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 * $FreeBSD$ 33 */ 34 35 #include "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_ipsec.h" 38 #include "opt_mac.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/kernel.h> 43 #include <sys/sysctl.h> 44 #include <sys/lock.h> 45 #include <sys/mutex.h> 46 #include <sys/malloc.h> 47 #include <sys/mbuf.h> 48 #include <sys/md5.h> 49 #include <sys/proc.h> /* for proc0 declaration */ 50 #include <sys/random.h> 51 #include <sys/socket.h> 52 #include <sys/socketvar.h> 53 54 #include <vm/uma.h> 55 56 #include <net/if.h> 57 #include <net/route.h> 58 59 #include <netinet/in.h> 60 #include <netinet/in_systm.h> 61 #include <netinet/ip.h> 62 #include <netinet/in_var.h> 63 #include <netinet/in_pcb.h> 64 #include <netinet/ip_var.h> 65 #include <netinet/ip_options.h> 66 #ifdef INET6 67 #include <netinet/ip6.h> 68 #include <netinet/icmp6.h> 69 #include <netinet6/nd6.h> 70 #include <netinet6/ip6_var.h> 71 #include <netinet6/in6_pcb.h> 72 #endif 73 #include <netinet/tcp.h> 74 #include <netinet/tcp_fsm.h> 75 #include <netinet/tcp_seq.h> 76 #include <netinet/tcp_timer.h> 77 #include <netinet/tcp_var.h> 78 #ifdef INET6 79 #include <netinet6/tcp6_var.h> 80 #endif 81 82 #ifdef IPSEC 83 #include <netinet6/ipsec.h> 84 #ifdef INET6 85 #include <netinet6/ipsec6.h> 86 #endif 87 #endif /*IPSEC*/ 88 89 #ifdef FAST_IPSEC 90 #include <netipsec/ipsec.h> 91 #ifdef INET6 92 #include <netipsec/ipsec6.h> 93 #endif 94 #include <netipsec/key.h> 95 #endif /*FAST_IPSEC*/ 96 97 #include <machine/in_cksum.h> 98 99 #include <security/mac/mac_framework.h> 100 101 static int tcp_syncookies = 1; 102 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, 103 &tcp_syncookies, 0, 104 "Use TCP SYN cookies if the syncache overflows"); 105 106 static int tcp_syncookiesonly = 0; 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, 108 &tcp_syncookiesonly, 0, 109 "Use only TCP SYN cookies"); 110 111 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ 112 #define SYNCOOKIE_LIFETIME 16 /* seconds */ 113 114 struct syncache { 115 TAILQ_ENTRY(syncache) sc_hash; 116 struct in_conninfo sc_inc; /* addresses */ 117 u_long sc_rxttime; /* retransmit time */ 118 u_int16_t sc_rxmits; /* retransmit counter */ 119 120 u_int32_t sc_tsreflect; /* timestamp to reflect */ 121 u_int32_t sc_ts; /* our timestamp to send */ 122 u_int32_t sc_tsoff; /* ts offset w/ syncookies */ 123 u_int32_t sc_flowlabel; /* IPv6 flowlabel */ 124 tcp_seq sc_irs; /* seq from peer */ 125 tcp_seq sc_iss; /* our ISS */ 126 struct mbuf *sc_ipopts; /* source route */ 127 128 u_int16_t sc_peer_mss; /* peer's MSS */ 129 u_int16_t sc_wnd; /* advertised window */ 130 u_int8_t sc_ip_ttl; /* IPv4 TTL */ 131 u_int8_t sc_ip_tos; /* IPv4 TOS */ 132 u_int8_t sc_requested_s_scale:4, 133 sc_requested_r_scale:4; 134 u_int8_t sc_flags; 135 #define SCF_NOOPT 0x01 /* no TCP options */ 136 #define SCF_WINSCALE 0x02 /* negotiated window scaling */ 137 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ 138 /* MSS is implicit */ 139 #define SCF_UNREACH 0x10 /* icmp unreachable received */ 140 #define SCF_SIGNATURE 0x20 /* send MD5 digests */ 141 #define SCF_SACK 0x80 /* send SACK option */ 142 }; 143 144 struct syncache_head { 145 struct mtx sch_mtx; 146 TAILQ_HEAD(sch_head, syncache) sch_bucket; 147 struct callout sch_timer; 148 int sch_nextc; 149 u_int sch_length; 150 u_int sch_oddeven; 151 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; 152 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; 153 u_int sch_reseed; /* time_uptime, seconds */ 154 }; 155 156 static void syncache_drop(struct syncache *, struct syncache_head *); 157 static void syncache_free(struct syncache *); 158 static void syncache_insert(struct syncache *, struct syncache_head *); 159 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); 160 static int syncache_respond(struct syncache *, struct mbuf *); 161 static struct socket *syncache_socket(struct syncache *, struct socket *, 162 struct mbuf *m); 163 static void syncache_timer(void *); 164 static void syncookie_generate(struct syncache_head *, struct syncache *, 165 u_int32_t *); 166 static struct syncache 167 *syncookie_lookup(struct in_conninfo *, struct syncache_head *, 168 struct syncache *, struct tcpopt *, struct tcphdr *, 169 struct socket *); 170 171 /* 172 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. 173 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds, 174 * the odds are that the user has given up attempting to connect by then. 175 */ 176 #define SYNCACHE_MAXREXMTS 3 177 178 /* Arbitrary values */ 179 #define TCP_SYNCACHE_HASHSIZE 512 180 #define TCP_SYNCACHE_BUCKETLIMIT 30 181 182 struct tcp_syncache { 183 struct syncache_head *hashbase; 184 uma_zone_t zone; 185 u_int hashsize; 186 u_int hashmask; 187 u_int bucket_limit; 188 u_int cache_count; /* XXX: unprotected */ 189 u_int cache_limit; 190 u_int rexmt_limit; 191 u_int hash_secret; 192 }; 193 static struct tcp_syncache tcp_syncache; 194 195 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); 196 197 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, 198 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); 199 200 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, 201 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); 202 203 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, 204 &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); 