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 #include "opt_pcbgroup.h" 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/hash.h> 46 #include <sys/refcount.h> 47 #include <sys/kernel.h> 48 #include <sys/sysctl.h> 49 #include <sys/limits.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/malloc.h> 53 #include <sys/mbuf.h> 54 #include <sys/proc.h> /* for proc0 declaration */ 55 #include <sys/random.h> 56 #include <sys/socket.h> 57 #include <sys/socketvar.h> 58 #include <sys/syslog.h> 59 #include <sys/ucred.h> 60 61 #include <sys/md5.h> 62 #include <crypto/siphash/siphash.h> 63 64 #include <vm/uma.h> 65 66 #include <net/if.h> 67 #include <net/if_var.h> 68 #include <net/route.h> 69 #include <net/vnet.h> 70 71 #include <netinet/in.h> 72 #include <netinet/in_kdtrace.h> 73 #include <netinet/in_systm.h> 74 #include <netinet/ip.h> 75 #include <netinet/in_var.h> 76 #include <netinet/in_pcb.h> 77 #include <netinet/ip_var.h> 78 #include <netinet/ip_options.h> 79 #ifdef INET6 80 #include <netinet/ip6.h> 81 #include <netinet/icmp6.h> 82 #include <netinet6/nd6.h> 83 #include <netinet6/ip6_var.h> 84 #include <netinet6/in6_pcb.h> 85 #endif 86 #include <netinet/tcp.h> 87 #include <netinet/tcp_fastopen.h> 88 #include <netinet/tcp_fsm.h> 89 #include <netinet/tcp_seq.h> 90 #include <netinet/tcp_timer.h> 91 #include <netinet/tcp_var.h> 92 #include <netinet/tcp_syncache.h> 93 #ifdef INET6 94 #include <netinet6/tcp6_var.h> 95 #endif 96 #ifdef TCP_OFFLOAD 97 #include <netinet/toecore.h> 98 #endif 99 #include <netinet/udp.h> 100 #include <netinet/udp_var.h> 101 102 #include <netipsec/ipsec_support.h> 103 104 #include <machine/in_cksum.h> 105 106 #include <security/mac/mac_framework.h> 107 108 VNET_DEFINE_STATIC(int, tcp_syncookies) = 1; 109 #define V_tcp_syncookies VNET(tcp_syncookies) 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW, 111 &VNET_NAME(tcp_syncookies), 0, 112 "Use TCP SYN cookies if the syncache overflows"); 113 114 VNET_DEFINE_STATIC(int, tcp_syncookiesonly) = 0; 115 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly) 116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW, 117 &VNET_NAME(tcp_syncookiesonly), 0, 118 "Use only TCP SYN cookies"); 119 120 VNET_DEFINE_STATIC(int, functions_inherit_listen_socket_stack) = 1; 121 #define V_functions_inherit_listen_socket_stack \ 122 VNET(functions_inherit_listen_socket_stack) 123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, functions_inherit_listen_socket_stack, 124 CTLFLAG_VNET | CTLFLAG_RW, 125 &VNET_NAME(functions_inherit_listen_socket_stack), 0, 126 "Inherit listen socket's stack"); 127 128 #ifdef TCP_OFFLOAD 129 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL) 130 #endif 131 132 static void syncache_drop(struct syncache *, struct syncache_head *); 133 static void syncache_free(struct syncache *); 134 static void syncache_insert(struct syncache *, struct syncache_head *); 135 static int syncache_respond(struct syncache *, const struct mbuf *, int); 136 static struct socket *syncache_socket(struct syncache *, struct socket *, 137 struct mbuf *m); 138 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 139 int docallout); 140 static void syncache_timer(void *); 141 142 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t, 143 uint8_t *, uintptr_t); 144 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *); 145 static struct syncache 146 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 147 struct syncache *, struct tcphdr *, struct tcpopt *, 148 struct socket *, uint16_t); 149 static void syncache_pause(struct in_conninfo *); 150 static void syncache_unpause(void *); 151 static void syncookie_reseed(void *); 152 #ifdef INVARIANTS 153 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 154 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 155 struct socket *lso, uint16_t port); 156 #endif 157 158 /* 159 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 160 * 3 retransmits corresponds to a timeout with default values of 161 * tcp_rexmit_initial * ( 1 + 162 * tcp_backoff[1] + 163 * tcp_backoff[2] + 164 * tcp_backoff[3]) + 3 * tcp_rexmit_slop, 165 * 1000 ms * (1 + 2 + 4 + 8) + 3 * 200 ms = 15600 ms, 166 * the odds are that the user has given up attempting to connect by then. 167 */ 168 #define SYNCACHE_MAXREXMTS 3 169 170 /* Arbitrary values */ 171 #define TCP_SYNCACHE_HASHSIZE 512 172 #define TCP_SYNCACHE_BUCKETLIMIT 30 173 174 VNET_DEFINE_STATIC(struct tcp_syncache, tcp_syncache); 175 #define V_tcp_syncache VNET(tcp_syncache) 176 177 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, 178 CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 179 "TCP SYN cache"); 180 181 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 182 &VNET_NAME(tcp_syncache.bucket_limit), 0, 183 "Per-bucket hash limit for syncache"); 184 185 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN, 186 &VNET_NAME(tcp_syncache.cache_limit), 0, 187 "Overall entry limit for syncache"); 188 189 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET, 190 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache"); 191 192 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN, 193 &VNET_NAME(tcp_syncache.hashsize), 0, 194 "Size of TCP syncache hashtable"); 195 196 SYSCTL_BOOL(_net_inet_tcp_syncache, OID_AUTO, see_other, CTLFLAG_VNET | 197 CTLFLAG_RW, &VNET_NAME(tcp_syncache.see_other), 0, 198 "All syncache(4) entries are visible, ignoring UID/GID, jail(2) " 199 "and mac(4) checks"); 200 201 static int 202 sysctl_net_inet_tcp_syncache_rexmtlimit_check(SYSCTL_HANDLER_ARGS) 203 { 204 int error; 205 u_int new; 206 207 new = V_tcp_syncache.rexmt_limit; 208 error = sysctl_handle_int(oidp, &new, 0, req); 209 if ((error == 0) && (req->newptr != NULL)) { 210 if (new > TCP_MAXRXTSHIFT) 211 error = EINVAL; 212 else 213 V_tcp_syncache.rexmt_limit = new; 214 } 215 return (error); 216 } 217 218 SYSCTL_PROC(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, 219 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 220 &VNET_NAME(tcp_syncache.rexmt_limit), 0, 221 sysctl_net_inet_tcp_syncache_rexmtlimit_check, "UI", 222 "Limit on SYN/ACK retransmissions"); 223 224 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1; 225 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, 226 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0, 227 "Send reset on socket allocation failure"); 228 229 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 230 231 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 232 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 233 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 234 235 /* 236 * Requires the syncache entry to be already removed from the bucket list. 237 */ 238 static void 239 syncache_free(struct syncache *sc) 240 { 241 242 if (sc->sc_ipopts) 243 (void) m_free(sc->sc_ipopts); 244 if (sc->sc_cred) 245 crfree(sc->sc_cred); 246 #ifdef MAC 247 mac_syncache_destroy(&sc->sc_label); 248 #endif 249 250 uma_zfree(V_tcp_syncache.zone, sc); 251 } 252 253 void 254 syncache_init(void) 255 { 256 int i; 257 258 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 259 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 260 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 261 V_tcp_syncache.hash_secret = arc4random(); 262 263 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 264 &V_tcp_syncache.hashsize); 265 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 266 &V_tcp_syncache.bucket_limit); 267 if (!powerof2(V_tcp_syncache.hashsize) || 268 V_tcp_syncache.hashsize == 0) { 269 printf("WARNING: syncache hash size is not a power of 2.\n"); 270 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 271 } 272 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1; 273 274 /* Set limits. */ 275 V_tcp_syncache.cache_limit = 276 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit; 277 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 278 &V_tcp_syncache.cache_limit); 279 280 /* Allocate the hash table. */ 281 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize * 282 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); 283 284 #ifdef VIMAGE 285 V_tcp_syncache.vnet = curvnet; 286 #endif 287 288 /* Initialize the hash buckets. */ 289 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 290 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket); 291 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 292 NULL, MTX_DEF); 293 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer, 294 &V_tcp_syncache.hashbase[i].sch_mtx, 0); 295 V_tcp_syncache.hashbase[i].sch_length = 0; 296 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache; 297 V_tcp_syncache.hashbase[i].sch_last_overflow = 298 -(SYNCOOKIE_LIFETIME + 1); 299 } 300 301 /* Create the syncache entry zone. */ 302 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 303 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 304 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone, 305 V_tcp_syncache.cache_limit); 306 307 /* Start the SYN cookie reseeder callout. */ 308 callout_init(&V_tcp_syncache.secret.reseed, 1); 309 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0); 310 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0); 311 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz, 312 syncookie_reseed, &V_tcp_syncache); 313 314 /* Initialize the pause machinery. */ 315 mtx_init(&V_tcp_syncache.pause_mtx, "tcp_sc_pause", NULL, MTX_DEF); 316 callout_init_mtx(&V_tcp_syncache.pause_co, &V_tcp_syncache.pause_mtx, 317 0); 318 V_tcp_syncache.pause_until = time_uptime - TCP_SYNCACHE_PAUSE_TIME; 319 V_tcp_syncache.pause_backoff = 0; 320 V_tcp_syncache.paused = false; 321 } 322 323 #ifdef VIMAGE 324 void 325 syncache_destroy(void) 326 { 327 struct syncache_head *sch; 328 struct syncache *sc, *nsc; 329 int i; 330 331 /* 332 * Stop the re-seed timer before freeing resources. No need to 333 * possibly schedule it another time. 334 */ 335 callout_drain(&V_tcp_syncache.secret.reseed); 336 337 /* Stop the SYN cache pause callout. */ 338 mtx_lock(&V_tcp_syncache.pause_mtx); 339 if (callout_stop(&V_tcp_syncache.pause_co) == 0) { 340 mtx_unlock(&V_tcp_syncache.pause_mtx); 341 callout_drain(&V_tcp_syncache.pause_co); 342 } else 343 mtx_unlock(&V_tcp_syncache.pause_mtx); 344 345 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */ 346 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 347 sch = &V_tcp_syncache.hashbase[i]; 348 callout_drain(&sch->sch_timer); 349 350 SCH_LOCK(sch); 351 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) 352 syncache_drop(sc, sch); 353 SCH_UNLOCK(sch); 354 KASSERT(TAILQ_EMPTY(&sch->sch_bucket), 355 ("%s: sch->sch_bucket not empty", __func__)); 356 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0", 357 __func__, sch->sch_length)); 358 mtx_destroy(&sch->sch_mtx); 359 } 360 361 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0, 362 ("%s: cache_count not 0", __func__)); 363 364 /* Free the allocated global resources. */ 365 uma_zdestroy(V_tcp_syncache.zone); 366 free(V_tcp_syncache.hashbase, M_SYNCACHE); 367 mtx_destroy(&V_tcp_syncache.pause_mtx); 368 } 369 #endif 370 371 /* 372 * Inserts a syncache entry into the specified bucket row. 373 * Locks and unlocks the syncache_head autonomously. 