1 /*- 2 * Copyright (c) 2001 McAfee, Inc. 3 * Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by Jonathan Lemon 7 * and McAfee Research, the Security Research Division of McAfee, Inc. under 8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __FBSDID("$FreeBSD$"); 35 36 #include "opt_inet.h" 37 #include "opt_inet6.h" 38 #include "opt_ipsec.h" 39 #include "opt_mac.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/lock.h> 46 #include <sys/mutex.h> 47 #include <sys/malloc.h> 48 #include <sys/mbuf.h> 49 #include <sys/md5.h> 50 #include <sys/proc.h> /* for proc0 declaration */ 51 #include <sys/random.h> 52 #include <sys/socket.h> 53 #include <sys/socketvar.h> 54 #include <sys/syslog.h> 55 56 #include <vm/uma.h> 57 58 #include <net/if.h> 59 #include <net/route.h> 60 61 #include <netinet/in.h> 62 #include <netinet/in_systm.h> 63 #include <netinet/ip.h> 64 #include <netinet/in_var.h> 65 #include <netinet/in_pcb.h> 66 #include <netinet/ip_var.h> 67 #include <netinet/ip_options.h> 68 #ifdef INET6 69 #include <netinet/ip6.h> 70 #include <netinet/icmp6.h> 71 #include <netinet6/nd6.h> 72 #include <netinet6/ip6_var.h> 73 #include <netinet6/in6_pcb.h> 74 #endif 75 #include <netinet/tcp.h> 76 #include <netinet/tcp_fsm.h> 77 #include <netinet/tcp_seq.h> 78 #include <netinet/tcp_timer.h> 79 #include <netinet/tcp_var.h> 80 #include <netinet/tcp_syncache.h> 81 #ifdef INET6 82 #include <netinet6/tcp6_var.h> 83 #endif 84 85 #ifdef IPSEC 86 #include <netipsec/ipsec.h> 87 #ifdef INET6 88 #include <netipsec/ipsec6.h> 89 #endif 90 #include <netipsec/key.h> 91 #endif /*IPSEC*/ 92 93 #include <machine/in_cksum.h> 94 95 #include <security/mac/mac_framework.h> 96 97 static int tcp_syncookies = 1; 98 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 99 &tcp_syncookies, 0, 100 "Use TCP SYN cookies if the syncache overflows"); 101 102 static int tcp_syncookiesonly = 0; 103 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 104 &tcp_syncookiesonly, 0, 105 "Use only TCP SYN cookies"); 106 107 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ 108 #define SYNCOOKIE_LIFETIME 16 /* seconds */ 109 110 struct syncache { 111 TAILQ_ENTRY(syncache) sc_hash; 112 struct in_conninfo sc_inc; /* addresses */ 113 u_long sc_rxttime; /* retransmit time */ 114 u_int16_t sc_rxmits; /* retransmit counter */ 115 116 u_int32_t sc_tsreflect; /* timestamp to reflect */ 117 u_int32_t sc_ts; /* our timestamp to send */ 118 u_int32_t sc_tsoff; /* ts offset w/ syncookies */ 119 u_int32_t sc_flowlabel; /* IPv6 flowlabel */ 120 tcp_seq sc_irs; /* seq from peer */ 121 tcp_seq sc_iss; /* our ISS */ 122 struct mbuf *sc_ipopts; /* source route */ 123 124 u_int16_t sc_peer_mss; /* peer's MSS */ 125 u_int16_t sc_wnd; /* advertised window */ 126 u_int8_t sc_ip_ttl; /* IPv4 TTL */ 127 u_int8_t sc_ip_tos; /* IPv4 TOS */ 128 u_int8_t sc_requested_s_scale:4, 129 sc_requested_r_scale:4; 130 u_int8_t sc_flags; 131 #define SCF_NOOPT 0x01 /* no TCP options */ 132 #define SCF_WINSCALE 0x02 /* negotiated window scaling */ 133 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ 134 /* MSS is implicit */ 135 #define SCF_UNREACH 0x10 /* icmp unreachable received */ 136 #define SCF_SIGNATURE 0x20 /* send MD5 digests */ 137 #define SCF_SACK 0x80 /* send SACK option */ 138 #ifdef MAC 139 struct label *sc_label; /* MAC label reference */ 140 #endif 141 }; 142 143 struct syncache_head { 144 struct mtx sch_mtx; 145 TAILQ_HEAD(sch_head, syncache) sch_bucket; 146 struct callout sch_timer; 147 int sch_nextc; 148 u_int sch_length; 149 u_int sch_oddeven; 150 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; 151 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; 152 u_int sch_reseed; /* time_uptime, seconds */ 153 }; 154 155 static void syncache_drop(struct syncache *, struct syncache_head *); 156 static void syncache_free(struct syncache *); 157 static void syncache_insert(struct syncache *, struct syncache_head *); 158 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 159 static int syncache_respond(struct syncache *); 160 static struct socket *syncache_socket(struct syncache *, struct socket *, 161 struct mbuf *m); 162 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, 163 int docallout); 164 static void syncache_timer(void *); 165 static void syncookie_generate(struct syncache_head *, struct syncache *, 166 u_int32_t *); 167 static struct syncache 168 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 169 struct syncache *, struct tcpopt *, struct tcphdr *, 170 struct socket *); 171 172 /* 173 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 174 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 175 * the odds are that the user has given up attempting to connect by then. 176 */ 177 #define SYNCACHE_MAXREXMTS 3 178 179 /* Arbitrary values */ 180 #define TCP_SYNCACHE_HASHSIZE 512 181 #define TCP_SYNCACHE_BUCKETLIMIT 30 182 183 struct tcp_syncache { 184 struct syncache_head *hashbase; 185 uma_zone_t zone; 186 u_int hashsize; 187 u_int hashmask; 188 u_int bucket_limit; 189 u_int cache_count; /* XXX: unprotected */ 190 u_int cache_limit; 191 u_int rexmt_limit; 192 u_int hash_secret; 193 }; 194 static struct tcp_syncache tcp_syncache; 195 196 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 197 198 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 199 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 200 201 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 202 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 203 204 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 205 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 206 207 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 208 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 209 210 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 211 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 212 213 int tcp_sc_rst_sock_fail = 1; 214 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW, 215 &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure"); 216 217 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 218 219 #define SYNCACHE_HASH(inc, mask) \ 220 ((tcp_syncache.hash_secret ^ \ 221 (inc)->inc_faddr.s_addr ^ \ 222 ((inc)->inc_faddr.s_addr >> 16) ^ \ 223 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 224 225 #define SYNCACHE_HASH6(inc, mask) \ 226 ((tcp_syncache.hash_secret ^ \ 227 (inc)->inc6_faddr.s6_addr32[0] ^ \ 228 (inc)->inc6_faddr.s6_addr32[3] ^ \ 229 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 230 231 #define ENDPTS_EQ(a, b) ( \ 232 (a)->ie_fport == (b)->ie_fport && \ 233 (a)->ie_lport == (b)->ie_lport && \ 234 