205 206 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, 207 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); 208 209 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, 210 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); 211 212 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); 213 214 #define SYNCACHE_HASH(inc, mask) \ 215 ((tcp_syncache.hash_secret ^ \ 216 (inc)->inc_faddr.s_addr ^ \ 217 ((inc)->inc_faddr.s_addr >> 16) ^ \ 218 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 219 220 #define SYNCACHE_HASH6(inc, mask) \ 221 ((tcp_syncache.hash_secret ^ \ 222 (inc)->inc6_faddr.s6_addr32[0] ^ \ 223 (inc)->inc6_faddr.s6_addr32[3] ^ \ 224 (inc)->inc_fport ^ (inc)->inc_lport) & mask) 225 226 #define ENDPTS_EQ(a, b) ( \ 227 (a)->ie_fport == (b)->ie_fport && \ 228 (a)->ie_lport == (b)->ie_lport && \ 229 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ 230 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ 231 ) 232 233 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) 234 235 #define SYNCACHE_TIMEOUT(sc, sch, co) do { \ 236 (sc)->sc_rxmits++; \ 237 (sc)->sc_rxttime = ticks + \ 238 TCPTV_RTOBASE * tcp_backoff[(sc)->sc_rxmits - 1]; \ 239 if ((sch)->sch_nextc > (sc)->sc_rxttime) \ 240 (sch)->sch_nextc = (sc)->sc_rxttime; \ 241 if (!TAILQ_EMPTY(&(sch)->sch_bucket) && !(co)) \ 242 callout_reset(&(sch)->sch_timer, \ 243 (sch)->sch_nextc - ticks, \ 244 syncache_timer, (void *)(sch)); \ 245 } while (0) 246 247 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) 248 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) 249 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) 250 251 /* 252 * Requires the syncache entry to be already removed from the bucket list. 253 */ 254 static void 255 syncache_free(struct syncache *sc) 256 { 257 if (sc->sc_ipopts) 258 (void) m_free(sc->sc_ipopts); 259 260 uma_zfree(tcp_syncache.zone, sc); 261 } 262 263 void 264 syncache_init(void) 265 { 266 int i; 267 268 tcp_syncache.cache_count = 0; 269 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 270 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; 271 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; 272 tcp_syncache.hash_secret = arc4random(); 273 274 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", 275 &tcp_syncache.hashsize); 276 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", 277 &tcp_syncache.bucket_limit); 278 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { 279 printf("WARNING: syncache hash size is not a power of 2.\n"); 280 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; 281 } 282 tcp_syncache.hashmask = tcp_syncache.hashsize - 1; 283 284 /* Set limits. */ 285 tcp_syncache.cache_limit = 286 tcp_syncache.hashsize * tcp_syncache.bucket_limit; 287 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", 288 &tcp_syncache.cache_limit); 289 290 /* Allocate the hash table. */ 291 MALLOC(tcp_syncache.hashbase, struct syncache_head *, 292 tcp_syncache.hashsize * sizeof(struct syncache_head), 293 M_SYNCACHE, M_WAITOK | M_ZERO); 294 295 /* Initialize the hash buckets. */ 296 for (i = 0; i < tcp_syncache.hashsize; i++) { 297 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); 298 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", 299 NULL, MTX_DEF); 300 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, 301 &tcp_syncache.hashbase[i].sch_mtx, 0); 302 tcp_syncache.hashbase[i].sch_length = 0; 303 } 304 305 /* Create the syncache entry zone. */ 306 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), 307 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); 308 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); 309 } 310 311 /* 312 * Inserts a syncache entry into the specified bucket row. 313 * Locks and unlocks the syncache_head autonomously. 314 */ 315 static void 316 syncache_insert(struct syncache *sc, struct syncache_head *sch) 317 { 318 struct syncache *sc2; 319 320 SCH_LOCK(sch); 321 322 /* 323 * Make sure that we don't overflow the per-bucket limit. 324 * If the bucket is full, toss the oldest element. 325 */ 326 if (sch->sch_length >= tcp_syncache.bucket_limit) { 327 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), 328 ("sch->sch_length incorrect")); 329 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); 330 syncache_drop(sc2, sch); 331 tcpstat.tcps_sc_bucketoverflow++; 332 } 333 334 /* Put it into the bucket. */ 335 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); 336 sch->sch_length++; 337 338 /* Reinitialize the bucket row's timer. */ 339 SYNCACHE_TIMEOUT(sc, sch, 1); 340 341 SCH_UNLOCK(sch); 342 343 tcp_syncache.cache_count++; 344 tcpstat.tcps_sc_added++; 345 } 346 347 /* 348 * Remove and free entry from syncache bucket row. 349 * Expects locked syncache head. 350 */ 351 static void 352 syncache_drop(struct syncache *sc, struct syncache_head *sch) 353 { 354 355 SCH_LOCK_ASSERT(sch); 356 357 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 358 sch->sch_length--; 359 360 syncache_free(sc); 361 tcp_syncache.cache_count--; 362 } 363 364 /* 365 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. 