 1606 } 1607 } 1608 } 1609 } 1610 1611 KASSERT(sc != NULL, ("sc == NULL")); 1612 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1613 sc->sc_tfo_cookie = &tfo_response_cookie; 1614 1615 /* 1616 * Fill in the syncache values. 1617 */ 1618 #ifdef MAC 1619 sc->sc_label = maclabel; 1620 #endif 1621 /* 1622 * sc_cred is only used in syncache_pcblist() to list TCP endpoints in 1623 * TCPS_SYN_RECEIVED state when V_tcp_syncache.see_other is false. 1624 * Therefore, store the credentials only when needed: 1625 * - sc is allocated from the zone and not using the on stack instance. 1626 * - the sysctl variable net.inet.tcp.syncache.see_other is false. 1627 * The reference count is decremented when a zone allocated sc is 1628 * freed in syncache_free(). 1629 */ 1630 if (sc != &scs && !V_tcp_syncache.see_other) { 1631 sc->sc_cred = cred; 1632 cred = NULL; 1633 } else 1634 sc->sc_cred = NULL; 1635 sc->sc_port = port; 1636 sc->sc_ipopts = ipopts; 1637 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1638 sc->sc_ip_tos = ip_tos; 1639 sc->sc_ip_ttl = ip_ttl; 1640 #ifdef TCP_OFFLOAD 1641 sc->sc_tod = tod; 1642 sc->sc_todctx = todctx; 1643 #endif 1644 sc->sc_irs = th->th_seq; 1645 sc->sc_flags = 0; 1646 sc->sc_flowlabel = 0; 1647 1648 /* 1649 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1650 * win was derived from socket earlier in the function. 1651 */ 1652 win = imax(win, 0); 1653 win = imin(win, TCP_MAXWIN); 1654 sc->sc_wnd = win; 1655 1656 if (V_tcp_do_rfc1323 && 1657 !(ltflags & TF_NOOPT)) { 1658 /* 1659 * A timestamp received in a SYN makes 1660 * it ok to send timestamp requests and replies. 1661 */ 1662 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1663 sc->sc_tsreflect = to->to_tsval; 1664 sc->sc_flags |= SCF_TIMESTAMP; 1665 sc->sc_tsoff = tcp_new_ts_offset(inc); 1666 } 1667 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1668 u_int wscale = 0; 1669 1670 /* 1671 * Pick the smallest possible scaling factor that 1672 * will still allow us to scale up to sb_max, aka 1673 * kern.ipc.maxsockbuf. 1674 * 1675 * We do this because there are broken firewalls that 1676 * will corrupt the window scale option, leading to 1677 * the other endpoint believing that our advertised 1678 * window is unscaled. At scale factors larger than 1679 * 5 the unscaled window will drop below 1500 bytes, 1680 * leading to serious problems when traversing these 1681 * broken firewalls. 1682 * 1683 * With the default maxsockbuf of 256K, a scale factor 1684 * of 3 will be chosen by this algorithm. Those who 1685 * choose a larger maxsockbuf should watch out 1686 * for the compatibility problems mentioned above. 1687 * 1688 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1689 * or <SYN,ACK>) segment itself is never scaled. 1690 */ 1691 while (wscale < TCP_MAX_WINSHIFT && 1692 (TCP_MAXWIN << wscale) < sb_max) 1693 wscale++; 1694 sc->sc_requested_r_scale = wscale; 1695 sc->sc_requested_s_scale = to->to_wscale; 1696 sc->sc_flags |= SCF_WINSCALE; 1697 } 1698 } 1699 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1700 /* 1701 * If incoming packet has an MD5 signature, flag this in the 1702 * syncache so that syncache_respond() will do the right thing 1703 * with the SYN+ACK. 1704 */ 1705 if (to->to_flags & TOF_SIGNATURE) 1706 sc->sc_flags |= SCF_SIGNATURE; 1707 #endif /* TCP_SIGNATURE */ 1708 if (to->to_flags & TOF_SACKPERM) 1709 sc->sc_flags |= SCF_SACK; 1710 if (to->to_flags & TOF_MSS) 1711 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1712 if (ltflags & TF_NOOPT) 1713 sc->sc_flags |= SCF_NOOPT; 1714 /* ECN Handshake */ 1715 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1716 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1717 1718 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1719 sc->sc_iss = syncookie_generate(sch, sc); 1720 else 1721 sc->sc_iss = arc4random(); 1722 #ifdef INET6 1723 if (autoflowlabel) { 1724 if (V_tcp_syncookies || V_tcp_syncookiesonly) 1725 sc->sc_flowlabel = sc->sc_iss; 1726 else 1727 sc->sc_flowlabel = ip6_randomflowlabel(); 1728 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1729 } 1730 #endif 1731 if (locked) 1732 SCH_UNLOCK(sch); 1733 1734 if (tfo_cookie_valid) { 1735 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1736 /* INP_RUNLOCK(inp) will be performed by the caller */ 1737 goto tfo_expanded; 1738 } 1739 1740 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1741 /* 1742 * Do a standard 3-way handshake. 