1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 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 __FBSDID("$FreeBSD$"); 37 38 #include "opt_inet.h" 39 #include "opt_inet6.h" 40 #include "opt_ipsec.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/hash.h> 45 #include <sys/refcount.h> 46 #include <sys/kernel.h> 47 #include <sys/sysctl.h> 48 #include <sys/limits.h> 49 #include <sys/lock.h> 50 #include <sys/mutex.h> 51 #include <sys/malloc.h> 52 #include <sys/mbuf.h> 53 #include <sys/proc.h> /* for proc0 declaration */ 54 #include <sys/random.h> 55 #include <sys/socket.h> 56 #include <sys/socketvar.h> 57 #include <sys/syslog.h> 58 #include <sys/ucred.h> 59 60 #include <sys/md5.h> 61 #include <crypto/siphash/siphash.h> 62 63 #include <vm/uma.h> 64 65 #include <net/if.h> 66 #include <net/if_var.h> 67 #include <net/route.h> 68 #include <net/vnet.h> 69 70 #include <netinet/in.h> 71 #include <netinet/in_kdtrace.h> 72 #include <netinet/in_systm.h> 73 #include <netinet/ip.h> 74 #include <netinet/in_var.h> 75 #include <netinet/in_pcb.h> 76 #include <netinet/ip_var.h> 77 #include <netinet/ip_options.h> 78 #ifdef INET6 79 #include <netinet/ip6.h> 80 #include <netinet/icmp6.h> 81 #include <netinet6/nd6.h> 82 #include <netinet6/ip6_var.h> 83 #include <netinet6/in6_pcb.h> 84 #endif 85 #include <netinet/tcp.h> 86 #include <netinet/tcp_fastopen.h> 87 #include <netinet/tcp_fsm.h> 88 #include <netinet/tcp_seq.h> 89 #include <netinet/tcp_timer.h> 90 #include <netinet/tcp_var.h> 91 #include <netinet/tcp_syncache.h> 92 #include <netinet/tcp_ecn.h> 93 #ifdef TCP_OFFLOAD 94 #include <netinet/toecore.h> 95 #endif 96 #include <netinet/udp.h> 97 #include <netinet/udp_var.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(int, tcp_syncookies) = 1; 106 #define V_tcp_syncookies VNET(tcp_syncookies) 107 SYSCTL_INT(_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(int, tcp_syncookiesonly) = 0; 112 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 113 SYSCTL_INT(_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 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 118 #define V_functions_inherit_listen_socket_stack \ 119 VNET(functions_inherit_listen_socket_stack) 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 121 CTLFLAG_VNET | CTLFLAG_RW, 122 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 123 "Inherit listen socket's stack"); 124 125 #ifdef TCP_OFFLOAD 126 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 127 #endif 128 129 static void syncache_drop(struct syncache *, struct syncache_head *); 130 static void syncache_free(struct syncache *); 131 static void syncache_insert(struct syncache *, struct syncache_head *); 132 static int syncache_respond(struct syncache *, const struct mbuf *, int); 133 static struct socket *syncache_socket(struct syncache *, struct socket *, 134 struct mbuf *m); 135 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 136 int docallout); 137 static void syncache_timer(void *); 138 139 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 140 uint8_t *, uintptr_t); 141 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 142 static struct syncache 143 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 144 struct syncache *, struct tcphdr *, struct tcpopt *, 145 struct socket *, uint16_t); 146 static void syncache_pause(struct in_conninfo *); 147 static void syncache_unpause(void *); 148 static void syncookie_reseed(void *); 149 #ifdef INVARIANTS 150 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 151 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 152 struct socket *lso, uint16_t port); 153 #endif 154 155 /* 156 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 157 * 3 retransmits corresponds to a timeout with default values of 158 * tcp_rexmit_initial * ( 1 + 159 * tcp_backoff[1] + 160 * tcp_backoff[2] + 161 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 162 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 163 * the odds are that the user has given up attempting to connect by then. 164 */ 165 #define SYNCACHE_MAXREXMTS 3 166 167 /* Arbitrary values */ 168 #define TCP_SYNCACHE_HASHSIZE 512 169 #define TCP_SYNCACHE_BUCKETLIMIT 30 170 171 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 172 #define V_tcp_syncache VNET(tcp_syncache) 173 174 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 175 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 176 "TCP SYN cache"); 177 178 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 179 &VNET_NAME(tcp_syncache.bucket_limit), 0, 180 "Per-bucket hash limit for syncache"); 181 182 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 183 &VNET_NAME(tcp_syncache.cache_limit), 0, 184 "Overall entry limit for syncache"); 185 186 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 187 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 188 189 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 190 &VNET_NAME(tcp_syncache.hashsize), 0, 191 "Size of TCP syncache hashtable"); 192 193 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 194 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 195 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 196 "and mac(4) checks"); 197 198 static int 199 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 200 { 201 int error; 202 u_int new; 203 204 new = V_tcp_syncache.rexmt_limit; 205 error = sysctl_handle_int(oidp, &new, 0, req); 206 if ((error == 0) && (req->newptr != NULL)) { 207 if (new > TCP_MAXRXTSHIFT) 208 error = EINVAL; 209 else 210 V_tcp_syncache.rexmt_limit = new; 211 } 212 return (error); 213 } 214 215 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 216 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 217 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 218 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 219 "Limit on SYN/ACK retransmissions"); 220 221 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 222 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 223 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 224 "Send reset on socket allocation failure"); 225 226 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 227 228 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 229 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 230 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 231 232 /* 233 * Requires the syncache entry to be already removed from the bucket list. 234 */ 235 static void 236 syncache_free(struct syncache *sc) 237 { 238 239 if (sc->sc_ipopts) 240 (void) m_free(sc->sc_ipopts); 241 if (sc->sc_cred) 242 crfree(sc->sc_cred); 243 #ifdef MAC 244 mac_syncache_destroy(&sc->sc_label); 245 #endif 246 247 uma_zfree(V_tcp_syncache.zone, sc); 248 } 249 250 void 251 syncache_init(void) 252 { 253 int i; 254 255 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 256 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 257 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 258 V_tcp_syncache.hash_secret = arc4random(); 259 260 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 261 &V_tcp_syncache.hashsize); 262 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 263 &V_tcp_syncache.bucket_limit); 264 if (!powerof2(V_tcp_syncache.hashsize) || 265 V_tcp_syncache.hashsize == 0) { 266 printf("WARNING: syncache hash size is not a power of 2.\n"); 267 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 268 } 269 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 270 271 /* Set limits. */ 272 V_tcp_syncache.cache_limit = 273 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 274 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 275 &V_tcp_syncache.cache_limit); 276 277 /* Allocate the hash table. */ 278 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 279 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 280 281 #ifdef VIMAGE 282 V_tcp_syncache.vnet = curvnet; 283 #endif 284 285 /* Initialize the hash buckets. */ 286 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 287 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 288 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 289 NULL, MTX_DEF); 290 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 291 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 292 V_tcp_syncache.hashbase[i].sch_length = 0; 293 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 294 V_tcp_syncache.hashbase[i].sch_last_overflow = 295 -(SYNCOOKIE_LIFETIME + 1); 296 } 297 298 /* Create the syncache entry zone. */ 299 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 300 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 301 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 302 V_tcp_syncache.cache_limit); 303 304 /* Start the SYN cookie reseeder callout. */ 305 callout_init(&V_tcp_syncache.secret.reseed, 1); 306 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 307 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 308 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 309 syncookie_reseed, &V_tcp_syncache); 310 311 /* Initialize the pause machinery. */ 312 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 313 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 314 0); 315 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 316 V_tcp_syncache.pause_backoff = 0; 317 V_tcp_syncache.paused = false; 318 } 319 320 #ifdef VIMAGE 321 void 322 syncache_destroy(void) 323 { 324 struct syncache_head *sch; 325 struct syncache *sc, *nsc; 326 int i; 327 328 /* 329 * Stop the re-seed timer before freeing resources. No need to 330 * possibly schedule it another time. 331 */ 332 callout_drain(&V_tcp_syncache.secret.reseed); 333 334 /* Stop the SYN cache pause callout. */ 335 mtx_lock(&V_tcp_syncache.pause_mtx); 336 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 337 mtx_unlock(&V_tcp_syncache.pause_mtx); 338 callout_drain(&V_tcp_syncache.pause_co); 339 } else 340 mtx_unlock(&V_tcp_syncache.pause_mtx); 341 342 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 343 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 344 sch = &V_tcp_syncache.hashbase[i]; 345 callout_drain(&sch->sch_timer); 346 347 SCH_LOCK(sch); 348 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 349 syncache_drop(sc, sch); 350 SCH_UNLOCK(sch); 351 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 352 ("%s: sch->sch_bucket not empty", __func__)); 353 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 354 __func__, sch->sch_length)); 355 mtx_destroy(&sch->sch_mtx); 356 } 357 358 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 359 ("%s: cache_count not 0", __func__)); 360 361 /* Free the allocated global resources. */ 362 uma_zdestroy(V_tcp_syncache.zone); 363 free(V_tcp_syncache.hashbase, M_SYNCACHE); 364 mtx_destroy(&V_tcp_syncache.pause_mtx); 365 } 366 #endif 367 368 /* 369 * Inserts a syncache entry into the specified bucket row. 370 * Locks and unlocks the syncache_head autonomously. 