1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2001 McAfee, Inc. 5 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by Jonathan Lemon 9 * and McAfee Research, the Security Research Division of McAfee, Inc. under 10 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. [2001 McAfee, Inc.] 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/hash.h> 43 #include <sys/refcount.h> 44 #include <sys/kernel.h> 45 #include <sys/sysctl.h> 46 #include <sys/limits.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/malloc.h> 50 #include <sys/mbuf.h> 51 #include <sys/proc.h> /* for proc0 declaration */ 52 #include <sys/random.h> 53 #include <sys/socket.h> 54 #include <sys/socketvar.h> 55 #include <sys/syslog.h> 56 #include <sys/ucred.h> 57 58 #include <sys/md5.h> 59 #include <crypto/siphash/siphash.h> 60 61 #include <vm/uma.h> 62 63 #include <net/if.h> 64 #include <net/if_var.h> 65 #include <net/route.h> 66 #include <net/vnet.h> 67 68 #include <netinet/in.h> 69 #include <netinet/in_kdtrace.h> 70 #include <netinet/in_systm.h> 71 #include <netinet/ip.h> 72 #include <netinet/in_var.h> 73 #include <netinet/in_pcb.h> 74 #include <netinet/ip_var.h> 75 #include <netinet/ip_options.h> 76 #ifdef INET6 77 #include <netinet/ip6.h> 78 #include <netinet/icmp6.h> 79 #include <netinet6/nd6.h> 80 #include <netinet6/ip6_var.h> 81 #include <netinet6/in6_pcb.h> 82 #endif 83 #include <netinet/tcp.h> 84 #include <netinet/tcp_fastopen.h> 85 #include <netinet/tcp_fsm.h> 86 #include <netinet/tcp_seq.h> 87 #include <netinet/tcp_timer.h> 88 #include <netinet/tcp_var.h> 89 #include <netinet/tcp_syncache.h> 90 #include <netinet/tcp_ecn.h> 91 #ifdef TCP_BLACKBOX 92 #include <netinet/tcp_log_buf.h> 93 #endif 94 #ifdef TCP_OFFLOAD 95 #include <netinet/toecore.h> 96 #endif 97 #include <netinet/udp.h> 98 99 #include <netipsec/ipsec_support.h> 100 101 #include <machine/in_cksum.h> 102 103 #include <security/mac/mac_framework.h> 104 105 VNET_DEFINE_STATIC(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 * No corresponding connection was found in syncache. 626 * If syncookies are enabled and possibly exclusively 627 * used, or we are under memory pressure, a valid RST 628 * may not find a syncache entry. In that case we're 629 * done and no SYN|ACK retransmissions will happen. 630 * Otherwise the RST was misdirected or spoofed. 631 */ 632 if (sc == NULL) { 633 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 634 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 635 "syncache entry (possibly syncookie only), " 636 "segment ignored\n", s, __func__); 637 TCPSTAT_INC(tcps_badrst); 638 goto done; 639 } 640 641 /* The remote UDP encaps port does not match. */ 642 if (sc->sc_port != port) { 643 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 644 log(LOG_DEBUG, "%s; %s: Spurious RST with matching " 645 "syncache entry but non-matching UDP encaps port, " 646 "segment ignored\n", s, __func__); 647 TCPSTAT_INC(tcps_badrst); 648 goto done; 649 } 650 651 /* 652 * If the RST bit is set, check the sequence number to see 653 * if this is a valid reset segment. 654 * 655 * RFC 793 page 37: 656 * In all states except SYN-SENT, all reset (RST) segments 657 * are validated by checking their SEQ-fields. A reset is 658 * valid if its sequence number is in the window. 659 * 660 * RFC 793 page 69: 661 * There are four cases for the acceptability test for an incoming 662 * segment: 663 * 664 * Segment Receive Test 665 * Length Window 666 * ------- ------- ------------------------------------------- 667 * 0 0 SEG.SEQ = RCV.NXT 668 * 0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 669 * >0 0 not acceptable 670 * >0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND 671 * or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND 672 * 673 * Note that when receiving a SYN segment in the LISTEN state, 674 * IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as 675 * described in RFC 793, page 66. 676 */ 677 if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) && 678 SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) || 679 (sc->sc_wnd == 0 && th->th_seq == sc->sc_irs + 1)) { 680 if (V_tcp_insecure_rst || 681 th->th_seq == sc->sc_irs + 1) { 682 syncache_drop(sc, sch); 683 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 684 log(LOG_DEBUG, 685 "%s; %s: Our SYN|ACK was rejected, " 686 "connection attempt aborted by remote " 687 "endpoint\n", 688 s, __func__); 689 TCPSTAT_INC(tcps_sc_reset); 690 } else { 691 TCPSTAT_INC(tcps_badrst); 692 /* Send challenge ACK. */ 693 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 694 log(LOG_DEBUG, "%s; %s: RST with invalid " 695 " SEQ %u != NXT %u (+WND %u), " 696 "sending challenge ACK\n", 697 s, __func__, 698 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 699 syncache_respond(sc, m, TH_ACK); 700 } 701 } else { 702 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 703 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != " 704 "NXT %u (+WND %u), segment ignored\n", 705 s, __func__, 706 th->th_seq, sc->sc_irs + 1, sc->sc_wnd); 707 TCPSTAT_INC(tcps_badrst); 708 } 709 710 done: 711 if (s != NULL) 712 free(s, M_TCPLOG); 713 SCH_UNLOCK(sch); 714 } 715 716 void 717 syncache_badack(struct in_conninfo *inc, uint16_t port) 718 { 719 struct syncache *sc; 720 struct syncache_head *sch; 721 722 if (syncache_cookiesonly()) 723 return; 724 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 725 SCH_LOCK_ASSERT(sch); 726 if ((sc != NULL) && (sc->sc_port == port)) { 727 syncache_drop(sc, sch); 728 TCPSTAT_INC(tcps_sc_badack); 729 } 730 SCH_UNLOCK(sch); 731 } 732 733 void 734 syncache_unreach(struct in_conninfo *inc, tcp_seq th_seq, uint16_t port) 735 { 736 struct syncache *sc; 737 struct syncache_head *sch; 738 739 if (syncache_cookiesonly()) 740 return; 741 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 742 SCH_LOCK_ASSERT(sch); 743 if (sc == NULL) 744 goto done; 745 746 /* If the port != sc_port, then it's a bogus ICMP msg */ 747 if (port != sc->sc_port) 748 goto done; 749 750 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 751 if (ntohl(th_seq) != sc->sc_iss) 752 goto done; 753 754 /* 755 * If we've rertransmitted 3 times and this is our second error, 756 * we remove the entry. Otherwise, we allow it to continue on. 757 * This prevents us from incorrectly nuking an entry during a 758 * spurious network outage. 759 * 760 * See tcp_notify(). 761 */ 762 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 763 sc->sc_flags |= SCF_UNREACH; 764 goto done; 765 } 766 syncache_drop(sc, sch); 767 TCPSTAT_INC(tcps_sc_unreach); 768 done: 769 SCH_UNLOCK(sch); 770 } 771 772 /* 773 * Build a new TCP socket structure from a syncache entry. 774 * 775 * On success return the newly created socket with its underlying inp locked. 776 */ 777 static struct socket * 778 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 779 { 780 struct tcp_function_block *blk; 781 struct inpcb *inp = NULL; 782 struct socket *so; 783 struct tcpcb *tp; 784 int error; 785 char *s; 786 787 NET_EPOCH_ASSERT(); 788 789 /* 790 * Ok, create the full blown connection, and set things up 791 * as they would have been set up if we had created the 792 * connection when the SYN arrived. 793 */ 794 if ((so = solisten_clone(lso)) == NULL) 795 goto allocfail; 796 #ifdef MAC 797 mac_socketpeer_set_from_mbuf(m, so); 798 #endif 799 error = in_pcballoc(so, &V_tcbinfo); 800 if (error) { 801 sodealloc(so); 802 goto allocfail; 803 } 804 inp = sotoinpcb(so); 805 if ((tp = tcp_newtcpcb(inp)) == NULL) { 806 in_pcbfree(inp); 807 sodealloc(so); 808 goto allocfail; 809 } 810 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags; 811 #ifdef INET6 812 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 813 inp->inp_vflag &= ~INP_IPV4; 814 inp->inp_vflag |= INP_IPV6; 815 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 816 } else { 817 inp->inp_vflag &= ~INP_IPV6; 818 inp->inp_vflag |= INP_IPV4; 819 #endif 820 inp->inp_ip_ttl = sc->sc_ip_ttl; 821 inp->inp_ip_tos = sc->sc_ip_tos; 822 inp->inp_laddr = sc->sc_inc.inc_laddr; 823 #ifdef INET6 824 } 825 #endif 826 827 /* 828 * If there's an mbuf and it has a flowid, then let's initialise the 829 * inp with that particular flowid. 