366 * If we have retransmitted an entry the maximum number of times, expire it. 367 * One separate timer for each bucket row. 368 */ 369 static void 370 syncache_timer(void *xsch) 371 { 372 struct syncache_head *sch = (struct syncache_head *)xsch; 373 struct syncache *sc, *nsc; 374 int tick = ticks; 375 376 /* NB: syncache_head has already been locked by the callout. */ 377 SCH_LOCK_ASSERT(sch); 378 379 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { 380 /* 381 * We do not check if the listen socket still exists 382 * and accept the case where the listen socket may be 383 * gone by the time we resend the SYN/ACK. We do 384 * not expect this to happens often. If it does, 385 * then the RST will be sent by the time the remote 386 * host does the SYN/ACK->ACK. 387 */ 388 if (sc->sc_rxttime >= tick) { 389 if (sc->sc_rxttime < sch->sch_nextc) 390 sch->sch_nextc = sc->sc_rxttime; 391 continue; 392 } 393 394 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { 395 syncache_drop(sc, sch); 396 tcpstat.tcps_sc_stale++; 397 continue; 398 } 399 400 (void) syncache_respond(sc, NULL); 401 tcpstat.tcps_sc_retransmitted++; 402 SYNCACHE_TIMEOUT(sc, sch, 0); 403 } 404 if (!TAILQ_EMPTY(&(sch)->sch_bucket)) 405 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, 406 syncache_timer, (void *)(sch)); 407 } 408 409 /* 410 * Find an entry in the syncache. 411 * Returns always with locked syncache_head plus a matching entry or NULL. 412 */ 413 struct syncache * 414 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) 415 { 416 struct syncache *sc; 417 struct syncache_head *sch; 418 419 #ifdef INET6 420 if (inc->inc_isipv6) { 421 sch = &tcp_syncache.hashbase[ 422 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; 423 *schp = sch; 424 425 SCH_LOCK(sch); 426 427 /* Circle through bucket row to find matching entry. */ 428 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 429 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 430 return (sc); 431 } 432 } else 433 #endif 434 { 435 sch = &tcp_syncache.hashbase[ 436 SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; 437 *schp = sch; 438 439 SCH_LOCK(sch); 440 441 /* Circle through bucket row to find matching entry. */ 442 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { 443 #ifdef INET6 444 if (sc->sc_inc.inc_isipv6) 445 continue; 446 #endif 447 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) 448 return (sc); 449 } 450 } 451 SCH_LOCK_ASSERT(*schp); 452 return (NULL); /* always returns with locked sch */ 453 } 454 455 /* 456 * This function is called when we get a RST for a 457 * non-existent connection, so that we can see if the 458 * connection is in the syn cache. If it is, zap it. 459 */ 460 void 461 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) 462 { 463 struct syncache *sc; 464 struct syncache_head *sch; 465 466 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 467 SCH_LOCK_ASSERT(sch); 468 if (sc == NULL) 469 goto done; 470 471 /* 472 * If the RST bit is set, check the sequence number to see 473 * if this is a valid reset segment. 474 * RFC 793 page 37: 475 * In all states except SYN-SENT, all reset (RST) segments 476 * are validated by checking their SEQ-fields. A reset is 477 * valid if its sequence number is in the window. 478 * 479 * The sequence number in the reset segment is normally an 480 * echo of our outgoing acknowlegement numbers, but some hosts 481 * send a reset with the sequence number at the rightmost edge 482 * of our receive window, and we have to handle this case. 483 */ 484 if (SEQ_GEQ(th->th_seq, sc->sc_irs) && 485 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { 486 syncache_drop(sc, sch); 487 tcpstat.tcps_sc_reset++; 488 } 489 done: 490 SCH_UNLOCK(sch); 491 } 492 493 void 494 syncache_badack(struct in_conninfo *inc) 495 { 496 struct syncache *sc; 497 struct syncache_head *sch; 498 499 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 500 SCH_LOCK_ASSERT(sch); 501 if (sc != NULL) { 502 syncache_drop(sc, sch); 503 tcpstat.tcps_sc_badack++; 504 } 505 SCH_UNLOCK(sch); 506 } 507 508 void 509 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) 510 { 511 struct syncache *sc; 512 struct syncache_head *sch; 513 514 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 515 SCH_LOCK_ASSERT(sch); 516 if (sc == NULL) 517 goto done; 518 519 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ 520 if (ntohl(th->th_seq) != sc->sc_iss) 521 goto done; 522 523 /* 524 * If we've rertransmitted 3 times and this is our second error, 525 * we remove the entry. Otherwise, we allow it to continue on. 526 * This prevents us from incorrectly nuking an entry during a 527 * spurious network outage. 528 * 529 * See tcp_notify(). 530 */ 531 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { 532 sc->sc_flags |= SCF_UNREACH; 533 goto done; 534 } 535 syncache_drop(sc, sch); 536 tcpstat.tcps_sc_unreach++; 537 done: 538 SCH_UNLOCK(sch); 539 } 540 541 /* 542 * Build a new TCP socket structure from a syncache entry. 543 */ 544 static struct socket * 545 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) 546 { 547 struct inpcb *inp = NULL; 548 struct socket *so; 549 struct tcpcb *tp; 550 551 NET_ASSERT_GIANT(); 552 INP_INFO_WLOCK_ASSERT(&tcbinfo); 553 554 /* 555 * Ok, create the full blown connection, and set things up 556 * as they would have been set up if we had created the 557 * connection when the SYN arrived. If we can't create 558 * the connection, abort it. 559 */ 560 so = sonewconn(lso, SS_ISCONNECTED); 561 if (so == NULL) { 562 /* 563 * Drop the connection; we will send a RST if the peer 564 * retransmits the ACK, 565 */ 566 tcpstat.tcps_listendrop++; 567 goto abort2; 568 } 569 #ifdef MAC 570 SOCK_LOCK(so); 571 mac_set_socket_peer_from_mbuf(m, so); 572 SOCK_UNLOCK(so); 573 #endif 574 575 inp = sotoinpcb(so); 576 INP_LOCK(inp); 577 578 /* Insert new socket into PCB hash list. */ 579 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; 580 #ifdef INET6 581 if (sc->sc_inc.inc_isipv6) { 582 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 583 } else { 584 inp->inp_vflag &= ~INP_IPV6; 585 inp->inp_vflag |= INP_IPV4; 586 #endif 587 inp->inp_laddr = sc->sc_inc.inc_laddr; 588 #ifdef INET6 589 } 590 #endif 591 inp->inp_lport = sc->sc_inc.inc_lport; 592 if (in_pcbinshash(inp) != 0) { 593 /* 594 * Undo the assignments above if we failed to 595 * put the PCB on the hash lists. 