1743 */ 1744 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1745 if (sc != &scs) 1746 syncache_insert(sc, sch); /* locks and unlocks sch */ 1747 TCPSTAT_INC(tcps_sndacks); 1748 TCPSTAT_INC(tcps_sndtotal); 1749 } else { 1750 if (sc != &scs) 1751 syncache_free(sc); 1752 TCPSTAT_INC(tcps_sc_dropped); 1753 } 1754 goto donenoprobe; 1755 1756 done: 1757 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1758 donenoprobe: 1759 if (m) 1760 m_freem(m); 1761 /* 1762 * If tfo_pending is not NULL here, then a TFO SYN that did not 1763 * result in a new socket was processed and the associated pending 1764 * counter has not yet been decremented. All such TFO processing paths 1765 * transit this point. 1766 */ 1767 if (tfo_pending != NULL) 1768 tcp_fastopen_decrement_counter(tfo_pending); 1769 1770 tfo_expanded: 1771 if (cred != NULL) 1772 crfree(cred); 1773 if (sc == NULL || sc == &scs) { 1774 #ifdef MAC 1775 mac_syncache_destroy(&maclabel); 1776 #endif 1777 if (ipopts) 1778 (void)m_free(ipopts); 1779 } 1780 return (rv); 1781 } 1782 1783 /* 1784 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1785 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1786 */ 1787 static int 1788 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1789 { 1790 struct ip *ip = NULL; 1791 struct mbuf *m; 1792 struct tcphdr *th = NULL; 1793 struct udphdr *udp = NULL; 1794 int optlen, error = 0; /* Make compiler happy */ 1795 u_int16_t hlen, tlen, mssopt, ulen; 1796 struct tcpopt to; 1797 #ifdef INET6 1798 struct ip6_hdr *ip6 = NULL; 1799 #endif 1800 1801 NET_EPOCH_ASSERT(); 1802 1803 hlen = 1804 #ifdef INET6 1805 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1806 #endif 1807 sizeof(struct ip); 1808 tlen = hlen + sizeof(struct tcphdr); 1809 if (sc->sc_port) { 1810 tlen += sizeof(struct udphdr); 1811 } 1812 /* Determine MSS we advertize to other end of connection. */ 1813 mssopt = tcp_mssopt(&sc->sc_inc); 1814 if (sc->sc_port) 1815 mssopt -= V_tcp_udp_tunneling_overhead; 1816 mssopt = max(mssopt, V_tcp_minmss); 1817 1818 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1819 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1820 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1821 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1822 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1823 1824 /* Create the IP+TCP header from scratch. */ 1825 m = m_gethdr(M_NOWAIT, MT_DATA); 1826 if (m == NULL) 1827 return (ENOBUFS); 1828 #ifdef MAC 1829 mac_syncache_create_mbuf(sc->sc_label, m); 1830 #endif 1831 m->m_data += max_linkhdr; 1832 m->m_len = tlen; 1833 m->m_pkthdr.len = tlen; 1834 m->m_pkthdr.rcvif = NULL; 1835 1836 #ifdef INET6 1837 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1838 ip6 = mtod(m, struct ip6_hdr *); 1839 ip6->ip6_vfc = IPV6_VERSION; 1840 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1841 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1842 ip6->ip6_plen = htons(tlen - hlen); 1843 /* ip6_hlim is set after checksum */ 1844 /* Zero out traffic class and flow label. */ 1845 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1846 ip6->ip6_flow |= sc->sc_flowlabel; 1847 if (sc->sc_port != 0) { 1848 ip6->ip6_nxt = IPPROTO_UDP; 1849 udp = (struct udphdr *)(ip6 + 1); 1850 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1851 udp->uh_dport = sc->sc_port; 1852 ulen = (tlen - sizeof(struct ip6_hdr)); 1853 th = (struct tcphdr *)(udp + 1); 1854 } else { 1855 ip6->ip6_nxt = IPPROTO_TCP; 1856 th = (struct tcphdr *)(ip6 + 1); 1857 } 1858 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1859 } 1860 #endif 1861 #if defined(INET6) && defined(INET) 1862 else 1863 #endif 1864 #ifdef INET 1865 { 1866 ip = mtod(m, struct ip *); 1867 ip->ip_v = IPVERSION; 1868 ip->ip_hl = sizeof(struct ip) >> 2; 1869 ip->ip_len = htons(tlen); 1870 ip->ip_id = 0; 1871 ip->ip_off = 0; 1872 ip->ip_sum = 0; 1873 ip->ip_src = sc->sc_inc.inc_laddr; 1874 ip->ip_dst = sc->sc_inc.inc_faddr; 1875 ip->ip_ttl = sc->sc_ip_ttl; 1876 ip->ip_tos = sc->sc_ip_tos; 1877 1878 /* 1879 * See if we should do MTU discovery. Route lookups are 1880 * expensive, so we will only unset the DF bit if: 1881 * 1882 * 1) path_mtu_discovery is disabled 1883 * 2) the SCF_UNREACH flag has been set 1884 */ 1885 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1886 ip->ip_off |= htons(IP_DF); 1887 if (sc->sc_port == 0) { 1888 ip->ip_p = IPPROTO_TCP; 1889 th = (struct tcphdr *)(ip + 1); 1890 } else { 1891 ip->ip_p = IPPROTO_UDP; 1892 udp = (struct udphdr *)(ip + 1); 1893 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1894 udp->uh_dport = sc->sc_port; 1895 ulen = (tlen - sizeof(struct ip)); 1896 th = (struct tcphdr *)(udp + 1); 1897 } 1898 } 1899 #endif /* INET */ 1900 th->th_sport = sc->sc_inc.inc_lport; 1901 th->th_dport = sc->sc_inc.inc_fport; 1902 1903 if (flags & TH_SYN) 1904 th->th_seq = htonl(sc->sc_iss); 1905 else 1906 th->th_seq = htonl(sc->sc_iss + 1); 1907 th->th_ack = htonl(sc->sc_irs + 1); 1908 th->th_off = sizeof(struct tcphdr) >> 2; 1909 th->th_win = htons(sc->sc_wnd); 1910 th->th_urp = 0; 1911 1912 flags = tcp_ecn_syncache_respond(flags, sc); 1913 tcp_set_flags(th, flags); 1914 1915 /* Tack on the TCP options. */ 1916 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1917 to.to_flags = 0; 1918 1919 if (flags & TH_SYN) { 1920 to.to_mss = mssopt; 1921 to.to_flags = TOF_MSS; 1922 if (sc->sc_flags & SCF_WINSCALE) { 1923 to.to_wscale = sc->sc_requested_r_scale; 1924 to.to_flags |= TOF_SCALE; 1925 } 1926 if (sc->sc_flags & SCF_SACK) 1927 to.to_flags |= TOF_SACKPERM; 1928 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1929 if (sc->sc_flags & SCF_SIGNATURE) 1930 to.to_flags |= TOF_SIGNATURE; 1931 #endif 1932 if (sc->sc_tfo_cookie) { 1933 to.to_flags |= TOF_FASTOPEN; 1934 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1935 to.to_tfo_cookie = sc->sc_tfo_cookie; 1936 /* don't send cookie again when retransmitting response */ 1937 sc->sc_tfo_cookie = NULL; 1938 } 1939 } 1940 if (sc->sc_flags & SCF_TIMESTAMP) { 1941 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1942 to.to_tsecr = sc->sc_tsreflect; 1943 to.to_flags |= TOF_TS; 1944 } 1945 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1946 1947 /* Adjust headers by option size. */ 1948 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1949 m->m_len += optlen; 1950 m->m_pkthdr.len += optlen; 1951 #ifdef INET6 1952 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1953 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1954 else 1955 #endif 1956 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1957 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1958 if (sc->sc_flags & SCF_SIGNATURE) { 1959 KASSERT(to.to_flags & TOF_SIGNATURE, 1960 ("tcp_addoptions() didn't set tcp_signature")); 1961 1962 /* NOTE: to.to_signature is inside of mbuf */ 1963 if (!TCPMD5_ENABLED() || 1964 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1965 m_freem(m); 1966 return (EACCES); 1967 } 1968 } 1969 #endif 1970 } else 1971 optlen = 0; 1972 1973 if (udp) { 1974 ulen += optlen; 1975 udp->uh_ulen = htons(ulen); 1976 } 1977 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1978 /* 1979 * If we have peer's SYN and it has a flowid, then let's assign it to 1980 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1981 * to SYN|ACK due to lack of inp here. 1982 */ 1983 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1984 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1985 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1986 } 1987 #ifdef INET6 1988 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1989 if (sc->sc_port) { 1990 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 1991 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 1992 