374 */ 375 static void 376 syncache_insert(struct syncache *sc, struct syncache_head *sch) 377 { 378 struct syncache *sc2; 379 380 SCH_LOCK(sch); 381 382 /* 383 * Make sure that we don't overflow the per-bucket limit. 384 * If the bucket is full, toss the oldest element. 385 */ 386 if (sch->sch_length >= V_tcp_syncache.bucket_limit) { 387 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 388 ("sch->sch_length incorrect")); 389 syncache_pause(&sc->sc_inc); 390 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 391 sch->sch_last_overflow = time_uptime; 392 syncache_drop(sc2, sch); 393 } 394 395 /* Put it into the bucket. */ 396 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 397 sch->sch_length++; 398 399 #ifdef TCP_OFFLOAD 400 if (ADDED_BY_TOE(sc)) { 401 struct toedev *tod = sc->sc_tod; 402 403 tod->tod_syncache_added(tod, sc->sc_todctx); 404 } 405 #endif 406 407 /* Reinitialize the bucket row's timer. */ 408 if (sch->sch_length == 1) 409 sch->sch_nextc = ticks + INT_MAX; 410 syncache_timeout(sc, sch, 1); 411 412 SCH_UNLOCK(sch); 413 414 TCPSTATES_INC(TCPS_SYN_RECEIVED); 415 TCPSTAT_INC(tcps_sc_added); 416 } 417 418 /* 419 * Remove and free entry from syncache bucket row. 420 * Expects locked syncache head. 421 */ 422 static void 423 syncache_drop(struct syncache *sc, struct syncache_head *sch) 424 { 425 426 SCH_LOCK_ASSERT(sch); 427 428 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 429 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 430 sch->sch_length--; 431 432 #ifdef TCP_OFFLOAD 433 if (ADDED_BY_TOE(sc)) { 434 struct toedev *tod = sc->sc_tod; 435 436 tod->tod_syncache_removed(tod, sc->sc_todctx); 437 } 438 #endif 439 440 syncache_free(sc); 441 } 442 443 /* 444 * Engage/reengage time on bucket row. 445 */ 446 static void 447 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 448 { 449 int rexmt; 450 451 if (sc->sc_rxmits == 0) 452 rexmt = tcp_rexmit_initial; 453 else 454 TCPT_RANGESET(rexmt, 455 tcp_rexmit_initial * tcp_backoff[sc->sc_rxmits], 456 tcp_rexmit_min, TCPTV_REXMTMAX); 457 sc->sc_rxttime = ticks + rexmt; 458 sc->sc_rxmits++; 459 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { 460 sch->sch_nextc = sc->sc_rxttime; 461 if (docallout) 462 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 463 syncache_timer, (void *)sch); 464 } 465 } 466 467 /* 468 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 469 * If we have retransmitted an entry the maximum number of times, expire it. 470 * One separate timer for each bucket row. 471 */ 472 static void 473 syncache_timer(void *xsch) 474 { 475 struct syncache_head *sch = (struct syncache_head *)xsch; 476 struct syncache *sc, *nsc; 477 struct epoch_tracker et; 478 int tick = ticks; 479 char *s; 480 bool paused; 481 482 CURVNET_SET(sch->sch_sc->vnet); 483 484 /* NB: syncache_head has already been locked by the callout. */ 485 SCH_LOCK_ASSERT(sch); 486 487 /* 488 * In the following cycle we may remove some entries and/or 489 * advance some timeouts, so re-initialize the bucket timer. 490 */ 491 sch->sch_nextc = tick + INT_MAX; 492 493 /* 494 * If we have paused processing, unconditionally remove 495 * all syncache entries. 496 */ 497 mtx_lock(&V_tcp_syncache.pause_mtx); 498 paused = V_tcp_syncache.paused; 499 mtx_unlock(&V_tcp_syncache.pause_mtx); 500 501 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 502 if (paused) { 503 syncache_drop(sc, sch); 504 continue; 505 } 506 /* 507 * We do not check if the listen socket still exists 508 * and accept the case where the listen socket may be 509 * gone by the time we resend the SYN/ACK. We do 510 * not expect this to happens often. If it does, 511 * then the RST will be sent by the time the remote 512 * host does the SYN/ACK->ACK. 513 */ 514 if (TSTMP_GT(sc->sc_rxttime, tick)) { 515 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) 516 sch->sch_nextc = sc->sc_rxttime; 517 continue; 518 } 519 if (sc->sc_rxmits > V_tcp_ecn_maxretries) { 520 sc->sc_flags &= ~SCF_ECN; 521 } 522 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) { 523 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 524 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 525 "giving up and removing syncache entry\n", 526 s, __func__); 527 free(s, M_TCPLOG); 528 } 529 syncache_drop(sc, sch); 530 TCPSTAT_INC(tcps_sc_stale); 531 continue; 532 } 533 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 534 log(LOG_DEBUG, "%s; %s: Response timeout, " 535 "retransmitting (%u) SYN|ACK\n", 536 s, __func__, sc->sc_rxmits); 537 free(s, M_TCPLOG); 538 } 539 540 NET_EPOCH_ENTER(et); 541 syncache_respond(sc, NULL, TH_SYN|TH_ACK); 542 NET_EPOCH_EXIT(et); 543 TCPSTAT_INC(tcps_sc_retransmitted); 544 syncache_timeout(sc, sch, 0); 545 } 546 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 547 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 548 syncache_timer, (void *)(sch)); 549 CURVNET_RESTORE(); 550 } 551 552 /* 553 * Returns true if the system is only using cookies at the moment. 554 * This could be due to a sysadmin decision to only use cookies, or it 555 * could be due to the system detecting an attack. 556 */ 557 static inline bool 558 syncache_cookiesonly(void) 559 { 560 561 return (V_tcp_syncookies && (V_tcp_syncache.paused || 562 V_tcp_syncookiesonly)); 563 } 564 565 /* 566 * Find the hash bucket for the given connection. 567 */ 568 static struct syncache_head * 569 syncache_hashbucket(struct in_conninfo *inc) 570 { 571 uint32_t hash; 572 573 /* 574 * The hash is built on foreign port + local port + foreign address. 575 * We rely on the fact that struct in_conninfo starts with 16 bits 576 * of foreign port, then 16 bits of local port then followed by 128 577 * bits of foreign address. In case of IPv4 address, the first 3 578 * 32-bit words of the address always are zeroes. 579 */ 580 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5, 581 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask; 582 583 return (&V_tcp_syncache.hashbase[hash]); 584 } 585 586 /* 587 * Find an entry in the syncache. 588 * Returns always with locked syncache_head plus a matching entry or NULL. 589 */ 590 static struct syncache * 591 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 592 { 593 struct syncache *sc; 594 struct syncache_head *sch; 595 596 *schp = sch = syncache_hashbucket(inc); 597 SCH_LOCK(sch); 598 599 /* Circle through bucket row to find matching entry. */ 600 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) 601 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie, 602 sizeof(struct in_endpoints)) == 0) 603 break; 604 605 return (sc); /* Always returns with locked sch. */ 606 } 607 608 /* 609 * This function is called when we get a RST for a 610 * non-existent connection, so that we can see if the 611 * connection is in the syn cache. If it is, zap it. 612 * If required send a challenge ACK. 613 */ 614 void 615 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, 616 uint16_t port) 617 { 618 struct syncache *sc; 619 struct syncache_head *sch; 620 char *s = NULL; 621 622 if (syncache_cookiesonly()) 623 return; 624 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 625 SCH_LOCK_ASSERT(sch); 626 627 /* 628 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 629 * See RFC 793 page 65, section SEGMENT ARRIVES. 630 */ 631 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 632 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 633 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 634 "FIN flag set, segment ignored\n", s, __func__); 635 TCPSTAT_INC(tcps_badrst); 636 goto done; 637 } 638 639 /* 640 * No corresponding connection was found in syncache. 641 * If syncookies are enabled and possibly exclusively 642 * used, or we are under memory pressure, a valid RST 643 * may not find a syncache entry. In that case we're 644 * done and no SYN|ACK retransmissions will happen. 645 * Otherwise the RST was misdirected or spoofed. 646 */ 647 if (sc == NULL) { 648 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 649 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 650 "syncache entry (possibly syncookie only), " 651 "segment ignored\n", s, __func__); 652 TCPSTAT_INC(tcps_badrst); 653 goto done; 654 } 655 656 /* The remote UDP encaps port does not match. */ 657 if (sc->sc_port != port) { 658 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 659 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 660 "syncache entry but non-matching UDP encaps port, " 661 "segment ignored\n", s, __func__); 662 TCPSTAT_INC(tcps_badrst); 663 goto done; 664 } 665 666 /* 667 * If the RST bit is set, check the sequence number to see 668 * if this is a valid reset segment. 669 * 670 * RFC 793 page 37: 671 * In all states except SYN-SENT, all reset (RST) segments 672 * are validated by checking their SEQ-fields. A reset is 673 * valid if its sequence number is in the window. 