596 */ 597 #ifdef INET6 598 if (sc->sc_inc.inc_isipv6) 599 inp->in6p_laddr = in6addr_any; 600 else 601 #endif 602 inp->inp_laddr.s_addr = INADDR_ANY; 603 inp->inp_lport = 0; 604 goto abort; 605 } 606 #ifdef IPSEC 607 /* Copy old policy into new socket's. */ 608 if (ipsec_copy_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 609 printf("syncache_socket: could not copy policy\n"); 610 #endif 611 #ifdef FAST_IPSEC 612 /* Copy old policy into new socket's. */ 613 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) 614 printf("syncache_socket: could not copy policy\n"); 615 #endif 616 #ifdef INET6 617 if (sc->sc_inc.inc_isipv6) { 618 struct inpcb *oinp = sotoinpcb(lso); 619 struct in6_addr laddr6; 620 struct sockaddr_in6 sin6; 621 /* 622 * Inherit socket options from the listening socket. 623 * Note that in6p_inputopts are not (and should not be) 624 * copied, since it stores previously received options and is 625 * used to detect if each new option is different than the 626 * previous one and hence should be passed to a user. 627 * If we copied in6p_inputopts, a user would not be able to 628 * receive options just after calling the accept system call. 629 */ 630 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; 631 if (oinp->in6p_outputopts) 632 inp->in6p_outputopts = 633 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); 634 635 sin6.sin6_family = AF_INET6; 636 sin6.sin6_len = sizeof(sin6); 637 sin6.sin6_addr = sc->sc_inc.inc6_faddr; 638 sin6.sin6_port = sc->sc_inc.inc_fport; 639 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; 640 laddr6 = inp->in6p_laddr; 641 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) 642 inp->in6p_laddr = sc->sc_inc.inc6_laddr; 643 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, 644 thread0.td_ucred)) { 645 inp->in6p_laddr = laddr6; 646 goto abort; 647 } 648 /* Override flowlabel from in6_pcbconnect. */ 649 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; 650 inp->in6p_flowinfo |= sc->sc_flowlabel; 651 } else 652 #endif 653 { 654 struct in_addr laddr; 655 struct sockaddr_in sin; 656 657 inp->inp_options = ip_srcroute(m); 658 if (inp->inp_options == NULL) { 659 inp->inp_options = sc->sc_ipopts; 660 sc->sc_ipopts = NULL; 661 } 662 663 sin.sin_family = AF_INET; 664 sin.sin_len = sizeof(sin); 665 sin.sin_addr = sc->sc_inc.inc_faddr; 666 sin.sin_port = sc->sc_inc.inc_fport; 667 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); 668 laddr = inp->inp_laddr; 669 if (inp->inp_laddr.s_addr == INADDR_ANY) 670 inp->inp_laddr = sc->sc_inc.inc_laddr; 671 if (in_pcbconnect(inp, (struct sockaddr *)&sin, 672 thread0.td_ucred)) { 673 inp->inp_laddr = laddr; 674 goto abort; 675 } 676 } 677 tp = intotcpcb(inp); 678 tp->t_state = TCPS_SYN_RECEIVED; 679 tp->iss = sc->sc_iss; 680 tp->irs = sc->sc_irs; 681 tcp_rcvseqinit(tp); 682 tcp_sendseqinit(tp); 683 tp->snd_wl1 = sc->sc_irs; 684 tp->rcv_up = sc->sc_irs + 1; 685 tp->rcv_wnd = sc->sc_wnd; 686 tp->rcv_adv += tp->rcv_wnd; 687 688 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); 689 if (sc->sc_flags & SCF_NOOPT) 690 tp->t_flags |= TF_NOOPT; 691 else { 692 if (sc->sc_flags & SCF_WINSCALE) { 693 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; 694 tp->snd_scale = sc->sc_requested_s_scale; 695 tp->request_r_scale = sc->sc_requested_r_scale; 696 } 697 if (sc->sc_flags & SCF_TIMESTAMP) { 698 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; 699 tp->ts_recent = sc->sc_tsreflect; 700 tp->ts_recent_age = ticks; 701 tp->ts_offset = sc->sc_tsoff; 702 } 703 #ifdef TCP_SIGNATURE 704 if (sc->sc_flags & SCF_SIGNATURE) 705 tp->t_flags |= TF_SIGNATURE; 706 #endif 707 if (sc->sc_flags & SCF_SACK) { 708 tp->sack_enable = 1; 709 tp->t_flags |= TF_SACK_PERMIT; 710 } 711 } 712 713 /* 714 * Set up MSS and get cached values from tcp_hostcache. 715 * This might overwrite some of the defaults we just set. 716 */ 717 tcp_mss(tp, sc->sc_peer_mss); 718 719 /* 720 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. 721 */ 722 if (sc->sc_rxmits > 1) 723 tp->snd_cwnd = tp->t_maxseg; 724 callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp); 725 726 INP_UNLOCK(inp); 727 728 tcpstat.tcps_accepts++; 729 return (so); 730 731 abort: 732 INP_UNLOCK(inp); 733 abort2: 734 if (so != NULL) 735 soabort(so); 736 return (NULL); 737 } 738 739 /* 740 * This function gets called when we receive an ACK for a 741 * socket in the LISTEN state. We look up the connection 742 * in the syncache, and if its there, we pull it out of 743 * the cache and turn it into a full-blown connection in 744 * the SYN-RECEIVED state. 