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 1993 IPPROTO_UDP, 0); 1994 th->th_sum = htons(0); 1995 } else { 1996 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 1997 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1998 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 1999 IPPROTO_TCP, 0); 2000 } 2001 ip6->ip6_hlim = sc->sc_ip_ttl; 2002 #ifdef TCP_OFFLOAD 2003 if (ADDED_BY_TOE(sc)) { 2004 struct toedev *tod = sc->sc_tod; 2005 2006 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2007 2008 return (error); 2009 } 2010 #endif 2011 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2012 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2013 } 2014 #endif 2015 #if defined(INET6) && defined(INET) 2016 else 2017 #endif 2018 #ifdef INET 2019 { 2020 if (sc->sc_port) { 2021 m->m_pkthdr.csum_flags = CSUM_UDP; 2022 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2023 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2024 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2025 th->th_sum = htons(0); 2026 } else { 2027 m->m_pkthdr.csum_flags = CSUM_TCP; 2028 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2029 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2030 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2031 } 2032 #ifdef TCP_OFFLOAD 2033 if (ADDED_BY_TOE(sc)) { 2034 struct toedev *tod = sc->sc_tod; 2035 2036 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2037 2038 return (error); 2039 } 2040 #endif 2041 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2042 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2043 } 2044 #endif 2045 return (error); 2046 } 2047 2048 static void 2049 syncache_send_challenge_ack(struct syncache *sc, struct mbuf *m) 2050 { 2051 if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, 2052 &sc->sc_challenge_ack_cnt)) { 2053 if (syncache_respond(sc, m, TH_ACK) == 0) { 2054 TCPSTAT_INC(tcps_sndacks); 2055 TCPSTAT_INC(tcps_sndtotal); 2056 } 2057 } 2058 } 2059 2060 /* 2061 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2062 * that exceed the capacity of the syncache by avoiding the storage of any 2063 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2064 * attacks where the attacker does not have access to our responses. 2065 * 2066 * Syncookies encode and include all necessary information about the 2067 * connection setup within the SYN|ACK that we send back. That way we 2068 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2069 * (if ever). Normally the syncache and syncookies are running in parallel 2070 * with the latter taking over when the former is exhausted. When matching 2071 * syncache entry is found the syncookie is ignored. 2072 * 2073 * The only reliable information persisting the 3WHS is our initial sequence 2074 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2075 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2076 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2077 * returns and signifies a legitimate connection if it matches the ACK. 2078 * 2079 * The available space of 32 bits to store the hash and to encode the SYN 2080 * option information is very tight and we should have at least 24 bits for 2081 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2082 * 2083 * SYN option information we have to encode to fully restore a connection: 2084 * MSS: is imporant to chose an optimal segment size to avoid IP level 2085 * fragmentation along the path. The common MSS values can be encoded 2086 * in a 3-bit table. Uncommon values are captured by the next lower value 2087 * in the table leading to a slight increase in packetization overhead. 2088 * WSCALE: is necessary to allow large windows to be used for high delay- 2089 * bandwidth product links. Not scaling the window when it was initially 2090 * negotiated is bad for performance as lack of scaling further decreases 2091 * the apparent available send window. We only need to encode the WSCALE 2092 * we received from the remote end. Our end can be recalculated at any 2093 * time. The common WSCALE values can be encoded in a 3-bit table. 