830 */ 831 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) { 832 inp->inp_flowid = m->m_pkthdr.flowid; 833 inp->inp_flowtype = M_HASHTYPE_GET(m); 834 #ifdef NUMA 835 inp->inp_numa_domain = m->m_pkthdr.numa_domain; 836 #endif 837 } 838 839 inp->inp_lport = sc->sc_inc.inc_lport; 840 #ifdef INET6 841 if (inp->inp_vflag & INP_IPV6PROTO) { 842 struct inpcb *oinp = sotoinpcb(lso); 843 844 /* 845 * Inherit socket options from the listening socket. 846 * Note that in6p_inputopts are not (and should not be) 847 * copied, since it stores previously received options and is 848 * used to detect if each new option is different than the 849 * previous one and hence should be passed to a user. 850 * If we copied in6p_inputopts, a user would not be able to 851 * receive options just after calling the accept system call. 852 */ 853 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 854 if (oinp->in6p_outputopts) 855 inp->in6p_outputopts = 856 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 857 inp->in6p_hops = oinp->in6p_hops; 858 } 859 860 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 861 struct sockaddr_in6 sin6; 862 863 sin6.sin6_family = AF_INET6; 864 sin6.sin6_len = sizeof(sin6); 865 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 866 sin6.sin6_port = sc->sc_inc.inc_fport; 867 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 868 INP_HASH_WLOCK(&V_tcbinfo); 869 error = in6_pcbconnect(inp, &sin6, thread0.td_ucred, false); 870 INP_HASH_WUNLOCK(&V_tcbinfo); 871 if (error != 0) 872 goto abort; 873 /* Override flowlabel from in6_pcbconnect. */ 874 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK; 875 inp->inp_flow |= sc->sc_flowlabel; 876 } 877 #endif /* INET6 */ 878 #if defined(INET) && defined(INET6) 879 else 880 #endif 881 #ifdef INET 882 { 883 struct sockaddr_in sin; 884 885 inp->inp_options = (m) ? ip_srcroute(m) : NULL; 886 887 if (inp->inp_options == NULL) { 888 inp->inp_options = sc->sc_ipopts; 889 sc->sc_ipopts = NULL; 890 } 891 892 sin.sin_family = AF_INET; 893 sin.sin_len = sizeof(sin); 894 sin.sin_addr = sc->sc_inc.inc_faddr; 895 sin.sin_port = sc->sc_inc.inc_fport; 896 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 897 INP_HASH_WLOCK(&V_tcbinfo); 898 error = in_pcbconnect(inp, &sin, thread0.td_ucred, false); 899 INP_HASH_WUNLOCK(&V_tcbinfo); 900 if (error != 0) 901 goto abort; 902 } 903 #endif /* INET */ 904 #if defined(IPSEC) || defined(IPSEC_SUPPORT) 905 /* Copy old policy into new socket's. */ 906 if (ipsec_copy_pcbpolicy(sotoinpcb(lso), inp) != 0) 907 printf("syncache_socket: could not copy policy\n"); 908 #endif 909 tp->t_state = TCPS_SYN_RECEIVED; 910 tp->iss = sc->sc_iss; 911 tp->irs = sc->sc_irs; 912 tp->t_port = sc->sc_port; 913 tcp_rcvseqinit(tp); 914 tcp_sendseqinit(tp); 915 blk = sototcpcb(lso)->t_fb; 916 if (V_functions_inherit_listen_socket_stack && blk != tp->t_fb) { 917 /* 918 * Our parents t_fb was not the default, 919 * we need to release our ref on tp->t_fb and 920 * pickup one on the new entry. 921 */ 922 struct tcp_function_block *rblk; 923 void *ptr = NULL; 924 925 rblk = find_and_ref_tcp_fb(blk); 926 KASSERT(rblk != NULL, 927 ("cannot find blk %p out of syncache?", blk)); 928 929 if (rblk->tfb_tcp_fb_init == NULL || 930 (*rblk->tfb_tcp_fb_init)(tp, &ptr) == 0) { 931 /* Release the old stack */ 932 if (tp->t_fb->tfb_tcp_fb_fini != NULL) 933 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0); 934 refcount_release(&tp->t_fb->tfb_refcnt); 935 /* Now set in all the pointers */ 936 tp->t_fb = rblk; 937 tp->t_fb_ptr = ptr; 938 } else { 939 /* 940 * Initialization failed. Release the reference count on 941 * the looked up default stack. 942 */ 943 refcount_release(&rblk->tfb_refcnt); 944 } 945 } 946 tp->snd_wl1 = sc->sc_irs; 947 tp->snd_max = tp->iss + 1; 948 tp->snd_nxt = tp->iss + 1; 949 tp->rcv_up = sc->sc_irs + 1; 950 tp->rcv_wnd = sc->sc_wnd; 951 tp->rcv_adv += tp->rcv_wnd; 952 tp->last_ack_sent = tp->rcv_nxt; 953 954 tp->t_flags = sototcpcb(lso)->t_flags & 955 (TF_LRD|TF_NOPUSH|TF_NODELAY); 956 if (sc->sc_flags & SCF_NOOPT) 957 tp->t_flags |= TF_NOOPT; 958 else { 959 if (sc->sc_flags & SCF_WINSCALE) { 960 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 961 tp->snd_scale = sc->sc_requested_s_scale; 962 tp->request_r_scale = sc->sc_requested_r_scale; 963 } 964 if (sc->sc_flags & SCF_TIMESTAMP) { 965 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 966 tp->ts_recent = sc->sc_tsreflect; 967 tp->ts_recent_age = tcp_ts_getticks(); 968 tp->ts_offset = sc->sc_tsoff; 969 } 970 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 971 if (sc->sc_flags & SCF_SIGNATURE) 972 tp->t_flags |= TF_SIGNATURE; 973 #endif 974 if (sc->sc_flags & SCF_SACK) 975 tp->t_flags |= TF_SACK_PERMIT; 976 } 977 978 tcp_ecn_syncache_socket(tp, sc); 979 980 /* 981 * Set up MSS and get cached values from tcp_hostcache. 982 * This might overwrite some of the defaults we just set. 983 */ 984 tcp_mss(tp, sc->sc_peer_mss); 985 986 /* 987 * If the SYN,ACK was retransmitted, indicate that CWND to be 988 * limited to one segment in cc_conn_init(). 989 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits. 990 */ 991 if (sc->sc_rxmits > 1) 992 tp->snd_cwnd = 1; 993 994 #ifdef TCP_OFFLOAD 995 /* 996 * Allow a TOE driver to install its hooks. Note that we hold the 997 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a 998 * new connection before the TOE driver has done its thing. 999 */ 1000 if (ADDED_BY_TOE(sc)) { 1001 struct toedev *tod = sc->sc_tod; 1002 1003 tod->tod_offload_socket(tod, sc->sc_todctx, so); 1004 } 1005 #endif 1006 #ifdef TCP_BLACKBOX 1007 /* 1008 * Inherit the log state from the listening socket, if 1009 * - the log state of the listening socket is not off and 1010 * - the listening socket was not auto selected from all sessions and 1011 * - a log id is not set on the listening socket. 1012 * This avoids inheriting a log state which was automatically set. 1013 */ 1014 if ((tcp_get_bblog_state(sototcpcb(lso)) != TCP_LOG_STATE_OFF) && 1015 ((sototcpcb(lso)->t_flags2 & TF2_LOG_AUTO) == 0) && 1016 (sototcpcb(lso)->t_lib == NULL)) { 1017 tcp_log_state_change(tp, tcp_get_bblog_state(sototcpcb(lso))); 1018 } 1019 #endif 1020 /* 1021 * Copy and activate timers. 1022 */ 1023 tp->t_maxunacktime = sototcpcb(lso)->t_maxunacktime; 1024 tp->t_keepinit = sototcpcb(lso)->t_keepinit; 1025 tp->t_keepidle = sototcpcb(lso)->t_keepidle; 1026 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl; 1027 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt; 1028 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp)); 1029 1030 TCPSTAT_INC(tcps_accepts); 1031 TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, TCPS_LISTEN); 1032 1033 if (!solisten_enqueue(so, SS_ISCONNECTED)) 1034 tp->t_flags |= TF_SONOTCONN; 1035 1036 return (so); 1037 1038 allocfail: 1039 /* 1040 * Drop the connection; we will either send a RST or have the peer 1041 * retransmit its SYN again after its RTO and try again. 1042 */ 1043 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1044 log(LOG_DEBUG, "%s; %s: Socket create failed " 1045 "due to limits or memory shortage\n", 1046 s, __func__); 1047 free(s, M_TCPLOG); 1048 } 1049 TCPSTAT_INC(tcps_listendrop); 1050 return (NULL); 1051 1052 abort: 1053 in_pcbfree(inp); 1054 sodealloc(so); 1055 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 1056 log(LOG_DEBUG, "%s; %s: in%s_pcbconnect failed with error %i\n", 1057 s, __func__, (sc->sc_inc.inc_flags & INC_ISIPV6) ? "6" : "", 1058 error); 1059 free(s, M_TCPLOG); 1060 } 1061 TCPSTAT_INC(tcps_listendrop); 1062 return (NULL); 1063 } 1064 1065 /* 1066 * This function gets called when we receive an ACK for a 1067 * socket in the LISTEN state. We look up the connection 1068 * in the syncache, and if its there, we pull it out of 1069 * the cache and turn it into a full-blown connection in 1070 * the SYN-RECEIVED state. 1071 * 1072 * On syncache_socket() success the newly created socket 1073 * has its underlying inp locked. 