745 */ 746 int 747 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 748 struct socket **lsop, struct mbuf *m) 749 { 750 struct syncache *sc; 751 struct syncache_head *sch; 752 struct socket *so; 753 struct syncache scs; 754 755 /* 756 * Global TCP locks are held because we manipulate the PCB lists 757 * and create a new socket. 758 */ 759 INP_INFO_WLOCK_ASSERT(&tcbinfo); 760 761 sc = syncache_lookup(inc, &sch); /* returns locked sch */ 762 SCH_LOCK_ASSERT(sch); 763 if (sc == NULL) { 764 /* 765 * There is no syncache entry, so see if this ACK is 766 * a returning syncookie. To do this, first: 767 * A. See if this socket has had a syncache entry dropped in 768 * the past. We don't want to accept a bogus syncookie 769 * if we've never received a SYN. 770 * B. check that the syncookie is valid. If it is, then 771 * cobble up a fake syncache entry, and return. 772 */ 773 if (!tcp_syncookies) { 774 SCH_UNLOCK(sch); 775 goto failed; 776 } 777 bzero(&scs, sizeof(scs)); 778 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); 779 SCH_UNLOCK(sch); 780 if (sc == NULL) 781 goto failed; 782 tcpstat.tcps_sc_recvcookie++; 783 } else { 784 /* Pull out the entry to unlock the bucket row. */ 785 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); 786 sch->sch_length--; 787 tcp_syncache.cache_count--; 788 SCH_UNLOCK(sch); 789 } 790 791 /* 792 * If seg contains an ACK, but not for our SYN/ACK, send a RST. 793 */ 794 if (th->th_ack != sc->sc_iss + 1) 795 goto failed; 796 797 so = syncache_socket(sc, *lsop, m); 798 799 if (so == NULL) { 800 #if 0 801 resetandabort: 802 /* XXXjlemon check this - is this correct? */ 803 (void) tcp_respond(NULL, m, m, th, 804 th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK); 805 #endif 806 m_freem(m); /* XXX: only needed for above */ 807 tcpstat.tcps_sc_aborted++; 808 if (sc != &scs) { 809 syncache_insert(sc, sch); /* try again later */ 810 sc = NULL; 811 } 812 goto failed; 813 } else 814 tcpstat.tcps_sc_completed++; 815 *lsop = so; 816 817 if (sc != &scs) 818 syncache_free(sc); 819 return (1); 820 failed: 821 if (sc != NULL && sc != &scs) 822 syncache_free(sc); 823 return (0); 824 } 825 826 /* 827 * Given a LISTEN socket and an inbound SYN request, add 828 * this to the syn cache, and send back a segment: 829 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> 830 * to the source. 831 * 832 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. 833 * Doing so would require that we hold onto the data and deliver it 834 * to the application. However, if we are the target of a SYN-flood 835 * DoS attack, an attacker could send data which would eventually 836 * consume all available buffer space if it were ACKed. By not ACKing 837 * the data, we avoid this DoS scenario. 838 */ 839 int 840 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, 841 struct inpcb *inp, struct socket **lsop, struct mbuf *m) 842 { 843 struct tcpcb *tp; 844 struct socket *so; 845 struct syncache *sc = NULL; 846 struct syncache_head *sch; 847 struct mbuf *ipopts = NULL; 848 u_int32_t flowtmp; 849 int win, sb_hiwat, ip_ttl, ip_tos, noopt; 850 #ifdef INET6 851 int autoflowlabel = 0; 852 #endif 853 struct syncache scs; 854 855 INP_INFO_WLOCK_ASSERT(&tcbinfo); 856 INP_LOCK_ASSERT(inp); /* listen socket */ 857 858 /* 859 * Combine all so/tp operations very early to drop the INP lock as 860 * soon as possible. 861 */ 862 so = *lsop; 863 tp = sototcpcb(so); 864 865 #ifdef INET6 866 if (inc->inc_isipv6 && 867 (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) 868 autoflowlabel = 1; 869 #endif 870 ip_ttl = inp->inp_ip_ttl; 871 ip_tos = inp->inp_ip_tos; 872 win = sbspace(&so->so_rcv); 873 sb_hiwat = so->so_rcv.sb_hiwat; 874 noopt = (tp->t_flags & TF_NOOPT); 875 876 so = NULL; 877 tp = NULL; 878 879 INP_UNLOCK(inp); 880 INP_INFO_WUNLOCK(&tcbinfo); 881 882 /* 883 * Remember the IP options, if any. 884 */ 885 #ifdef INET6 886 if (!inc->inc_isipv6) 887 #endif 888 ipopts = ip_srcroute(m); 889 890 /* 891 * See if we already have an entry for this connection. 892 * If we do, resend the SYN,ACK, and reset the retransmit timer. 893 * 894 * XXX: should the syncache be re-initialized with the contents 895 * of the new SYN here (which may have different options?) 896 */ 897 sc = syncache_lookup(inc, &sch); /* returns locked entry */ 898 SCH_LOCK_ASSERT(sch); 899 if (sc != NULL) { 900 tcpstat.tcps_sc_dupsyn++; 901 if (ipopts) { 902 /* 903 * If we were remembering a previous source route, 904 * forget it and use the new one we've been given. 905 */ 906 if (sc->sc_ipopts) 907 (void) m_free(sc->sc_ipopts); 908 sc->sc_ipopts = ipopts; 909 } 910 /* 911 * Update timestamp if present. 912 */ 913 if (sc->sc_flags & SCF_TIMESTAMP) 914 sc->sc_tsreflect = to->to_tsval; 915 if (syncache_respond(sc, m) == 0) { 916 SYNCACHE_TIMEOUT(sc, sch, 1); 917 tcpstat.tcps_sndacks++; 918 tcpstat.tcps_sndtotal++; 919 } 920 SCH_UNLOCK(sch); 921 goto done; 922 } 923 924 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 925 if (sc == NULL) { 926 /* 927 * The zone allocator couldn't provide more entries. 928 * Treat this as if the cache was full; drop the oldest 929 * entry and insert the new one. 930 */ 931 tcpstat.tcps_sc_zonefail++; 932 sc = TAILQ_LAST(&sch->sch_bucket, sch_head); 933 syncache_drop(sc, sch); 934 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); 935 if (sc == NULL) { 936 if (tcp_syncookies) { 937 bzero(&scs, sizeof(scs)); 938 sc = &scs; 939 } else { 940 SCH_UNLOCK(sch); 941 if (ipopts) 942 (void) m_free(ipopts); 943 goto done; 944 } 945 } 946 } 947 948 /* 949 * Fill in the syncache values. 