371 */ 372 static void 373 syncache_insert(struct syncache *sc, struct syncache_head *sch) 374 { 375 struct syncache *sc2; 376 377 SCH_LOCK(sch); 378 379 /* 380 * Make sure that we don't overflow the per-bucket limit. 381 * If the bucket is full, toss the oldest element. 382 */ 383 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 384 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 385 ("sch->sch_length incorrect")); 386 syncache_pause(&sc->sc_inc); 387 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 388 sch->sch_last_overflow = time_uptime; 389 syncache_drop(sc2, sch); 390 } 391 392 /* Put it into the bucket. */ 393 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 394 sch->sch_length++; 395 396 #ifdef TCP_OFFLOAD 397 if (ADDED_BY_TOE(sc)) { 398 struct toedev *tod = sc->sc_tod; 399 400 tod->tod_syncache_added(tod, sc->sc_todctx); 401 } 402 #endif 403 404 /* Reinitialize the bucket row's timer. */ 405 if (sch->sch_length == 1) 406 sch->sch_nextc = ticks + INT_MAX; 407 syncache_timeout(sc, sch, 1); 408 409 SCH_UNLOCK(sch); 410 411 TCPSTATES_INC(TCPS_SYN_RECEIVED); 412 TCPSTAT_INC(tcps_sc_added); 413 } 414 415 /* 416 * Remove and free entry from syncache bucket row. 417 * Expects locked syncache head. 418 */ 419 static void 420 syncache_drop(struct syncache *sc, struct syncache_head *sch) 421 { 422 423 SCH_LOCK_ASSERT(sch); 424 425 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 426 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 427 sch->sch_length--; 428 429 #ifdef TCP_OFFLOAD 430 if (ADDED_BY_TOE(sc)) { 431 struct toedev *tod = sc->sc_tod; 432 433 tod->tod_syncache_removed(tod, sc->sc_todctx); 434 } 435 #endif 436 437 syncache_free(sc); 438 } 439 440 /* 441 * Engage/reengage time on bucket row. 442 */ 443 static void 444 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 445 { 446 int rexmt; 447 448 if (sc->sc_rxmits == 0) 449 rexmt = tcp_rexmit_initial; 450 else 451 TCPT_RANGESET(rexmt, 452 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 453 tcp_rexmit_min, TCPTV_REXMTMAX); 454 sc->sc_rxttime = ticks + rexmt; 455 sc->sc_rxmits++; 456 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 457 sch->sch_nextc = sc->sc_rxttime; 458 if (docallout) 459 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 460 syncache_timer, (void *)sch); 461 } 462 } 463 464 /* 465 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 466 * If we have retransmitted an entry the maximum number of times, expire it. 467 * One separate timer for each bucket row. 468 */ 469 static void 470 syncache_timer(void *xsch) 471 { 472 struct syncache_head *sch = (struct syncache_head *)xsch; 473 struct syncache *sc, *nsc; 474 struct epoch_tracker et; 475 int tick = ticks; 476 char *s; 477 bool paused; 478 479 CURVNET_SET(sch->sch_sc->vnet); 480 481 /* NB: syncache_head has already been locked by the callout. */ 482 SCH_LOCK_ASSERT(sch); 483 484 /* 485 * In the following cycle we may remove some entries and/or 486 * advance some timeouts, so re-initialize the bucket timer. 487 */ 488 sch->sch_nextc = tick + INT_MAX; 489 490 /* 491 * If we have paused processing, unconditionally remove 492 * all syncache entries. 493 */ 494 mtx_lock(&V_tcp_syncache.pause_mtx); 495 paused = V_tcp_syncache.paused; 496 mtx_unlock(&V_tcp_syncache.pause_mtx); 497 498 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 499 if (paused) { 500 syncache_drop(sc, sch); 501 continue; 502 } 503 /* 504 * We do not check if the listen socket still exists 505 * and accept the case where the listen socket may be 506 * gone by the time we resend the SYN/ACK. We do 507 * not expect this to happens often. If it does, 508 * then the RST will be sent by the time the remote 509 * host does the SYN/ACK->ACK. 510 */ 511 if (TSTMP_GT(sc->sc_rxttime, tick)) { 512 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 513 sch->sch_nextc = sc->sc_rxttime; 514 continue; 515 } 516 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 517 sc->sc_flags &= ~SCF_ECN_MASK; 518 } 519 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 520 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 521 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 522 "giving up and removing syncache entry\n", 523 s, __func__); 524 free(s, M_TCPLOG); 525 } 526 syncache_drop(sc, sch); 527 TCPSTAT_INC(tcps_sc_stale); 528 continue; 529 } 530 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 531 log(LOG_DEBUG, "%s; %s: Response timeout, " 532 "retransmitting (%u) SYN|ACK\n", 533 s, __func__, sc->sc_rxmits); 534 free(s, M_TCPLOG); 535 } 536 537 NET_EPOCH_ENTER(et); 538 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 539 NET_EPOCH_EXIT(et); 540 TCPSTAT_INC(tcps_sc_retransmitted); 541 syncache_timeout(sc, sch, 0); 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 { 557 558 return (V_tcp_syncookies && (V_tcp_syncache.paused || 559 V_tcp_syncookiesonly)); 560 } 561 562 /* 563 * Find the hash bucket for the given connection. 564 */ 565 static struct syncache_head * 566 syncache_hashbucket(struct in_conninfo *inc) 567 { 568 uint32_t hash; 569 570 /* 571 * The hash is built on foreign port + local port + foreign address. 572 * We rely on the fact that struct in_conninfo starts with 16 bits 573 * of foreign port, then 16 bits of local port then followed by 128 574 * bits of foreign address. In case of IPv4 address, the first 3 575 * 32-bit words of the address always are zeroes. 576 */ 577 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 578 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 579 580 return (&V_tcp_syncache.hashbase[hash]); 581 } 582 583 /* 584 * Find an entry in the syncache. 585 * Returns always with locked syncache_head plus a matching entry or NULL. 586 */ 587 static struct syncache * 588 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 589 { 590 struct syncache *sc; 591 struct syncache_head *sch; 592 593 *schp = sch = syncache_hashbucket(inc); 594 SCH_LOCK(sch); 595 596 /* Circle through bucket row to find matching entry. */ 597 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 598 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 599 sizeof(struct in_endpoints)) == 0) 600 break; 601 602 return (sc); /* Always returns with locked sch. */ 603 } 604 605 /* 606 * This function is called when we get a RST for a 607 * non-existent connection, so that we can see if the 608 * connection is in the syn cache. If it is, zap it. 609 * If required send a challenge ACK. 610 */ 611 void 612 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 613 uint16_t port) 614 { 615 struct syncache *sc; 616 struct syncache_head *sch; 617 char *s = NULL; 618 619 if (syncache_cookiesonly()) 620 return; 621 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 622 SCH_LOCK_ASSERT(sch); 623 624 /* 625 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 626 * See RFC 793 page 65, section SEGMENT ARRIVES. 627 */ 628 if (tcp_get_flags(th) & (TH_ACK|TH_SYN|TH_FIN)) { 629 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 630 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 631 "FIN flag set, segment ignored\n", s, __func__); 632 TCPSTAT_INC(tcps_badrst); 633 goto done; 634 } 635 636 /* 637 * No corresponding connection was found in syncache. 638 * If syncookies are enabled and possibly exclusively 639 * used, or we are under memory pressure, a valid RST 640 * may not find a syncache entry. In that case we're 641 * done and no SYN|ACK retransmissions will happen. 642 * Otherwise the RST was misdirected or spoofed. 643 */ 644 if (sc == NULL) { 645 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 646 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 647 "syncache entry (possibly syncookie only), " 648 "segment ignored\n", s, __func__); 649 TCPSTAT_INC(tcps_badrst); 650 goto done; 651 } 652 653 /* The remote UDP encaps port does not match. */ 654 if (sc->sc_port != port) { 655 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 656 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 657 "syncache entry but non-matching UDP encaps port, " 658 "segment ignored\n", s, __func__); 659 TCPSTAT_INC(tcps_badrst); 660 goto done; 661 } 662 663 /* 664 * If the RST bit is set, check the sequence number to see 665 * if this is a valid reset segment. 666 * 667 * RFC 793 page 37: 668 * In all states except SYN-SENT, all reset (RST) segments 669 * are validated by checking their SEQ-fields. A reset is 670 * valid if its sequence number is in the window. 671 * 672 * RFC 793 page 69: 673 * There are four cases for the acceptability test for an incoming 674 * segment: 675 * 676 * Segment Receive Test 677 * Length Window 678 * ------- ------- ------------------------------------------- 679 * 0 0 SEG.SEQ = RCV.NXT 680 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 681 * >0 0 not acceptable 682 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 683 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 684 * 685 * Note that when receiving a SYN segment in the LISTEN state, 686 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 687 * described in RFC 793, page 66. 