1074 */ 1075 int 1076 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1077 struct socket **lsop, struct mbuf *m, uint16_t port) 1078 { 1079 struct syncache *sc; 1080 struct syncache_head *sch; 1081 struct syncache scs; 1082 char *s; 1083 bool locked; 1084 1085 NET_EPOCH_ASSERT(); 1086 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 1087 ("%s: can handle only ACK", __func__)); 1088 1089 if (syncache_cookiesonly()) { 1090 sc = NULL; 1091 sch = syncache_hashbucket(inc); 1092 locked = false; 1093 } else { 1094 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1095 locked = true; 1096 SCH_LOCK_ASSERT(sch); 1097 } 1098 1099 #ifdef INVARIANTS 1100 /* 1101 * Test code for syncookies comparing the syncache stored 1102 * values with the reconstructed values from the cookie. 1103 */ 1104 if (sc != NULL) 1105 syncookie_cmp(inc, sch, sc, th, to, *lsop, port); 1106 #endif 1107 1108 if (sc == NULL) { 1109 /* 1110 * There is no syncache entry, so see if this ACK is 1111 * a returning syncookie. To do this, first: 1112 * A. Check if syncookies are used in case of syncache 1113 * overflows 1114 * B. See if this socket has had a syncache entry dropped in 1115 * the recent past. We don't want to accept a bogus 1116 * syncookie if we've never received a SYN or accept it 1117 * twice. 1118 * C. check that the syncookie is valid. If it is, then 1119 * cobble up a fake syncache entry, and return. 1120 */ 1121 if (locked && !V_tcp_syncookies) { 1122 SCH_UNLOCK(sch); 1123 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1124 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1125 "segment rejected (syncookies disabled)\n", 1126 s, __func__); 1127 goto failed; 1128 } 1129 if (locked && !V_tcp_syncookiesonly && 1130 sch->sch_last_overflow < time_uptime - SYNCOOKIE_LIFETIME) { 1131 SCH_UNLOCK(sch); 1132 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1133 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 1134 "segment rejected (no syncache entry)\n", 1135 s, __func__); 1136 goto failed; 1137 } 1138 bzero(&scs, sizeof(scs)); 1139 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop, port); 1140 if (locked) 1141 SCH_UNLOCK(sch); 1142 if (sc == NULL) { 1143 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1144 log(LOG_DEBUG, "%s; %s: Segment failed " 1145 "SYNCOOKIE authentication, segment rejected " 1146 "(probably spoofed)\n", s, __func__); 1147 goto failed; 1148 } 1149 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1150 /* If received ACK has MD5 signature, check it. */ 1151 if ((to->to_flags & TOF_SIGNATURE) != 0 && 1152 (!TCPMD5_ENABLED() || 1153 TCPMD5_INPUT(m, th, to->to_signature) != 0)) { 1154 /* Drop the ACK. */ 1155 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1156 log(LOG_DEBUG, "%s; %s: Segment rejected, " 1157 "MD5 signature doesn't match.\n", 1158 s, __func__); 1159 free(s, M_TCPLOG); 1160 } 1161 TCPSTAT_INC(tcps_sig_err_sigopt); 1162 return (-1); /* Do not send RST */ 1163 } 1164 #endif /* TCP_SIGNATURE */ 1165 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1166 } else { 1167 if (sc->sc_port != port) { 1168 SCH_UNLOCK(sch); 1169 return (0); 1170 } 1171 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1172 /* 1173 * If listening socket requested TCP digests, check that 1174 * received ACK has signature and it is correct. 1175 * If not, drop the ACK and leave sc entry in th cache, 1176 * because SYN was received with correct signature. 1177 */ 1178 if (sc->sc_flags & SCF_SIGNATURE) { 1179 if ((to->to_flags & TOF_SIGNATURE) == 0) { 1180 /* No signature */ 1181 TCPSTAT_INC(tcps_sig_err_nosigopt); 1182 SCH_UNLOCK(sch); 1183 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1184 log(LOG_DEBUG, "%s; %s: Segment " 1185 "rejected, MD5 signature wasn't " 1186 "provided.\n", s, __func__); 1187 free(s, M_TCPLOG); 1188 } 1189 return (-1); /* Do not send RST */ 1190 } 1191 if (!TCPMD5_ENABLED() || 1192 TCPMD5_INPUT(m, th, to->to_signature) != 0) { 1193 /* Doesn't match or no SA */ 1194 SCH_UNLOCK(sch); 1195 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1196 log(LOG_DEBUG, "%s; %s: Segment " 1197 "rejected, MD5 signature doesn't " 1198 "match.\n", s, __func__); 1199 free(s, M_TCPLOG); 1200 } 1201 return (-1); /* Do not send RST */ 1202 } 1203 } 1204 #endif /* TCP_SIGNATURE */ 1205 1206 /* 1207 * RFC 7323 PAWS: If we have a timestamp on this segment and 1208 * it's less than ts_recent, drop it. 1209 * XXXMT: RFC 7323 also requires to send an ACK. 1210 * In tcp_input.c this is only done for TCP segments 1211 * with user data, so be consistent here and just drop 1212 * the segment. 1213 */ 1214 if (sc->sc_flags & SCF_TIMESTAMP && to->to_flags & TOF_TS && 1215 TSTMP_LT(to->to_tsval, sc->sc_tsreflect)) { 1216 SCH_UNLOCK(sch); 1217 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1218 log(LOG_DEBUG, 1219 "%s; %s: SEG.TSval %u < TS.Recent %u, " 1220 "segment dropped\n", s, __func__, 1221 to->to_tsval, sc->sc_tsreflect); 1222 free(s, M_TCPLOG); 1223 } 1224 return (-1); /* Do not send RST */ 1225 } 1226 1227 /* 1228 * If timestamps were not negotiated during SYN/ACK and a 1229 * segment with a timestamp is received, ignore the 1230 * timestamp and process the packet normally. 1231 * See section 3.2 of RFC 7323. 1232 */ 1233 if (!(sc->sc_flags & SCF_TIMESTAMP) && 1234 (to->to_flags & TOF_TS)) { 1235 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1236 log(LOG_DEBUG, "%s; %s: Timestamp not " 1237 "expected, segment processed normally\n", 1238 s, __func__); 1239 free(s, M_TCPLOG); 1240 s = NULL; 1241 } 1242 } 1243 1244 /* 1245 * If timestamps were negotiated during SYN/ACK and a 1246 * segment without a timestamp is received, silently drop 1247 * the segment, unless the missing timestamps are tolerated. 1248 * See section 3.2 of RFC 7323. 1249 */ 1250 if ((sc->sc_flags & SCF_TIMESTAMP) && 1251 !(to->to_flags & TOF_TS)) { 1252 if (V_tcp_tolerate_missing_ts) { 1253 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1254 log(LOG_DEBUG, 1255 "%s; %s: Timestamp missing, " 1256 "segment processed normally\n", 1257 s, __func__); 1258 free(s, M_TCPLOG); 1259 } 1260 } else { 1261 SCH_UNLOCK(sch); 1262 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 1263 log(LOG_DEBUG, 1264 "%s; %s: Timestamp missing, " 1265 "segment silently dropped\n", 1266 s, __func__); 1267 free(s, M_TCPLOG); 1268 } 1269 return (-1); /* Do not send RST */ 1270 } 1271 } 1272 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 1273 sch->sch_length--; 1274 #ifdef TCP_OFFLOAD 1275 if (ADDED_BY_TOE(sc)) { 1276 struct toedev *tod = sc->sc_tod; 1277 1278 tod->tod_syncache_removed(tod, sc->sc_todctx); 1279 } 1280 #endif 1281 SCH_UNLOCK(sch); 1282 } 1283 1284 /* 1285 * Segment validation: 1286 * ACK must match our initial sequence number + 1 (the SYN|ACK). 1287 */ 1288 if (th->th_ack != sc->sc_iss + 1) { 1289 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1290 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 1291 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 1292 goto failed; 1293 } 1294 1295 /* 1296 * The SEQ must fall in the window starting at the received 1297 * initial receive sequence number + 1 (the SYN). 1298 */ 1299 if (SEQ_LEQ(th->th_seq, sc->sc_irs) || 1300 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 1301 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 1302 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 1303 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 1304 goto failed; 1305 } 1306 1307 *lsop = syncache_socket(sc, *lsop, m); 1308 1309 if (__predict_false(*lsop == NULL)) { 1310 TCPSTAT_INC(tcps_sc_aborted); 1311 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1312 } else 1313 TCPSTAT_INC(tcps_sc_completed); 1314 1315 /* how do we find the inp for the new socket? */ 1316 if (sc != &scs) 1317 syncache_free(sc); 1318 return (1); 1319 failed: 1320 if (sc != NULL) { 1321 TCPSTATES_DEC(TCPS_SYN_RECEIVED); 1322 if (sc != &scs) 1323 syncache_free(sc); 1324 } 1325 if (s != NULL) 1326 free(s, M_TCPLOG); 1327 *lsop = NULL; 1328 return (0); 1329 } 1330 1331 static struct socket * 1332 syncache_tfo_expand(struct syncache *sc, struct socket *lso, struct mbuf *m, 1333 uint64_t response_cookie) 1334 { 1335 struct inpcb *inp; 1336 struct tcpcb *tp; 1337 unsigned int *pending_counter; 1338 struct socket *so; 1339 1340 NET_EPOCH_ASSERT(); 1341 1342 pending_counter = intotcpcb(sotoinpcb(lso))->t_tfo_pending; 1343 so = syncache_socket(sc, lso, m); 1344 if (so == NULL) { 1345 TCPSTAT_INC(tcps_sc_aborted); 1346 atomic_subtract_int(pending_counter, 1); 1347 } else { 1348 soisconnected(so); 1349 inp = sotoinpcb(so); 1350 tp = intotcpcb(inp); 1351 tp->t_flags |= TF_FASTOPEN; 1352 tp->t_tfo_cookie.server = response_cookie; 1353 tp->snd_max = tp->iss; 1354 tp->snd_nxt = tp->iss; 1355 tp->t_tfo_pending = pending_counter; 1356 TCPSTATES_INC(TCPS_SYN_RECEIVED); 1357 TCPSTAT_INC(tcps_sc_completed); 1358 } 1359 1360 return (so); 1361 } 1362 1363 /* 1364 * Given a LISTEN socket and an inbound SYN request, add 1365 * this to the syn cache, and send back a segment: 1366 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 1367 * to the source. 