674 * 675 * RFC 793 page 69: 676 * There are four cases for the acceptability test for an incoming 677 * segment: 678 * 679 * Segment Receive Test 680 * Length Window 681 * ------- ------- ------------------------------------------- 682 * 0 0 SEG.SEQ = RCV.NXT 683 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 684 * >0 0 not acceptable 685 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 686 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 687 * 688 * Note that when receiving a SYN segment in the LISTEN state, 689 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 690 * described in RFC 793, page 66. 691 */ 692 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 693 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 694 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 695 if (V_tcp_insecure_rst || 696 th->th_seq == sc->sc_irs + 1) { 697 syncache_drop(sc, sch); 698 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 699 log(LOG_DEBUG, 700 "%s; %s: Our SYN|ACK was rejected, " 701 "connection attempt aborted by remote " 702 "endpoint\n", 703 s, __func__); 704 TCPSTAT_INC(tcps_sc_reset); 705 } else { 706 TCPSTAT_INC(tcps_badrst); 707 /* Send challenge ACK. */ 708 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 709 log(LOG_DEBUG, "%s; %s: RST with invalid " 710 " SEQ %u != NXT %u (+WND %u), " 711 "sending challenge ACK\n", 712 s, __func__, 713 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 714 syncache_respond(sc, m, TH_ACK); 715 } 716 } else { 717 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 718 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 719 "NXT %u (+WND %u), segment ignored\n", 720 s, __func__, 721 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 722 TCPSTAT_INC(tcps_badrst); 723 } 724 725 done: 726 if (s != NULL) 727 free(s, M_TCPLOG); 728 SCH_UNLOCK(sch); 729 } 730 731 void 732 syncache_badack(struct in_conninfo *inc, uint16_t port) 733 { 734 struct syncache *sc; 735 struct syncache_head *sch; 736 737 if (syncache_cookiesonly()) 738 return; 739 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 740 SCH_LOCK_ASSERT(sch); 741 if ((sc != NULL) && (sc->sc_port == port)) { 742 syncache_drop(sc, sch); 743 TCPSTAT_INC(tcps_sc_badack); 744 } 745 SCH_UNLOCK(sch); 746 } 747 748 void 749 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 750 { 751 struct syncache *sc; 752 struct syncache_head *sch; 753 754 if (syncache_cookiesonly()) 755 return; 756 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 757 SCH_LOCK_ASSERT(sch); 758 if (sc == NULL) 759 goto done; 760 761 /* If the port != sc_port, then it's a bogus ICMP msg */ 762 if (port != sc->sc_port) 763 goto done; 764 765 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 766 if (ntohl(th_seq) != sc->sc_iss) 767 goto done; 768 769 /* 770 * If we've rertransmitted 3 times and this is our second error, 771 * we remove the entry. Otherwise, we allow it to continue on. 772 * This prevents us from incorrectly nuking an entry during a 773 * spurious network outage. 774 * 775 * See tcp_notify(). 776 */ 777 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 778 sc->sc_flags |= SCF_UNREACH; 779 goto done; 780 } 781 syncache_drop(sc, sch); 782 TCPSTAT_INC(tcps_sc_unreach); 783 done: 784 SCH_UNLOCK(sch); 785 } 786 787 /* 788 * Build a new TCP socket structure from a syncache entry. 789 * 790 * On success return the newly created socket with its underlying inp locked. 791 */ 792 static struct socket * 793 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 794 { 795 struct tcp_function_block *blk; 796 struct inpcb *inp = NULL; 797 struct socket *so; 798 struct tcpcb *tp; 799 int error; 800 char *s; 801 802 NET_EPOCH_ASSERT(); 803 804 /* 805 * Ok, create the full blown connection, and set things up 806 * as they would have been set up if we had created the 807 * connection when the SYN arrived. If we can't create 808 * the connection, abort it. 809 */ 810 so = sonewconn(lso, 0); 811 if (so == NULL) { 812 /* 813 * Drop the connection; we will either send a RST or 814 * have the peer retransmit its SYN again after its 815 * RTO and try again. 816 */ 817 TCPSTAT_INC(tcps_listendrop); 818 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 819 log(LOG_DEBUG, "%s; %s: Socket create failed " 820 "due to limits or memory shortage\n", 821 s, __func__); 822 free(s, M_TCPLOG); 823 } 824 goto abort2; 825 } 826 #ifdef MAC 827 mac_socketpeer_set_from_mbuf(m, so); 828 #endif 829 830 inp = sotoinpcb(so); 831 inp->inp_inc.inc_fibnum = so->so_fibnum; 832 INP_WLOCK(inp); 833 /* 834 * Exclusive pcbinfo lock is not required in syncache socket case even 835 * if two inpcb locks can be acquired simultaneously: 836 * - the inpcb in LISTEN state, 837 * - the newly created inp. 838 * 839 * In this case, an inp cannot be at same time in LISTEN state and 840 * just created by an accept() call. 841 */ 842 INP_HASH_WLOCK(&V_tcbinfo); 843 844 /* Insert new socket into PCB hash list. */ 845 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 846 #ifdef INET6 847 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 848 inp->inp_vflag &= ~INP_IPV4; 849 inp->inp_vflag |= INP_IPV6; 850 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 851 } else { 852 inp->inp_vflag &= ~INP_IPV6; 853 inp->inp_vflag |= INP_IPV4; 854 #endif 855 inp->inp_ip_ttl = sc->sc_ip_ttl; 856 inp->inp_ip_tos = sc->sc_ip_tos; 857 inp->inp_laddr = sc->sc_inc.inc_laddr; 858 #ifdef INET6 859 } 860 #endif 861 862 /* 863 * If there's an mbuf and it has a flowid, then let's initialise the 864 * inp with that particular flowid. 865 */ 866 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 867 inp->inp_flowid = m->m_pkthdr.flowid; 868 inp->inp_flowtype = M_HASHTYPE_GET(m); 869 #ifdef NUMA 870 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 871 #endif 872 } 873 874 inp->inp_lport = sc->sc_inc.inc_lport; 875 #ifdef INET6 876 if (inp->inp_vflag & INP_IPV6PROTO) { 877 struct inpcb *oinp = sotoinpcb(lso); 878 879 /* 880 * Inherit socket options from the listening socket. 881 * Note that in6p_inputopts are not (and should not be) 882 * copied, since it stores previously received options and is 883 * used to detect if each new option is different than the 884 * previous one and hence should be passed to a user. 885 * If we copied in6p_inputopts, a user would not be able to 886 * receive options just after calling the accept system call. 887 */ 888 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 889 if (oinp->in6p_outputopts) 890 inp->in6p_outputopts = 891 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 892 inp->in6p_hops = oinp->in6p_hops; 893 } 894 895 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 896 struct in6_addr laddr6; 897 struct sockaddr_in6 sin6; 898 899 sin6.sin6_family = AF_INET6; 900 sin6.sin6_len = sizeof(sin6); 901 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 902 sin6.sin6_port = sc->sc_inc.inc_fport; 903 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 904 laddr6 = inp->in6p_laddr; 905 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 906 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 907 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6, 908 thread0.td_ucred, m, false)) != 0) { 909 inp->in6p_laddr = laddr6; 910 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 911 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed " 912 "with error %i\n", 913 s, __func__, error); 914 free(s, M_TCPLOG); 915 } 916 INP_HASH_WUNLOCK(&V_tcbinfo); 917 goto abort; 918 } 919 /* Override flowlabel from in6_pcbconnect. */ 920 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 921 inp->inp_flow |= sc->sc_flowlabel; 922 } 923 #endif /* INET6 */ 924 #if defined(INET) && defined(INET6) 925 else 926 #endif 927 #ifdef INET 928 { 929 struct in_addr laddr; 930 struct sockaddr_in sin; 931 932 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 933 934 if (inp->inp_options == NULL) { 935 inp->inp_options = sc->sc_ipopts; 936 sc->sc_ipopts = NULL; 937 } 938 939 sin.sin_family = AF_INET; 940 sin.sin_len = sizeof(sin); 941 sin.sin_addr = sc->sc_inc.inc_faddr; 942 sin.sin_port = sc->sc_inc.inc_fport; 943 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 944 laddr = inp->inp_laddr; 945 if (inp->inp_laddr.s_addr == INADDR_ANY) 946 inp->inp_laddr = sc->sc_inc.inc_laddr; 947 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin, 948 thread0.td_ucred, m, false)) != 0) { 949 inp->inp_laddr = laddr; 950 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 951 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed " 952 "with error %i\n", 953 s, __func__, error); 954 free(s, M_TCPLOG); 955 } 956 INP_HASH_WUNLOCK(&V_tcbinfo); 957 goto abort; 958 } 959 } 960 #endif /* INET */ 961 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 962 /* Copy old policy into new socket's. */ 963 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 964 printf("syncache_socket: could not copy policy\n"); 965 #endif 966 INP_HASH_WUNLOCK(&V_tcbinfo); 967 tp = intotcpcb(inp); 968 tcp_state_change(tp, TCPS_SYN_RECEIVED); 969 tp->iss = sc->sc_iss; 970 tp->irs = sc->sc_irs; 971 tp->t_port = sc->sc_port; 972 tcp_rcvseqinit(tp); 973 tcp_sendseqinit(tp); 974 blk = sototcpcb(lso)->t_fb; 975 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 976 /* 977 * Our parents t_fb was not the default, 978 * we need to release our ref on tp->t_fb and 979 * pickup one on the new entry. 980 */ 981 struct tcp_function_block *rblk; 982 983 rblk = find_and_ref_tcp_fb(blk); 984 KASSERT(rblk != NULL, 985 ("cannot find blk %p out of syncache?", blk)); 986 if (tp->t_fb->tfb_tcp_fb_fini) 987 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 988 refcount_release(&tp->t_fb->tfb_refcnt); 989 tp->t_fb = rblk; 990 /* 991 * XXXrrs this is quite dangerous, it is possible 992 * for the new function to fail to init. We also 993 * are not asking if the handoff_is_ok though at 994 * the very start thats probalbly ok. 995 */ 996 if (tp->t_fb->tfb_tcp_fb_init) { 997 (*tp->t_fb->tfb_tcp_fb_init)(tp); 998 } 999 } 1000 tp->snd_wl1 = sc->sc_irs; 1001 tp->snd_max = tp->iss + 1; 1002 tp->snd_nxt = tp->iss + 1; 1003 tp->rcv_up = sc->sc_irs + 1; 1004 tp->rcv_wnd = sc->sc_wnd; 1005 tp->rcv_adv += tp->rcv_wnd; 1006 tp->last_ack_sent = tp->rcv_nxt; 1007 1008 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 1009 if (sc->sc_flags & SCF_NOOPT) 1010 tp->t_flags |= TF_NOOPT; 1011 else { 1012 if (sc->sc_flags & SCF_WINSCALE) { 1013 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 1014 tp->snd_scale = sc->sc_requested_s_scale; 1015 tp->request_r_scale = sc->sc_requested_r_scale; 1016 } 1017 if (sc->sc_flags & SCF_TIMESTAMP) { 1018 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 1019 tp->ts_recent = sc->sc_tsreflect; 1020 tp->ts_recent_age = tcp_ts_getticks(); 1021 tp->ts_offset = sc->sc_tsoff; 1022 } 1023 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1024 if (sc->sc_flags & SCF_SIGNATURE) 1025 tp->t_flags |= TF_SIGNATURE; 1026 #endif 1027 if (sc->sc_flags & SCF_SACK) 1028 tp->t_flags |= TF_SACK_PERMIT; 1029 } 1030 1031 if (sc->sc_flags & SCF_ECN) 1032 tp->t_flags2 |= TF2_ECN_PERMIT; 1033 1034 /* 1035 * Set up MSS and get cached values from tcp_hostcache. 