688 */ 689 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 690 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 691 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 692 if (V_tcp_insecure_rst || 693 th->th_seq == sc->sc_irs + 1) { 694 syncache_drop(sc, sch); 695 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 696 log(LOG_DEBUG, 697 "%s; %s: Our SYN|ACK was rejected, " 698 "connection attempt aborted by remote " 699 "endpoint\n", 700 s, __func__); 701 TCPSTAT_INC(tcps_sc_reset); 702 } else { 703 TCPSTAT_INC(tcps_badrst); 704 /* Send challenge ACK. */ 705 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 706 log(LOG_DEBUG, "%s; %s: RST with invalid " 707 " SEQ %u != NXT %u (+WND %u), " 708 "sending challenge ACK\n", 709 s, __func__, 710 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 711 syncache_respond(sc, m, TH_ACK); 712 } 713 } else { 714 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 715 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 716 "NXT %u (+WND %u), segment ignored\n", 717 s, __func__, 718 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 719 TCPSTAT_INC(tcps_badrst); 720 } 721 722 done: 723 if (s != NULL) 724 free(s, M_TCPLOG); 725 SCH_UNLOCK(sch); 726 } 727 728 void 729 syncache_badack(struct in_conninfo *inc, uint16_t port) 730 { 731 struct syncache *sc; 732 struct syncache_head *sch; 733 734 if (syncache_cookiesonly()) 735 return; 736 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 737 SCH_LOCK_ASSERT(sch); 738 if ((sc != NULL) && (sc->sc_port == port)) { 739 syncache_drop(sc, sch); 740 TCPSTAT_INC(tcps_sc_badack); 741 } 742 SCH_UNLOCK(sch); 743 } 744 745 void 746 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 747 { 748 struct syncache *sc; 749 struct syncache_head *sch; 750 751 if (syncache_cookiesonly()) 752 return; 753 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 754 SCH_LOCK_ASSERT(sch); 755 if (sc == NULL) 756 goto done; 757 758 /* If the port != sc_port, then it's a bogus ICMP msg */ 759 if (port != sc->sc_port) 760 goto done; 761 762 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 763 if (ntohl(th_seq) != sc->sc_iss) 764 goto done; 765 766 /* 767 * If we've rertransmitted 3 times and this is our second error, 768 * we remove the entry. Otherwise, we allow it to continue on. 769 * This prevents us from incorrectly nuking an entry during a 770 * spurious network outage. 771 * 772 * See tcp_notify(). 773 */ 774 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 775 sc->sc_flags |= SCF_UNREACH; 776 goto done; 777 } 778 syncache_drop(sc, sch); 779 TCPSTAT_INC(tcps_sc_unreach); 780 done: 781 SCH_UNLOCK(sch); 782 } 783 784 /* 785 * Build a new TCP socket structure from a syncache entry. 786 * 787 * On success return the newly created socket with its underlying inp locked. 788 */ 789 static struct socket * 790 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 791 { 792 struct tcp_function_block *blk; 793 struct inpcb *inp = NULL; 794 struct socket *so; 795 struct tcpcb *tp; 796 int error; 797 char *s; 798 799 NET_EPOCH_ASSERT(); 800 801 /* 802 * Ok, create the full blown connection, and set things up 803 * as they would have been set up if we had created the 804 * connection when the SYN arrived. 805 */ 806 if ((so = solisten_clone(lso)) == NULL) 807 goto allocfail; 808 #ifdef MAC 809 mac_socketpeer_set_from_mbuf(m, so); 810 #endif 811 error = in_pcballoc(so, &V_tcbinfo); 812 if (error) { 813 sodealloc(so); 814 goto allocfail; 815 } 816 inp = sotoinpcb(so); 817 if ((tp = tcp_newtcpcb(inp)) == NULL) { 818 in_pcbdetach(inp); 819 in_pcbfree(inp); 820 sodealloc(so); 821 goto allocfail; 822 } 823 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 824 #ifdef INET6 825 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 826 inp->inp_vflag &= ~INP_IPV4; 827 inp->inp_vflag |= INP_IPV6; 828 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 829 } else { 830 inp->inp_vflag &= ~INP_IPV6; 831 inp->inp_vflag |= INP_IPV4; 832 #endif 833 inp->inp_ip_ttl = sc->sc_ip_ttl; 834 inp->inp_ip_tos = sc->sc_ip_tos; 835 inp->inp_laddr = sc->sc_inc.inc_laddr; 836 #ifdef INET6 837 } 838 #endif 839 840 /* 841 * If there's an mbuf and it has a flowid, then let's initialise the 842 * inp with that particular flowid. 843 */ 844 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 845 inp->inp_flowid = m->m_pkthdr.flowid; 846 inp->inp_flowtype = M_HASHTYPE_GET(m); 847 #ifdef NUMA 848 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 849 #endif 850 } 851 852 inp->inp_lport = sc->sc_inc.inc_lport; 853 #ifdef INET6 854 if (inp->inp_vflag & INP_IPV6PROTO) { 855 struct inpcb *oinp = sotoinpcb(lso); 856 857 /* 858 * Inherit socket options from the listening socket. 859 * Note that in6p_inputopts are not (and should not be) 860 * copied, since it stores previously received options and is 861 * used to detect if each new option is different than the 862 * previous one and hence should be passed to a user. 863 * If we copied in6p_inputopts, a user would not be able to 864 * receive options just after calling the accept system call. 865 */ 866 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 867 if (oinp->in6p_outputopts) 868 inp->in6p_outputopts = 869 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 870 inp->in6p_hops = oinp->in6p_hops; 871 } 872 873 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 874 struct in6_addr laddr6; 875 struct sockaddr_in6 sin6; 876 877 sin6.sin6_family = AF_INET6; 878 sin6.sin6_len = sizeof(sin6); 879 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 880 sin6.sin6_port = sc->sc_inc.inc_fport; 881 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 882 laddr6 = inp->in6p_laddr; 883 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 884 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 885 INP_HASH_WLOCK(&V_tcbinfo); 886 error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 887 thread0.td_ucred, m, false); 888 INP_HASH_WUNLOCK(&V_tcbinfo); 889 if (error != 0) { 890 inp->in6p_laddr = laddr6; 891 goto abort; 892 } 893 /* Override flowlabel from in6_pcbconnect. */ 894 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 895 inp->inp_flow |= sc->sc_flowlabel; 896 } 897 #endif /* INET6 */ 898 #if defined(INET) && defined(INET6) 899 else 900 #endif 901 #ifdef INET 902 { 903 struct in_addr laddr; 904 struct sockaddr_in sin; 905 906 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 907 908 if (inp->inp_options == NULL) { 909 inp->inp_options = sc->sc_ipopts; 910 sc->sc_ipopts = NULL; 911 } 912 913 sin.sin_family = AF_INET; 914 sin.sin_len = sizeof(sin); 915 sin.sin_addr = sc->sc_inc.inc_faddr; 916 sin.sin_port = sc->sc_inc.inc_fport; 917 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 918 laddr = inp->inp_laddr; 919 if (inp->inp_laddr.s_addr == INADDR_ANY) 920 inp->inp_laddr = sc->sc_inc.inc_laddr; 921 INP_HASH_WLOCK(&V_tcbinfo); 922 error = in_pcbconnect(inp, (struct sockaddr *)&sin, 923 thread0.td_ucred, false); 924 INP_HASH_WUNLOCK(&V_tcbinfo); 925 if (error != 0) { 926 inp->inp_laddr = laddr; 927 goto abort; 928 } 929 } 930 #endif /* INET */ 931 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 932 /* Copy old policy into new socket's. */ 933 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 934 printf("syncache_socket: could not copy policy\n"); 935 #endif 936 tp->t_state = TCPS_SYN_RECEIVED; 937 tp->iss = sc->sc_iss; 938 tp->irs = sc->sc_irs; 939 tp->t_port = sc->sc_port; 940 tcp_rcvseqinit(tp); 941 tcp_sendseqinit(tp); 942 blk = sototcpcb(lso)->t_fb; 943 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 944 /* 945 * Our parents t_fb was not the default, 946 * we need to release our ref on tp->t_fb and 947 * pickup one on the new entry. 948 */ 949 struct tcp_function_block *rblk; 950 951 rblk = find_and_ref_tcp_fb(blk); 952 KASSERT(rblk != NULL, 953 ("cannot find blk %p out of syncache?", blk)); 954 if (tp->t_fb->tfb_tcp_fb_fini) 955 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 956 refcount_release(&tp->t_fb->tfb_refcnt); 957 tp->t_fb = rblk; 958 /* 959 * XXXrrs this is quite dangerous, it is possible 960 * for the new function to fail to init. We also 961 * are not asking if the handoff_is_ok though at 962 * the very start thats probalbly ok. 963 */ 964 if (tp->t_fb->tfb_tcp_fb_init) { 965 (*tp->t_fb->tfb_tcp_fb_init)(tp); 966 } 967 } 968 tp->snd_wl1 = sc->sc_irs; 969 tp->snd_max = tp->iss + 1; 970 tp->snd_nxt = tp->iss + 1; 971 tp->rcv_up = sc->sc_irs + 1; 972 tp->rcv_wnd = sc->sc_wnd; 973 tp->rcv_adv += tp->rcv_wnd; 974 tp->last_ack_sent = tp->rcv_nxt; 975 976 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 977 if (sc->sc_flags & SCF_NOOPT) 978 tp->t_flags |= TF_NOOPT; 979 else { 980 if (sc->sc_flags & SCF_WINSCALE) { 981 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 982 tp->snd_scale = sc->sc_requested_s_scale; 983 tp->request_r_scale = sc->sc_requested_r_scale; 984 } 985 if (sc->sc_flags & SCF_TIMESTAMP) { 986 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 987 tp->ts_recent = sc->sc_tsreflect; 988 tp->ts_recent_age = tcp_ts_getticks(); 989 tp->ts_offset = sc->sc_tsoff; 990 } 991 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 992 if (sc->sc_flags & SCF_SIGNATURE) 993 tp->t_flags |= TF_SIGNATURE; 994 #endif 995 if (sc->sc_flags & SCF_SACK) 996 tp->t_flags |= TF_SACK_PERMIT; 997 } 998 999 tcp_ecn_syncache_socket(tp, sc); 1000 1001 /* 1002 * Set up MSS and get cached values from tcp_hostcache. 1003 * This might overwrite some of the defaults we just set. 1004 */ 1005 tcp_mss(tp, sc->sc_peer_mss); 1006 1007 /* 1008 * If the SYN,ACK was retransmitted, indicate that CWND to be 1009 * limited to one segment in cc_conn_init(). 1010 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1011 */ 1012 if (sc->sc_rxmits > 1) 1013 tp->snd_cwnd = 1; 1014 1015 #ifdef TCP_OFFLOAD 1016 /* 1017 * Allow a TOE driver to install its hooks. Note that we hold the 1018 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1019 * new connection before the TOE driver has done its thing. 1020 */ 1021 if (ADDED_BY_TOE(sc)) { 1022 struct toedev *tod = sc->sc_tod; 1023 1024 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1025 } 1026 #endif 1027 /* 1028 * Copy and activate timers. 