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 235 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 236 ) 237 238 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 239 240 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 241 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 242 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 243 244 /* 245 * Requires the syncache entry to be already removed from the bucket list. 246 */ 247 static void 248 syncache_free(struct syncache *sc) 249 { 250 if (sc->sc_ipopts) 251 (void) m_free(sc->sc_ipopts); 252 #ifdef MAC 253 mac_syncache_destroy(&sc->sc_label); 254 #endif 255 256 uma_zfree(tcp_syncache.zone, sc); 257 } 258 259 void 260 syncache_init(void) 261 { 262 int i; 263 264 tcp_syncache.cache_count = 0; 265 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 266 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 267 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 268 tcp_syncache.hash_secret = arc4random(); 269 270 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 271 &tcp_syncache.hashsize); 272 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 273 &tcp_syncache.bucket_limit); 274 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { 275 printf("WARNING: syncache hash size is not a power of 2.\n"); 276 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 277 } 278 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 279 280 /* Set limits. */ 281 tcp_syncache.cache_limit = 282 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 283 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 284 &tcp_syncache.cache_limit); 285 286 /* Allocate the hash table. */ 287 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 288 tcp_syncache.hashsize * sizeof(struct syncache_head), 289 M_SYNCACHE, M_WAITOK | M_ZERO); 290 291 /* Initialize the hash buckets. */ 292 for (i = 0; i < tcp_syncache.hashsize; i++) { 293 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 294 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 295 NULL, MTX_DEF); 296 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, 297 &tcp_syncache.hashbase[i].sch_mtx, 0); 298 tcp_syncache.hashbase[i].sch_length = 0; 299 } 300 301 /* Create the syncache entry zone. */ 302 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 303 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 304 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 305 } 306 307 /* 308 * Inserts a syncache entry into the specified bucket row. 309 * Locks and unlocks the syncache_head autonomously. 310 */ 311 static void 312 syncache_insert(struct syncache *sc, struct syncache_head *sch) 313 { 314 struct syncache *sc2; 315 316 SCH_LOCK(sch); 317 318 /* 319 * Make sure that we don't overflow the per-bucket limit. 320 * If the bucket is full, toss the oldest element. 321 */ 322 if (sch->sch_length >= tcp_syncache.bucket_limit) { 323 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 324 ("sch->sch_length incorrect")); 325 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 326 syncache_drop(sc2, sch); 327 tcpstat.tcps_sc_bucketoverflow++; 328 } 329 330 /* Put it into the bucket. */ 331 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 332 sch->sch_length++; 333 334 /* Reinitialize the bucket row's timer. */ 335 syncache_timeout(sc, sch, 1); 336 337 SCH_UNLOCK(sch); 338 339 tcp_syncache.cache_count++; 340 tcpstat.tcps_sc_added++; 341 } 342 343 /* 344 * Remove and free entry from syncache bucket row. 345 * Expects locked syncache head. 346 */ 347 static void 348 syncache_drop(struct syncache *sc, struct syncache_head *sch) 349 { 350 351 SCH_LOCK_ASSERT(sch); 352 353 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 354 sch->sch_length--; 355 356 syncache_free(sc); 357 tcp_syncache.cache_count--; 358 } 359 360 /* 361 * Engage/reengage time on bucket row. 362 */ 363 static void 364 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) 365 { 366 sc->sc_rxttime = ticks + 367 TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]); 368 sc->sc_rxmits++; 369 if (sch->sch_nextc > sc->sc_rxttime) 370 sch->sch_nextc = sc->sc_rxttime; 371 if (!TAILQ_EMPTY(&sch->sch_bucket) && docallout) 372 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, 373 syncache_timer, (void *)sch); 374 } 375 376 /* 377 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 378 * If we have retransmitted an entry the maximum number of times, expire it. 379 * One separate timer for each bucket row. 380 */ 381 static void 382 syncache_timer(void *xsch) 383 { 384 struct syncache_head *sch = (struct syncache_head *)xsch; 385 struct syncache *sc, *nsc; 386 int tick = ticks; 387 char *s; 388 389 /* NB: syncache_head has already been locked by the callout. */ 390 SCH_LOCK_ASSERT(sch); 391 392 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 393 /* 394 * We do not check if the listen socket still exists 395 * and accept the case where the listen socket may be 396 * gone by the time we resend the SYN/ACK. We do 397 * not expect this to happens often. If it does, 398 * then the RST will be sent by the time the remote 399 * host does the SYN/ACK->ACK. 400 */ 401 if (sc->sc_rxttime > tick) { 402 if (sc->sc_rxttime < sch->sch_nextc) 403 sch->sch_nextc = sc->sc_rxttime; 404 continue; 405 } 406 407 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { 408 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 409 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " 410 "giving up and removing syncache entry\n", 411 s, __func__); 412 free(s, M_TCPLOG); 413 } 414 syncache_drop(sc, sch); 415 tcpstat.tcps_sc_stale++; 416 continue; 417 } 418 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 419 log(LOG_DEBUG, "%s; %s: Response timeout, " 420 "retransmitting (%u) SYN|ACK\n", 421 s, __func__, sc->sc_rxmits); 422 free(s, M_TCPLOG); 423 } 424 425 (void) syncache_respond(sc); 426 tcpstat.tcps_sc_retransmitted++; 427 syncache_timeout(sc, sch, 0); 428 } 429 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 430 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 431 syncache_timer, (void *)(sch)); 432 } 433 434 /* 435 * Find an entry in the syncache. 