1036 * This might overwrite some of the defaults we just set. 1037 */ 1038 tcp_mss(tp, sc->sc_peer_mss); 1039 1040 /* 1041 * If the SYN,ACK was retransmitted, indicate that CWND to be 1042 * limited to one segment in cc_conn_init(). 1043 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 1044 */ 1045 if (sc->sc_rxmits > 1) 1046 tp->snd_cwnd = 1; 1047 1048 #ifdef TCP_OFFLOAD 1049 /* 1050 * Allow a TOE driver to install its hooks. Note that we hold the 1051 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 1052 * new connection before the TOE driver has done its thing. 1053 */ 1054 if (ADDED_BY_TOE(sc)) { 1055 struct toedev *tod = sc->sc_tod; 1056 1057 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1058 } 1059 #endif 1060 /* 1061 * Copy and activate timers. 1062 */ 1063 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1064 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1065 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1066 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1067 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1068 1069 TCPSTAT_INC(tcps_accepts); 1070 return (so); 1071 1072 abort: 1073 INP_WUNLOCK(inp); 1074 abort2: 1075 if (so != NULL) 1076 soabort(so); 1077 return (NULL); 1078 } 1079 1080 /* 1081 * This function gets called when we receive an ACK for a 1082 * socket in the LISTEN state. We look up the connection 1083 * in the syncache, and if its there, we pull it out of 1084 * the cache and turn it into a full-blown connection in 1085 * the SYN-RECEIVED state. 1086 * 1087 * On syncache_socket() success the newly created socket 1088 * has its underlying inp locked. 1089 */ 1090 int 1091 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1092 struct socket **lsop, struct mbuf *m, uint16_t port) 1093 { 1094 struct syncache *sc; 1095 struct syncache_head *sch; 1096 struct syncache scs; 1097 char *s; 1098 bool locked; 1099 1100 NET_EPOCH_ASSERT(); 1101 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1102 ("%s: can handle only ACK", __func__)); 1103 1104 if (syncache_cookiesonly()) { 1105 sc = NULL; 1106 sch = syncache_hashbucket(inc); 1107 locked = false; 1108 } else { 1109 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1110 locked = true; 1111 SCH_LOCK_ASSERT(sch); 1112 } 1113 1114 #ifdef INVARIANTS 1115 /* 1116 * Test code for syncookies comparing the syncache stored 1117 * values with the reconstructed values from the cookie. 1118 */ 1119 if (sc != NULL) 1120 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1121 #endif 1122 1123 if (sc == NULL) { 1124 /* 1125 * There is no syncache entry, so see if this ACK is 1126 * a returning syncookie. To do this, first: 1127 * A. Check if syncookies are used in case of syncache 1128 * overflows 1129 * B. See if this socket has had a syncache entry dropped in 1130 * the recent past. We don't want to accept a bogus 1131 * syncookie if we've never received a SYN or accept it 1132 * twice. 1133 * C. check that the syncookie is valid. If it is, then 1134 * cobble up a fake syncache entry, and return. 1135 */ 1136 if (locked && !V_tcp_syncookies) { 1137 SCH_UNLOCK(sch); 1138 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1139 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1140 "segment rejected (syncookies disabled)\n", 1141 s, __func__); 1142 goto failed; 1143 } 1144 if (locked && !V_tcp_syncookiesonly && 1145 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1146 SCH_UNLOCK(sch); 1147 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1148 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1149 "segment rejected (no syncache entry)\n", 1150 s, __func__); 1151 goto failed; 1152 } 1153 bzero(&scs, sizeof(scs)); 1154 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1155 if (locked) 1156 SCH_UNLOCK(sch); 1157 if (sc == NULL) { 1158 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1159 log(LOG_DEBUG, "%s; %s: Segment failed " 1160 "SYNCOOKIE authentication, segment rejected " 1161 "(probably spoofed)\n", s, __func__); 1162 goto failed; 1163 } 1164 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1165 /* If received ACK has MD5 signature, check it. */ 1166 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1167 (!TCPMD5_ENABLED() || 1168 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1169 /* Drop the ACK. */ 1170 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1171 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1172 "MD5 signature doesn't match.\n", 1173 s, __func__); 1174 free(s, M_TCPLOG); 1175 } 1176 TCPSTAT_INC(tcps_sig_err_sigopt); 1177 return (-1); /* Do not send RST */ 1178 } 1179 #endif /* TCP_SIGNATURE */ 1180 } else { 1181 if (sc->sc_port != port) { 1182 SCH_UNLOCK(sch); 1183 return (0); 1184 } 1185 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1186 /* 1187 * If listening socket requested TCP digests, check that 1188 * received ACK has signature and it is correct. 1189 * If not, drop the ACK and leave sc entry in th cache, 1190 * because SYN was received with correct signature. 1191 */ 1192 if (sc->sc_flags & SCF_SIGNATURE) { 1193 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1194 /* No signature */ 1195 TCPSTAT_INC(tcps_sig_err_nosigopt); 1196 SCH_UNLOCK(sch); 1197 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1198 log(LOG_DEBUG, "%s; %s: Segment " 1199 "rejected, MD5 signature wasn't " 1200 "provided.\n", s, __func__); 1201 free(s, M_TCPLOG); 1202 } 1203 return (-1); /* Do not send RST */ 1204 } 1205 if (!TCPMD5_ENABLED() || 1206 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1207 /* Doesn't match or no SA */ 1208 SCH_UNLOCK(sch); 1209 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1210 log(LOG_DEBUG, "%s; %s: Segment " 1211 "rejected, MD5 signature doesn't " 1212 "match.\n", s, __func__); 1213 free(s, M_TCPLOG); 1214 } 1215 return (-1); /* Do not send RST */ 1216 } 1217 } 1218 #endif /* TCP_SIGNATURE */ 1219 1220 /* 1221 * RFC 7323 PAWS: If we have a timestamp on this segment and 1222 * it's less than ts_recent, drop it. 1223 * XXXMT: RFC 7323 also requires to send an ACK. 1224 * In tcp_input.c this is only done for TCP segments 1225 * with user data, so be consistent here and just drop 1226 * the segment. 1227 */ 1228 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1229 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1230 SCH_UNLOCK(sch); 1231 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1232 log(LOG_DEBUG, 1233 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1234 "segment dropped\n", s, __func__, 1235 to->to_tsval, sc->sc_tsreflect); 1236 free(s, M_TCPLOG); 1237 } 1238 return (-1); /* Do not send RST */ 1239 } 1240 1241 /* 1242 * If timestamps were not negotiated during SYN/ACK and a 1243 * segment with a timestamp is received, ignore the 1244 * timestamp and process the packet normally. 1245 * See section 3.2 of RFC 7323. 1246 */ 1247 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1248 (to->to_flags & TOF_TS)) { 1249 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1250 log(LOG_DEBUG, "%s; %s: Timestamp not " 1251 "expected, segment processed normally\n", 1252 s, __func__); 1253 free(s, M_TCPLOG); 1254 s = NULL; 1255 } 1256 } 1257 1258 /* 1259 * If timestamps were negotiated during SYN/ACK and a 1260 * segment without a timestamp is received, silently drop 1261 * the segment, unless the missing timestamps are tolerated. 1262 * See section 3.2 of RFC 7323. 1263 */ 1264 if ((sc->sc_flags & SCF_TIMESTAMP) && 1265 !(to->to_flags & TOF_TS)) { 1266 if (V_tcp_tolerate_missing_ts) { 1267 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1268 log(LOG_DEBUG, 1269 "%s; %s: Timestamp missing, " 1270 "segment processed normally\n", 1271 s, __func__); 1272 free(s, M_TCPLOG); 1273 } 1274 } else { 1275 SCH_UNLOCK(sch); 1276 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1277 log(LOG_DEBUG, 1278 "%s; %s: Timestamp missing, " 1279 "segment silently dropped\n", 1280 s, __func__); 1281 free(s, M_TCPLOG); 1282 } 1283 return (-1); /* Do not send RST */ 1284 } 1285 } 1286 1287 /* 1288 * Pull out the entry to unlock the bucket row. 1289 * 1290 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not 1291 * tcp_state_change(). The tcpcb is not existent at this 1292 * moment. A new one will be allocated via syncache_socket-> 1293 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then 1294 * syncache_socket() will change it to TCPS_SYN_RECEIVED. 1295 */ 1296 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1297 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1298 sch->sch_length--; 1299 #ifdef TCP_OFFLOAD 1300 if (ADDED_BY_TOE(sc)) { 1301 struct toedev *tod = sc->sc_tod; 1302 1303 tod->tod_syncache_removed(tod, sc->sc_todctx); 1304 } 1305 #endif 1306 SCH_UNLOCK(sch); 1307 } 1308 1309 /* 1310 * Segment validation: 1311 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1312 */ 1313 if (th->th_ack != sc->sc_iss + 1) { 1314 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1315 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1316 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1317 goto failed; 1318 } 1319 1320 /* 1321 * The SEQ must fall in the window starting at the received 1322 * initial receive sequence number + 1 (the SYN). 