1029 */ 1030 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1031 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1032 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1033 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1034 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1035 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1036 1037 TCPSTAT_INC(tcps_accepts); 1038 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1039 1040 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1041 tp->t_flags |= TF_SONOTCONN; 1042 1043 return (so); 1044 1045 allocfail: 1046 /* 1047 * Drop the connection; we will either send a RST or have the peer 1048 * retransmit its SYN again after its RTO and try again. 1049 */ 1050 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1051 log(LOG_DEBUG, "%s; %s: Socket create failed " 1052 "due to limits or memory shortage\n", 1053 s, __func__); 1054 free(s, M_TCPLOG); 1055 } 1056 TCPSTAT_INC(tcps_listendrop); 1057 return (NULL); 1058 1059 abort: 1060 in_pcbdetach(inp); 1061 in_pcbfree(inp); 1062 sodealloc(so); 1063 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1064 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1065 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1066 error); 1067 free(s, M_TCPLOG); 1068 } 1069 TCPSTAT_INC(tcps_listendrop); 1070 return (NULL); 1071 } 1072 1073 /* 1074 * This function gets called when we receive an ACK for a 1075 * socket in the LISTEN state. We look up the connection 1076 * in the syncache, and if its there, we pull it out of 1077 * the cache and turn it into a full-blown connection in 1078 * the SYN-RECEIVED state. 1079 * 1080 * On syncache_socket() success the newly created socket 1081 * has its underlying inp locked. 1082 */ 1083 int 1084 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1085 struct socket **lsop, struct mbuf *m, uint16_t port) 1086 { 1087 struct syncache *sc; 1088 struct syncache_head *sch; 1089 struct syncache scs; 1090 char *s; 1091 bool locked; 1092 1093 NET_EPOCH_ASSERT(); 1094 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1095 ("%s: can handle only ACK", __func__)); 1096 1097 if (syncache_cookiesonly()) { 1098 sc = NULL; 1099 sch = syncache_hashbucket(inc); 1100 locked = false; 1101 } else { 1102 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1103 locked = true; 1104 SCH_LOCK_ASSERT(sch); 1105 } 1106 1107 #ifdef INVARIANTS 1108 /* 1109 * Test code for syncookies comparing the syncache stored 1110 * values with the reconstructed values from the cookie. 1111 */ 1112 if (sc != NULL) 1113 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1114 #endif 1115 1116 if (sc == NULL) { 1117 /* 1118 * There is no syncache entry, so see if this ACK is 1119 * a returning syncookie. To do this, first: 1120 * A. Check if syncookies are used in case of syncache 1121 * overflows 1122 * B. See if this socket has had a syncache entry dropped in 1123 * the recent past. We don't want to accept a bogus 1124 * syncookie if we've never received a SYN or accept it 1125 * twice. 1126 * C. check that the syncookie is valid. If it is, then 1127 * cobble up a fake syncache entry, and return. 1128 */ 1129 if (locked && !V_tcp_syncookies) { 1130 SCH_UNLOCK(sch); 1131 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1132 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1133 "segment rejected (syncookies disabled)\n", 1134 s, __func__); 1135 goto failed; 1136 } 1137 if (locked && !V_tcp_syncookiesonly && 1138 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1139 SCH_UNLOCK(sch); 1140 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1141 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1142 "segment rejected (no syncache entry)\n", 1143 s, __func__); 1144 goto failed; 1145 } 1146 bzero(&scs, sizeof(scs)); 1147 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1148 if (locked) 1149 SCH_UNLOCK(sch); 1150 if (sc == NULL) { 1151 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1152 log(LOG_DEBUG, "%s; %s: Segment failed " 1153 "SYNCOOKIE authentication, segment rejected " 1154 "(probably spoofed)\n", s, __func__); 1155 goto failed; 1156 } 1157 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1158 /* If received ACK has MD5 signature, check it. */ 1159 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1160 (!TCPMD5_ENABLED() || 1161 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1162 /* Drop the ACK. */ 1163 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1164 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1165 "MD5 signature doesn't match.\n", 1166 s, __func__); 1167 free(s, M_TCPLOG); 1168 } 1169 TCPSTAT_INC(tcps_sig_err_sigopt); 1170 return (-1); /* Do not send RST */ 1171 } 1172 #endif /* TCP_SIGNATURE */ 1173 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1174 } else { 1175 if (sc->sc_port != port) { 1176 SCH_UNLOCK(sch); 1177 return (0); 1178 } 1179 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1180 /* 1181 * If listening socket requested TCP digests, check that 1182 * received ACK has signature and it is correct. 1183 * If not, drop the ACK and leave sc entry in th cache, 1184 * because SYN was received with correct signature. 1185 */ 1186 if (sc->sc_flags & SCF_SIGNATURE) { 1187 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1188 /* No signature */ 1189 TCPSTAT_INC(tcps_sig_err_nosigopt); 1190 SCH_UNLOCK(sch); 1191 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1192 log(LOG_DEBUG, "%s; %s: Segment " 1193 "rejected, MD5 signature wasn't " 1194 "provided.\n", s, __func__); 1195 free(s, M_TCPLOG); 1196 } 1197 return (-1); /* Do not send RST */ 1198 } 1199 if (!TCPMD5_ENABLED() || 1200 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1201 /* Doesn't match or no SA */ 1202 SCH_UNLOCK(sch); 1203 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1204 log(LOG_DEBUG, "%s; %s: Segment " 1205 "rejected, MD5 signature doesn't " 1206 "match.\n", s, __func__); 1207 free(s, M_TCPLOG); 1208 } 1209 return (-1); /* Do not send RST */ 1210 } 1211 } 1212 #endif /* TCP_SIGNATURE */ 1213 1214 /* 1215 * RFC 7323 PAWS: If we have a timestamp on this segment and 1216 * it's less than ts_recent, drop it. 1217 * XXXMT: RFC 7323 also requires to send an ACK. 1218 * In tcp_input.c this is only done for TCP segments 1219 * with user data, so be consistent here and just drop 1220 * the segment. 1221 */ 1222 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1223 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1224 SCH_UNLOCK(sch); 1225 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1226 log(LOG_DEBUG, 1227 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1228 "segment dropped\n", s, __func__, 1229 to->to_tsval, sc->sc_tsreflect); 1230 free(s, M_TCPLOG); 1231 } 1232 return (-1); /* Do not send RST */ 1233 } 1234 1235 /* 1236 * If timestamps were not negotiated during SYN/ACK and a 1237 * segment with a timestamp is received, ignore the 1238 * timestamp and process the packet normally. 1239 * See section 3.2 of RFC 7323. 1240 */ 1241 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1242 (to->to_flags & TOF_TS)) { 1243 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1244 log(LOG_DEBUG, "%s; %s: Timestamp not " 1245 "expected, segment processed normally\n", 1246 s, __func__); 1247 free(s, M_TCPLOG); 1248 s = NULL; 1249 } 1250 } 1251 1252 /* 1253 * If timestamps were negotiated during SYN/ACK and a 1254 * segment without a timestamp is received, silently drop 1255 * the segment, unless the missing timestamps are tolerated. 1256 * See section 3.2 of RFC 7323. 1257 */ 1258 if ((sc->sc_flags & SCF_TIMESTAMP) && 1259 !(to->to_flags & TOF_TS)) { 1260 if (V_tcp_tolerate_missing_ts) { 1261 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1262 log(LOG_DEBUG, 1263 "%s; %s: Timestamp missing, " 1264 "segment processed normally\n", 1265 s, __func__); 1266 free(s, M_TCPLOG); 1267 } 1268 } else { 1269 SCH_UNLOCK(sch); 1270 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1271 log(LOG_DEBUG, 1272 "%s; %s: Timestamp missing, " 1273 "segment silently dropped\n", 1274 s, __func__); 1275 free(s, M_TCPLOG); 1276 } 1277 return (-1); /* Do not send RST */ 1278 } 1279 } 1280 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1281 sch->sch_length--; 1282 #ifdef TCP_OFFLOAD 1283 if (ADDED_BY_TOE(sc)) { 1284 struct toedev *tod = sc->sc_tod; 1285 1286 tod->tod_syncache_removed(tod, sc->sc_todctx); 1287 } 1288 #endif 1289 SCH_UNLOCK(sch); 1290 } 1291 1292 /* 1293 * Segment validation: 1294 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1295 */ 1296 if (th->th_ack != sc->sc_iss + 1) { 1297 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1298 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1299 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1300 goto failed; 1301 } 1302 1303 /* 1304 * The SEQ must fall in the window starting at the received 1305 * initial receive sequence number + 1 (the SYN). 1306 */ 1307 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1308 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1309 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1310 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1311 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1312 goto failed; 1313 } 1314 1315 *lsop = syncache_socket(sc, *lsop, m); 1316 1317 if (*lsop == NULL) 1318 TCPSTAT_INC(tcps_sc_aborted); 1319 else 1320 TCPSTAT_INC(tcps_sc_completed); 1321 1322 /* how do we find the inp for the new socket? */ 1323 if (sc != &scs) 1324 syncache_free(sc); 1325 return (1); 1326 failed: 1327 if (sc != NULL) { 1328 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1329 if (sc != &scs) 1330 syncache_free(sc); 1331 } 1332 if (s != NULL) 1333 free(s, M_TCPLOG); 1334 *lsop = NULL; 1335 return (0); 1336 } 1337 1338 static struct socket * 1339 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1340 uint64_t response_cookie) 1341 { 1342 struct inpcb *inp; 1343 struct tcpcb *tp; 1344 unsigned int *pending_counter; 1345 struct socket *so; 1346 1347 NET_EPOCH_ASSERT(); 1348 1349 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1350 so = syncache_socket(sc, lso, m); 1351 if (so == NULL) { 1352 TCPSTAT_INC(tcps_sc_aborted); 1353 atomic_subtract_int(pending_counter, 1); 1354 } else { 1355 soisconnected(so); 1356 inp = sotoinpcb(so); 1357 tp = intotcpcb(inp); 1358 tp->t_flags |= TF_FASTOPEN; 1359 tp->t_tfo_cookie.server = response_cookie; 1360 tp->snd_max = tp->iss; 1361 tp->snd_nxt = tp->iss; 1362 tp->t_tfo_pending = pending_counter; 1363 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1364 TCPSTAT_INC(tcps_sc_completed); 1365 } 1366 1367 return (so); 1368 } 1369 1370 /* 1371 * Given a LISTEN socket and an inbound SYN request, add 1372 * this to the syn cache, and send back a segment: 1373 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1374 * to the source. 