436 * Returns always with locked syncache_head plus a matching entry or NULL. 437 */ 438 struct syncache * 439 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 440 { 441 struct syncache *sc; 442 struct syncache_head *sch; 443 444 #ifdef INET6 445 if (inc->inc_isipv6) { 446 sch = &tcp_syncache.hashbase[ 447 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 448 *schp = sch; 449 450 SCH_LOCK(sch); 451 452 /* Circle through bucket row to find matching entry. */ 453 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 454 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 455 return (sc); 456 } 457 } else 458 #endif 459 { 460 sch = &tcp_syncache.hashbase[ 461 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 462 *schp = sch; 463 464 SCH_LOCK(sch); 465 466 /* Circle through bucket row to find matching entry. */ 467 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 468 #ifdef INET6 469 if (sc->sc_inc.inc_isipv6) 470 continue; 471 #endif 472 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 473 return (sc); 474 } 475 } 476 SCH_LOCK_ASSERT(*schp); 477 return (NULL); /* always returns with locked sch */ 478 } 479 480 /* 481 * This function is called when we get a RST for a 482 * non-existent connection, so that we can see if the 483 * connection is in the syn cache. If it is, zap it. 484 */ 485 void 486 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 487 { 488 struct syncache *sc; 489 struct syncache_head *sch; 490 char *s = NULL; 491 492 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 493 SCH_LOCK_ASSERT(sch); 494 495 /* 496 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. 497 * See RFC 793 page 65, section SEGMENT ARRIVES. 498 */ 499 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { 500 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 501 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " 502 "FIN flag set, segment ignored\n", s, __func__); 503 tcpstat.tcps_badrst++; 504 goto done; 505 } 506 507 /* 508 * No corresponding connection was found in syncache. 509 * If syncookies are enabled and possibly exclusively 510 * used, or we are under memory pressure, a valid RST 511 * may not find a syncache entry. In that case we're 512 * done and no SYN|ACK retransmissions will happen. 513 * Otherwise the the RST was misdirected or spoofed. 514 */ 515 if (sc == NULL) { 516 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 517 log(LOG_DEBUG, "%s; %s: Spurious RST without matching " 518 "syncache entry (possibly syncookie only), " 519 "segment ignored\n", s, __func__); 520 tcpstat.tcps_badrst++; 521 goto done; 522 } 523 524 /* 525 * If the RST bit is set, check the sequence number to see 526 * if this is a valid reset segment. 527 * RFC 793 page 37: 528 * In all states except SYN-SENT, all reset (RST) segments 529 * are validated by checking their SEQ-fields. A reset is 530 * valid if its sequence number is in the window. 531 * 532 * The sequence number in the reset segment is normally an 533 * echo of our outgoing acknowlegement numbers, but some hosts 534 * send a reset with the sequence number at the rightmost edge 535 * of our receive window, and we have to handle this case. 536 */ 537 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 538 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 539 syncache_drop(sc, sch); 540 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 541 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " 542 "connection attempt aborted by remote endpoint\n", 543 s, __func__); 544 tcpstat.tcps_sc_reset++; 545 } else if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { 546 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != IRS %u " 547 "(+WND %u), segment ignored\n", 548 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); 549 tcpstat.tcps_badrst++; 550 } 551 552 done: 553 if (s != NULL) 554 free(s, M_TCPLOG); 555 SCH_UNLOCK(sch); 556 } 557 558 void 559 syncache_badack(struct in_conninfo *inc) 560 { 561 struct syncache *sc; 562 struct syncache_head *sch; 563 564 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 565 SCH_LOCK_ASSERT(sch); 566 if (sc != NULL) { 567 syncache_drop(sc, sch); 568 tcpstat.tcps_sc_badack++; 569 } 570 SCH_UNLOCK(sch); 571 } 572 573 void 574 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 575 { 576 struct syncache *sc; 577 struct syncache_head *sch; 578 579 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 580 SCH_LOCK_ASSERT(sch); 581 if (sc == NULL) 582 goto done; 583 584 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 585 if (ntohl(th->th_seq) != sc->sc_iss) 586 goto done; 587 588 /* 589 * If we've rertransmitted 3 times and this is our second error, 590 * we remove the entry. Otherwise, we allow it to continue on. 591 * This prevents us from incorrectly nuking an entry during a 592 * spurious network outage. 593 * 594 * See tcp_notify(). 595 */ 596 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 597 sc->sc_flags |= SCF_UNREACH; 598 goto done; 599 } 600 syncache_drop(sc, sch); 601 tcpstat.tcps_sc_unreach++; 602 done: 603 SCH_UNLOCK(sch); 604 } 605 606 /* 607 * Build a new TCP socket structure from a syncache entry. 608 */ 609 static struct socket * 610 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 611 { 612 struct inpcb *inp = NULL; 613 struct socket *so; 614 struct tcpcb *tp; 615 char *s; 616 617 INP_INFO_WLOCK_ASSERT(&tcbinfo); 618 619 /* 620 * Ok, create the full blown connection, and set things up 621 * as they would have been set up if we had created the 622 * connection when the SYN arrived. If we can't create 623 * the connection, abort it. 624 */ 625 so = sonewconn(lso, SS_ISCONNECTED); 626 if (so == NULL) { 627 /* 628 * Drop the connection; we will either send a RST or 629 * have the peer retransmit its SYN again after its 630 * RTO and try again. 631 */ 632 tcpstat.tcps_listendrop++; 633 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { 634 log(LOG_DEBUG, "%s; %s: Socket create failed " 635 "due to limits or memory shortage\n", 636 s, __func__); 637 free(s, M_TCPLOG); 638 } 639 goto abort2; 640 } 641 #ifdef MAC 642 SOCK_LOCK(so); 643 mac_socketpeer_set_from_mbuf(m, so); 644 SOCK_UNLOCK(so); 645 #endif 646 647 inp = sotoinpcb(so); 648 INP_LOCK(inp); 649 650 /* Insert new socket into PCB hash list. */ 651 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 652 #ifdef INET6 653 if (sc->sc_inc.inc_isipv6) { 654 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 655 } else { 656 inp->inp_vflag &= ~INP_IPV6; 657 inp->inp_vflag |= INP_IPV4; 658 #endif 659 inp->inp_laddr = sc->sc_inc.inc_laddr; 660 #ifdef INET6 661 } 662 #endif 663 inp->inp_lport = sc->sc_inc.inc_lport; 664 if (in_pcbinshash(inp) != 0) { 665 /* 666 * Undo the assignments above if we failed to 667 * put the PCB on the hash lists. 668 */ 669 #ifdef INET6 670 if (sc->sc_inc.inc_isipv6) 671 inp->in6p_laddr = in6addr_any; 672 else 673 #endif 674 inp->inp_laddr.s_addr = INADDR_ANY; 675 inp->inp_lport = 0; 676 goto abort; 677 } 678 #ifdef IPSEC 679 /* Copy old policy into new socket's. */ 680 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 681 printf("syncache_socket: could not copy policy\n"); 682 #endif 683 #ifdef INET6 684 if (sc->sc_inc.inc_isipv6) { 685 struct inpcb *oinp = sotoinpcb(lso); 686 struct in6_addr laddr6; 687 struct sockaddr_in6 sin6; 688 /* 689 * Inherit socket options from the listening socket. 