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