1368 * 1369 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 1370 * Doing so would require that we hold onto the data and deliver it 1371 * to the application. However, if we are the target of a SYN-flood 1372 * DoS attack, an attacker could send data which would eventually 1373 * consume all available buffer space if it were ACKed. By not ACKing 1374 * the data, we avoid this DoS scenario. 1375 * 1376 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO) 1377 * cookie is processed and a new socket is created. In this case, any data 1378 * accompanying the SYN will be queued to the socket by tcp_input() and will 1379 * be ACKed either when the application sends response data or the delayed 1380 * ACK timer expires, whichever comes first. 1381 */ 1382 struct socket * 1383 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 1384 struct inpcb *inp, struct socket *so, struct mbuf *m, void *tod, 1385 void *todctx, uint8_t iptos, uint16_t port) 1386 { 1387 struct tcpcb *tp; 1388 struct socket *rv = NULL; 1389 struct syncache *sc = NULL; 1390 struct syncache_head *sch; 1391 struct mbuf *ipopts = NULL; 1392 u_int ltflags; 1393 int win, ip_ttl, ip_tos; 1394 char *s; 1395 #ifdef INET6 1396 int autoflowlabel = 0; 1397 #endif 1398 #ifdef MAC 1399 struct label *maclabel; 1400 #endif 1401 struct syncache scs; 1402 struct ucred *cred; 1403 uint64_t tfo_response_cookie; 1404 unsigned int *tfo_pending = NULL; 1405 int tfo_cookie_valid = 0; 1406 int tfo_response_cookie_valid = 0; 1407 bool locked; 1408 1409 INP_RLOCK_ASSERT(inp); /* listen socket */ 1410 KASSERT((tcp_get_flags(th) & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 1411 ("%s: unexpected tcp flags", __func__)); 1412 1413 /* 1414 * Combine all so/tp operations very early to drop the INP lock as 1415 * soon as possible. 1416 */ 1417 KASSERT(SOLISTENING(so), ("%s: %p not listening", __func__, so)); 1418 tp = sototcpcb(so); 1419 cred = V_tcp_syncache.see_other ? NULL : crhold(so->so_cred); 1420 1421 #ifdef INET6 1422 if (inc->inc_flags & INC_ISIPV6) { 1423 if (inp->inp_flags & IN6P_AUTOFLOWLABEL) { 1424 autoflowlabel = 1; 1425 } 1426 ip_ttl = in6_selecthlim(inp, NULL); 1427 if ((inp->in6p_outputopts == NULL) || 1428 (inp->in6p_outputopts->ip6po_tclass == -1)) { 1429 ip_tos = 0; 1430 } else { 1431 ip_tos = inp->in6p_outputopts->ip6po_tclass; 1432 } 1433 } 1434 #endif 1435 #if defined(INET6) && defined(INET) 1436 else 1437 #endif 1438 #ifdef INET 1439 { 1440 ip_ttl = inp->inp_ip_ttl; 1441 ip_tos = inp->inp_ip_tos; 1442 } 1443 #endif 1444 win = so->sol_sbrcv_hiwat; 1445 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE)); 1446 1447 if (V_tcp_fastopen_server_enable && IS_FASTOPEN(tp->t_flags) && 1448 (tp->t_tfo_pending != NULL) && 1449 (to->to_flags & TOF_FASTOPEN)) { 1450 /* 1451 * Limit the number of pending TFO connections to 1452 * approximately half of the queue limit. This prevents TFO 1453 * SYN floods from starving the service by filling the 1454 * listen queue with bogus TFO connections. 1455 */ 1456 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <= 1457 (so->sol_qlimit / 2)) { 1458 int result; 1459 1460 result = tcp_fastopen_check_cookie(inc, 1461 to->to_tfo_cookie, to->to_tfo_len, 1462 &tfo_response_cookie); 1463 tfo_cookie_valid = (result > 0); 1464 tfo_response_cookie_valid = (result >= 0); 1465 } 1466 1467 /* 1468 * Remember the TFO pending counter as it will have to be 1469 * decremented below if we don't make it to syncache_tfo_expand(). 1470 */ 1471 tfo_pending = tp->t_tfo_pending; 1472 } 1473 1474 #ifdef MAC 1475 if (mac_syncache_init(&maclabel) != 0) { 1476 INP_RUNLOCK(inp); 1477 goto done; 1478 } else 1479 mac_syncache_create(maclabel, inp); 1480 #endif 1481 if (!tfo_cookie_valid) 1482 INP_RUNLOCK(inp); 1483 1484 /* 1485 * Remember the IP options, if any. 1486 */ 1487 #ifdef INET6 1488 if (!(inc->inc_flags & INC_ISIPV6)) 1489 #endif 1490 #ifdef INET 1491 ipopts = (m) ? ip_srcroute(m) : NULL; 1492 #else 1493 ipopts = NULL; 1494 #endif 1495 1496 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1497 /* 1498 * When the socket is TCP-MD5 enabled check that, 1499 * - a signed packet is valid 1500 * - a non-signed packet does not have a security association 1501 * 1502 * If a signed packet fails validation or a non-signed packet has a 1503 * security association, the packet will be dropped. 1504 */ 1505 if (ltflags & TF_SIGNATURE) { 1506 if (to->to_flags & TOF_SIGNATURE) { 1507 if (!TCPMD5_ENABLED() || 1508 TCPMD5_INPUT(m, th, to->to_signature) != 0) 1509 goto done; 1510 } else { 1511 if (TCPMD5_ENABLED() && 1512 TCPMD5_INPUT(m, NULL, NULL) != ENOENT) 1513 goto done; 1514 } 1515 } else if (to->to_flags & TOF_SIGNATURE) 1516 goto done; 1517 #endif /* TCP_SIGNATURE */ 1518 /* 1519 * See if we already have an entry for this connection. 1520 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1521 * 1522 * XXX: should the syncache be re-initialized with the contents 1523 * of the new SYN here (which may have different options?) 1524 * 1525 * XXX: We do not check the sequence number to see if this is a 1526 * real retransmit or a new connection attempt. The question is 1527 * how to handle such a case; either ignore it as spoofed, or 1528 * drop the current entry and create a new one? 1529 */ 1530 if (syncache_cookiesonly()) { 1531 sc = NULL; 1532 sch = syncache_hashbucket(inc); 1533 locked = false; 1534 } else { 1535 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 1536 locked = true; 1537 SCH_LOCK_ASSERT(sch); 1538 } 1539 if (sc != NULL) { 1540 if (tfo_cookie_valid) 1541 INP_RUNLOCK(inp); 1542 TCPSTAT_INC(tcps_sc_dupsyn); 1543 if (ipopts) { 1544 /* 1545 * If we were remembering a previous source route, 1546 * forget it and use the new one we've been given. 1547 */ 1548 if (sc->sc_ipopts) 1549 (void) m_free(sc->sc_ipopts); 1550 sc->sc_ipopts = ipopts; 1551 } 1552 /* 1553 * Update timestamp if present. 1554 */ 1555 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1556 sc->sc_tsreflect = to->to_tsval; 1557 else 1558 sc->sc_flags &= ~SCF_TIMESTAMP; 1559 /* 1560 * Adjust ECN response if needed, e.g. different 1561 * IP ECN field, or a fallback by the remote host. 1562 */ 1563 if (sc->sc_flags & SCF_ECN_MASK) { 1564 sc->sc_flags &= ~SCF_ECN_MASK; 1565 sc->sc_flags = tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1566 } 1567 #ifdef MAC 1568 /* 1569 * Since we have already unconditionally allocated label 1570 * storage, free it up. The syncache entry will already 1571 * have an initialized label we can use. 1572 */ 1573 mac_syncache_destroy(&maclabel); 1574 #endif 1575 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1576 /* Retransmit SYN|ACK and reset retransmit count. */ 1577 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1578 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1579 "resetting timer and retransmitting SYN|ACK\n", 1580 s, __func__); 1581 free(s, M_TCPLOG); 1582 } 1583 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1584 sc->sc_rxmits = 0; 1585 syncache_timeout(sc, sch, 1); 1586 TCPSTAT_INC(tcps_sndacks); 1587 TCPSTAT_INC(tcps_sndtotal); 1588 } 1589 SCH_UNLOCK(sch); 1590 goto donenoprobe; 1591 } 1592 1593 if (tfo_cookie_valid) { 1594 bzero(&scs, sizeof(scs)); 1595 sc = &scs; 1596 goto skip_alloc; 1597 } 1598 1599 /* 1600 * Skip allocating a syncache entry if we are just going to discard 1601 * it later. 