1323 */ 1324 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1325 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1326 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1327 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1328 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1329 goto failed; 1330 } 1331 1332 *lsop = syncache_socket(sc, *lsop, m); 1333 1334 if (*lsop == NULL) 1335 TCPSTAT_INC(tcps_sc_aborted); 1336 else 1337 TCPSTAT_INC(tcps_sc_completed); 1338 1339 /* how do we find the inp for the new socket? */ 1340 if (sc != &scs) 1341 syncache_free(sc); 1342 return (1); 1343 failed: 1344 if (sc != NULL && sc != &scs) 1345 syncache_free(sc); 1346 if (s != NULL) 1347 free(s, M_TCPLOG); 1348 *lsop = NULL; 1349 return (0); 1350 } 1351 1352 static struct socket * 1353 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1354 uint64_t response_cookie) 1355 { 1356 struct inpcb *inp; 1357 struct tcpcb *tp; 1358 unsigned int *pending_counter; 1359 struct socket *so; 1360 1361 NET_EPOCH_ASSERT(); 1362 1363 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1364 so = syncache_socket(sc, lso, m); 1365 if (so == NULL) { 1366 TCPSTAT_INC(tcps_sc_aborted); 1367 atomic_subtract_int(pending_counter, 1); 1368 } else { 1369 soisconnected(so); 1370 inp = sotoinpcb(so); 1371 tp = intotcpcb(inp); 1372 tp->t_flags |= TF_FASTOPEN; 1373 tp->t_tfo_cookie.server = response_cookie; 1374 tp->snd_max = tp->iss; 1375 tp->snd_nxt = tp->iss; 1376 tp->t_tfo_pending = pending_counter; 1377 TCPSTAT_INC(tcps_sc_completed); 1378 } 1379 1380 return (so); 1381 } 1382 1383 /* 1384 * Given a LISTEN socket and an inbound SYN request, add 1385 * this to the syn cache, and send back a segment: 1386 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1387 * to the source. 1388 * 1389 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1390 * Doing so would require that we hold onto the data and deliver it 1391 * to the application. However, if we are the target of a SYN-flood 1392 * DoS attack, an attacker could send data which would eventually 1393 * consume all available buffer space if it were ACKed. By not ACKing 1394 * the data, we avoid this DoS scenario. 1395 * 1396 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1397 * cookie is processed and a new socket is created. In this case, any data 1398 * accompanying the SYN will be queued to the socket by tcp_input() and will 1399 * be ACKed either when the application sends response data or the delayed 1400 * ACK timer expires, whichever comes first. 1401 */ 1402 struct socket * 1403 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1404 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1405 void *todctx, uint8_t iptos, uint16_t port) 1406 { 1407 struct tcpcb *tp; 1408 struct socket *rv = NULL; 1409 struct syncache *sc = NULL; 1410 struct syncache_head *sch; 1411 struct mbuf *ipopts = NULL; 1412 u_int ltflags; 1413 int win, ip_ttl, ip_tos; 1414 char *s; 1415 #ifdef INET6 1416 int autoflowlabel = 0; 1417 #endif 1418 #ifdef MAC 1419 struct label *maclabel; 1420 #endif 1421 struct syncache scs; 1422 struct ucred *cred; 1423 uint64_t tfo_response_cookie; 1424 unsigned int *tfo_pending = NULL; 1425 int tfo_cookie_valid = 0; 1426 int tfo_response_cookie_valid = 0; 1427 bool locked; 1428 1429 INP_RLOCK_ASSERT(inp); /* listen socket */ 1430 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1431 ("%s: unexpected tcp flags", __func__)); 1432 1433 /* 1434 * Combine all so/tp operations very early to drop the INP lock as 1435 * soon as possible. 1436 */ 1437 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1438 tp = sototcpcb(so); 1439 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1440 1441 #ifdef INET6 1442 if (inc->inc_flags & INC_ISIPV6) { 1443 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1444 autoflowlabel = 1; 1445 } 1446 ip_ttl = in6_selecthlim(inp, NULL); 1447 if ((inp->in6p_outputopts == NULL) || 1448 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1449 ip_tos = 0; 1450 } else { 1451 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1452 } 1453 } 1454 #endif 1455 #if defined(INET6) && defined(INET) 1456 else 1457 #endif 1458 #ifdef INET 1459 { 1460 ip_ttl = inp->inp_ip_ttl; 1461 ip_tos = inp->inp_ip_tos; 1462 } 1463 #endif 1464 win = so->sol_sbrcv_hiwat; 1465 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1466 1467 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1468 (tp->t_tfo_pending != NULL) && 1469 (to->to_flags & TOF_FASTOPEN)) { 1470 /* 1471 * Limit the number of pending TFO connections to 1472 * approximately half of the queue limit. This prevents TFO 1473 * SYN floods from starving the service by filling the 1474 * listen queue with bogus TFO connections. 1475 */ 1476 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1477 (so->sol_qlimit / 2)) { 1478 int result; 1479 1480 result = tcp_fastopen_check_cookie(inc, 1481 to->to_tfo_cookie, to->to_tfo_len, 1482 &tfo_response_cookie); 1483 tfo_cookie_valid = (result > 0); 1484 tfo_response_cookie_valid = (result >= 0); 1485 } 1486 1487 /* 1488 * Remember the TFO pending counter as it will have to be 1489 * decremented below if we don't make it to syncache_tfo_expand(). 1490 */ 1491 tfo_pending = tp->t_tfo_pending; 1492 } 1493 1494 #ifdef MAC 1495 if (mac_syncache_init(&maclabel) != 0) { 1496 INP_RUNLOCK(inp); 1497 goto done; 1498 } else 1499 mac_syncache_create(maclabel, inp); 1500 #endif 1501 if (!tfo_cookie_valid) 1502 INP_RUNLOCK(inp); 1503 1504 /* 1505 * Remember the IP options, if any. 1506 */ 1507 #ifdef INET6 1508 if (!(inc->inc_flags & INC_ISIPV6)) 1509 #endif 1510 #ifdef INET 1511 ipopts = (m) ? ip_srcroute(m) : NULL; 1512 #else 1513 ipopts = NULL; 1514 #endif 1515 1516 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1517 /* 1518 * If listening socket requested TCP digests, check that received 1519 * SYN has signature and it is correct. If signature doesn't match 1520 * or TCP_SIGNATURE support isn't enabled, drop the packet. 1521 */ 1522 if (ltflags & TF_SIGNATURE) { 1523 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1524 TCPSTAT_INC(tcps_sig_err_nosigopt); 1525 goto done; 1526 } 1527 if (!TCPMD5_ENABLED() || 1528 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1529 goto done; 1530 } 1531 #endif /* TCP_SIGNATURE */ 1532 /* 1533 * See if we already have an entry for this connection. 1534 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1535 * 1536 * XXX: should the syncache be re-initialized with the contents 1537 * of the new SYN here (which may have different options?) 1538 * 1539 * XXX: We do not check the sequence number to see if this is a 1540 * real retransmit or a new connection attempt. The question is 1541 * how to handle such a case; either ignore it as spoofed, or 1542 * drop the current entry and create a new one? 1543 */ 1544 if (syncache_cookiesonly()) { 1545 sc = NULL; 1546 sch = syncache_hashbucket(inc); 1547 locked = false; 1548 } else { 1549 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1550 locked = true; 1551 SCH_LOCK_ASSERT(sch); 1552 } 1553 if (sc != NULL) { 1554 if (tfo_cookie_valid) 1555 INP_RUNLOCK(inp); 1556 TCPSTAT_INC(tcps_sc_dupsyn); 1557 if (ipopts) { 1558 /* 1559 * If we were remembering a previous source route, 1560 * forget it and use the new one we've been given. 1561 */ 1562 if (sc->sc_ipopts) 1563 (void) m_free(sc->sc_ipopts); 1564 sc->sc_ipopts = ipopts; 1565 } 1566 /* 1567 * Update timestamp if present. 1568 */ 1569 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1570 sc->sc_tsreflect = to->to_tsval; 1571 else 1572 sc->sc_flags &= ~SCF_TIMESTAMP; 1573 /* 1574 * Disable ECN if needed. 1575 */ 1576 if ((sc->sc_flags & SCF_ECN) && 1577 ((th->th_flags & (TH_ECE|TH_CWR)) != (TH_ECE|TH_CWR))) { 1578 sc->sc_flags &= ~SCF_ECN; 1579 } 1580 #ifdef MAC 1581 /* 1582 * Since we have already unconditionally allocated label 1583 * storage, free it up. The syncache entry will already 1584 * have an initialized label we can use. 1585 */ 1586 mac_syncache_destroy(&maclabel); 1587 #endif 1588 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1589 /* Retransmit SYN|ACK and reset retransmit count. */ 1590 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1591 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1592 "resetting timer and retransmitting SYN|ACK\n", 1593 s, __func__); 1594 free(s, M_TCPLOG); 1595 } 1596 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1597 sc->sc_rxmits = 0; 1598 syncache_timeout(sc, sch, 1); 1599 TCPSTAT_INC(tcps_sndacks); 1600 TCPSTAT_INC(tcps_sndtotal); 1601 } 1602 SCH_UNLOCK(sch); 1603 goto donenoprobe; 1604 } 1605 1606 if (tfo_cookie_valid) { 1607 bzero(&scs, sizeof(scs)); 1608 sc = &scs; 1609 goto skip_alloc; 1610 } 1611 1612 /* 1613 * Skip allocating a syncache entry if we are just going to discard 1614 * it later. 1615 */ 1616 if (!locked) { 1617 bzero(&scs, sizeof(scs)); 1618 sc = &scs; 1619 } else 1620 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1621 if (sc == NULL) { 1622 /* 1623 * The zone allocator couldn't provide more entries. 1624 * Treat this as if the cache was full; drop the oldest 1625 * entry and insert the new one. 1626 */ 1627 TCPSTAT_INC(tcps_sc_zonefail); 1628 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1629 sch->sch_last_overflow = time_uptime; 1630 syncache_drop(sc, sch); 1631 syncache_pause(inc); 1632 } 1633 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1634 if (sc == NULL) { 1635 if (V_tcp_syncookies) { 1636 bzero(&scs, sizeof(scs)); 1637 sc = &scs; 1638 } else { 1639 KASSERT(locked, 1640 ("%s: bucket unexpectedly unlocked", 1641 __func__)); 1642 SCH_UNLOCK(sch); 1643 if (ipopts) 1644 (void) m_free(ipopts); 1645 goto done; 1646 } 1647 } 1648 } 1649 1650 skip_alloc: 1651 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1652 sc->sc_tfo_cookie = &tfo_response_cookie; 1653 1654 /* 1655 * Fill in the syncache values. 1656 */ 1657 #ifdef MAC 1658 sc->sc_label = maclabel; 1659 #endif 1660 sc->sc_cred = cred; 1661 sc->sc_port = port; 1662 cred = NULL; 1663 sc->sc_ipopts = ipopts; 1664 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1665 sc->sc_ip_tos = ip_tos; 1666 sc->sc_ip_ttl = ip_ttl; 1667 #ifdef TCP_OFFLOAD 1668 sc->sc_tod = tod; 1669 sc->sc_todctx = todctx; 1670 #endif 1671 sc->sc_irs = th->th_seq; 1672 sc->sc_flags = 0; 1673 sc->sc_flowlabel = 0; 1674 1675 /* 1676 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1677 * win was derived from socket earlier in the function. 