690 * Note that in6p_inputopts are not (and should not be) 691 * copied, since it stores previously received options and is 692 * used to detect if each new option is different than the 693 * previous one and hence should be passed to a user. 694 * If we copied in6p_inputopts, a user would not be able to 695 * receive options just after calling the accept system call. 696 */ 697 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 698 if (oinp->in6p_outputopts) 699 inp->in6p_outputopts = 700 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 701 702 sin6.sin6_family = AF_INET6; 703 sin6.sin6_len = sizeof(sin6); 704 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 705 sin6.sin6_port = sc->sc_inc.inc_fport; 706 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 707 laddr6 = inp->in6p_laddr; 708 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 709 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 710 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, 711 thread0.td_ucred)) { 712 inp->in6p_laddr = laddr6; 713 goto abort; 714 } 715 /* Override flowlabel from in6_pcbconnect. */ 716 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; 717 inp->in6p_flowinfo |= sc->sc_flowlabel; 718 } else 719 #endif 720 { 721 struct in_addr laddr; 722 struct sockaddr_in sin; 723 724 inp->inp_options = ip_srcroute(m); 725 if (inp->inp_options == NULL) { 726 inp->inp_options = sc->sc_ipopts; 727 sc->sc_ipopts = NULL; 728 } 729 730 sin.sin_family = AF_INET; 731 sin.sin_len = sizeof(sin); 732 sin.sin_addr = sc->sc_inc.inc_faddr; 733 sin.sin_port = sc->sc_inc.inc_fport; 734 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 735 laddr = inp->inp_laddr; 736 if (inp->inp_laddr.s_addr == INADDR_ANY) 737 inp->inp_laddr = sc->sc_inc.inc_laddr; 738 if (in_pcbconnect(inp, (struct sockaddr *)&sin, 739 thread0.td_ucred)) { 740 inp->inp_laddr = laddr; 741 goto abort; 742 } 743 } 744 tp = intotcpcb(inp); 745 tp->t_state = TCPS_SYN_RECEIVED; 746 tp->iss = sc->sc_iss; 747 tp->irs = sc->sc_irs; 748 tcp_rcvseqinit(tp); 749 tcp_sendseqinit(tp); 750 tp->snd_wl1 = sc->sc_irs; 751 tp->snd_max = tp->iss + 1; 752 tp->snd_nxt = tp->iss + 1; 753 tp->rcv_up = sc->sc_irs + 1; 754 tp->rcv_wnd = sc->sc_wnd; 755 tp->rcv_adv += tp->rcv_wnd; 756 tp->last_ack_sent = tp->rcv_nxt; 757 758 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 759 if (sc->sc_flags & SCF_NOOPT) 760 tp->t_flags |= TF_NOOPT; 761 else { 762 if (sc->sc_flags & SCF_WINSCALE) { 763 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 764 tp->snd_scale = sc->sc_requested_s_scale; 765 tp->request_r_scale = sc->sc_requested_r_scale; 766 } 767 if (sc->sc_flags & SCF_TIMESTAMP) { 768 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 769 tp->ts_recent = sc->sc_tsreflect; 770 tp->ts_recent_age = ticks; 771 tp->ts_offset = sc->sc_tsoff; 772 } 773 #ifdef TCP_SIGNATURE 774 if (sc->sc_flags & SCF_SIGNATURE) 775 tp->t_flags |= TF_SIGNATURE; 776 #endif 777 if (sc->sc_flags & SCF_SACK) 778 tp->t_flags |= TF_SACK_PERMIT; 779 } 780 781 /* 782 * Set up MSS and get cached values from tcp_hostcache. 783 * This might overwrite some of the defaults we just set. 784 */ 785 tcp_mss(tp, sc->sc_peer_mss); 786 787 /* 788 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 789 */ 790 if (sc->sc_rxmits) 791 tp->snd_cwnd = tp->t_maxseg; 792 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit); 793 794 INP_UNLOCK(inp); 795 796 tcpstat.tcps_accepts++; 797 return (so); 798 799 abort: 800 INP_UNLOCK(inp); 801 abort2: 802 if (so != NULL) 803 soabort(so); 804 return (NULL); 805 } 806 807 /* 808 * This function gets called when we receive an ACK for a 809 * socket in the LISTEN state. We look up the connection 810 * in the syncache, and if its there, we pull it out of 811 * the cache and turn it into a full-blown connection in 812 * the SYN-RECEIVED state. 813 */ 814 int 815 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 816 struct socket **lsop, struct mbuf *m) 817 { 818 struct syncache *sc; 819 struct syncache_head *sch; 820 struct syncache scs; 821 char *s; 822 823 /* 824 * Global TCP locks are held because we manipulate the PCB lists 825 * and create a new socket. 826 */ 827 INP_INFO_WLOCK_ASSERT(&tcbinfo); 828 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, 829 ("%s: can handle only ACK", __func__)); 830 831 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 832 SCH_LOCK_ASSERT(sch); 833 if (sc == NULL) { 834 /* 835 * There is no syncache entry, so see if this ACK is 836 * a returning syncookie. To do this, first: 837 * A. See if this socket has had a syncache entry dropped in 838 * the past. We don't want to accept a bogus syncookie 839 * if we've never received a SYN. 840 * B. check that the syncookie is valid. If it is, then 841 * cobble up a fake syncache entry, and return. 842 */ 843 if (!tcp_syncookies) { 844 SCH_UNLOCK(sch); 845 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 846 log(LOG_DEBUG, "%s; %s: Spurious ACK, " 847 "segment rejected (syncookies disabled)\n", 848 s, __func__); 849 goto failed; 850 } 851 bzero(&scs, sizeof(scs)); 852 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); 853 SCH_UNLOCK(sch); 854 if (sc == NULL) { 855 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 856 log(LOG_DEBUG, "%s; %s: Segment failed " 857 "SYNCOOKIE authentication, segment rejected " 858 "(probably spoofed)\n", s, __func__); 859 goto failed; 860 } 861 } else { 862 /* Pull out the entry to unlock the bucket row. */ 863 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 864 sch->sch_length--; 865 tcp_syncache.cache_count--; 866 SCH_UNLOCK(sch); 867 } 868 869 /* 870 * Segment validation: 871 * ACK must match our initial sequence number + 1 (the SYN|ACK). 872 */ 873 if (th->th_ack != sc->sc_iss + 1) { 874 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 875 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " 876 "rejected\n", s, __func__, th->th_ack, sc->sc_iss); 877 goto failed; 878 } 879 /* 880 * The SEQ must match the received initial receive sequence 881 * number + 1 (the SYN) because we didn't ACK any data that 882 * may have come with the SYN. 883 */ 884 if (th->th_seq != sc->sc_irs + 1) { 885 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 886 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " 887 "rejected\n", s, __func__, th->th_seq, sc->sc_irs); 888 goto failed; 889 } 890 #if 0 891 /* 892 * If timestamps were present in the SYN and we accepted 893 * them in our SYN|ACK we require them to be present from 894 * now on. And vice versa. 