1602 */ 1603 if (!locked) { 1604 bzero(&scs, sizeof(scs)); 1605 sc = &scs; 1606 } else 1607 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1608 if (sc == NULL) { 1609 /* 1610 * The zone allocator couldn't provide more entries. 1611 * Treat this as if the cache was full; drop the oldest 1612 * entry and insert the new one. 1613 */ 1614 TCPSTAT_INC(tcps_sc_zonefail); 1615 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) { 1616 sch->sch_last_overflow = time_uptime; 1617 syncache_drop(sc, sch); 1618 syncache_pause(inc); 1619 } 1620 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO); 1621 if (sc == NULL) { 1622 if (V_tcp_syncookies) { 1623 bzero(&scs, sizeof(scs)); 1624 sc = &scs; 1625 } else { 1626 KASSERT(locked, 1627 ("%s: bucket unexpectedly unlocked", 1628 __func__)); 1629 SCH_UNLOCK(sch); 1630 if (ipopts) 1631 (void) m_free(ipopts); 1632 goto done; 1633 } 1634 } 1635 } 1636 1637 skip_alloc: 1638 if (!tfo_cookie_valid && tfo_response_cookie_valid) 1639 sc->sc_tfo_cookie = &tfo_response_cookie; 1640 1641 /* 1642 * Fill in the syncache values. 1643 */ 1644 #ifdef MAC 1645 sc->sc_label = maclabel; 1646 #endif 1647 sc->sc_cred = cred; 1648 sc->sc_port = port; 1649 cred = NULL; 1650 sc->sc_ipopts = ipopts; 1651 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1652 sc->sc_ip_tos = ip_tos; 1653 sc->sc_ip_ttl = ip_ttl; 1654 #ifdef TCP_OFFLOAD 1655 sc->sc_tod = tod; 1656 sc->sc_todctx = todctx; 1657 #endif 1658 sc->sc_irs = th->th_seq; 1659 sc->sc_flags = 0; 1660 sc->sc_flowlabel = 0; 1661 1662 /* 1663 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1664 * win was derived from socket earlier in the function. 1665 */ 1666 win = imax(win, 0); 1667 win = imin(win, TCP_MAXWIN); 1668 sc->sc_wnd = win; 1669 1670 if (V_tcp_do_rfc1323 && 1671 !(ltflags & TF_NOOPT)) { 1672 /* 1673 * A timestamp received in a SYN makes 1674 * it ok to send timestamp requests and replies. 1675 */ 1676 if ((to->to_flags & TOF_TS) && (V_tcp_do_rfc1323 != 2)) { 1677 sc->sc_tsreflect = to->to_tsval; 1678 sc->sc_flags |= SCF_TIMESTAMP; 1679 sc->sc_tsoff = tcp_new_ts_offset(inc); 1680 } 1681 if ((to->to_flags & TOF_SCALE) && (V_tcp_do_rfc1323 != 3)) { 1682 int wscale = 0; 1683 1684 /* 1685 * Pick the smallest possible scaling factor that 1686 * will still allow us to scale up to sb_max, aka 1687 * kern.ipc.maxsockbuf. 1688 * 1689 * We do this because there are broken firewalls that 1690 * will corrupt the window scale option, leading to 1691 * the other endpoint believing that our advertised 1692 * window is unscaled. At scale factors larger than 1693 * 5 the unscaled window will drop below 1500 bytes, 1694 * leading to serious problems when traversing these 1695 * broken firewalls. 1696 * 1697 * With the default maxsockbuf of 256K, a scale factor 1698 * of 3 will be chosen by this algorithm. Those who 1699 * choose a larger maxsockbuf should watch out 1700 * for the compatibility problems mentioned above. 1701 * 1702 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1703 * or <SYN,ACK>) segment itself is never scaled. 1704 */ 1705 while (wscale < TCP_MAX_WINSHIFT && 1706 (TCP_MAXWIN << wscale) < sb_max) 1707 wscale++; 1708 sc->sc_requested_r_scale = wscale; 1709 sc->sc_requested_s_scale = to->to_wscale; 1710 sc->sc_flags |= SCF_WINSCALE; 1711 } 1712 } 1713 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1714 /* 1715 * If incoming packet has an MD5 signature, flag this in the 1716 * syncache so that syncache_respond() will do the right thing 1717 * with the SYN+ACK. 1718 */ 1719 if (to->to_flags & TOF_SIGNATURE) 1720 sc->sc_flags |= SCF_SIGNATURE; 1721 #endif /* TCP_SIGNATURE */ 1722 if (to->to_flags & TOF_SACKPERM) 1723 sc->sc_flags |= SCF_SACK; 1724 if (to->to_flags & TOF_MSS) 1725 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1726 if (ltflags & TF_NOOPT) 1727 sc->sc_flags |= SCF_NOOPT; 1728 /* ECN Handshake */ 1729 if (V_tcp_do_ecn && (tp->t_flags2 & TF2_CANNOT_DO_ECN) == 0) 1730 sc->sc_flags |= tcp_ecn_syncache_add(tcp_get_flags(th), iptos); 1731 1732 if (V_tcp_syncookies) 1733 sc->sc_iss = syncookie_generate(sch, sc); 1734 else 1735 sc->sc_iss = arc4random(); 1736 #ifdef INET6 1737 if (autoflowlabel) { 1738 if (V_tcp_syncookies) 1739 sc->sc_flowlabel = sc->sc_iss; 1740 else 1741 sc->sc_flowlabel = ip6_randomflowlabel(); 1742 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK; 1743 } 1744 #endif 1745 if (locked) 1746 SCH_UNLOCK(sch); 1747 1748 if (tfo_cookie_valid) { 1749 rv = syncache_tfo_expand(sc, so, m, tfo_response_cookie); 1750 /* INP_RUNLOCK(inp) will be performed by the caller */ 1751 goto tfo_expanded; 1752 } 1753 1754 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1755 /* 1756 * Do a standard 3-way handshake. 1757 */ 1758 if (syncache_respond(sc, m, TH_SYN|TH_ACK) == 0) { 1759 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs) 1760 syncache_free(sc); 1761 else if (sc != &scs) 1762 syncache_insert(sc, sch); /* locks and unlocks sch */ 1763 TCPSTAT_INC(tcps_sndacks); 1764 TCPSTAT_INC(tcps_sndtotal); 1765 } else { 1766 if (sc != &scs) 1767 syncache_free(sc); 1768 TCPSTAT_INC(tcps_sc_dropped); 1769 } 1770 goto donenoprobe; 1771 1772 done: 1773 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 1774 donenoprobe: 1775 if (m) 1776 m_freem(m); 1777 /* 1778 * If tfo_pending is not NULL here, then a TFO SYN that did not 1779 * result in a new socket was processed and the associated pending 1780 * counter has not yet been decremented. All such TFO processing paths 1781 * transit this point. 1782 */ 1783 if (tfo_pending != NULL) 1784 tcp_fastopen_decrement_counter(tfo_pending); 1785 1786 tfo_expanded: 1787 if (cred != NULL) 1788 crfree(cred); 1789 #ifdef MAC 1790 if (sc == &scs) 1791 mac_syncache_destroy(&maclabel); 1792 #endif 1793 return (rv); 1794 } 1795 1796 /* 1797 * Send SYN|ACK or ACK to the peer. Either in response to a peer's segment, 1798 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL. 1799 */ 1800 static int 1801 syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) 1802 { 1803 struct ip *ip = NULL; 1804 struct mbuf *m; 1805 struct tcphdr *th = NULL; 1806 struct udphdr *udp = NULL; 1807 int optlen, error = 0; /* Make compiler happy */ 1808 u_int16_t hlen, tlen, mssopt, ulen; 1809 struct tcpopt to; 1810 #ifdef INET6 1811 struct ip6_hdr *ip6 = NULL; 1812 #endif 1813 1814 NET_EPOCH_ASSERT(); 1815 1816 hlen = 1817 #ifdef INET6 1818 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) : 1819 #endif 1820 sizeof(struct ip); 1821 tlen = hlen + sizeof(struct tcphdr); 1822 if (sc->sc_port) { 1823 tlen += sizeof(struct udphdr); 1824 } 1825 /* Determine MSS we advertize to other end of connection. */ 1826 mssopt = tcp_mssopt(&sc->sc_inc); 1827 if (sc->sc_port) 1828 mssopt -= V_tcp_udp_tunneling_overhead; 1829 mssopt = max(mssopt, V_tcp_minmss); 1830 1831 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1832 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1833 ("syncache: mbuf too small: hlen %u, sc_port %u, max_linkhdr %d + " 1834 "tlen %d + TCP_MAXOLEN %ju <= MHLEN %d", hlen, sc->sc_port, 1835 max_linkhdr, tlen, (uintmax_t)TCP_MAXOLEN, MHLEN)); 1836 1837 /* Create the IP+TCP header from scratch. */ 1838 m = m_gethdr(M_NOWAIT, MT_DATA); 1839 if (m == NULL) 1840 return (ENOBUFS); 1841 #ifdef MAC 1842 mac_syncache_create_mbuf(sc->sc_label, m); 1843 #endif 1844 m->m_data += max_linkhdr; 1845 m->m_len = tlen; 1846 m->m_pkthdr.len = tlen; 1847 m->m_pkthdr.rcvif = NULL; 1848 1849 #ifdef INET6 1850 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 1851 ip6 = mtod(m, struct ip6_hdr *); 1852 ip6->ip6_vfc = IPV6_VERSION; 1853 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1854 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1855 ip6->ip6_plen = htons(tlen - hlen); 1856 /* ip6_hlim is set after checksum */ 1857 /* Zero out traffic class and flow label. */ 1858 ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK; 1859 ip6->ip6_flow |= sc->sc_flowlabel; 1860 if (sc->sc_port != 0) { 1861 ip6->ip6_nxt = IPPROTO_UDP; 1862 udp = (struct udphdr *)(ip6 + 1); 1863 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1864 