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