1678 */ 1679 win = imax(win, 0); 1680 win = imin(win, TCP_MAXWIN); 1681 sc->sc_wnd = win; 1682 1683 if (V_tcp_do_rfc1323 && 1684 !(ltflags & TF_NOOPT)) { 1685 /* 1686 * A timestamp received in a SYN makes 1687 * it ok to send timestamp requests and replies. 1688 */ 1689 if (to->to_flags & TOF_TS) { 1690 sc->sc_tsreflect = to->to_tsval; 1691 sc->sc_flags |= SCF_TIMESTAMP; 1692 sc->sc_tsoff = tcp_new_ts_offset(inc); 1693 } 1694 if (to->to_flags & TOF_SCALE) { 1695 int wscale = 0; 1696 1697 /* 1698 * Pick the smallest possible scaling factor that 1699 * will still allow us to scale up to sb_max, aka 1700 * kern.ipc.maxsockbuf. 1701 * 1702 * We do this because there are broken firewalls that 1703 * will corrupt the window scale option, leading to 1704 * the other endpoint believing that our advertised 1705 * window is unscaled. At scale factors larger than 1706 * 5 the unscaled window will drop below 1500 bytes, 1707 * leading to serious problems when traversing these 1708 * broken firewalls. 1709 * 1710 * With the default maxsockbuf of 256K, a scale factor 1711 * of 3 will be chosen by this algorithm. Those who 1712 * choose a larger maxsockbuf should watch out 1713 * for the compatibility problems mentioned above. 1714 * 1715 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1716 * or <SYN,ACK>) segment itself is never scaled. 1717 */ 1718 while (wscale < TCP_MAX_WINSHIFT && 1719 (TCP_MAXWIN << wscale) < sb_max) 1720 wscale++; 1721 sc->sc_requested_r_scale = wscale; 1722 sc->sc_requested_s_scale = to->to_wscale; 1723 sc->sc_flags |= SCF_WINSCALE; 1724 } 1725 } 1726 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1727 /* 1728 * If listening socket requested TCP digests, flag this in the 1729 * syncache so that syncache_respond() will do the right thing 1730 * with the SYN+ACK. 1731 */ 1732 if (ltflags & TF_SIGNATURE) 1733 sc->sc_flags |= SCF_SIGNATURE; 1734 #endif /* TCP_SIGNATURE */ 1735 if (to->to_flags & TOF_SACKPERM) 1736 sc->sc_flags |= SCF_SACK; 1737 if (to->to_flags & TOF_MSS) 1738 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1739 if (ltflags & TF_NOOPT) 1740 sc->sc_flags |= SCF_NOOPT; 1741 if (((th->th_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR)) && 1742 V_tcp_do_ecn) 1743 sc->sc_flags |= SCF_ECN; 1744 1745 if (V_tcp_syncookies) 1746 sc->sc_iss = syncookie_generate(sch, sc); 1747 else 1748 sc->sc_iss = arc4random(); 1749 #ifdef INET6 1750 if (autoflowlabel) { 1751 if (V_tcp_syncookies) 1752 sc->sc_flowlabel = sc->sc_iss; 1753 else 1754 sc->sc_flowlabel = ip6_randomflowlabel(); 1755 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1756 } 1757 #endif 1758 if (locked) 1759 SCH_UNLOCK(sch); 1760 1761 if (tfo_cookie_valid) { 1762 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1763 /* INP_RUNLOCK(inp) will be performed by the caller */ 1764 goto tfo_expanded; 1765 } 1766 1767 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1768 /* 1769 * Do a standard 3-way handshake. 1770 */ 1771 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1772 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1773 syncache_free(sc); 1774 else if (sc != &scs) 1775 syncache_insert(sc, sch); /* locks and unlocks sch */ 1776 TCPSTAT_INC(tcps_sndacks); 1777 TCPSTAT_INC(tcps_sndtotal); 1778 } else { 1779 if (sc != &scs) 1780 syncache_free(sc); 1781 TCPSTAT_INC(tcps_sc_dropped); 1782 } 1783 goto donenoprobe; 1784 1785 done: 1786 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1787 donenoprobe: 1788 if (m) 1789 m_freem(m); 1790 /* 1791 * If tfo_pending is not NULL here, then a TFO SYN that did not 1792 * result in a new socket was processed and the associated pending 1793 * counter has not yet been decremented. All such TFO processing paths 1794 * transit this point. 1795 */ 1796 if (tfo_pending != NULL) 1797 tcp_fastopen_decrement_counter(tfo_pending); 1798 1799 tfo_expanded: 1800 if (cred != NULL) 1801 crfree(cred); 1802 #ifdef MAC 1803 if (sc == &scs) 1804 mac_syncache_destroy(&maclabel); 1805 #endif 1806 return (rv); 1807 } 1808 1809 /* 1810 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1811 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1812 */ 1813 static int 1814 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1815 { 1816 struct ip *ip = NULL; 1817 struct mbuf *m; 1818 struct tcphdr *th = NULL; 1819 struct udphdr *udp = NULL; 1820 int optlen, error = 0; /* Make compiler happy */ 1821 u_int16_t hlen, tlen, mssopt, ulen; 1822 struct tcpopt to; 1823 #ifdef INET6 1824 struct ip6_hdr *ip6 = NULL; 1825 #endif 1826 1827 NET_EPOCH_ASSERT(); 1828 1829 hlen = 1830 #ifdef INET6 1831 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1832 #endif 1833 sizeof(struct ip); 1834 tlen = hlen + sizeof(struct tcphdr); 1835 if (sc->sc_port) { 1836 tlen += sizeof(struct udphdr); 1837 } 1838 /* Determine MSS we advertize to other end of connection. */ 1839 mssopt = tcp_mssopt(&sc->sc_inc); 1840 if (sc->sc_port) 1841 mssopt -= V_tcp_udp_tunneling_overhead; 1842 mssopt = max(mssopt, V_tcp_minmss); 1843 1844 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1845 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1846 ("syncache: mbuf too small")); 1847 1848 /* Create the IP+TCP header from scratch. */ 1849 m = m_gethdr(M_NOWAIT, MT_DATA); 1850 if (m == NULL) 1851 return (ENOBUFS); 1852 #ifdef MAC 1853 mac_syncache_create_mbuf(sc->sc_label, m); 1854 #endif 1855 m->m_data += max_linkhdr; 1856 m->m_len = tlen; 1857 m->m_pkthdr.len = tlen; 1858 m->m_pkthdr.rcvif = NULL; 1859 1860 #ifdef INET6 1861 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1862 ip6 = mtod(m, struct ip6_hdr *); 1863 ip6->ip6_vfc = IPV6_VERSION; 1864 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1865 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1866 ip6->ip6_plen = htons(tlen - hlen); 1867 /* ip6_hlim is set after checksum */ 1868 /* Zero out traffic class and flow label. */ 1869 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1870 ip6->ip6_flow |= sc->sc_flowlabel; 1871 if (sc->sc_port != 0) { 1872 ip6->ip6_nxt = IPPROTO_UDP; 1873 udp = (struct udphdr *)(ip6 + 1); 1874 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1875 udp->uh_dport = sc->sc_port; 1876 ulen = (tlen - sizeof(struct ip6_hdr)); 1877 th = (struct tcphdr *)(udp + 1); 1878 } else { 1879 ip6->ip6_nxt = IPPROTO_TCP; 1880 th = (struct tcphdr *)(ip6 + 1); 1881 } 1882 ip6->ip6_flow |= htonl(sc->sc_ip_tos << 20); 1883 } 1884 #endif 1885 #if defined(INET6) && defined(INET) 1886 else 1887 #endif 1888 #ifdef INET 1889 { 1890 ip = mtod(m, struct ip *); 1891 ip->ip_v = IPVERSION; 1892 ip->ip_hl = sizeof(struct ip) >> 2; 1893 ip->ip_len = htons(tlen); 1894 ip->ip_id = 0; 1895 ip->ip_off = 0; 1896 ip->ip_sum = 0; 1897 ip->ip_src = sc->sc_inc.inc_laddr; 1898 ip->ip_dst = sc->sc_inc.inc_faddr; 1899 ip->ip_ttl = sc->sc_ip_ttl; 1900 ip->ip_tos = sc->sc_ip_tos; 1901 1902 /* 1903 * See if we should do MTU discovery. Route lookups are 1904 * expensive, so we will only unset the DF bit if: 1905 * 1906 * 1) path_mtu_discovery is disabled 1907 * 2) the SCF_UNREACH flag has been set 1908 */ 1909 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1910 ip->ip_off |= htons(IP_DF); 1911 if (sc->sc_port == 0) { 1912 ip->ip_p = IPPROTO_TCP; 1913 th = (struct tcphdr *)(ip + 1); 1914 } else { 1915 ip->ip_p = IPPROTO_UDP; 1916 udp = (struct udphdr *)(ip + 1); 1917 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1918 udp->uh_dport = sc->sc_port; 1919 ulen = (tlen - sizeof(struct ip)); 1920 th = (struct tcphdr *)(udp + 1); 1921 } 1922 } 1923 #endif /* INET */ 1924 th->th_sport = sc->sc_inc.inc_lport; 1925 th->th_dport = sc->sc_inc.inc_fport; 1926 1927 if (flags & TH_SYN) 1928 th->th_seq = htonl(sc->sc_iss); 1929 else 1930 th->th_seq = htonl(sc->sc_iss + 1); 1931 th->th_ack = htonl(sc->sc_irs + 1); 1932 th->th_off = sizeof(struct tcphdr) >> 2; 1933 th->th_x2 = 0; 1934 th->th_flags = flags; 1935 th->th_win = htons(sc->sc_wnd); 1936 th->th_urp = 0; 1937 1938 if ((flags & TH_SYN) && (sc->sc_flags & SCF_ECN)) { 1939 th->th_flags |= TH_ECE; 1940 TCPSTAT_INC(tcps_ecn_shs); 1941 } 1942 1943 /* Tack on the TCP options. */ 1944 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1945 to.to_flags = 0; 1946 1947 if (flags & TH_SYN) { 1948 to.to_mss = mssopt; 1949 to.to_flags = TOF_MSS; 1950 if (sc->sc_flags & SCF_WINSCALE) { 1951 to.to_wscale = sc->sc_requested_r_scale; 1952 to.to_flags |= TOF_SCALE; 1953 } 1954 if (sc->sc_flags & SCF_SACK) 1955 to.to_flags |= TOF_SACKPERM; 1956 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1957 if (sc->sc_flags & SCF_SIGNATURE) 1958 to.to_flags |= TOF_SIGNATURE; 1959 #endif 1960 if (sc->sc_tfo_cookie) { 1961 to.to_flags |= TOF_FASTOPEN; 1962 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1963 to.to_tfo_cookie = sc->sc_tfo_cookie; 1964 /* don't send cookie again when retransmitting response */ 1965 sc->sc_tfo_cookie = NULL; 1966 } 1967 } 1968 if (sc->sc_flags & SCF_TIMESTAMP) { 1969 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1970 to.to_tsecr = sc->sc_tsreflect; 1971 to.to_flags |= TOF_TS; 1972 } 1973 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1974 1975 /* Adjust headers by option size. */ 1976 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1977 m->m_len += optlen; 1978 m->m_pkthdr.len += optlen; 1979 #ifdef INET6 1980 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1981 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1982 else 1983 #endif 1984 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1985 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1986 if (sc->sc_flags & SCF_SIGNATURE) { 1987 KASSERT(to.to_flags & TOF_SIGNATURE, 1988 ("tcp_addoptions() didn't set tcp_signature")); 1989 1990 /* NOTE: to.to_signature is inside of mbuf */ 1991 if (!TCPMD5_ENABLED() || 1992 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1993 m_freem(m); 1994 return (EACCES); 1995 } 1996 } 1997 #endif 1998 } else 1999 optlen = 0; 2000 2001 if (udp) { 2002 ulen += optlen; 2003 udp->uh_ulen = htons(ulen); 2004 } 2005 M_SETFIB(m, sc->sc_inc.inc_fibnum); 2006 /* 2007 * If we have