1375 * 1376 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1377 * Doing so would require that we hold onto the data and deliver it 1378 * to the application. However, if we are the target of a SYN-flood 1379 * DoS attack, an attacker could send data which would eventually 1380 * consume all available buffer space if it were ACKed. By not ACKing 1381 * the data, we avoid this DoS scenario. 1382 * 1383 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1384 * cookie is processed and a new socket is created. In this case, any data 1385 * accompanying the SYN will be queued to the socket by tcp_input() and will 1386 * be ACKed either when the application sends response data or the delayed 1387 * ACK timer expires, whichever comes first. 1388 */ 1389 struct socket * 1390 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1391 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1392 void *todctx, uint8_t iptos, uint16_t port) 1393 { 1394 struct tcpcb *tp; 1395 struct socket *rv = NULL; 1396 struct syncache *sc = NULL; 1397 struct syncache_head *sch; 1398 struct mbuf *ipopts = NULL; 1399 u_int ltflags; 1400 int win, ip_ttl, ip_tos; 1401 char *s; 1402 #ifdef INET6 1403 int autoflowlabel = 0; 1404 #endif 1405 #ifdef MAC 1406 struct label *maclabel; 1407 #endif 1408 struct syncache scs; 1409 struct ucred *cred; 1410 uint64_t tfo_response_cookie; 1411 unsigned int *tfo_pending = NULL; 1412 int tfo_cookie_valid = 0; 1413 int tfo_response_cookie_valid = 0; 1414 bool locked; 1415 1416 INP_RLOCK_ASSERT(inp); /* listen socket */ 1417 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1418 ("%s: unexpected tcp flags", __func__)); 1419 1420 /* 1421 * Combine all so/tp operations very early to drop the INP lock as 1422 * soon as possible. 1423 */ 1424 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1425 tp = sototcpcb(so); 1426 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1427 1428 #ifdef INET6 1429 if (inc->inc_flags & INC_ISIPV6) { 1430 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1431 autoflowlabel = 1; 1432 } 1433 ip_ttl = in6_selecthlim(inp, NULL); 1434 if ((inp->in6p_outputopts == NULL) || 1435 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1436 ip_tos = 0; 1437 } else { 1438 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1439 } 1440 } 1441 #endif 1442 #if defined(INET6) && defined(INET) 1443 else 1444 #endif 1445 #ifdef INET 1446 { 1447 ip_ttl = inp->inp_ip_ttl; 1448 ip_tos = inp->inp_ip_tos; 1449 } 1450 #endif 1451 win = so->sol_sbrcv_hiwat; 1452 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1453 1454 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1455 (tp->t_tfo_pending != NULL) && 1456 (to->to_flags & TOF_FASTOPEN)) { 1457 /* 1458 * Limit the number of pending TFO connections to 1459 * approximately half of the queue limit. This prevents TFO 1460 * SYN floods from starving the service by filling the 1461 * listen queue with bogus TFO connections. 1462 */ 1463 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1464 (so->sol_qlimit / 2)) { 1465 int result; 1466 1467 result = tcp_fastopen_check_cookie(inc, 1468 to->to_tfo_cookie, to->to_tfo_len, 1469 &tfo_response_cookie); 1470 tfo_cookie_valid = (result > 0); 1471 tfo_response_cookie_valid = (result >= 0); 1472 } 1473 1474 /* 1475 * Remember the TFO pending counter as it will have to be 1476 * decremented below if we don't make it to syncache_tfo_expand(). 1477 */ 1478 tfo_pending = tp->t_tfo_pending; 1479 } 1480 1481 #ifdef MAC 1482 if (mac_syncache_init(&maclabel) != 0) { 1483 INP_RUNLOCK(inp); 1484 goto done; 1485 } else 1486 mac_syncache_create(maclabel, inp); 1487 #endif 1488 if (!tfo_cookie_valid) 1489 INP_RUNLOCK(inp); 1490 1491 /* 1492 * Remember the IP options, if any. 1493 */ 1494 #ifdef INET6 1495 if (!(inc->inc_flags & INC_ISIPV6)) 1496 #endif 1497 #ifdef INET 1498 ipopts = (m) ? ip_srcroute(m) : NULL; 1499 #else 1500 ipopts = NULL; 1501 #endif 1502 1503 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1504 /* 1505 * When the socket is TCP-MD5 enabled check that, 1506 * - a signed packet is valid 1507 * - a non-signed packet does not have a security association 1508 * 1509 * If a signed packet fails validation or a non-signed packet has a 1510 * security association, the packet will be dropped. 1511 */ 1512 if (ltflags & TF_SIGNATURE) { 1513 if (to->to_flags & TOF_SIGNATURE) { 1514 if (!TCPMD5_ENABLED() || 1515 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1516 goto done; 1517 } else { 1518 if (TCPMD5_ENABLED() && 1519 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1520 goto done; 1521 } 1522 } else if (to->to_flags & TOF_SIGNATURE) 1523 goto done; 1524 #endif /* TCP_SIGNATURE */ 1525 /* 1526 * See if we already have an entry for this connection. 1527 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1528 * 1529 * XXX: should the syncache be re-initialized with the contents 1530 * of the new SYN here (which may have different options?) 1531 * 1532 * XXX: We do not check the sequence number to see if this is a 1533 * real retransmit or a new connection attempt. The question is 1534 * how to handle such a case; either ignore it as spoofed, or 1535 * drop the current entry and create a new one? 1536 */ 1537 if (syncache_cookiesonly()) { 1538 sc = NULL; 1539 sch = syncache_hashbucket(inc); 1540 locked = false; 1541 } else { 1542 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1543 locked = true; 1544 SCH_LOCK_ASSERT(sch); 1545 } 1546 if (sc != NULL) { 1547 if (tfo_cookie_valid) 1548 INP_RUNLOCK(inp); 1549 TCPSTAT_INC(tcps_sc_dupsyn); 1550 if (ipopts) { 1551 /* 1552 * If we were remembering a previous source route, 1553 * forget it and use the new one we've been given. 1554 */ 1555 if (sc->sc_ipopts) 1556 (void) m_free(sc->sc_ipopts); 1557 sc->sc_ipopts = ipopts; 1558 } 1559 /* 1560 * Update timestamp if present. 1561 */ 1562 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1563 sc->sc_tsreflect = to->to_tsval; 1564 else 1565 sc->sc_flags &= ~SCF_TIMESTAMP; 1566 /* 1567 * Adjust ECN response if needed, e.g. different 1568 * IP ECN field, or a fallback by the remote host. 1569 */ 1570 if (sc->sc_flags & SCF_ECN_MASK) { 1571 sc->sc_flags &= ~SCF_ECN_MASK; 1572 sc->sc_flags = tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1573 } 1574 #ifdef MAC 1575 /* 1576 * Since we have already unconditionally allocated label 1577 * storage, free it up. The syncache entry will already 1578 * have an initialized label we can use. 1579 */ 1580 mac_syncache_destroy(&maclabel); 1581 #endif 1582 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1583 /* Retransmit SYN|ACK and reset retransmit count. */ 1584 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1585 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1586 "resetting timer and retransmitting SYN|ACK\n", 1587 s, __func__); 1588 free(s, M_TCPLOG); 1589 } 1590 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1591 sc->sc_rxmits = 0; 1592 syncache_timeout(sc, sch, 1); 1593 TCPSTAT_INC(tcps_sndacks); 1594 TCPSTAT_INC(tcps_sndtotal); 1595 } 1596 SCH_UNLOCK(sch); 1597 goto donenoprobe; 1598 } 1599 1600 if (tfo_cookie_valid) { 1601 bzero(&scs, sizeof(scs)); 1602 sc = &scs; 1603 goto skip_alloc; 1604 } 1605 1606 /* 1607 * Skip allocating a syncache entry if we are just going to discard 1608 * it later. 1609 */ 1610 if (!locked) { 1611 bzero(&scs, sizeof(scs)); 1612 sc = &scs; 1613 } else 1614 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1615 if (sc == NULL) { 1616 /* 1617 * The zone allocator couldn't provide more entries. 1618 * Treat this as if the cache was full; drop the oldest 1619 * entry and insert the new one. 1620 */ 1621 TCPSTAT_INC(tcps_sc_zonefail); 1622 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1623 sch->sch_last_overflow = time_uptime; 1624 syncache_drop(sc, sch); 1625 syncache_pause(inc); 1626 } 1627 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1628 if (sc == NULL) { 1629 if (V_tcp_syncookies) { 1630 bzero(&scs, sizeof(scs)); 1631 sc = &scs; 1632 } else { 1633 KASSERT(locked, 1634 ("%s: bucket unexpectedly unlocked", 1635 __func__)); 1636 SCH_UNLOCK(sch); 1637 if (ipopts) 1638 (void) m_free(ipopts); 1639 goto done; 1640 } 1641 } 1642 } 1643 1644 skip_alloc: 1645 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1646 sc->sc_tfo_cookie = &tfo_response_cookie; 1647 1648 /* 1649 * Fill in the syncache values. 1650 */ 1651 #ifdef MAC 1652 sc->sc_label = maclabel; 1653 #endif 1654 sc->sc_cred = cred; 1655 sc->sc_port = port; 1656 cred = NULL; 1657 sc->sc_ipopts = ipopts; 1658 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1659 sc->sc_ip_tos = ip_tos; 1660 sc->sc_ip_ttl = ip_ttl; 1661 #ifdef TCP_OFFLOAD 1662 sc->sc_tod = tod; 1663 sc->sc_todctx = todctx; 1664 #endif 1665 sc->sc_irs = th->th_seq; 1666 sc->sc_flags = 0; 1667 sc->sc_flowlabel = 0; 1668 1669 /* 1670 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1671 * win was derived from socket earlier in the function. 1672 */ 1673 win = imax(win, 0); 1674 win = imin(win, TCP_MAXWIN); 1675 sc->sc_wnd = win; 1676 1677 if (V_tcp_do_rfc1323 && 1678 !(ltflags & TF_NOOPT)) { 1679 /* 1680 * A timestamp received in a SYN makes 1681 * it ok to send timestamp requests and replies. 