2094 * Uncommon values are captured by the next lower value in the table 2095 * making us under-estimate the available window size halving our 2096 * theoretically possible maximum throughput for that connection. 2097 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2098 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2099 * that are included in all segments on a connection. We enable them when 2100 * the ACK has them. 2101 * 2102 * Security of syncookies and attack vectors: 2103 * 2104 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2105 * together with the gloabl secret to make it unique per connection attempt. 2106 * Thus any change of any of those parameters results in a different MAC output 2107 * in an unpredictable way unless a collision is encountered. 24 bits of the 2108 * MAC are embedded into the ISS. 2109 * 2110 * To prevent replay attacks two rotating global secrets are updated with a 2111 * new random value every 15 seconds. The life-time of a syncookie is thus 2112 * 15-30 seconds. 2113 * 2114 * Vector 1: Attacking the secret. This requires finding a weakness in the 2115 * MAC itself or the way it is used here. The attacker can do a chosen plain 2116 * text attack by varying and testing the all parameters under his control. 2117 * The strength depends on the size and randomness of the secret, and the 2118 * cryptographic security of the MAC function. Due to the constant updating 2119 * of the secret the attacker has at most 29.999 seconds to find the secret 2120 * and launch spoofed connections. After that he has to start all over again. 2121 * 2122 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2123 * size an average of 4,823 attempts are required for a 50% chance of success 2124 * to spoof a single syncookie (birthday collision paradox). However the 2125 * attacker is blind and doesn't know if one of his attempts succeeded unless 2126 * he has a side channel to interfere success from. A single connection setup 2127 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2128 * This many attempts are required for each one blind spoofed connection. For 2129 * every additional spoofed connection he has to launch another N attempts. 2130 * Thus for a sustained rate 100 spoofed connections per second approximately 2131 * 1,800,000 packets per second would have to be sent. 2132 * 2133 * NB: The MAC function should be fast so that it doesn't become a CPU 2134 * exhaustion attack vector itself. 2135 * 2136 * References: 2137 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2138 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2139 * http://cr.yp.to/syncookies.html (overview) 2140 * http://cr.yp.to/syncookies/archive (details) 2141 * 2142 * 2143 * Schematic construction of a syncookie enabled Initial Sequence Number: 2144 * 0 1 2 3 2145 * 12345678901234567890123456789012 2146 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2147 * 2148 * x 24 MAC (truncated) 2149 * W 3 Send Window Scale index 2150 * M 3 MSS index 2151 * S 1 SACK permitted 2152 * P 1 Odd/even secret 2153 */ 2154 2155 /* 2156 * Distribution and probability of certain MSS values. Those in between are 2157 * rounded down to the next lower one. 2158 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2159 * .2% .3% 5% 7% 7% 20% 15% 45% 2160 */ 2161 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2162 2163 /* 2164 * Distribution and probability of certain WSCALE values. We have to map the 2165 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2166 * bits based on prevalence of certain values. Where we don't have an exact 2167 * match for are rounded down to the next lower one letting us under-estimate 2168 * the true available window. At the moment this would happen only for the 2169 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2170 * and window size). The absence of the WSCALE option (no scaling in either 2171 * direction) is encoded with index zero. 2172 * [WSCALE values histograms, Allman, 2012] 2173 * X 10 10 35 5 6 14 10% by host 2174 * X 11 4 5 5 18 49 3% by connections 2175 */ 2176 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2177 2178 /* 2179 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2180 * and good cryptographic properties. 