udp->uh_dport = sc->sc_port; 1865 ulen = (tlen - sizeof(struct ip6_hdr)); 1866 th = (struct tcphdr *)(udp + 1); 1867 } else { 1868 ip6->ip6_nxt = IPPROTO_TCP; 1869 th = (struct tcphdr *)(ip6 + 1); 1870 } 1871 ip6->ip6_flow |= htonl(sc->sc_ip_tos << IPV6_FLOWLABEL_LEN); 1872 } 1873 #endif 1874 #if defined(INET6) && defined(INET) 1875 else 1876 #endif 1877 #ifdef INET 1878 { 1879 ip = mtod(m, struct ip *); 1880 ip->ip_v = IPVERSION; 1881 ip->ip_hl = sizeof(struct ip) >> 2; 1882 ip->ip_len = htons(tlen); 1883 ip->ip_id = 0; 1884 ip->ip_off = 0; 1885 ip->ip_sum = 0; 1886 ip->ip_src = sc->sc_inc.inc_laddr; 1887 ip->ip_dst = sc->sc_inc.inc_faddr; 1888 ip->ip_ttl = sc->sc_ip_ttl; 1889 ip->ip_tos = sc->sc_ip_tos; 1890 1891 /* 1892 * See if we should do MTU discovery. Route lookups are 1893 * expensive, so we will only unset the DF bit if: 1894 * 1895 * 1) path_mtu_discovery is disabled 1896 * 2) the SCF_UNREACH flag has been set 1897 */ 1898 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1899 ip->ip_off |= htons(IP_DF); 1900 if (sc->sc_port == 0) { 1901 ip->ip_p = IPPROTO_TCP; 1902 th = (struct tcphdr *)(ip + 1); 1903 } else { 1904 ip->ip_p = IPPROTO_UDP; 1905 udp = (struct udphdr *)(ip + 1); 1906 udp->uh_sport = htons(V_tcp_udp_tunneling_port); 1907 udp->uh_dport = sc->sc_port; 1908 ulen = (tlen - sizeof(struct ip)); 1909 th = (struct tcphdr *)(udp + 1); 1910 } 1911 } 1912 #endif /* INET */ 1913 th->th_sport = sc->sc_inc.inc_lport; 1914 th->th_dport = sc->sc_inc.inc_fport; 1915 1916 if (flags & TH_SYN) 1917 th->th_seq = htonl(sc->sc_iss); 1918 else 1919 th->th_seq = htonl(sc->sc_iss + 1); 1920 th->th_ack = htonl(sc->sc_irs + 1); 1921 th->th_off = sizeof(struct tcphdr) >> 2; 1922 th->th_win = htons(sc->sc_wnd); 1923 th->th_urp = 0; 1924 1925 flags = tcp_ecn_syncache_respond(flags, sc); 1926 tcp_set_flags(th, flags); 1927 1928 /* Tack on the TCP options. */ 1929 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1930 to.to_flags = 0; 1931 1932 if (flags & TH_SYN) { 1933 to.to_mss = mssopt; 1934 to.to_flags = TOF_MSS; 1935 if (sc->sc_flags & SCF_WINSCALE) { 1936 to.to_wscale = sc->sc_requested_r_scale; 1937 to.to_flags |= TOF_SCALE; 1938 } 1939 if (sc->sc_flags & SCF_SACK) 1940 to.to_flags |= TOF_SACKPERM; 1941 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1942 if (sc->sc_flags & SCF_SIGNATURE) 1943 to.to_flags |= TOF_SIGNATURE; 1944 #endif 1945 if (sc->sc_tfo_cookie) { 1946 to.to_flags |= TOF_FASTOPEN; 1947 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN; 1948 to.to_tfo_cookie = sc->sc_tfo_cookie; 1949 /* don't send cookie again when retransmitting response */ 1950 sc->sc_tfo_cookie = NULL; 1951 } 1952 } 1953 if (sc->sc_flags & SCF_TIMESTAMP) { 1954 to.to_tsval = sc->sc_tsoff + tcp_ts_getticks(); 1955 to.to_tsecr = sc->sc_tsreflect; 1956 to.to_flags |= TOF_TS; 1957 } 1958 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1959 1960 /* Adjust headers by option size. */ 1961 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1962 m->m_len += optlen; 1963 m->m_pkthdr.len += optlen; 1964 #ifdef INET6 1965 if (sc->sc_inc.inc_flags & INC_ISIPV6) 1966 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1967 else 1968 #endif 1969 ip->ip_len = htons(ntohs(ip->ip_len) + optlen); 1970 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) 1971 if (sc->sc_flags & SCF_SIGNATURE) { 1972 KASSERT(to.to_flags & TOF_SIGNATURE, 1973 ("tcp_addoptions() didn't set tcp_signature")); 1974 1975 /* NOTE: to.to_signature is inside of mbuf */ 1976 if (!TCPMD5_ENABLED() || 1977 TCPMD5_OUTPUT(m, th, to.to_signature) != 0) { 1978 m_freem(m); 1979 return (EACCES); 1980 } 1981 } 1982 #endif 1983 } else 1984 optlen = 0; 1985 1986 if (udp) { 1987 ulen += optlen; 1988 udp->uh_ulen = htons(ulen); 1989 } 1990 M_SETFIB(m, sc->sc_inc.inc_fibnum); 1991 /* 1992 * If we have peer's SYN and it has a flowid, then let's assign it to 1993 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid 1994 * to SYN|ACK due to lack of inp here. 1995 */ 1996 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) { 1997 m->m_pkthdr.flowid = m0->m_pkthdr.flowid; 1998 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0)); 1999 } 2000 #ifdef INET6 2001 if (sc->sc_inc.inc_flags & INC_ISIPV6) { 2002 if (sc->sc_port) { 2003 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6; 2004 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2005 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, 2006 IPPROTO_UDP, 0); 2007 th->th_sum = htons(0); 2008 } else { 2009 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6; 2010 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2011 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen, 2012 IPPROTO_TCP, 0); 2013 } 2014 ip6->ip6_hlim = sc->sc_ip_ttl; 2015 #ifdef TCP_OFFLOAD 2016 if (ADDED_BY_TOE(sc)) { 2017 struct toedev *tod = sc->sc_tod; 2018 2019 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2020 2021 return (error); 2022 } 2023 #endif 2024 TCP_PROBE5(send, NULL, NULL, ip6, NULL, th); 2025 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 2026 } 2027 #endif 2028 #if defined(INET6) && defined(INET) 2029 else 2030 #endif 2031 #ifdef INET 2032 { 2033 if (sc->sc_port) { 2034 m->m_pkthdr.csum_flags = CSUM_UDP; 2035 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum); 2036 udp->uh_sum = in_pseudo(ip->ip_src.s_addr, 2037 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP)); 2038 th->th_sum = htons(0); 2039 } else { 2040 m->m_pkthdr.csum_flags = CSUM_TCP; 2041 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 2042 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 2043 htons(tlen + optlen - hlen + IPPROTO_TCP)); 2044 } 2045 #ifdef TCP_OFFLOAD 2046 if (ADDED_BY_TOE(sc)) { 2047 struct toedev *tod = sc->sc_tod; 2048 2049 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m); 2050 2051 return (error); 2052 } 2053 #endif 2054 TCP_PROBE5(send, NULL, NULL, ip, NULL, th); 2055 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 2056 } 2057 #endif 2058 return (error); 2059 } 2060 2061 /* 2062 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks 2063 * that exceed the capacity of the syncache by avoiding the storage of any 2064 * of the SYNs we receive. Syncookies defend against blind SYN flooding 2065 * attacks where the attacker does not have access to our responses. 2066 * 2067 * Syncookies encode and include all necessary information about the 2068 * connection setup within the SYN|ACK that we send back. That way we 2069 * can avoid keeping any local state until the ACK to our SYN|ACK returns 2070 * (if ever). Normally the syncache and syncookies are running in parallel 2071 * with the latter taking over when the former is exhausted. When matching 2072 * syncache entry is found the syncookie is ignored. 2073 * 2074 * The only reliable information persisting the 3WHS is our initial sequence 2075 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient 2076 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS 2077 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK 2078 * returns and signifies a legitimate connection if it matches the ACK. 2079 * 2080 * The available space of 32 bits to store the hash and to encode the SYN 2081 * option information is very tight and we should have at least 24 bits for 2082 * the MAC to keep the number of guesses by blind spoofing reasonably high. 2083 * 2084 * SYN option information we have to encode to fully restore a connection: 2085 * MSS: is imporant to chose an optimal segment size to avoid IP level 2086 * fragmentation along the path. The common MSS values can be encoded 2087 * in a 3-bit table. Uncommon values are captured by the next lower value 2088 * in the table leading to a slight increase in packetization overhead. 2089 * WSCALE: is necessary to allow large windows to be used for high delay- 2090 * bandwidth product links. Not scaling the window when it was initially 2091 * negotiated is bad for performance as lack of scaling further decreases 2092 * the apparent available send window. We only need to encode the WSCALE 2093 * we received from the remote end. Our end can be recalculated at any 2094 * time. The common WSCALE values can be encoded in a 3-bit table. 