1682 */ 1683 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1684 sc->sc_tsreflect = to->to_tsval; 1685 sc->sc_flags |= SCF_TIMESTAMP; 1686 sc->sc_tsoff = tcp_new_ts_offset(inc); 1687 } 1688 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1689 int wscale = 0; 1690 1691 /* 1692 * Pick the smallest possible scaling factor that 1693 * will still allow us to scale up to sb_max, aka 1694 * kern.ipc.maxsockbuf. 1695 * 1696 * We do this because there are broken firewalls that 1697 * will corrupt the window scale option, leading to 1698 * the other endpoint believing that our advertised 1699 * window is unscaled. At scale factors larger than 1700 * 5 the unscaled window will drop below 1500 bytes, 1701 * leading to serious problems when traversing these 1702 * broken firewalls. 1703 * 1704 * With the default maxsockbuf of 256K, a scale factor 1705 * of 3 will be chosen by this algorithm. Those who 1706 * choose a larger maxsockbuf should watch out 1707 * for the compatibility problems mentioned above. 1708 * 1709 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1710 * or <SYN,ACK>) segment itself is never scaled. 1711 */ 1712 while (wscale < TCP_MAX_WINSHIFT && 1713 (TCP_MAXWIN << wscale) < sb_max) 1714 wscale++; 1715 sc->sc_requested_r_scale = wscale; 1716 sc->sc_requested_s_scale = to->to_wscale; 1717 sc->sc_flags |= SCF_WINSCALE; 1718 } 1719 } 1720 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1721 /* 1722 * If incoming packet has an MD5 signature, flag this in the 1723 * syncache so that syncache_respond() will do the right thing 1724 * with the SYN+ACK. 1725 */ 1726 if (to->to_flags & TOF_SIGNATURE) 1727 sc->sc_flags |= SCF_SIGNATURE; 1728 #endif /* TCP_SIGNATURE */ 1729 if (to->to_flags & TOF_SACKPERM) 1730 sc->sc_flags |= SCF_SACK; 1731 if (to->to_flags & TOF_MSS) 1732 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1733 if (ltflags & TF_NOOPT) 1734 sc->sc_flags |= SCF_NOOPT; 1735 /* ECN Handshake */ 1736 if (V_tcp_do_ecn) 1737 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1738 1739 if (V_tcp_syncookies) 1740 sc->sc_iss = syncookie_generate(sch, sc); 1741 else 1742 sc->sc_iss = arc4random(); 1743 #ifdef INET6 1744 if (autoflowlabel) { 1745 if (V_tcp_syncookies) 1746 sc->sc_flowlabel = sc->sc_iss; 1747 else 1748 sc->sc_flowlabel = ip6_randomflowlabel(); 1749 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1750 } 1751 #endif 1752 if (locked) 1753 SCH_UNLOCK(sch); 1754 1755 if (tfo_cookie_valid) { 1756 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1757 /* INP_RUNLOCK(inp) will be performed by the caller */ 1758 goto tfo_expanded; 1759 } 1760 1761 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1762 /* 1763 * Do a standard 3-way handshake. 1764 */ 1765 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1766 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1767 syncache_free(sc); 1768 else if (sc != &scs) 1769 syncache_insert(sc, sch); /* locks and unlocks sch */ 1770 TCPSTAT_INC(tcps_sndacks); 1771 TCPSTAT_INC(tcps_sndtotal); 1772 } else { 1773 if (sc != &scs) 1774 syncache_free(sc); 1775 TCPSTAT_INC(tcps_sc_dropped); 1776 } 1777 goto donenoprobe; 1778 1779 done: 1780 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1781 donenoprobe: 1782 if (m) 1783 m_freem(m); 1784 /* 1785 * If tfo_pending is not NULL here, then a TFO SYN that did not 1786 * result in a new socket was processed and the associated pending 1787 * counter has not yet been decremented. All such TFO processing paths 1788 * transit this point. 1789 */ 1790 if (tfo_pending != NULL) 1791 tcp_fastopen_decrement_counter(tfo_pending); 1792 1793 tfo_expanded: 1794 if (cred != NULL) 1795 crfree(cred); 1796 #ifdef MAC 1797 if (sc == &scs) 1798 mac_syncache_destroy(&maclabel); 1799 #endif 1800 return (rv); 1801 } 1802 1803 /* 1804 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1805 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1806 */ 1807 static int 1808 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1809 { 1810 struct ip *ip = NULL; 1811 struct mbuf *m; 1812 struct tcphdr *th = NULL; 1813 struct udphdr *udp = NULL; 1814 int optlen, error = 0; /* Make compiler happy */ 1815 u_int16_t hlen, tlen, mssopt, ulen; 1816 struct tcpopt to; 1817 #ifdef INET6 1818 struct ip6_hdr *ip6 = NULL; 1819 #endif 1820 1821 NET_EPOCH_ASSERT(); 1822 1823 hlen = 1824 #ifdef INET6 1825 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1826 #endif 1827 sizeof(struct ip); 1828 tlen = hlen + sizeof(struct tcphdr); 1829 if (sc->sc_port) { 1830 tlen += sizeof(struct udphdr); 1831 } 1832 /* Determine MSS we advertize to other end of connection. */ 1833 mssopt = tcp_mssopt(&sc->sc_inc); 1834 if (sc->sc_port) 1835 mssopt -= V_tcp_udp_tunneling_overhead; 1836 mssopt = max(mssopt, V_tcp_minmss); 1837 1838 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1839 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1840 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1841 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1842 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1843 1844 /* Create the IP+TCP header from scratch. */ 1845 m = m_gethdr(M_NOWAIT, MT_DATA); 1846 if (m == NULL) 1847 return (ENOBUFS); 1848 #ifdef MAC 1849 mac_syncache_create_mbuf(sc->sc_label, m); 1850 #endif 1851 m->m_data += max_linkhdr; 1852 m->m_len = tlen; 1853 m->m_pkthdr.len = tlen; 1854 m->m_pkthdr.rcvif = NULL; 1855 1856 #ifdef INET6 1857 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1858 ip6 = mtod(m, struct ip6_hdr *); 1859 ip6->ip6_vfc = IPV6_VERSION; 1860 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1861 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1862 ip6->ip6_plen = htons(tlen - hlen); 1863 /* ip6_hlim is set after checksum */ 1864 /* Zero out traffic class and flow label. */ 1865 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1866 ip6->ip6_flow |= sc->sc_flowlabel; 1867 if (sc->sc_port != 0) { 1868 ip6->ip6_nxt = IPPROTO_UDP; 1869 udp = (struct udphdr *)(ip6 + 1); 1870 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1871 udp->uh_dport = sc->sc_port; 1872 ulen = (tlen - sizeof(struct ip6_hdr)); 1873 th = (struct tcphdr *)(udp + 1); 1874 } else { 1875 ip6->ip6_nxt = IPPROTO_TCP; 1876 th = (struct tcphdr *)(ip6 + 1); 1877 } 1878 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20); 1879 } 1880 #endif 1881 #if defined(INET6) && defined(INET) 1882 else 1883 #endif 1884 #ifdef INET 1885 { 1886 ip = mtod(m, struct ip *); 1887 ip->ip_v = IPVERSION; 1888 ip->ip_hl = sizeof(struct ip) >> 2; 1889 ip->ip_len = htons(tlen); 1890 ip->ip_id = 0; 1891 ip->ip_off = 0; 1892 ip->ip_sum = 0; 1893 ip->ip_src = sc->sc_inc.inc_laddr; 1894 ip->ip_dst = sc->sc_inc.inc_faddr; 1895 ip->ip_ttl = sc->sc_ip_ttl; 1896 ip->ip_tos = sc->sc_ip_tos; 1897 1898 /* 1899 * See if we should do MTU discovery. Route lookups are 1900 * expensive, so we will only unset the DF bit if: 1901 * 1902 * 1) path_mtu_discovery is disabled 1903 * 2) the SCF_UNREACH flag has been set 1904 */ 1905 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1906 ip->ip_off |= htons(IP_DF); 1907 if (sc->sc_port == 0) { 1908 ip->ip_p = IPPROTO_TCP; 1909 th = (struct tcphdr *)(ip + 1); 1910 } else { 1911 ip->ip_p = IPPROTO_UDP; 1912 udp = (struct udphdr *)(ip + 1); 1913 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1914 udp->uh_dport = sc->sc_port; 1915 ulen = (tlen - sizeof(struct ip)); 1916 th = (struct tcphdr *)(udp + 1); 1917 } 1918 } 1919 #endif /* INET */ 1920 th->th_sport = sc->sc_inc.inc_lport; 1921 th->th_dport = sc->sc_inc.inc_fport; 1922 1923 if (flags & TH_SYN) 1924 th->th_seq = htonl(sc->sc_iss); 1925 else 1926 th->th_seq = htonl(sc->sc_iss + 1); 1927 th->th_ack = htonl(sc->sc_irs + 1); 1928 th->th_off = sizeof(struct tcphdr) >> 2; 1929 th->th_win = htons(sc->sc_wnd); 1930 th->th_urp = 0; 1931 1932 flags = tcp_ecn_syncache_respond(flags, sc); 1933 tcp_set_flags(th, flags); 1934 1935 /* Tack on the TCP options. */ 1936 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1937 to.to_flags = 0; 1938 1939 if (flags & TH_SYN) { 1940 to.to_mss = mssopt; 1941 to.to_flags = TOF_MSS; 1942 if (sc->sc_flags & SCF_WINSCALE) { 1943 to.to_wscale = sc->sc_requested_r_scale; 1944 to.to_flags |= TOF_SCALE; 1945 } 1946 if (sc->sc_flags & SCF_SACK) 1947 to.to_flags |= TOF_SACKPERM; 1948 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1949 if (sc->sc_flags & SCF_SIGNATURE) 1950 to.to_flags |= TOF_SIGNATURE; 1951 #endif 1952 if (sc->sc_tfo_cookie) { 1953 to.to_flags |= TOF_FASTOPEN; 1954 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1955 to.to_tfo_cookie = sc->sc_tfo_cookie; 1956 /* don't send cookie again when retransmitting response */ 1957 sc->sc_tfo_cookie = NULL; 1958 } 1959 } 1960 if (sc->sc_flags & SCF_TIMESTAMP) { 1961 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1962 to.to_tsecr = sc->sc_tsreflect; 1963 to.to_flags |= TOF_TS; 1964 } 1965 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1966 1967 /* Adjust headers by option size. */ 1968 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1969 m->m_len += optlen; 1970 m->m_pkthdr.len += optlen; 1971 #ifdef INET6 1972 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1973 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1974 else 1975 #endif 1976 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1977 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1978 if (sc->sc_flags & SCF_SIGNATURE) { 1979 KASSERT(to.to_flags & TOF_SIGNATURE, 1980 ("tcp_addoptions() didn't set tcp_signature")); 1981 1982 /* NOTE: to.to_signature is inside of mbuf */ 1983 if (!TCPMD5_ENABLED() || 1984 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1985 m_freem(m); 1986 return (EACCES); 1987 } 1988 } 1989 #endif 1990 } else 1991 optlen = 0; 1992 1993 if (udp) { 1994 ulen += optlen; 1995 udp->uh_ulen = htons(ulen); 1996 } 1997 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1998 /* 1999 * If we have peer's SYN and it has a flowid, then let's assign it to 2000 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 2001 * to SYN|ACK due to lack of inp here. 2002 */ 2003 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2004 