950 */ 951 sc->sc_ipopts = ipopts; 952 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 953 #ifdef INET6 954 if (!inc->inc_isipv6) 955 #endif 956 { 957 sc->sc_ip_tos = ip_tos; 958 sc->sc_ip_ttl = ip_ttl; 959 } 960 961 sc->sc_irs = th->th_seq; 962 sc->sc_iss = arc4random(); 963 sc->sc_flags = 0; 964 sc->sc_flowlabel = 0; 965 966 /* 967 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. 968 * win was derived from socket earlier in the function. 969 */ 970 win = imax(win, 0); 971 win = imin(win, TCP_MAXWIN); 972 sc->sc_wnd = win; 973 974 if (tcp_do_rfc1323) { 975 /* 976 * A timestamp received in a SYN makes 977 * it ok to send timestamp requests and replies. 978 */ 979 if (to->to_flags & TOF_TS) { 980 sc->sc_tsreflect = to->to_tsval; 981 sc->sc_flags |= SCF_TIMESTAMP; 982 } 983 if (to->to_flags & TOF_SCALE) { 984 int wscale = 0; 985 986 /* Compute proper scaling value from buffer space */ 987 while (wscale < TCP_MAX_WINSHIFT && 988 (TCP_MAXWIN << wscale) < sb_hiwat) 989 wscale++; 990 sc->sc_requested_r_scale = wscale; 991 sc->sc_requested_s_scale = to->to_requested_s_scale; 992 sc->sc_flags |= SCF_WINSCALE; 993 } 994 } 995 #ifdef TCP_SIGNATURE 996 /* 997 * If listening socket requested TCP digests, and received SYN 998 * contains the option, flag this in the syncache so that 999 * syncache_respond() will do the right thing with the SYN+ACK. 1000 * XXX: Currently we always record the option by default and will 1001 * attempt to use it in syncache_respond(). 1002 */ 1003 if (to->to_flags & TOF_SIGNATURE) 1004 sc->sc_flags |= SCF_SIGNATURE; 1005 #endif 1006 if (to->to_flags & TOF_SACK) 1007 sc->sc_flags |= SCF_SACK; 1008 if (to->to_flags & TOF_MSS) 1009 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ 1010 if (noopt) 1011 sc->sc_flags |= SCF_NOOPT; 1012 1013 if (tcp_syncookies) { 1014 syncookie_generate(sch, sc, &flowtmp); 1015 #ifdef INET6 1016 if (autoflowlabel) 1017 sc->sc_flowlabel = flowtmp; 1018 #endif 1019 } else { 1020 #ifdef INET6 1021 if (autoflowlabel) 1022 sc->sc_flowlabel = 1023 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); 1024 #endif 1025 } 1026 SCH_UNLOCK(sch); 1027 1028 /* 1029 * Do a standard 3-way handshake. 1030 */ 1031 if (syncache_respond(sc, m) == 0) { 1032 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) 1033 syncache_free(sc); 1034 else if (sc != &scs) 1035 syncache_insert(sc, sch); /* locks and unlocks sch */ 1036 tcpstat.tcps_sndacks++; 1037 tcpstat.tcps_sndtotal++; 1038 } else { 1039 syncache_free(sc); 1040 tcpstat.tcps_sc_dropped++; 1041 } 1042 1043 done: 1044 *lsop = NULL; 1045 return (1); 1046 } 1047 1048 static int 1049 syncache_respond(struct syncache *sc, struct mbuf *m) 1050 { 1051 struct ip *ip = NULL; 1052 struct tcphdr *th; 1053 int optlen, error; 1054 u_int16_t tlen, hlen, mssopt; 1055 u_int8_t *optp; 1056 #ifdef INET6 1057 struct ip6_hdr *ip6 = NULL; 1058 #endif 1059 #ifdef MAC 1060 struct inpcb *inp = NULL; 1061 #endif 1062 1063 hlen = 1064 #ifdef INET6 1065 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : 1066 #endif 1067 sizeof(struct ip); 1068 1069 /* Determine MSS we advertize to other end of connection. */ 1070 mssopt = tcp_mssopt(&sc->sc_inc); 1071 if (sc->sc_peer_mss) 1072 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); 1073 1074 /* Compute the size of the TCP options. */ 1075 if (sc->sc_flags & SCF_NOOPT) { 1076 optlen = 0; 1077 } else { 1078 optlen = TCPOLEN_MAXSEG + 1079 ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) + 1080 ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0); 1081 #ifdef TCP_SIGNATURE 1082 if (sc->sc_flags & SCF_SIGNATURE) 1083 optlen += TCPOLEN_SIGNATURE; 1084 #endif 1085 if (sc->sc_flags & SCF_SACK) 1086 optlen += TCPOLEN_SACK_PERMITTED; 1087 optlen = roundup2(optlen, 4); 1088 } 1089 tlen = hlen + sizeof(struct tcphdr) + optlen; 1090 1091 /* 1092 * XXX: Assume that the entire packet will fit in a header mbuf. 1093 */ 1094 KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small")); 1095 1096 /* Create the IP+TCP header from scratch. */ 1097 if (m) 1098 m_freem(m); 1099 1100 m = m_gethdr(M_DONTWAIT, MT_DATA); 1101 if (m == NULL) 1102 return (ENOBUFS); 1103 m->m_data += max_linkhdr; 1104 m->m_len = tlen; 1105 m->m_pkthdr.len = tlen; 1106 m->m_pkthdr.rcvif = NULL; 1107 1108 #ifdef MAC 1109 /* 1110 * For MAC look up the inpcb to get access to the label information. 1111 * We don't store the inpcb pointer in struct syncache to make locking 1112 * less complicated and to save locking operations. However for MAC 1113 * this gives a slight overhead as we have to do a full pcblookup here. 1114 */ 1115 INP_INFO_RLOCK(&tcbinfo); 1116 if (inp == NULL) { 1117 #ifdef INET6 /* && MAC */ 1118 if (sc->sc_inc.inc_isipv6) 1119 inp = in6_pcblookup_hash(&tcbinfo, 1120 &sc->sc_inc.inc6_faddr, sc->sc_inc.inc_fport, 1121 &sc->sc_inc.inc6_laddr, sc->sc_inc.inc_lport, 1122 1, NULL); 1123 else 1124 #endif /* INET6 */ 1125 inp = in_pcblookup_hash(&tcbinfo, 1126 sc->sc_inc.inc_faddr, sc->sc_inc.inc_fport, 1127 sc->sc_inc.inc_laddr, sc->sc_inc.inc_lport, 1128 1, NULL); 1129 if (inp == NULL) { 1130 m_freem(m); 1131 INP_INFO_RUNLOCK(&tcbinfo); 1132 return (ESHUTDOWN); 1133 } 1134 } 1135 INP_LOCK(inp); 1136 if (!inp->inp_socket->so_options & SO_ACCEPTCONN) { 1137 m_freem(m); 1138 INP_UNLOCK(inp); 1139 INP_INFO_RUNLOCK(&tcbinfo); 1140 return (ESHUTDOWN); 1141 } 1142 mac_create_mbuf_from_inpcb(inp, m); 