895 * 896 * Unfortunately, during testing of 7.0 some users found 897 * network devices that violate this constraint, so it must 898 * be disabled. 899 */ 900 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) { 901 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 902 log(LOG_DEBUG, "%s; %s: Timestamp missing, " 903 "segment rejected\n", s, __func__); 904 goto failed; 905 } 906 #endif 907 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { 908 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 909 log(LOG_DEBUG, "%s; %s: Timestamp not expected, " 910 "segment rejected\n", s, __func__); 911 goto failed; 912 } 913 /* 914 * If timestamps were negotiated the reflected timestamp 915 * must be equal to what we actually sent in the SYN|ACK. 916 */ 917 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) { 918 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) 919 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " 920 "segment rejected\n", 921 s, __func__, to->to_tsecr, sc->sc_ts); 922 goto failed; 923 } 924 925 *lsop = syncache_socket(sc, *lsop, m); 926 927 if (*lsop == NULL) 928 tcpstat.tcps_sc_aborted++; 929 else 930 tcpstat.tcps_sc_completed++; 931 932 if (sc != &scs) 933 syncache_free(sc); 934 return (1); 935 failed: 936 if (sc != NULL && sc != &scs) 937 syncache_free(sc); 938 if (s != NULL) 939 free(s, M_TCPLOG); 940 *lsop = NULL; 941 return (0); 942 } 943 944 /* 945 * Given a LISTEN socket and an inbound SYN request, add 946 * this to the syn cache, and send back a segment: 947 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 948 * to the source. 949 * 950 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 951 * Doing so would require that we hold onto the data and deliver it 952 * to the application. However, if we are the target of a SYN-flood 953 * DoS attack, an attacker could send data which would eventually 954 * consume all available buffer space if it were ACKed. By not ACKing 955 * the data, we avoid this DoS scenario. 956 */ 957 void 958 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 959 struct inpcb *inp, struct socket **lsop, struct mbuf *m) 960 { 961 struct tcpcb *tp; 962 struct socket *so; 963 struct syncache *sc = NULL; 964 struct syncache_head *sch; 965 struct mbuf *ipopts = NULL; 966 u_int32_t flowtmp; 967 int win, sb_hiwat, ip_ttl, ip_tos, noopt; 968 char *s; 969 #ifdef INET6 970 int autoflowlabel = 0; 971 #endif 972 #ifdef MAC 973 struct label *maclabel; 974 #endif 975 struct syncache scs; 976 977 INP_INFO_WLOCK_ASSERT(&tcbinfo); 978 INP_LOCK_ASSERT(inp); /* listen socket */ 979 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, 980 ("%s: unexpected tcp flags", __func__)); 981 982 /* 983 * Combine all so/tp operations very early to drop the INP lock as 984 * soon as possible. 985 */ 986 so = *lsop; 987 tp = sototcpcb(so); 988 989 #ifdef INET6 990 if (inc->inc_isipv6 && 991 (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) 992 autoflowlabel = 1; 993 #endif 994 ip_ttl = inp->inp_ip_ttl; 995 ip_tos = inp->inp_ip_tos; 996 win = sbspace(&so->so_rcv); 997 sb_hiwat = so->so_rcv.sb_hiwat; 998 noopt = (tp->t_flags & TF_NOOPT); 999 1000 so = NULL; 1001 tp = NULL; 1002 1003 #ifdef MAC 1004 if (mac_syncache_init(&maclabel) != 0) { 1005 INP_UNLOCK(inp); 1006 INP_INFO_WUNLOCK(&tcbinfo); 1007 goto done; 1008 } else 1009 mac_syncache_create(maclabel, inp); 1010 #endif 1011 INP_UNLOCK(inp); 1012 INP_INFO_WUNLOCK(&tcbinfo); 1013 1014 /* 1015 * Remember the IP options, if any. 1016 */ 1017 #ifdef INET6 1018 if (!inc->inc_isipv6) 1019 #endif 1020 ipopts = ip_srcroute(m); 1021 1022 /* 1023 * See if we already have an entry for this connection. 1024 * If we do, resend the SYN,ACK, and reset the retransmit timer. 1025 * 1026 * XXX: should the syncache be re-initialized with the contents 1027 * of the new SYN here (which may have different options?) 1028 * 1029 * XXX: We do not check the sequence number to see if this is a 1030 * real retransmit or a new connection attempt. The question is 1031 * how to handle such a case; either ignore it as spoofed, or 1032 * drop the current entry and create a new one? 1033 */ 1034 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 1035 SCH_LOCK_ASSERT(sch); 1036 if (sc != NULL) { 1037 tcpstat.tcps_sc_dupsyn++; 1038 if (ipopts) { 1039 /* 1040 * If we were remembering a previous source route, 1041 * forget it and use the new one we've been given. 1042 */ 1043 if (sc->sc_ipopts) 1044 (void) m_free(sc->sc_ipopts); 1045 sc->sc_ipopts = ipopts; 1046 } 1047 /* 1048 * Update timestamp if present. 1049 */ 1050 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) 1051 sc->sc_tsreflect = to->to_tsval; 1052 else 1053 sc->sc_flags &= ~SCF_TIMESTAMP; 1054 #ifdef MAC 1055 /* 1056 * Since we have already unconditionally allocated label 1057 * storage, free it up. The syncache entry will already 1058 * have an initialized label we can use. 1059 */ 1060 mac_syncache_destroy(&maclabel); 1061 KASSERT(sc->sc_label != NULL, 1062 ("%s: label not initialized", __func__)); 1063 #endif 1064 /* Retransmit SYN|ACK and reset retransmit count. */ 1065 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { 1066 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " 1067 "resetting timer and retransmitting SYN|ACK\n", 1068 s, __func__); 1069 free(s, M_TCPLOG); 1070 } 1071 if (syncache_respond(sc) == 0) { 1072 sc->sc_rxmits = 0; 1073 syncache_timeout(sc, sch, 1); 1074 tcpstat.tcps_sndacks++; 1075 tcpstat.tcps_sndtotal++; 1076 } 1077 SCH_UNLOCK(sch); 1078 goto done; 1079 } 1080 1081 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1082 if (sc == NULL) { 1083 /* 1084 * The zone allocator couldn't provide more entries. 1085 * Treat this as if the cache was full; drop the oldest 1086 * entry and insert the new one. 1087 */ 1088 tcpstat.tcps_sc_zonefail++; 1089 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) 1090 syncache_drop(sc, sch); 1091 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 1092 if (sc == NULL) { 1093 if (tcp_syncookies) { 1094 bzero(&scs, sizeof(scs)); 1095 sc = &scs; 1096 } else { 1097 SCH_UNLOCK(sch); 1098 if (ipopts) 1099 (void) m_free(ipopts); 1100 goto done; 1101 } 1102 } 1103 } 1104 1105 /* 1106 * Fill in the syncache values. 