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2005 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2006 } 2007 #ifdef INET6 2008 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2009 if (sc->sc_port) { 2010 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2011 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2012 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2013 IPPROTO_UDP, 0); 2014 th->th_sum = htons(0); 2015 } else { 2016 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2017 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2018 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2019 IPPROTO_TCP, 0); 2020 } 2021 ip6->ip6_hlim = sc->sc_ip_ttl; 2022 #ifdef TCP_OFFLOAD 2023 if (ADDED_BY_TOE(sc)) { 2024 struct toedev *tod = sc->sc_tod; 2025 2026 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2027 2028 return (error); 2029 } 2030 #endif 2031 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2032 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2033 } 2034 #endif 2035 #if defined(INET6) && defined(INET) 2036 else 2037 #endif 2038 #ifdef INET 2039 { 2040 if (sc->sc_port) { 2041 m->m_pkthdr.csum_flags = CSUM_UDP; 2042 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2043 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2044 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2045 th->th_sum = htons(0); 2046 } else { 2047 m->m_pkthdr.csum_flags = CSUM_TCP; 2048 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2049 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2050 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2051 } 2052 #ifdef TCP_OFFLOAD 2053 if (ADDED_BY_TOE(sc)) { 2054 struct toedev *tod = sc->sc_tod; 2055 2056 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2057 2058 return (error); 2059 } 2060 #endif 2061 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2062 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2063 } 2064 #endif 2065 return (error); 2066 } 2067 2068 /* 2069 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2070 * that exceed the capacity of the syncache by avoiding the storage of any 2071 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2072 * attacks where the attacker does not have access to our responses. 2073 * 2074 * Syncookies encode and include all necessary information about the 2075 * connection setup within the SYN|ACK that we send back. That way we 2076 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2077 * (if ever). Normally the syncache and syncookies are running in parallel 2078 * with the latter taking over when the former is exhausted. When matching 2079 * syncache entry is found the syncookie is ignored. 2080 * 2081 * The only reliable information persisting the 3WHS is our initial sequence 2082 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2083 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2084 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2085 * returns and signifies a legitimate connection if it matches the ACK. 2086 * 2087 * The available space of 32 bits to store the hash and to encode the SYN 2088 * option information is very tight and we should have at least 24 bits for 2089 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2090 * 2091 * SYN option information we have to encode to fully restore a connection: 2092 * MSS: is imporant to chose an optimal segment size to avoid IP level 2093 * fragmentation along the path. The common MSS values can be encoded 2094 * in a 3-bit table. Uncommon values are captured by the next lower value 2095 * in the table leading to a slight increase in packetization overhead. 2096 * WSCALE: is necessary to allow large windows to be used for high delay- 2097 * bandwidth product links. Not scaling the window when it was initially 2098 * negotiated is bad for performance as lack of scaling further decreases 2099 * the apparent available send window. We only need to encode the WSCALE 2100 * we received from the remote end. Our end can be recalculated at any 2101 * time. The common WSCALE values can be encoded in a 3-bit table. 2102 * Uncommon values are captured by the next lower value in the table 2103 * making us under-estimate the available window size halving our 2104 * theoretically possible maximum throughput for that connection. 2105 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2106 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2107 * that are included in all segments on a connection. We enable them when 2108 * the ACK has them. 2109 * 2110 * Security of syncookies and attack vectors: 2111 * 2112 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2113 * together with the gloabl secret to make it unique per connection attempt. 2114 * Thus any change of any of those parameters results in a different MAC output 2115 * in an unpredictable way unless a collision is encountered. 24 bits of the 2116 * MAC are embedded into the ISS. 2117 * 2118 * To prevent replay attacks two rotating global secrets are updated with a 2119 * new random value every 15 seconds. The life-time of a syncookie is thus 2120 * 15-30 seconds. 2121 * 2122 * Vector 1: Attacking the secret. This requires finding a weakness in the 2123 * MAC itself or the way it is used here. The attacker can do a chosen plain 2124 * text attack by varying and testing the all parameters under his control. 2125 * The strength depends on the size and randomness of the secret, and the 2126 * cryptographic security of the MAC function. Due to the constant updating 2127 * of the secret the attacker has at most 29.999 seconds to find the secret 2128 * and launch spoofed connections. After that he has to start all over again. 2129 * 2130 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2131 * size an average of 4,823 attempts are required for a 50% chance of success 2132 * to spoof a single syncookie (birthday collision paradox). However the 2133 * attacker is blind and doesn't know if one of his attempts succeeded unless 2134 * he has a side channel to interfere success from. A single connection setup 2135 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2136 * This many attempts are required for each one blind spoofed connection. For 2137 * every additional spoofed connection he has to launch another N attempts. 2138 * Thus for a sustained rate 100 spoofed connections per second approximately 2139 * 1,800,000 packets per second would have to be sent. 2140 * 2141 * NB: The MAC function should be fast so that it doesn't become a CPU 2142 * exhaustion attack vector itself. 2143 * 2144 * References: 2145 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2146 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2147 * http://cr.yp.to/syncookies.html (overview) 2148 * http://cr.yp.to/syncookies/archive (details) 2149 * 2150 * 2151 * Schematic construction of a syncookie enabled Initial Sequence Number: 2152 * 0 1 2 3 2153 * 12345678901234567890123456789012 2154 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2155 * 2156 * x 24 MAC (truncated) 2157 * W 3 Send Window Scale index 2158 * M 3 MSS index 2159 * S 1 SACK permitted 2160 * P 1 Odd/even secret 2161 */ 2162 2163 /* 2164 * Distribution and probability of certain MSS values. Those in between are 2165 * rounded down to the next lower one. 2166 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2167 * .2% .3% 5% 7% 7% 20% 15% 45% 2168 */ 2169 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2170 2171 /* 2172 * Distribution and probability of certain WSCALE values. We have to map the 2173 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2174 * bits based on prevalence of certain values. Where we don't have an exact 2175 * match for are rounded down to the next lower one letting us under-estimate 2176 * the true available window. At the moment this would happen only for the 2177 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2178 * and window size). The absence of the WSCALE option (no scaling in either 2179 * direction) is encoded with index zero. 2180 * [WSCALE values histograms, Allman, 2012] 2181 * X 10 10 35 5 6 14 10% by host 2182 * X 11 4 5 5 18 49 3% by connections 2183 */ 2184 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2185 2186 /* 2187 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2188 * and good cryptographic properties. 2189 */ 2190 static uint32_t 2191 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2192 uint8_t *secbits, uintptr_t secmod) 2193 { 2194 SIPHASH_CTX ctx; 2195 uint32_t siphash[2]; 2196 2197 SipHash24_Init(&ctx); 2198 SipHash_SetKey(&ctx, secbits); 2199 switch (inc->inc_flags & INC_ISIPV6) { 2200 #ifdef INET 2201 case 0: 2202 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2203 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2204 break; 2205 #endif 2206 #ifdef INET6 2207 case INC_ISIPV6: 2208 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2209 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2210 break; 2211 #endif 2212 } 2213 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2214 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2215 SipHash_Update(&ctx, &irs, sizeof(irs)); 2216 SipHash_Update(&ctx, &flags, sizeof(flags)); 2217 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2218 SipHash_Final((u_int8_t *)&siphash, &ctx); 2219 2220 return (siphash[0] ^ siphash[1]); 2221 } 2222 2223 static tcp_seq 2224 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2225 { 2226 u_int i, secbit, wscale; 2227 uint32_t iss, hash; 2228 uint8_t *secbits; 2229 union syncookie cookie; 2230 2231 cookie.cookie = 0; 2232 2233 /* Map our computed MSS into the 3-bit index. */ 2234 for (i = nitems(tcp_sc_msstab) - 1; 2235 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2236 i--) 2237 ; 2238 cookie.flags.mss_idx = i; 2239 2240 /* 2241 * Map the send window scale into the 3-bit index but only if 2242 * the wscale option was received. 