1143 INP_UNLOCK(inp); 1144 INP_INFO_RUNLOCK(&tcbinfo); 1145 #endif /* MAC */ 1146 1147 #ifdef INET6 1148 if (sc->sc_inc.inc_isipv6) { 1149 ip6 = mtod(m, struct ip6_hdr *); 1150 ip6->ip6_vfc = IPV6_VERSION; 1151 ip6->ip6_nxt = IPPROTO_TCP; 1152 ip6->ip6_src = sc->sc_inc.inc6_laddr; 1153 ip6->ip6_dst = sc->sc_inc.inc6_faddr; 1154 ip6->ip6_plen = htons(tlen - hlen); 1155 /* ip6_hlim is set after checksum */ 1156 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; 1157 ip6->ip6_flow |= sc->sc_flowlabel; 1158 1159 th = (struct tcphdr *)(ip6 + 1); 1160 } else 1161 #endif 1162 { 1163 ip = mtod(m, struct ip *); 1164 ip->ip_v = IPVERSION; 1165 ip->ip_hl = sizeof(struct ip) >> 2; 1166 ip->ip_len = tlen; 1167 ip->ip_id = 0; 1168 ip->ip_off = 0; 1169 ip->ip_sum = 0; 1170 ip->ip_p = IPPROTO_TCP; 1171 ip->ip_src = sc->sc_inc.inc_laddr; 1172 ip->ip_dst = sc->sc_inc.inc_faddr; 1173 ip->ip_ttl = sc->sc_ip_ttl; 1174 ip->ip_tos = sc->sc_ip_tos; 1175 1176 /* 1177 * See if we should do MTU discovery. Route lookups are 1178 * expensive, so we will only unset the DF bit if: 1179 * 1180 * 1) path_mtu_discovery is disabled 1181 * 2) the SCF_UNREACH flag has been set 1182 */ 1183 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) 1184 ip->ip_off |= IP_DF; 1185 1186 th = (struct tcphdr *)(ip + 1); 1187 } 1188 th->th_sport = sc->sc_inc.inc_lport; 1189 th->th_dport = sc->sc_inc.inc_fport; 1190 1191 th->th_seq = htonl(sc->sc_iss); 1192 th->th_ack = htonl(sc->sc_irs + 1); 1193 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 1194 th->th_x2 = 0; 1195 th->th_flags = TH_SYN|TH_ACK; 1196 th->th_win = htons(sc->sc_wnd); 1197 th->th_urp = 0; 1198 1199 /* Tack on the TCP options. */ 1200 if (optlen != 0) { 1201 optp = (u_int8_t *)(th + 1); 1202 *optp++ = TCPOPT_MAXSEG; 1203 *optp++ = TCPOLEN_MAXSEG; 1204 *optp++ = (mssopt >> 8) & 0xff; 1205 *optp++ = mssopt & 0xff; 1206 1207 if (sc->sc_flags & SCF_WINSCALE) { 1208 *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 | 1209 TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 | 1210 sc->sc_requested_r_scale); 1211 optp += 4; 1212 } 1213 1214 if (sc->sc_flags & SCF_TIMESTAMP) { 1215 u_int32_t *lp = (u_int32_t *)(optp); 1216 1217 /* Form timestamp option per appendix A of RFC 1323. */ 1218 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 1219 if (sc->sc_ts) 1220 *lp++ = htonl(sc->sc_ts); 1221 else 1222 *lp++ = htonl(ticks); 1223 *lp = htonl(sc->sc_tsreflect); 1224 optp += TCPOLEN_TSTAMP_APPA; 1225 } 1226 1227 #ifdef TCP_SIGNATURE 1228 /* 1229 * Handle TCP-MD5 passive opener response. 1230 */ 1231 if (sc->sc_flags & SCF_SIGNATURE) { 1232 u_int8_t *bp = optp; 1233 int i; 1234 1235 *bp++ = TCPOPT_SIGNATURE; 1236 *bp++ = TCPOLEN_SIGNATURE; 1237 for (i = 0; i < TCP_SIGLEN; i++) 1238 *bp++ = 0; 1239 tcp_signature_compute(m, sizeof(struct ip), 0, optlen, 1240 optp + 2, IPSEC_DIR_OUTBOUND); 1241 optp += TCPOLEN_SIGNATURE; 1242 } 1243 #endif /* TCP_SIGNATURE */ 1244 1245 if (sc->sc_flags & SCF_SACK) { 1246 *optp++ = TCPOPT_SACK_PERMITTED; 1247 *optp++ = TCPOLEN_SACK_PERMITTED; 1248 } 1249 1250 { 1251 /* Pad TCP options to a 4 byte boundary */ 1252 int padlen = optlen - (optp - (u_int8_t *)(th + 1)); 1253 while (padlen-- > 0) 1254 *optp++ = TCPOPT_EOL; 1255 } 1256 } 1257 1258 #ifdef INET6 1259 if (sc->sc_inc.inc_isipv6) { 1260 th->th_sum = 0; 1261 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen); 1262 ip6->ip6_hlim = in6_selecthlim(NULL, NULL); 1263 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); 1264 } else 1265 #endif 1266 { 1267 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 1268 htons(tlen - hlen + IPPROTO_TCP)); 1269 m->m_pkthdr.csum_flags = CSUM_TCP; 1270 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 1271 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); 1272 } 1273 return (error); 1274 } 1275 1276 /* 1277 * The purpose of SYN cookies is to avoid keeping track of all SYN's we 1278 * receive and to be able to handle SYN floods from bogus source addresses 1279 * (where we will never receive any reply). SYN floods try to exhaust all 1280 * our memory and available slots in the SYN cache table to cause a denial 1281 * of service to legitimate users of the local host. 1282 * 1283 * The idea of SYN cookies is to encode and include all necessary information 1284 * about the connection setup state within the SYN-ACK we send back and thus 1285 * to get along without keeping any local state until the ACK to the SYN-ACK 1286 * arrives (if ever). Everything we need to know should be available from 1287 * the information we encoded in the SYN-ACK. 1288 * 1289 * More information about the theory behind SYN cookies and its first 1290 * discussion and specification can be found at: 1291 * http://cr.yp.to/syncookies.html (overview) 1292 * http://cr.yp.to/syncookies/archive (gory details) 1293 * 1294 * This implementation extends the orginal idea and first implementation 1295 * of FreeBSD by using not only the initial sequence number field to store 1296 * information but also the timestamp field if present. This way we can 1297 * keep track of the entire state we need to know to recreate the session in 1298 * its original form. Almost all TCP speakers implement RFC1323 timestamps 1299 * these days. For those that do not we still have to live with the known 1300 * shortcomings of the ISN only SYN cookies. 