2095 * Uncommon values are captured by the next lower value in the table 2096 * making us under-estimate the available window size halving our 2097 * theoretically possible maximum throughput for that connection. 2098 * SACK: Greatly assists in packet loss recovery and requires 1 bit. 2099 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options 2100 * that are included in all segments on a connection. We enable them when 2101 * the ACK has them. 2102 * 2103 * Security of syncookies and attack vectors: 2104 * 2105 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod) 2106 * together with the gloabl secret to make it unique per connection attempt. 2107 * Thus any change of any of those parameters results in a different MAC output 2108 * in an unpredictable way unless a collision is encountered. 24 bits of the 2109 * MAC are embedded into the ISS. 2110 * 2111 * To prevent replay attacks two rotating global secrets are updated with a 2112 * new random value every 15 seconds. The life-time of a syncookie is thus 2113 * 15-30 seconds. 2114 * 2115 * Vector 1: Attacking the secret. This requires finding a weakness in the 2116 * MAC itself or the way it is used here. The attacker can do a chosen plain 2117 * text attack by varying and testing the all parameters under his control. 2118 * The strength depends on the size and randomness of the secret, and the 2119 * cryptographic security of the MAC function. Due to the constant updating 2120 * of the secret the attacker has at most 29.999 seconds to find the secret 2121 * and launch spoofed connections. After that he has to start all over again. 2122 * 2123 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC 2124 * size an average of 4,823 attempts are required for a 50% chance of success 2125 * to spoof a single syncookie (birthday collision paradox). However the 2126 * attacker is blind and doesn't know if one of his attempts succeeded unless 2127 * he has a side channel to interfere success from. A single connection setup 2128 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets. 2129 * This many attempts are required for each one blind spoofed connection. For 2130 * every additional spoofed connection he has to launch another N attempts. 2131 * Thus for a sustained rate 100 spoofed connections per second approximately 2132 * 1,800,000 packets per second would have to be sent. 2133 * 2134 * NB: The MAC function should be fast so that it doesn't become a CPU 2135 * exhaustion attack vector itself. 2136 * 2137 * References: 2138 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations 2139 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996 2140 * http://cr.yp.to/syncookies.html (overview) 2141 * http://cr.yp.to/syncookies/archive (details) 2142 * 2143 * 2144 * Schematic construction of a syncookie enabled Initial Sequence Number: 2145 * 0 1 2 3 2146 * 12345678901234567890123456789012 2147 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP| 2148 * 2149 * x 24 MAC (truncated) 2150 * W 3 Send Window Scale index 2151 * M 3 MSS index 2152 * S 1 SACK permitted 2153 * P 1 Odd/even secret 2154 */ 2155 2156 /* 2157 * Distribution and probability of certain MSS values. Those in between are 2158 * rounded down to the next lower one. 2159 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011] 2160 * .2% .3% 5% 7% 7% 20% 15% 45% 2161 */ 2162 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 }; 2163 2164 /* 2165 * Distribution and probability of certain WSCALE values. We have to map the 2166 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3 2167 * bits based on prevalence of certain values. Where we don't have an exact 2168 * match for are rounded down to the next lower one letting us under-estimate 2169 * the true available window. At the moment this would happen only for the 2170 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer 2171 * and window size). The absence of the WSCALE option (no scaling in either 2172 * direction) is encoded with index zero. 2173 * [WSCALE values histograms, Allman, 2012] 2174 * X 10 10 35 5 6 14 10% by host 2175 * X 11 4 5 5 18 49 3% by connections 2176 */ 2177 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 }; 2178 2179 /* 2180 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed 2181 * and good cryptographic properties. 2182 */ 2183 static uint32_t 2184 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags, 2185 uint8_t *secbits, uintptr_t secmod) 2186 { 2187 SIPHASH_CTX ctx; 2188 uint32_t siphash[2]; 2189 2190 SipHash24_Init(&ctx); 2191 SipHash_SetKey(&ctx, secbits); 2192 switch (inc->inc_flags & INC_ISIPV6) { 2193 #ifdef INET 2194 case 0: 2195 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr)); 2196 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr)); 2197 break; 2198 #endif 2199 #ifdef INET6 2200 case INC_ISIPV6: 2201 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr)); 2202 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr)); 2203 break; 2204 #endif 2205 } 2206 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport)); 2207 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport)); 2208 SipHash_Update(&ctx, &irs, sizeof(irs)); 2209 SipHash_Update(&ctx, &flags, sizeof(flags)); 2210 SipHash_Update(&ctx, &secmod, sizeof(secmod)); 2211 SipHash_Final((u_int8_t *)&siphash, &ctx); 2212 2213 return (siphash[0] ^ siphash[1]); 2214 } 2215 2216 static tcp_seq 2217 syncookie_generate(struct syncache_head *sch, struct syncache *sc) 2218 { 2219 u_int i, secbit, wscale; 2220 uint32_t iss, hash; 2221 uint8_t *secbits; 2222 union syncookie cookie; 2223 2224 cookie.cookie = 0; 2225 2226 /* Map our computed MSS into the 3-bit index. */ 2227 for (i = nitems(tcp_sc_msstab) - 1; 2228 tcp_sc_msstab[i] > sc->sc_peer_mss && i > 0; 2229 i--) 2230 ; 2231 cookie.flags.mss_idx = i; 2232 2233 /* 2234 * Map the send window scale into the 3-bit index but only if 2235 * the wscale option was received. 2236 */ 2237 if (sc->sc_flags & SCF_WINSCALE) { 2238 wscale = sc->sc_requested_s_scale; 2239 for (i = nitems(tcp_sc_wstab) - 1; 2240 tcp_sc_wstab[i] > wscale && i > 0; 2241 i--) 2242 ; 2243 cookie.flags.wscale_idx = i; 2244 } 2245 2246 /* Can we do SACK? */ 2247 if (sc->sc_flags & SCF_SACK) 2248 cookie.flags.sack_ok = 1; 2249 2250 /* Which of the two secrets to use. */ 2251 secbit = V_tcp_syncache.secret.oddeven & 0x1; 2252 cookie.flags.odd_even = secbit; 2253 2254 secbits = V_tcp_syncache.secret.key[secbit]; 2255 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits, 2256 (uintptr_t)sch); 2257 2258 /* 2259 * Put the flags into the hash and XOR them to get better ISS number 2260 * variance. This doesn't enhance the cryptographic strength and is 2261 * done to prevent the 8 cookie bits from showing up directly on the 2262 * wire. 2263 */ 2264 iss = hash & ~0xff; 2265 iss |= cookie.cookie ^ (hash >> 24); 2266 2267 TCPSTAT_INC(tcps_sc_sendcookie); 2268 return (iss); 2269 } 2270 2271 static struct syncache * 2272 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 2273 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2274 struct socket *lso, uint16_t port) 2275 { 2276 uint32_t hash; 2277 uint8_t *secbits; 2278 tcp_seq ack, seq; 2279 int wnd, wscale = 0; 2280 union syncookie cookie; 2281 2282 /* 2283 * Pull information out of SYN-ACK/ACK and revert sequence number 2284 * advances. 2285 */ 2286 ack = th->th_ack - 1; 2287 seq = th->th_seq - 1; 2288 2289 /* 2290 * Unpack the flags containing enough information to restore the 2291 * connection. 