2181 */ 2182 static uint32_t 2183 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2184 uint8_t *secbits, uintptr_t secmod) 2185 { 2186 SIPHASH_CTX ctx; 2187 uint32_t siphash[2]; 2188 2189 SipHash24_Init(&ctx); 2190 SipHash_SetKey(&ctx, secbits); 2191 switch (inc->inc_flags & INC_ISIPV6) { 2192 #ifdef INET 2193 case 0: 2194 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2195 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2196 break; 2197 #endif 2198 #ifdef INET6 2199 case INC_ISIPV6: 2200 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2201 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2202 break; 2203 #endif 2204 } 2205 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2206 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2207 SipHash_Update(&ctx, &irs, sizeof(irs)); 2208 SipHash_Update(&ctx, &flags, sizeof(flags)); 2209 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2210 SipHash_Final((u_int8_t *)&siphash, &ctx); 2211 2212 return (siphash[0] ^ siphash[1]); 2213 } 2214 2215 static tcp_seq 2216 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2217 { 2218 u_int i, secbit, wscale; 2219 uint32_t iss, hash; 2220 uint8_t *secbits; 2221 union syncookie cookie; 2222 2223 cookie.cookie = 0; 2224 2225 /* Map our computed MSS into the 3-bit index. */ 2226 for (i = nitems(tcp_sc_msstab) - 1; 2227 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2228 i--) 2229 ; 2230 cookie.flags.mss_idx = i; 2231 2232 /* 2233 * Map the send window scale into the 3-bit index but only if 2234 * the wscale option was received. 2235 */ 2236 if (sc->sc_flags & SCF_WINSCALE) { 2237 wscale = sc->sc_requested_s_scale; 2238 for (i = nitems(tcp_sc_wstab) - 1; 2239 tcp_sc_wstab[i] > wscale && i > 0; 2240 i--) 2241 ; 2242 cookie.flags.wscale_idx = i; 2243 } 2244 2245 /* Can we do SACK? */ 2246 if (sc->sc_flags & SCF_SACK) 2247 cookie.flags.sack_ok = 1; 2248 2249 /* Which of the two secrets to use. */ 2250 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2251 cookie.flags.odd_even = secbit; 2252 2253 secbits = V_tcp_syncache.secret.key[secbit]; 2254 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2255 (uintptr_t)sch); 2256 2257 /* 2258 * Put the flags into the hash and XOR them to get better ISS number 2259 * variance. This doesn't enhance the cryptographic strength and is 2260 * done to prevent the 8 cookie bits from showing up directly on the 2261 * wire. 2262 */ 2263 iss = hash & ~0xff; 2264 iss |= cookie.cookie ^ (hash >> 24); 2265 2266 TCPSTAT_INC(tcps_sc_sendcookie); 2267 return (iss); 2268 } 2269 2270 static bool 2271 syncookie_expand(struct in_conninfo *inc, const struct syncache_head *sch, 2272 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2273 struct socket *lso, uint16_t port) 2274 { 2275 uint32_t hash; 2276 uint8_t *secbits; 2277 tcp_seq ack, seq; 2278 int wnd; 2279 union syncookie cookie; 2280 2281 /* 2282 * Pull information out of SYN-ACK/ACK and revert sequence number 2283 * advances. 2284 */ 2285 ack = th->th_ack - 1; 2286 seq = th->th_seq - 1; 2287 2288 /* 2289 * Unpack the flags containing enough information to restore the 2290 * connection. 2291 */ 2292 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2293 2294 /* Which of the two secrets to use. */ 2295 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2296 2297 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2298 2299 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2300 if ((ack & ~0xff) != (hash & ~0xff)) 2301 return (false); 2302 2303 /* Fill in the syncache values. */ 2304 sc->sc_flags = 0; 2305 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2306 sc->sc_ipopts = NULL; 2307 2308 sc->sc_irs = seq; 2309 sc->sc_iss = ack; 2310 2311 switch (inc->inc_flags & INC_ISIPV6) { 2312 #ifdef INET 2313 case 0: 2314 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2315 