peer's SYN and it has a flowid, then let's assign it to 2008 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 2009 * to SYN|ACK due to lack of inp here. 2010 */ 2011 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 2012 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 2013 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 2014 } 2015 #ifdef INET6 2016 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2017 if (sc->sc_port) { 2018 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2019 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2020 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2021 IPPROTO_UDP, 0); 2022 th->th_sum = htons(0); 2023 } else { 2024 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2025 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2026 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2027 IPPROTO_TCP, 0); 2028 } 2029 ip6->ip6_hlim = sc->sc_ip_ttl; 2030 #ifdef TCP_OFFLOAD 2031 if (ADDED_BY_TOE(sc)) { 2032 struct toedev *tod = sc->sc_tod; 2033 2034 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2035 2036 return (error); 2037 } 2038 #endif 2039 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2040 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2041 } 2042 #endif 2043 #if defined(INET6) && defined(INET) 2044 else 2045 #endif 2046 #ifdef INET 2047 { 2048 if (sc->sc_port) { 2049 m->m_pkthdr.csum_flags = CSUM_UDP; 2050 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2051 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2052 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2053 th->th_sum = htons(0); 2054 } else { 2055 m->m_pkthdr.csum_flags = CSUM_TCP; 2056 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2057 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2058 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2059 } 2060 #ifdef TCP_OFFLOAD 2061 if (ADDED_BY_TOE(sc)) { 2062 struct toedev *tod = sc->sc_tod; 2063 2064 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2065 2066 return (error); 2067 } 2068 #endif 2069 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2070 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2071 } 2072 #endif 2073 return (error); 2074 } 2075 2076 /* 2077 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2078 * that exceed the capacity of the syncache by avoiding the storage of any 2079 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2080 * attacks where the attacker does not have access to our responses. 2081 * 2082 * Syncookies encode and include all necessary information about the 2083 * connection setup within the SYN|ACK that we send back. That way we 2084 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2085 * (if ever). Normally the syncache and syncookies are running in parallel 2086 * with the latter taking over when the former is exhausted. When matching 2087 * syncache entry is found the syncookie is ignored. 2088 * 2089 * The only reliable information persisting the 3WHS is our initial sequence 2090 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2091 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2092 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2093 * returns and signifies a legitimate connection if it matches the ACK. 2094 * 2095 * The available space of 32 bits to store the hash and to encode the SYN 2096 * option information is very tight and we should have at least 24 bits for 2097 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2098 * 2099 * SYN option information we have to encode to fully restore a connection: 2100 * MSS: is imporant to chose an optimal segment size to avoid IP level 2101 * fragmentation along the path. The common MSS values can be encoded 2102 * in a 3-bit table. Uncommon values are captured by the next lower value 2103 * in the table leading to a slight increase in packetization overhead. 2104 * WSCALE: is necessary to allow large windows to be used for high delay- 2105 * bandwidth product links. Not scaling the window when it was initially 2106 * negotiated is bad for performance as lack of scaling further decreases 2107 * the apparent available send window. We only need to encode the WSCALE 2108 * we received from the remote end. Our end can be recalculated at any 2109 * time. The common WSCALE values can be encoded in a 3-bit table. 2110 * Uncommon values are captured by the next lower value in the table 2111 * making us under-estimate the available window size halving our 2112 * theoretically possible maximum throughput for that connection. 2113 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2114 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2115 * that are included in all segments on a connection. We enable them when 2116 * the ACK has them. 2117 * 2118 * Security of syncookies and attack vectors: 2119 * 2120 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2121 * together with the gloabl secret to make it unique per connection attempt. 2122 * Thus any change of any of those parameters results in a different MAC output 2123 * in an unpredictable way unless a collision is encountered. 24 bits of the 2124 * MAC are embedded into the ISS. 2125 * 2126 * To prevent replay attacks two rotating global secrets are updated with a 2127 * new random value every 15 seconds. The life-time of a syncookie is thus 2128 * 15-30 seconds. 2129 * 2130 * Vector 1: Attacking the secret. This requires finding a weakness in the 2131 * MAC itself or the way it is used here. The attacker can do a chosen plain 2132 * text attack by varying and testing the all parameters under his control. 2133 * The strength depends on the size and randomness of the secret, and the 2134 * cryptographic security of the MAC function. Due to the constant updating 2135 * of the secret the attacker has at most 29.999 seconds to find the secret 2136 * and launch spoofed connections. After that he has to start all over again. 2137 * 2138 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2139 * size an average of 4,823 attempts are required for a 50% chance of success 2140 * to spoof a single syncookie (birthday collision paradox). However the 2141 * attacker is blind and doesn't know if one of his attempts succeeded unless 2142 * he has a side channel to interfere success from. A single connection setup 2143 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2144 * This many attempts are required for each one blind spoofed connection. For 2145 * every additional spoofed connection he has to launch another N attempts. 2146 * Thus for a sustained rate 100 spoofed connections per second approximately 2147 * 1,800,000 packets per second would have to be sent. 2148 * 2149 * NB: The MAC function should be fast so that it doesn't become a CPU 2150 * exhaustion attack vector itself. 2151 * 2152 * References: 2153 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2154 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2155 * http://cr.yp.to/syncookies.html (overview) 2156 * http://cr.yp.to/syncookies/archive (details) 2157 * 2158 * 2159 * Schematic construction of a syncookie enabled Initial Sequence Number: 2160 * 0 1 2 3 2161 * 12345678901234567890123456789012 2162 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2163 * 2164 * x 24 MAC (truncated) 2165 * W 3 Send Window Scale index 2166 * M 3 MSS index 2167 * S 1 SACK permitted 2168 * P 1 Odd/even secret 2169 */ 2170 2171 /* 2172 * Distribution and probability of certain MSS values. Those in between are 2173 * rounded down to the next lower one. 2174 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2175 * .2% .3% 5% 7% 7% 20% 15% 45% 2176 */ 2177 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2178 2179 /* 2180 * Distribution and probability of certain WSCALE values. We have to map the 2181 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2182 * bits based on prevalence of certain values. Where we don't have an exact 2183 * match for are rounded down to the next lower one letting us under-estimate 2184 * the true available window. At the moment this would happen only for the 2185 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2186 * and window size). The absence of the WSCALE option (no scaling in either 2187 * direction) is encoded with index zero. 2188 * [WSCALE values histograms, Allman, 2012] 2189 * X 10 10 35 5 6 14 10% by host 2190 * X 11 4 5 5 18 49 3% by connections 2191 */ 2192 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2193 2194 /* 2195 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2196 * and good cryptographic properties. 2197 */ 2198 static uint32_t 2199 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2200 uint8_t *secbits, uintptr_t secmod) 2201 { 2202 SIPHASH_CTX ctx; 2203 uint32_t siphash[2]; 2204 2205 SipHash24_Init(&ctx); 2206 SipHash_SetKey(&ctx, secbits); 2207 switch (inc->inc_flags & INC_ISIPV6) { 2208 #ifdef INET 2209 case 0: 2210 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2211 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2212 break; 2213 #endif 2214 #ifdef INET6 2215 case INC_ISIPV6: 2216 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2217 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2218 break; 2219 #endif 2220 } 2221 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2222 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2223 SipHash_Update(&ctx, &irs, sizeof(irs)); 2224 SipHash_Update(&ctx, &flags, sizeof(flags)); 2225 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2226 SipHash_Final((u_int8_t *)&siphash, &ctx); 2227 2228 return (siphash[0] ^ siphash[1]); 2229 } 2230 2231 static tcp_seq 2232 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2233 { 2234 u_int i, secbit, wscale; 2235 uint32_t iss, hash; 2236 uint8_t *secbits; 2237 union syncookie cookie; 2238 2239 cookie.cookie = 0; 2240 2241 /* Map our computed MSS into the 3-bit index. */ 2242 for (i = nitems(tcp_sc_msstab) - 1; 2243 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2244 i--) 2245 ; 2246 cookie.flags.mss_idx = i; 2247 2248 /* 2249 * Map the send window scale into the 3-bit index but only if 2250 * the wscale option was received. 