2243 */ 2244 if (sc->sc_flags & SCF_WINSCALE) { 2245 wscale = sc->sc_requested_s_scale; 2246 for (i = nitems(tcp_sc_wstab) - 1; 2247 tcp_sc_wstab[i] > wscale && i > 0; 2248 i--) 2249 ; 2250 cookie.flags.wscale_idx = i; 2251 } 2252 2253 /* Can we do SACK? */ 2254 if (sc->sc_flags & SCF_SACK) 2255 cookie.flags.sack_ok = 1; 2256 2257 /* Which of the two secrets to use. */ 2258 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2259 cookie.flags.odd_even = secbit; 2260 2261 secbits = V_tcp_syncache.secret.key[secbit]; 2262 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2263 (uintptr_t)sch); 2264 2265 /* 2266 * Put the flags into the hash and XOR them to get better ISS number 2267 * variance. This doesn't enhance the cryptographic strength and is 2268 * done to prevent the 8 cookie bits from showing up directly on the 2269 * wire. 2270 */ 2271 iss = hash & ~0xff; 2272 iss |= cookie.cookie ^ (hash >> 24); 2273 2274 TCPSTAT_INC(tcps_sc_sendcookie); 2275 return (iss); 2276 } 2277 2278 static struct syncache * 2279 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2280 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2281 struct socket *lso, uint16_t port) 2282 { 2283 uint32_t hash; 2284 uint8_t *secbits; 2285 tcp_seq ack, seq; 2286 int wnd, wscale = 0; 2287 union syncookie cookie; 2288 2289 /* 2290 * Pull information out of SYN-ACK/ACK and revert sequence number 2291 * advances. 2292 */ 2293 ack = th->th_ack - 1; 2294 seq = th->th_seq - 1; 2295 2296 /* 2297 * Unpack the flags containing enough information to restore the 2298 * connection. 2299 */ 2300 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2301 2302 /* Which of the two secrets to use. */ 2303 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2304 2305 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2306 2307 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2308 if ((ack & ~0xff) != (hash & ~0xff)) 2309 return (NULL); 2310 2311 /* Fill in the syncache values. */ 2312 sc->sc_flags = 0; 2313 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2314 sc->sc_ipopts = NULL; 2315 2316 sc->sc_irs = seq; 2317 sc->sc_iss = ack; 2318 2319 switch (inc->inc_flags & INC_ISIPV6) { 2320 #ifdef INET 2321 case 0: 2322 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2323 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2324 break; 2325 #endif 2326 #ifdef INET6 2327 case INC_ISIPV6: 2328 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2329 sc->sc_flowlabel = 2330 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2331 break; 2332 #endif 2333 } 2334 2335 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2336 2337 /* We can simply recompute receive window scale we sent earlier. */ 2338 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2339 wscale++; 2340 2341 /* Only use wscale if it was enabled in the orignal SYN. */ 2342 if (cookie.flags.wscale_idx > 0) { 2343 sc->sc_requested_r_scale = wscale; 2344 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2345 sc->sc_flags |= SCF_WINSCALE; 2346 } 2347 2348 wnd = lso->sol_sbrcv_hiwat; 2349 wnd = imax(wnd, 0); 2350 wnd = imin(wnd, TCP_MAXWIN); 2351 sc->sc_wnd = wnd; 2352 2353 if (cookie.flags.sack_ok) 2354 sc->sc_flags |= SCF_SACK; 2355 2356 if (to->to_flags & TOF_TS) { 2357 sc->sc_flags |= SCF_TIMESTAMP; 2358 sc->sc_tsreflect = to->to_tsval; 2359 sc->sc_tsoff = tcp_new_ts_offset(inc); 2360 } 2361 2362 if (to->to_flags & TOF_SIGNATURE) 2363 sc->sc_flags |= SCF_SIGNATURE; 2364 2365 sc->sc_rxmits = 0; 2366 2367 sc->sc_port = port; 2368 2369 TCPSTAT_INC(tcps_sc_recvcookie); 2370 return (sc); 2371 } 2372 2373 #ifdef INVARIANTS 2374 static int 2375 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2376 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2377 struct socket *lso, uint16_t port) 2378 { 2379 struct syncache scs, *scx; 2380 char *s; 2381 2382 bzero(&scs, sizeof(scs)); 2383 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2384 2385 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2386 return (0); 2387 2388 if (scx != NULL) { 2389 if (sc->sc_peer_mss != scx->sc_peer_mss) 2390 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2391 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2392 2393 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2394 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2395 s, __func__, sc->sc_requested_r_scale, 2396 scx->sc_requested_r_scale); 2397 2398 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2399 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2400 s, __func__, sc->sc_requested_s_scale, 2401 scx->sc_requested_s_scale); 2402 2403 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2404 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2405 } 2406 2407 if (s != NULL) 2408 free(s, M_TCPLOG); 2409 return (0); 2410 } 2411 #endif /* INVARIANTS */ 2412 2413 static void 2414 syncookie_reseed(void *arg) 2415 { 2416 struct tcp_syncache *sc = arg; 2417 uint8_t *secbits; 2418 int secbit; 2419 2420 /* 2421 * Reseeding the secret doesn't have to be protected by a lock. 2422 * It only must be ensured that the new random values are visible 2423 * to all CPUs in a SMP environment. The atomic with release 2424 * semantics ensures that. 2425 */ 2426 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2427 secbits = sc->secret.key[secbit]; 2428 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2429 atomic_add_rel_int(&sc->secret.oddeven, 1); 2430 2431 /* Reschedule ourself. */ 2432 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2433 } 2434 2435 /* 2436 * We have overflowed a bucket. Let's pause dealing with the syncache. 2437 * This function will increment the bucketoverflow statistics appropriately 2438 * (once per pause when pausing is enabled; otherwise, once per overflow). 2439 */ 2440 static void 2441 syncache_pause(struct in_conninfo *inc) 2442 { 2443 time_t delta; 2444 const char *s; 2445 2446 /* XXX: 2447 * 2. Add sysctl read here so we don't get the benefit of this 2448 * change without the new sysctl. 2449 */ 2450 2451 /* 2452 * Try an unlocked read. If we already know that another thread 2453 * has activated the feature, there is no need to proceed. 2454 */ 2455 if (V_tcp_syncache.paused) 2456 return; 2457 2458 /* Are cookied enabled? If not, we can't pause. */ 2459 if (!V_tcp_syncookies) { 2460 TCPSTAT_INC(tcps_sc_bucketoverflow); 2461 return; 2462 } 2463 2464 /* 2465 * We may be the first thread to find an overflow. Get the lock 2466 * and evaluate if we need to take action. 2467 */ 2468 mtx_lock(&V_tcp_syncache.pause_mtx); 2469 if (V_tcp_syncache.paused) { 2470 mtx_unlock(&V_tcp_syncache.pause_mtx); 2471 return; 2472 } 2473 2474 /* Activate protection. */ 2475 V_tcp_syncache.paused = true; 2476 TCPSTAT_INC(tcps_sc_bucketoverflow); 2477 2478 /* 2479 * Determine the last backoff time. If we are seeing a re-newed 2480 * attack within that same time after last reactivating the syncache, 2481 * consider it an extension of the same attack. 2482 */ 2483 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2484 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2485 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2486 delta <<= 1; 2487 V_tcp_syncache.pause_backoff++; 2488 } 2489 } else { 2490 delta = TCP_SYNCACHE_PAUSE_TIME; 2491 V_tcp_syncache.pause_backoff = 0; 2492 } 2493 2494 /* Log a warning, including IP addresses, if able. */ 2495 if (inc != NULL) 2496 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2497 else 2498 s = (const char *)NULL; 2499 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2500 "the next %lld seconds%s%s%s\n", (long long)delta, 2501 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2502 (s != NULL) ? ")" : ""); 2503 free(__DECONST(void *, s), M_TCPLOG); 2504 2505 /* Use the calculated delta to set a new pause time. */ 2506 V_tcp_syncache.pause_until = time_uptime + delta; 2507 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2508 &V_tcp_syncache); 2509 mtx_unlock(&V_tcp_syncache.pause_mtx); 2510 } 2511 2512 /* Evaluate whether we need to unpause. */ 2513 static void 2514 syncache_unpause(void *arg) 2515 { 2516 struct tcp_syncache *sc; 2517 time_t delta; 2518 2519 sc = arg; 2520 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2521 callout_deactivate(&sc->pause_co); 2522 2523 /* 2524 * Check to make sure we are not running early. If the pause 2525 * time has expired, then deactivate the protection. 2526 */ 2527 if ((delta = sc->pause_until - time_uptime) > 0) 2528 callout_schedule(&sc->pause_co, delta * hz); 2529 else 2530 sc->paused = false; 2531 } 2532 2533 /* 2534 * Exports the syncache entries to userland so that netstat can display 2535 * them alongside the other sockets. This function is intended to be 2536 * called only from tcp_pcblist. 2537 * 2538 * Due to concurrency on an active system, the number of pcbs exported 2539 * may have no relation to max_pcbs. max_pcbs merely indicates the 2540 * amount of space the caller allocated for this function to use. 2541 */ 2542 int 2543 syncache_pcblist(struct sysctl_req *req) 2544 { 2545 struct xtcpcb xt; 2546 struct syncache *sc; 2547 struct syncache_head *sch; 2548 int error, i; 2549 2550 bzero(&xt, sizeof(xt)); 2551 xt.xt_len = sizeof(xt); 2552 xt.t_state = TCPS_SYN_RECEIVED; 2553 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2554 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2555 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2556 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2557 2558 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2559 sch = &V_tcp_syncache.hashbase[i]; 2560 SCH_LOCK(sch); 2561 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2562 if (sc->sc_cred != NULL && 2563 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2564 continue; 2565 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2566 xt.xt_inp.inp_vflag = INP_IPV6; 2567 else 2568 xt.xt_inp.inp_vflag = INP_IPV4; 2569 xt.xt_encaps_port = sc->sc_port; 2570 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2571 sizeof (struct in_conninfo)); 2572 error = SYSCTL_OUT(req, &xt, sizeof xt); 2573 if (error) { 2574 SCH_UNLOCK(sch); 2575 return (0); 2576 } 2577 } 2578 SCH_UNLOCK(sch); 2579 } 2580 2581 return (0); 2582 } 2583