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2316 break; 2317 #endif 2318 #ifdef INET6 2319 case INC_ISIPV6: 2320 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2321 sc->sc_flowlabel = 2322 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2323 break; 2324 #endif 2325 } 2326 2327 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2328 2329 /* Only use wscale if it was enabled in the orignal SYN. */ 2330 if (cookie.flags.wscale_idx > 0) { 2331 u_int wscale = 0; 2332 2333 /* Recompute the receive window scale that was sent earlier. */ 2334 while (wscale < TCP_MAX_WINSHIFT && 2335 (TCP_MAXWIN << wscale) < sb_max) 2336 wscale++; 2337 sc->sc_requested_r_scale = wscale; 2338 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2339 sc->sc_flags |= SCF_WINSCALE; 2340 } 2341 2342 wnd = lso->sol_sbrcv_hiwat; 2343 wnd = imax(wnd, 0); 2344 wnd = imin(wnd, TCP_MAXWIN); 2345 sc->sc_wnd = wnd; 2346 2347 if (cookie.flags.sack_ok) 2348 sc->sc_flags |= SCF_SACK; 2349 2350 if (to->to_flags & TOF_TS) { 2351 sc->sc_flags |= SCF_TIMESTAMP; 2352 sc->sc_tsreflect = to->to_tsval; 2353 sc->sc_tsoff = tcp_new_ts_offset(inc); 2354 } 2355 2356 if (to->to_flags & TOF_SIGNATURE) 2357 sc->sc_flags |= SCF_SIGNATURE; 2358 2359 sc->sc_rxmits = 0; 2360 2361 sc->sc_port = port; 2362 2363 return (true); 2364 } 2365 2366 #ifdef INVARIANTS 2367 static void 2368 syncookie_cmp(struct in_conninfo *inc, const struct syncache_head *sch, 2369 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2370 struct socket *lso, uint16_t port) 2371 { 2372 struct syncache scs; 2373 char *s; 2374 2375 bzero(&scs, sizeof(scs)); 2376 if (syncookie_expand(inc, sch, &scs, th, to, lso, port) && 2377 (sc->sc_peer_mss != scs.sc_peer_mss || 2378 sc->sc_requested_r_scale != scs.sc_requested_r_scale || 2379 sc->sc_requested_s_scale != scs.sc_requested_s_scale || 2380 (sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK))) { 2381 2382 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2383 return; 2384 2385 if (sc->sc_peer_mss != scs.sc_peer_mss) 2386 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2387 s, __func__, sc->sc_peer_mss, scs.sc_peer_mss); 2388 2389 if (sc->sc_requested_r_scale != scs.sc_requested_r_scale) 2390 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2391 s, __func__, sc->sc_requested_r_scale, 2392 scs.sc_requested_r_scale); 2393 2394 if (sc->sc_requested_s_scale != scs.sc_requested_s_scale) 2395 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2396 s, __func__, sc->sc_requested_s_scale, 2397 scs.sc_requested_s_scale); 2398 2399 if ((sc->sc_flags & SCF_SACK) != (scs.sc_flags & SCF_SACK)) 2400 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2401 2402 free(s, M_TCPLOG); 2403 } 2404 } 2405 #endif /* INVARIANTS */ 2406 2407 static void 2408 syncookie_reseed(void *arg) 2409 { 2410 struct tcp_syncache *sc = arg; 2411 uint8_t *secbits; 2412 int secbit; 2413 2414 /* 2415 * Reseeding the secret doesn't have to be protected by a lock. 2416 * It only must be ensured that the new random values are visible 2417 * to all CPUs in a SMP environment. The atomic with release 2418 * semantics ensures that. 2419 */ 2420 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2421 secbits = sc->secret.key[secbit]; 2422 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2423 atomic_add_rel_int(&sc->secret.oddeven, 1); 2424 2425 /* Reschedule ourself. */ 2426 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2427 } 2428 2429 /* 2430 * We have overflowed a bucket. Let's pause dealing with the syncache. 2431 * This function will increment the bucketoverflow statistics appropriately 2432 * (once per pause when pausing is enabled; otherwise, once per overflow). 2433 */ 2434 static void 2435 syncache_pause(struct in_conninfo *inc) 2436 { 2437 time_t delta; 2438 const char *s; 2439 2440 /* XXX: 2441 * 2. Add sysctl read here so we don't get the benefit of this 2442 * change without the new sysctl. 2443 */ 2444 2445 /* 2446 * Try an unlocked read. If we already know that another thread 2447 * has activated the feature, there is no need to proceed. 