1107 */ 1108 #ifdef MAC 1109 sc->sc_label = maclabel; 1110 #endif 1111 sc->sc_ipopts = ipopts; 1112 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1113 #ifdef INET6 1114 if (!inc->inc_isipv6) 1115 #endif 1116 { 1117 sc->sc_ip_tos = ip_tos; 1118 sc->sc_ip_ttl = ip_ttl; 1119 } 1120 1121 sc->sc_irs = th->th_seq; 1122 sc->sc_iss = arc4random(); 1123 sc->sc_flags = 0; 1124 sc->sc_flowlabel = 0; 1125 1126 /* 1127 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 1128 * win was derived from socket earlier in the function. 1129 */ 1130 win = imax(win, 0); 1131 win = imin(win, TCP_MAXWIN); 1132 sc->sc_wnd = win; 1133 1134 if (tcp_do_rfc1323) { 1135 /* 1136 * A timestamp received in a SYN makes 1137 * it ok to send timestamp requests and replies. 1138 */ 1139 if (to->to_flags & TOF_TS) { 1140 sc->sc_tsreflect = to->to_tsval; 1141 sc->sc_ts = ticks; 1142 sc->sc_flags |= SCF_TIMESTAMP; 1143 } 1144 if (to->to_flags & TOF_SCALE) { 1145 int wscale = 0; 1146 1147 /* 1148 * Pick the smallest possible scaling factor that 1149 * will still allow us to scale up to sb_max, aka 1150 * kern.ipc.maxsockbuf. 1151 * 1152 * We do this because there are broken firewalls that 1153 * will corrupt the window scale option, leading to 1154 * the other endpoint believing that our advertised 1155 * window is unscaled. At scale factors larger than 1156 * 5 the unscaled window will drop below 1500 bytes, 1157 * leading to serious problems when traversing these 1158 * broken firewalls. 1159 * 1160 * With the default maxsockbuf of 256K, a scale factor 1161 * of 3 will be chosen by this algorithm. Those who 1162 * choose a larger maxsockbuf should watch out 1163 * for the compatiblity problems mentioned above. 1164 * 1165 * RFC1323: The Window field in a SYN (i.e., a <SYN> 1166 * or <SYN,ACK>) segment itself is never scaled. 1167 */ 1168 while (wscale < TCP_MAX_WINSHIFT && 1169 (TCP_MAXWIN << wscale) < sb_max) 1170 wscale++; 1171 sc->sc_requested_r_scale = wscale; 1172 sc->sc_requested_s_scale = to->to_wscale; 1173 sc->sc_flags |= SCF_WINSCALE; 1174 } 1175 } 1176 #ifdef TCP_SIGNATURE 1177 /* 1178 * If listening socket requested TCP digests, and received SYN 1179 * contains the option, flag this in the syncache so that 1180 * syncache_respond() will do the right thing with the SYN+ACK. 1181 * XXX: Currently we always record the option by default and will 1182 * attempt to use it in syncache_respond(). 1183 */ 1184 if (to->to_flags & TOF_SIGNATURE) 1185 sc->sc_flags |= SCF_SIGNATURE; 1186 #endif 1187 if (to->to_flags & TOF_SACK) 1188 sc->sc_flags |= SCF_SACK; 1189 if (to->to_flags & TOF_MSS) 1190 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1191 if (noopt) 1192 sc->sc_flags |= SCF_NOOPT; 1193 1194 if (tcp_syncookies) { 1195 syncookie_generate(sch, sc, &flowtmp); 1196 #ifdef INET6 1197 if (autoflowlabel) 1198 sc->sc_flowlabel = flowtmp; 1199 #endif 1200 } else { 1201 #ifdef INET6 1202 if (autoflowlabel) 1203 sc->sc_flowlabel = 1204 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); 1205 #endif 1206 } 1207 SCH_UNLOCK(sch); 1208 1209 /* 1210 * Do a standard 3-way handshake. 1211 */ 1212 if (syncache_respond(sc) == 0) { 1213 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) 1214 syncache_free(sc); 1215 else if (sc != &scs) 1216 syncache_insert(sc, sch); /* locks and unlocks sch */ 1217 tcpstat.tcps_sndacks++; 1218 tcpstat.tcps_sndtotal++; 1219 } else { 1220 if (sc != &scs) 1221 syncache_free(sc); 1222 tcpstat.tcps_sc_dropped++; 1223 } 1224 1225 done: 1226 #ifdef MAC 1227 if (sc == &scs) 1228 mac_syncache_destroy(&maclabel); 1229 #endif 1230 *lsop = NULL; 1231 m_freem(m); 1232 return; 1233 } 1234 1235 static int 1236 syncache_respond(struct syncache *sc) 1237 { 1238 struct ip *ip = NULL; 1239 struct mbuf *m; 1240 struct tcphdr *th; 1241 int optlen, error; 1242 u_int16_t hlen, tlen, mssopt; 1243 struct tcpopt to; 1244 #ifdef INET6 1245 struct ip6_hdr *ip6 = NULL; 1246 #endif 1247 1248 hlen = 1249 #ifdef INET6 1250 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 1251 #endif 1252 sizeof(struct ip); 1253 tlen = hlen + sizeof(struct tcphdr); 1254 1255 /* Determine MSS we advertize to other end of connection. */ 1256 mssopt = tcp_mssopt(&sc->sc_inc); 1257 if (sc->sc_peer_mss) 1258 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); 1259 1260 /* XXX: Assume that the entire packet will fit in a header mbuf. */ 1261 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, 1262 ("syncache: mbuf too small")); 1263 1264 /* Create the IP+TCP header from scratch. */ 1265 m = m_gethdr(M_DONTWAIT, MT_DATA); 1266 if (m == NULL) 1267 return (ENOBUFS); 1268 #ifdef MAC 1269 mac_syncache_create_mbuf(sc->sc_label, m); 1270 #endif 1271 m->m_data += max_linkhdr; 1272 m->m_len = tlen; 1273 m->m_pkthdr.len = tlen; 1274 m->m_pkthdr.rcvif = NULL; 1275 1276 #ifdef INET6 1277 if (sc->sc_inc.inc_isipv6) { 1278 ip6 = mtod(m, struct ip6_hdr *); 1279 ip6->ip6_vfc = IPV6_VERSION; 1280 ip6->ip6_nxt = IPPROTO_TCP; 1281 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1282 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1283 ip6->ip6_plen = htons(tlen - hlen); 1284 /* ip6_hlim is set after checksum */ 1285 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1286 ip6->ip6_flow |= sc->sc_flowlabel; 1287 1288 th = (struct tcphdr *)(ip6 + 1); 1289 } else 1290 #endif 1291 { 1292 ip = mtod(m, struct ip *); 1293 ip->ip_v = IPVERSION; 1294 ip->ip_hl = sizeof(struct ip) >> 2; 1295 ip->ip_len = tlen; 1296 ip->ip_id = 0; 1297 ip->ip_off = 0; 1298 ip->ip_sum = 0; 1299 ip->ip_p = IPPROTO_TCP; 1300 ip->ip_src = sc->sc_inc.inc_laddr; 1301 ip->ip_dst = sc->sc_inc.inc_faddr; 1302 ip->ip_ttl = sc->sc_ip_ttl; 1303 ip->ip_tos = sc->sc_ip_tos; 1304 1305 /* 1306 * See if we should do MTU discovery. Route lookups are 1307 * expensive, so we will only unset the DF bit if: 1308 * 1309 * 1) path_mtu_discovery is disabled 1310 * 2) the SCF_UNREACH flag has been set 1311 */ 1312 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1313 ip->ip_off |= IP_DF; 1314 1315 th = (struct tcphdr *)(ip + 1); 1316 } 1317 th->th_sport = sc->sc_inc.inc_lport; 1318 th->th_dport = sc->sc_inc.inc_fport; 1319 1320 th->th_seq = htonl(sc->sc_iss); 1321 th->th_ack = htonl(sc->sc_irs + 1); 1322 th->th_off = sizeof(struct tcphdr) >> 2; 1323 th->th_x2 = 0; 1324 th->th_flags = TH_SYN|TH_ACK; 1325 th->th_win = htons(sc->sc_wnd); 1326 th->th_urp = 0; 1327 1328 /* Tack on the TCP options. */ 1329 if ((sc->sc_flags & SCF_NOOPT) == 0) { 1330 to.to_flags = 0; 1331 1332 to.to_mss = mssopt; 1333 to.to_flags = TOF_MSS; 1334 if (sc->sc_flags & SCF_WINSCALE) { 1335 to.to_wscale = sc->sc_requested_r_scale; 1336 to.to_flags |= TOF_SCALE; 1337 } 1338 if (sc->sc_flags & SCF_TIMESTAMP) { 1339 /* Virgin timestamp or TCP cookie enhanced one. */ 1340 to.to_tsval = sc->sc_ts; 1341 to.to_tsecr = sc->sc_tsreflect; 1342 to.to_flags |= TOF_TS; 1343 } 1344 if (sc->sc_flags & SCF_SACK) 1345 to.to_flags |= TOF_SACKPERM; 1346 #ifdef TCP_SIGNATURE 1347 if (sc->sc_flags & SCF_SIGNATURE) 1348 to.to_flags |= TOF_SIGNATURE; 1349 #endif 1350 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 1351 1352 #ifdef TCP_SIGNATURE 1353 tcp_signature_compute(m, sizeof(struct ip), 0, optlen, 1354 to.to_signature, IPSEC_DIR_OUTBOUND); 1355 #endif 1356 1357 /* Adjust headers by option size. */ 1358 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1359 m->m_len += optlen; 1360 m->m_pkthdr.len += optlen; 1361 #ifdef INET6 1362 if (sc->sc_inc.inc_isipv6) 1363 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); 1364 else 1365 #endif 1366 ip->ip_len += optlen; 1367 } else 1368 optlen = 0; 1369 1370 #ifdef INET6 1371 if (sc->sc_inc.inc_isipv6) { 1372 th->th_sum = 0; 1373 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, 1374 tlen + optlen - hlen); 1375 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1376 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1377 } else 1378 #endif 1379 { 1380 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1381 htons(tlen + optlen - hlen + IPPROTO_TCP)); 1382 m->m_pkthdr.csum_flags = CSUM_TCP; 1383 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1384 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1385 } 1386 return (error); 1387 } 1388 1389 /* 1390 * The purpose of SYN cookies is to avoid keeping track of all SYN's we 1391 * receive and to be able to handle SYN floods from bogus source addresses 1392 * (where we will never receive any reply). SYN floods try to exhaust all 1393 * our memory and available slots in the SYN cache table to cause a denial 1394 * of service to legitimate users of the local host. 1395 * 1396 * The idea of SYN cookies is to encode and include all necessary information 1397 * about the connection setup state within the SYN-ACK we send back and thus 1398 * to get along without keeping any local state until the ACK to the SYN-ACK 1399 * arrives (if ever). Everything we need to know should be available from 1400 * the information we encoded in the SYN-ACK. 1401 * 1402 * More information about the theory behind SYN cookies and its first 1403 * discussion and specification can be found at: 1404 * http://cr.yp.to/syncookies.html (overview) 1405 * http://cr.yp.to/syncookies/archive (gory details) 1406 * 1407 * This implementation extends the orginal idea and first implementation 1408 * of FreeBSD by using not only the initial sequence number field to store 1409 * information but also the timestamp field if present. This way we can 1410 * keep track of the entire state we need to know to recreate the session in 1411 * its original form. Almost all TCP speakers implement RFC1323 timestamps 1412 * these days. For those that do not we still have to live with the known 1413 * shortcomings of the ISN only SYN cookies. 1414 * 1415 * Cookie layers: 1416 * 1417 * Initial sequence number we send: 1418 * 31|................................|0 1419 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP 1420 * D = MD5 Digest (first dword) 1421 * M = MSS index 1422 * R = Rotation of secret 1423 * P = Odd or Even secret 1424 * 1425 * The MD5 Digest is computed with over following parameters: 1426 * a) randomly rotated secret 1427 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) 1428 * c) the received initial sequence number from remote host 1429 * d) the rotation offset and odd/even bit 1430 * 1431 * Timestamp we send: 1432 * 31|................................|0 1433 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 1434 * D = MD5 Digest (third dword) (only as filler) 1435 * S = Requested send window scale 1436 * R = Requested receive window scale 1437 * A = SACK allowed 1438 * 5 = TCP-MD5 enabled (not implemented yet) 1439 * XORed with MD5 Digest (forth dword) 1440 * 1441 * The timestamp isn't cryptographically secure and doesn't need to be. 1442 * The double use of the MD5 digest dwords ties it to a specific remote/ 1443 * local host/port, remote initial sequence number and our local time 1444 * limited secret. A received timestamp is reverted (XORed) and then 1445 * the contained MD5 dword is compared to the computed one to ensure the 1446 * timestamp belongs to the SYN-ACK we sent. The other parameters may 1447 * have been tampered with but this isn't different from supplying bogus 1448 * values in the SYN in the first place. 1449 * 1450 * Some problems with SYN cookies remain however: 1451 * Consider the problem of a recreated (and retransmitted) cookie. If the 1452 * original SYN was accepted, the connection is established. The second 1453 * SYN is inflight, and if it arrives with an ISN that falls within the 1454 * receive window, the connection is killed. 1455 * 1456 * Notes: 1457 * A heuristic to determine when to accept syn cookies is not necessary. 1458 * An ACK flood would cause the syncookie verification to be attempted, 1459 * but a SYN flood causes syncookies to be generated. Both are of equal 1460 * cost, so there's no point in trying to optimize the ACK flood case. 1461 * Also, if you don't process certain ACKs for some reason, then all someone 1462 * would have to do is launch a SYN and ACK flood at the same time, which 1463 * would stop cookie verification and defeat the entire purpose of syncookies. 1464 */ 1465 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; 1466 1467 static void 1468 syncookie_generate(struct syncache_head *sch, struct syncache *sc, 1469 u_int32_t *flowlabel) 1470 { 1471 MD5_CTX ctx; 1472 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1473 u_int32_t data; 1474 u_int32_t *secbits; 1475 u_int off, pmss, mss; 1476 int i; 1477 1478 SCH_LOCK_ASSERT(sch); 1479 1480 /* Which of the two secrets to use. */ 1481 secbits = sch->sch_oddeven ? 1482 sch->sch_secbits_odd : sch->sch_secbits_even; 1483 1484 /* Reseed secret if too old. */ 1485 if (sch->sch_reseed < time_uptime) { 1486 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ 1487 secbits = sch->sch_oddeven ? 