2251 */ 2252 if (sc->sc_flags & SCF_WINSCALE) { 2253 wscale = sc->sc_requested_s_scale; 2254 for (i = nitems(tcp_sc_wstab) - 1; 2255 tcp_sc_wstab[i] > wscale && i > 0; 2256 i--) 2257 ; 2258 cookie.flags.wscale_idx = i; 2259 } 2260 2261 /* Can we do SACK? */ 2262 if (sc->sc_flags & SCF_SACK) 2263 cookie.flags.sack_ok = 1; 2264 2265 /* Which of the two secrets to use. */ 2266 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2267 cookie.flags.odd_even = secbit; 2268 2269 secbits = V_tcp_syncache.secret.key[secbit]; 2270 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2271 (uintptr_t)sch); 2272 2273 /* 2274 * Put the flags into the hash and XOR them to get better ISS number 2275 * variance. This doesn't enhance the cryptographic strength and is 2276 * done to prevent the 8 cookie bits from showing up directly on the 2277 * wire. 2278 */ 2279 iss = hash & ~0xff; 2280 iss |= cookie.cookie ^ (hash >> 24); 2281 2282 TCPSTAT_INC(tcps_sc_sendcookie); 2283 return (iss); 2284 } 2285 2286 static struct syncache * 2287 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2288 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2289 struct socket *lso, uint16_t port) 2290 { 2291 uint32_t hash; 2292 uint8_t *secbits; 2293 tcp_seq ack, seq; 2294 int wnd, wscale = 0; 2295 union syncookie cookie; 2296 2297 /* 2298 * Pull information out of SYN-ACK/ACK and revert sequence number 2299 * advances. 2300 */ 2301 ack = th->th_ack - 1; 2302 seq = th->th_seq - 1; 2303 2304 /* 2305 * Unpack the flags containing enough information to restore the 2306 * connection. 2307 */ 2308 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2309 2310 /* Which of the two secrets to use. */ 2311 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2312 2313 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2314 2315 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2316 if ((ack & ~0xff) != (hash & ~0xff)) 2317 return (NULL); 2318 2319 /* Fill in the syncache values. */ 2320 sc->sc_flags = 0; 2321 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2322 sc->sc_ipopts = NULL; 2323 2324 sc->sc_irs = seq; 2325 sc->sc_iss = ack; 2326 2327 switch (inc->inc_flags & INC_ISIPV6) { 2328 #ifdef INET 2329 case 0: 2330 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2331 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2332 break; 2333 #endif 2334 #ifdef INET6 2335 case INC_ISIPV6: 2336 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2337 sc->sc_flowlabel = 2338 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2339 break; 2340 #endif 2341 } 2342 2343 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2344 2345 /* We can simply recompute receive window scale we sent earlier. */ 2346 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2347 wscale++; 2348 2349 /* Only use wscale if it was enabled in the orignal SYN. */ 2350 if (cookie.flags.wscale_idx > 0) { 2351 sc->sc_requested_r_scale = wscale; 2352 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2353 sc->sc_flags |= SCF_WINSCALE; 2354 } 2355 2356 wnd = lso->sol_sbrcv_hiwat; 2357 wnd = imax(wnd, 0); 2358 wnd = imin(wnd, TCP_MAXWIN); 2359 sc->sc_wnd = wnd; 2360 2361 if (cookie.flags.sack_ok) 2362 sc->sc_flags |= SCF_SACK; 2363 2364 if (to->to_flags & TOF_TS) { 2365 sc->sc_flags |= SCF_TIMESTAMP; 2366 sc->sc_tsreflect = to->to_tsval; 2367 sc->sc_tsoff = tcp_new_ts_offset(inc); 2368 } 2369 2370 if (to->to_flags & TOF_SIGNATURE) 2371 sc->sc_flags |= SCF_SIGNATURE; 2372 2373 sc->sc_rxmits = 0; 2374 2375 sc->sc_port = port; 2376 2377 TCPSTAT_INC(tcps_sc_recvcookie); 2378 return (sc); 2379 } 2380 2381 #ifdef INVARIANTS 2382 static int 2383 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2384 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2385 struct socket *lso, uint16_t port) 2386 { 2387 struct syncache scs, *scx; 2388 char *s; 2389 2390 bzero(&scs, sizeof(scs)); 2391 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2392 2393 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2394 return (0); 2395 2396 if (scx != NULL) { 2397 if (sc->sc_peer_mss != scx->sc_peer_mss) 2398 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2399 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2400 2401 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2402 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2403 s, __func__, sc->sc_requested_r_scale, 2404 scx->sc_requested_r_scale); 2405 2406 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2407 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2408 s, __func__, sc->sc_requested_s_scale, 2409 scx->sc_requested_s_scale); 2410 2411 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2412 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2413 } 2414 2415 if (s != NULL) 2416 free(s, M_TCPLOG); 2417 return (0); 2418 } 2419 #endif /* INVARIANTS */ 2420 2421 static void 2422 syncookie_reseed(void *arg) 2423 { 2424 struct tcp_syncache *sc = arg; 2425 uint8_t *secbits; 2426 int secbit; 2427 2428 /* 2429 * Reseeding the secret doesn't have to be protected by a lock. 2430 * It only must be ensured that the new random values are visible 2431 * to all CPUs in a SMP environment. The atomic with release 2432 * semantics ensures that. 2433 */ 2434 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2435 secbits = sc->secret.key[secbit]; 2436 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2437 atomic_add_rel_int(&sc->secret.oddeven, 1); 2438 2439 /* Reschedule ourself. */ 2440 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2441 } 2442 2443 /* 2444 * We have overflowed a bucket. Let's pause dealing with the syncache. 2445 * This function will increment the bucketoverflow statistics appropriately 2446 * (once per pause when pausing is enabled; otherwise, once per overflow). 2447 */ 2448 static void 2449 syncache_pause(struct in_conninfo *inc) 2450 { 2451 time_t delta; 2452 const char *s; 2453 2454 /* XXX: 2455 * 2. Add sysctl read here so we don't get the benefit of this 2456 * change without the new sysctl. 2457 */ 2458 2459 /* 2460 * Try an unlocked read. If we already know that another thread 2461 * has activated the feature, there is no need to proceed. 2462 */ 2463 if (V_tcp_syncache.paused) 2464 return; 2465 2466 /* Are cookied enabled? If not, we can't pause. */ 2467 if (!V_tcp_syncookies) { 2468 TCPSTAT_INC(tcps_sc_bucketoverflow); 2469 return; 2470 } 2471 2472 /* 2473 * We may be the first thread to find an overflow. Get the lock 2474 * and evaluate if we need to take action. 2475 */ 2476 mtx_lock(&V_tcp_syncache.pause_mtx); 2477 if (V_tcp_syncache.paused) { 2478 mtx_unlock(&V_tcp_syncache.pause_mtx); 2479 return; 2480 } 2481 2482 /* Activate protection. */ 2483 V_tcp_syncache.paused = true; 2484 TCPSTAT_INC(tcps_sc_bucketoverflow); 2485 2486 /* 2487 * Determine the last backoff time. If we are seeing a re-newed 2488 * attack within that same time after last reactivating the syncache, 2489 * consider it an extension of the same attack. 2490 */ 2491 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2492 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2493 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2494 delta <<= 1; 2495 V_tcp_syncache.pause_backoff++; 2496 } 2497 } else { 2498 delta = TCP_SYNCACHE_PAUSE_TIME; 2499 V_tcp_syncache.pause_backoff = 0; 2500 } 2501 2502 /* Log a warning, including IP addresses, if able. */ 2503 if (inc != NULL) 2504 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2505 else 2506 s = (const char *)NULL; 2507 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2508 "the next %lld seconds%s%s%s\n", (long long)delta, 2509 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2510 (s != NULL) ? ")" : ""); 2511 free(__DECONST(void *, s), M_TCPLOG); 2512 2513 /* Use the calculated delta to set a new pause time. */ 2514 V_tcp_syncache.pause_until = time_uptime + delta; 2515 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2516 &V_tcp_syncache); 2517 mtx_unlock(&V_tcp_syncache.pause_mtx); 2518 } 2519 2520 /* Evaluate whether we need to unpause. */ 2521 static void 2522 syncache_unpause(void *arg) 2523 { 2524 struct tcp_syncache *sc; 2525 time_t delta; 2526 2527 sc = arg; 2528 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2529 callout_deactivate(&sc->pause_co); 2530 2531 /* 2532 * Check to make sure we are not running early. If the pause 2533 * time has expired, then deactivate the protection. 2534 */ 2535 if ((delta = sc->pause_until - time_uptime) > 0) 2536 callout_schedule(&sc->pause_co, delta * hz); 2537 else 2538 sc->paused = false; 2539 } 2540 2541 /* 2542 * Exports the syncache entries to userland so that netstat can display 2543 * them alongside the other sockets. This function is intended to be 2544 * called only from tcp_pcblist. 2545 * 2546 * Due to concurrency on an active system, the number of pcbs exported 2547 * may have no relation to max_pcbs. max_pcbs merely indicates the 2548 * amount of space the caller allocated for this function to use. 2549 */ 2550 int 2551 syncache_pcblist(struct sysctl_req *req) 2552 { 2553 struct xtcpcb xt; 2554 struct syncache *sc; 2555 struct syncache_head *sch; 2556 int error, i; 2557 2558 bzero(&xt, sizeof(xt)); 2559 xt.xt_len = sizeof(xt); 2560 xt.t_state = TCPS_SYN_RECEIVED; 2561 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2562 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2563 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2564 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2565 2566 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2567 sch = &V_tcp_syncache.hashbase[i]; 2568 SCH_LOCK(sch); 2569 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2570 if (sc->sc_cred != NULL && 2571 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2572 continue; 2573 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2574 xt.xt_inp.inp_vflag = INP_IPV6; 2575 else 2576 xt.xt_inp.inp_vflag = INP_IPV4; 2577 xt.xt_encaps_port = sc->sc_port; 2578 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2579 sizeof (struct in_conninfo)); 2580 error = SYSCTL_OUT(req, &xt, sizeof xt); 2581 if (error) { 2582 SCH_UNLOCK(sch); 2583 return (0); 2584 } 2585 } 2586 SCH_UNLOCK(sch); 2587 } 2588 2589 return (0); 2590 } 2591