2292 */ 2293 cookie.cookie = (ack & 0xff) ^ (ack >> 24); 2294 2295 /* Which of the two secrets to use. */ 2296 secbits = V_tcp_syncache.secret.key[cookie.flags.odd_even]; 2297 2298 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch); 2299 2300 /* The recomputed hash matches the ACK if this was a genuine cookie. */ 2301 if ((ack & ~0xff) != (hash & ~0xff)) 2302 return (NULL); 2303 2304 /* Fill in the syncache values. */ 2305 sc->sc_flags = 0; 2306 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 2307 sc->sc_ipopts = NULL; 2308 2309 sc->sc_irs = seq; 2310 sc->sc_iss = ack; 2311 2312 switch (inc->inc_flags & INC_ISIPV6) { 2313 #ifdef INET 2314 case 0: 2315 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl; 2316 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos; 2317 break; 2318 #endif 2319 #ifdef INET6 2320 case INC_ISIPV6: 2321 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL) 2322 sc->sc_flowlabel = 2323 htonl(sc->sc_iss) & IPV6_FLOWLABEL_MASK; 2324 break; 2325 #endif 2326 } 2327 2328 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx]; 2329 2330 /* We can simply recompute receive window scale we sent earlier. */ 2331 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) 2332 wscale++; 2333 2334 /* Only use wscale if it was enabled in the orignal SYN. */ 2335 if (cookie.flags.wscale_idx > 0) { 2336 sc->sc_requested_r_scale = wscale; 2337 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx]; 2338 sc->sc_flags |= SCF_WINSCALE; 2339 } 2340 2341 wnd = lso->sol_sbrcv_hiwat; 2342 wnd = imax(wnd, 0); 2343 wnd = imin(wnd, TCP_MAXWIN); 2344 sc->sc_wnd = wnd; 2345 2346 if (cookie.flags.sack_ok) 2347 sc->sc_flags |= SCF_SACK; 2348 2349 if (to->to_flags & TOF_TS) { 2350 sc->sc_flags |= SCF_TIMESTAMP; 2351 sc->sc_tsreflect = to->to_tsval; 2352 sc->sc_tsoff = tcp_new_ts_offset(inc); 2353 } 2354 2355 if (to->to_flags & TOF_SIGNATURE) 2356 sc->sc_flags |= SCF_SIGNATURE; 2357 2358 sc->sc_rxmits = 0; 2359 2360 sc->sc_port = port; 2361 2362 TCPSTAT_INC(tcps_sc_recvcookie); 2363 return (sc); 2364 } 2365 2366 #ifdef INVARIANTS 2367 static int 2368 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch, 2369 struct syncache *sc, struct tcphdr *th, struct tcpopt *to, 2370 struct socket *lso, uint16_t port) 2371 { 2372 struct syncache scs, *scx; 2373 char *s; 2374 2375 bzero(&scs, sizeof(scs)); 2376 scx = syncookie_lookup(inc, sch, &scs, th, to, lso, port); 2377 2378 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL) 2379 return (0); 2380 2381 if (scx != NULL) { 2382 if (sc->sc_peer_mss != scx->sc_peer_mss) 2383 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n", 2384 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss); 2385 2386 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale) 2387 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n", 2388 s, __func__, sc->sc_requested_r_scale, 2389 scx->sc_requested_r_scale); 2390 2391 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale) 2392 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n", 2393 s, __func__, sc->sc_requested_s_scale, 2394 scx->sc_requested_s_scale); 2395 2396 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK)) 2397 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__); 2398 } 2399 2400 if (s != NULL) 2401 free(s, M_TCPLOG); 2402 return (0); 2403 } 2404 #endif /* INVARIANTS */ 2405 2406 static void 2407 syncookie_reseed(void *arg) 2408 { 2409 struct tcp_syncache *sc = arg; 2410 uint8_t *secbits; 2411 int secbit; 2412 2413 /* 2414 * Reseeding the secret doesn't have to be protected by a lock. 2415 * It only must be ensured that the new random values are visible 2416 * to all CPUs in a SMP environment. The atomic with release 2417 * semantics ensures that. 2418 */ 2419 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1; 2420 secbits = sc->secret.key[secbit]; 2421 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0); 2422 atomic_add_rel_int(&sc->secret.oddeven, 1); 2423 2424 /* Reschedule ourself. */ 2425 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz); 2426 } 2427 2428 /* 2429 * We have overflowed a bucket. Let's pause dealing with the syncache. 2430 * This function will increment the bucketoverflow statistics appropriately 2431 * (once per pause when pausing is enabled; otherwise, once per overflow). 2432 */ 2433 static void 2434 syncache_pause(struct in_conninfo *inc) 2435 { 2436 time_t delta; 2437 const char *s; 2438 2439 /* XXX: 2440 * 2. Add sysctl read here so we don't get the benefit of this 2441 * change without the new sysctl. 2442 */ 2443 2444 /* 2445 * Try an unlocked read. If we already know that another thread 2446 * has activated the feature, there is no need to proceed. 2447 */ 2448 if (V_tcp_syncache.paused) 2449 return; 2450 2451 /* Are cookied enabled? If not, we can't pause. */ 2452 if (!V_tcp_syncookies) { 2453 TCPSTAT_INC(tcps_sc_bucketoverflow); 2454 return; 2455 } 2456 2457 /* 2458 * We may be the first thread to find an overflow. Get the lock 2459 * and evaluate if we need to take action. 2460 */ 2461 mtx_lock(&V_tcp_syncache.pause_mtx); 2462 if (V_tcp_syncache.paused) { 2463 mtx_unlock(&V_tcp_syncache.pause_mtx); 2464 return; 2465 } 2466 2467 /* Activate protection. */ 2468 V_tcp_syncache.paused = true; 2469 TCPSTAT_INC(tcps_sc_bucketoverflow); 2470 2471 /* 2472 * Determine the last backoff time. If we are seeing a re-newed 2473 * attack within that same time after last reactivating the syncache, 2474 * consider it an extension of the same attack. 2475 */ 2476 delta = TCP_SYNCACHE_PAUSE_TIME << V_tcp_syncache.pause_backoff; 2477 if (V_tcp_syncache.pause_until + delta - time_uptime > 0) { 2478 if (V_tcp_syncache.pause_backoff < TCP_SYNCACHE_MAX_BACKOFF) { 2479 delta <<= 1; 2480 V_tcp_syncache.pause_backoff++; 2481 } 2482 } else { 2483 delta = TCP_SYNCACHE_PAUSE_TIME; 2484 V_tcp_syncache.pause_backoff = 0; 2485 } 2486 2487 /* Log a warning, including IP addresses, if able. */ 2488 if (inc != NULL) 2489 s = tcp_log_addrs(inc, NULL, NULL, NULL); 2490 else 2491 s = (const char *)NULL; 2492 log(LOG_WARNING, "TCP syncache overflow detected; using syncookies for " 2493 "the next %lld seconds%s%s%s\n", (long long)delta, 2494 (s != NULL) ? " (last SYN: " : "", (s != NULL) ? s : "", 2495 (s != NULL) ? ")" : ""); 2496 free(__DECONST(void *, s), M_TCPLOG); 2497 2498 /* Use the calculated delta to set a new pause time. */ 2499 V_tcp_syncache.pause_until = time_uptime + delta; 2500 callout_reset(&V_tcp_syncache.pause_co, delta * hz, syncache_unpause, 2501 &V_tcp_syncache); 2502 mtx_unlock(&V_tcp_syncache.pause_mtx); 2503 } 2504 2505 /* Evaluate whether we need to unpause. */ 2506 static void 2507 syncache_unpause(void *arg) 2508 { 2509 struct tcp_syncache *sc; 2510 time_t delta; 2511 2512 sc = arg; 2513 mtx_assert(&sc->pause_mtx, MA_OWNED | MA_NOTRECURSED); 2514 callout_deactivate(&sc->pause_co); 2515 2516 /* 2517 * Check to make sure we are not running early. If the pause 2518 * time has expired, then deactivate the protection. 2519 */ 2520 if ((delta = sc->pause_until - time_uptime) > 0) 2521 callout_schedule(&sc->pause_co, delta * hz); 2522 else 2523 sc->paused = false; 2524 } 2525 2526 /* 2527 * Exports the syncache entries to userland so that netstat can display 2528 * them alongside the other sockets. This function is intended to be 2529 * called only from tcp_pcblist. 2530 * 2531 * Due to concurrency on an active system, the number of pcbs exported 2532 * may have no relation to max_pcbs. max_pcbs merely indicates the 2533 * amount of space the caller allocated for this function to use. 2534 */ 2535 int 2536 syncache_pcblist(struct sysctl_req *req) 2537 { 2538 struct xtcpcb xt; 2539 struct syncache *sc; 2540 struct syncache_head *sch; 2541 int error, i; 2542 2543 bzero(&xt, sizeof(xt)); 2544 xt.xt_len = sizeof(xt); 2545 xt.t_state = TCPS_SYN_RECEIVED; 2546 xt.xt_inp.xi_socket.xso_protocol = IPPROTO_TCP; 2547 xt.xt_inp.xi_socket.xso_len = sizeof (struct xsocket); 2548 xt.xt_inp.xi_socket.so_type = SOCK_STREAM; 2549 xt.xt_inp.xi_socket.so_state = SS_ISCONNECTING; 2550 2551 for (i = 0; i < V_tcp_syncache.hashsize; i++) { 2552 sch = &V_tcp_syncache.hashbase[i]; 2553 SCH_LOCK(sch); 2554 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 2555 if (sc->sc_cred != NULL && 2556 cr_cansee(req->td->td_ucred, sc->sc_cred) != 0) 2557 continue; 2558 if (sc->sc_inc.inc_flags & INC_ISIPV6) 2559 xt.xt_inp.inp_vflag = INP_IPV6; 2560 else 2561 xt.xt_inp.inp_vflag = INP_IPV4; 2562 xt.xt_encaps_port = sc->sc_port; 2563 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, 2564 sizeof (struct in_conninfo)); 2565 error = SYSCTL_OUT(req, &xt, sizeof xt); 2566 if (error) { 2567 SCH_UNLOCK(sch); 2568 return (0); 2569 } 2570 } 2571 SCH_UNLOCK(sch); 2572 } 2573 2574 return (0); 2575 } 2576