1488 sch->sch_secbits_odd : sch->sch_secbits_even; 1489 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) 1490 secbits[i] = arc4random(); 1491 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; 1492 } 1493 1494 /* Secret rotation offset. */ 1495 off = sc->sc_iss & 0x7; /* iss was randomized before */ 1496 1497 /* Maximum segment size calculation. */ 1498 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); 1499 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) 1500 if (tcp_sc_msstab[mss] <= pmss) 1501 break; 1502 1503 /* Fold parameters and MD5 digest into the ISN we will send. */ 1504 data = sch->sch_oddeven;/* odd or even secret, 1 bit */ 1505 data |= off << 1; /* secret offset, derived from iss, 3 bits */ 1506 data |= mss << 4; /* mss, 3 bits */ 1507 1508 MD5Init(&ctx); 1509 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1510 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1511 MD5Update(&ctx, secbits, off); 1512 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); 1513 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); 1514 MD5Update(&ctx, &data, sizeof(data)); 1515 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1516 1517 data |= (md5_buffer[0] << 7); 1518 sc->sc_iss = data; 1519 1520 #ifdef INET6 1521 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1522 #endif 1523 1524 /* Additional parameters are stored in the timestamp if present. */ 1525 if (sc->sc_flags & SCF_TIMESTAMP) { 1526 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ 1527 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ 1528 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ 1529 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ 1530 data |= md5_buffer[2] << 10; /* more digest bits */ 1531 data ^= md5_buffer[3]; 1532 sc->sc_ts = data; 1533 sc->sc_tsoff = data - ticks; /* after XOR */ 1534 } 1535 1536 tcpstat.tcps_sc_sendcookie++; 1537 return; 1538 } 1539 1540 static struct syncache * 1541 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1542 struct syncache *sc, struct tcpopt *to, struct tcphdr *th, 1543 struct socket *so) 1544 { 1545 MD5_CTX ctx; 1546 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1547 u_int32_t data = 0; 1548 u_int32_t *secbits; 1549 tcp_seq ack, seq; 1550 int off, mss, wnd, flags; 1551 1552 SCH_LOCK_ASSERT(sch); 1553 1554 /* 1555 * Pull information out of SYN-ACK/ACK and 1556 * revert sequence number advances. 1557 */ 1558 ack = th->th_ack - 1; 1559 seq = th->th_seq - 1; 1560 off = (ack >> 1) & 0x7; 1561 mss = (ack >> 4) & 0x7; 1562 flags = ack & 0x7f; 1563 1564 /* Which of the two secrets to use. */ 1565 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; 1566 1567 /* 1568 * The secret wasn't updated for the lifetime of a syncookie, 1569 * so this SYN-ACK/ACK is either too old (replay) or totally bogus. 1570 */ 1571 if (sch->sch_reseed < time_uptime) { 1572 return (NULL); 1573 } 1574 1575 /* Recompute the digest so we can compare it. */ 1576 MD5Init(&ctx); 1577 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1578 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1579 MD5Update(&ctx, secbits, off); 1580 MD5Update(&ctx, inc, sizeof(*inc)); 1581 MD5Update(&ctx, &seq, sizeof(seq)); 1582 MD5Update(&ctx, &flags, sizeof(flags)); 1583 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1584 1585 /* Does the digest part of or ACK'ed ISS match? */ 1586 if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) 1587 return (NULL); 1588 1589 /* Does the digest part of our reflected timestamp match? */ 1590 if (to->to_flags & TOF_TS) { 1591 data = md5_buffer[3] ^ to->to_tsecr; 1592 if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) 1593 return (NULL); 1594 } 1595 1596 /* Fill in the syncache values. */ 1597 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1598 sc->sc_ipopts = NULL; 1599 1600 sc->sc_irs = seq; 1601 sc->sc_iss = ack; 1602 1603 #ifdef INET6 1604 if (inc->inc_isipv6) { 1605 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) 1606 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1607 } else 1608 #endif 1609 { 1610 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; 1611 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; 1612 } 1613 1614 /* Additional parameters that were encoded in the timestamp. */ 1615 if (data) { 1616 sc->sc_flags |= SCF_TIMESTAMP; 1617 sc->sc_tsreflect = to->to_tsval; 1618 sc->sc_ts = to->to_tsecr; 1619 sc->sc_tsoff = to->to_tsecr - ticks; 1620 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; 1621 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; 1622 sc->sc_requested_s_scale = min((data >> 2) & 0xf, 1623 TCP_MAX_WINSHIFT); 1624 sc->sc_requested_r_scale = min((data >> 6) & 0xf, 1625 TCP_MAX_WINSHIFT); 1626 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) 1627 sc->sc_flags |= SCF_WINSCALE; 1628 } else 1629 sc->sc_flags |= SCF_NOOPT; 1630 1631 wnd = sbspace(&so->so_rcv); 1632 wnd = imax(wnd, 0); 1633 wnd = imin(wnd, TCP_MAXWIN); 1634 sc->sc_wnd = wnd; 1635 1636 sc->sc_rxmits = 0; 1637 sc->sc_peer_mss = tcp_sc_msstab[mss]; 1638 1639 tcpstat.tcps_sc_recvcookie++; 1640 return (sc); 1641 } 1642 1643 /* 1644 * Returns the current number of syncache entries. This number 1645 * will probably change before you get around to calling 1646 * syncache_pcblist. 1647 */ 1648 1649 int 1650 syncache_pcbcount(void) 1651 { 1652 struct syncache_head *sch; 1653 int count, i; 1654 1655 for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) { 1656 /* No need to lock for a read. */ 1657 sch = &tcp_syncache.hashbase[i]; 1658 count += sch->sch_length; 1659 } 1660 return count; 1661 } 1662 1663 /* 1664 * Exports the syncache entries to userland so that netstat can display 1665 * them alongside the other sockets. This function is intended to be 1666 * called only from tcp_pcblist. 1667 * 1668 * Due to concurrency on an active system, the number of pcbs exported 1669 * may have no relation to max_pcbs. max_pcbs merely indicates the 1670 * amount of space the caller allocated for this function to use. 1671 */ 1672 int 1673 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) 1674 { 1675 struct xtcpcb xt; 1676 struct syncache *sc; 1677 struct syncache_head *sch; 1678 int count, error, i; 1679 1680 for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) { 1681 sch = &tcp_syncache.hashbase[i]; 1682 SCH_LOCK(sch); 1683 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 1684 if (count >= max_pcbs) { 1685 SCH_UNLOCK(sch); 1686 goto exit; 1687 } 1688 bzero(&xt, sizeof(xt)); 1689 xt.xt_len = sizeof(xt); 1690 if (sc->sc_inc.inc_isipv6) 1691 xt.xt_inp.inp_vflag = INP_IPV6; 1692 else 1693 xt.xt_inp.inp_vflag = INP_IPV4; 1694 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); 1695 xt.xt_tp.t_inpcb = &xt.xt_inp; 1696 xt.xt_tp.t_state = TCPS_SYN_RECEIVED; 1697 xt.xt_socket.xso_protocol = IPPROTO_TCP; 1698 xt.xt_socket.xso_len = sizeof (struct xsocket); 1699 xt.xt_socket.so_type = SOCK_STREAM; 1700 xt.xt_socket.so_state = SS_ISCONNECTING; 1701 error = SYSCTL_OUT(req, &xt, sizeof xt); 1702 if (error) { 1703 SCH_UNLOCK(sch); 1704 goto exit; 1705 } 1706 count++; 1707 } 1708 SCH_UNLOCK(sch); 1709 } 1710 exit: 1711 *pcbs_exported = count; 1712 return error; 1713 } 1714 1715