2448 */ 2449 if (V_tcp_syncache.paused) 2450 return; 2451 2452 /* Are cookied enabled? If not, we can't pause. */ 2453 if (!V_tcp_syncookies) { 2454 TCPSTAT_INC(tcps_sc_bucketoverflow); 2455 return; 2456 } 2457 2458 /* 2459 * We may be the first thread to find an overflow. Get the lock 2460 * and evaluate if we need to take action. 2461 */ 2462 mtx_lock(&V_tcp_syncache.pause_mtx); 2463 if (V_tcp_syncache.paused) { 2464 mtx_unlock(&V_tcp_syncache.pause_mtx); 2465 return; 2466 } 2467 2468 /* Activate protection. */ 2469 V_tcp_syncache.paused = true; 2470 TCPSTAT_INC(tcps_sc_bucketoverflow); 2471 2472 /* 2473 * Determine the last backoff time. If we are seeing a re-newed 2474 * attack within that same time after last reactivating the syncache, 2475 * consider it an extension of the same attack. 2476 */ 2477 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2478 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2479 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2480 delta <<= 1; 2481 V_tcp_syncache.pause_backoff++; 2482 } 2483 } else { 2484 delta = TCP_SYNCACHE_PAUSE_TIME; 2485 V_tcp_syncache.pause_backoff = 0; 2486 } 2487 2488 /* Log a warning, including IP addresses, if able. */ 2489 if (inc != NULL) 2490 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2491 else 2492 s = (const char *)NULL; 2493 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2494 "the next %lld seconds%s%s%s\n", (long long)delta, 2495 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2496 (s != NULL) ? ")" : ""); 2497 free(__DECONST(void *, s), M_TCPLOG); 2498 2499 /* Use the calculated delta to set a new pause time. */ 2500 V_tcp_syncache.pause_until = time_uptime + delta; 2501 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2502 &V_tcp_syncache); 2503 mtx_unlock(&V_tcp_syncache.pause_mtx); 2504 } 2505 2506 /* Evaluate whether we need to unpause. */ 2507 static void 2508 syncache_unpause(void *arg) 2509 { 2510 struct tcp_syncache *sc; 2511 time_t delta; 2512 2513 sc = arg; 2514 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2515 callout_deactivate(&sc->pause_co); 2516 2517 /* 2518 * Check to make sure we are not running early. If the pause 2519 * time has expired, then deactivate the protection. 2520 */ 2521 if ((delta = sc->pause_until - time_uptime) > 0) 2522 callout_schedule(&sc->pause_co, delta * hz); 2523 else 2524 sc->paused = false; 2525 } 2526 2527 /* 2528 * Exports the syncache entries to userland so that netstat can display 2529 * them alongside the other sockets. This function is intended to be 2530 * called only from tcp_pcblist. 2531 * 2532 * Due to concurrency on an active system, the number of pcbs exported 2533 * may have no relation to max_pcbs. max_pcbs merely indicates the 2534 * amount of space the caller allocated for this function to use. 2535 */ 2536 int 2537 syncache_pcblist(struct sysctl_req *req) 2538 { 2539 struct xtcpcb xt; 2540 struct syncache *sc; 2541 struct syncache_head *sch; 2542 int error, i; 2543 2544 bzero(&xt, sizeof(xt)); 2545 xt.xt_len = sizeof(xt); 2546 xt.t_state = TCPS_SYN_RECEIVED; 2547 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2548 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2549 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2550 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2551 2552 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2553 sch = &V_tcp_syncache.hashbase[i]; 2554 SCH_LOCK(sch); 2555 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2556 if (sc->sc_cred != NULL && 2557 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2558 continue; 2559 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2560 xt.xt_inp.inp_vflag = INP_IPV6; 2561 else 2562 xt.xt_inp.inp_vflag = INP_IPV4; 2563 xt.xt_encaps_port = sc->sc_port; 2564 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2565 sizeof (struct in_conninfo)); 2566 error = SYSCTL_OUT(req, &xt, sizeof xt); 2567 if (error) { 2568 SCH_UNLOCK(sch); 2569 return (0); 2570 } 2571 } 2572 SCH_UNLOCK(sch); 2573 } 2574 2575 return (0); 2576 } 2577