1301 * 1302 * Cookie layers: 1303 * 1304 * Initial sequence number we send: 1305 * 31|................................|0 1306 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP 1307 * D = MD5 Digest (first dword) 1308 * M = MSS index 1309 * R = Rotation of secret 1310 * P = Odd or Even secret 1311 * 1312 * The MD5 Digest is computed with over following parameters: 1313 * a) randomly rotated secret 1314 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) 1315 * c) the received initial sequence number from remote host 1316 * d) the rotation offset and odd/even bit 1317 * 1318 * Timestamp we send: 1319 * 31|................................|0 1320 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 1321 * D = MD5 Digest (third dword) (only as filler) 1322 * S = Requested send window scale 1323 * R = Requested receive window scale 1324 * A = SACK allowed 1325 * 5 = TCP-MD5 enabled (not implemented yet) 1326 * XORed with MD5 Digest (forth dword) 1327 * 1328 * The timestamp isn't cryptographically secure and doesn't need to be. 1329 * The double use of the MD5 digest dwords ties it to a specific remote/ 1330 * local host/port, remote initial sequence number and our local time 1331 * limited secret. A received timestamp is reverted (XORed) and then 1332 * the contained MD5 dword is compared to the computed one to ensure the 1333 * timestamp belongs to the SYN-ACK we sent. The other parameters may 1334 * have been tampered with but this isn't different from supplying bogus 1335 * values in the SYN in the first place. 1336 * 1337 * Some problems with SYN cookies remain however: 1338 * Consider the problem of a recreated (and retransmitted) cookie. If the 1339 * original SYN was accepted, the connection is established. The second 1340 * SYN is inflight, and if it arrives with an ISN that falls within the 1341 * receive window, the connection is killed. 1342 * 1343 * Notes: 1344 * A heuristic to determine when to accept syn cookies is not necessary. 1345 * An ACK flood would cause the syncookie verification to be attempted, 1346 * but a SYN flood causes syncookies to be generated. Both are of equal 1347 * cost, so there's no point in trying to optimize the ACK flood case. 1348 * Also, if you don't process certain ACKs for some reason, then all someone 1349 * would have to do is launch a SYN and ACK flood at the same time, which 1350 * would stop cookie verification and defeat the entire purpose of syncookies. 1351 */ 1352 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; 1353 1354 static void 1355 syncookie_generate(struct syncache_head *sch, struct syncache *sc, 1356 u_int32_t *flowlabel) 1357 { 1358 MD5_CTX ctx; 1359 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1360 u_int32_t data; 1361 u_int32_t *secbits; 1362 u_int off, pmss, mss; 1363 int i; 1364 1365 SCH_LOCK_ASSERT(sch); 1366 1367 /* Which of the two secrets to use. */ 1368 secbits = sch->sch_oddeven ? 1369 sch->sch_secbits_odd : sch->sch_secbits_even; 1370 1371 /* Reseed secret if too old. */ 1372 if (sch->sch_reseed < time_uptime) { 1373 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ 1374 secbits = sch->sch_oddeven ? 1375 sch->sch_secbits_odd : sch->sch_secbits_even; 1376 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) 1377 secbits[i] = arc4random(); 1378 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; 1379 } 1380 1381 /* Secret rotation offset. */ 1382 off = sc->sc_iss & 0x7; /* iss was randomized before */ 1383 1384 /* Maximum segment size calculation. */ 1385 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); 1386 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) 1387 if (tcp_sc_msstab[mss] <= pmss) 1388 break; 1389 1390 /* Fold parameters and MD5 digest into the ISN we will send. */ 1391 data = sch->sch_oddeven;/* odd or even secret, 1 bit */ 1392 data |= off << 1; /* secret offset, derived from iss, 3 bits */ 1393 data |= mss << 4; /* mss, 3 bits */ 1394 1395 MD5Init(&ctx); 1396 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1397 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1398 MD5Update(&ctx, secbits, off); 1399 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); 1400 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); 1401 MD5Update(&ctx, &data, sizeof(data)); 1402 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1403 1404 data |= (md5_buffer[0] << 7); 1405 sc->sc_iss = data; 1406 1407 #ifdef INET6 1408 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1409 #endif 1410 1411 /* Additional parameters are stored in the timestamp if present. */ 1412 if (sc->sc_flags & SCF_TIMESTAMP) { 1413 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ 1414 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ 1415 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ 1416 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ 1417 data |= md5_buffer[2] << 10; /* more digest bits */ 1418 data ^= md5_buffer[3]; 1419 sc->sc_ts = data; 1420 sc->sc_tsoff = data - ticks; /* after XOR */ 1421 } else 1422 sc->sc_ts = 0; 1423 1424 return; 1425 } 1426 1427 static struct syncache * 1428 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, 1429 struct syncache *sc, struct tcpopt *to, struct tcphdr *th, 1430 struct socket *so) 1431 { 1432 MD5_CTX ctx; 1433 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; 1434 u_int32_t data = 0; 1435 u_int32_t *secbits; 1436 tcp_seq ack, seq; 1437 int off, mss, wnd, flags; 1438 1439 SCH_LOCK_ASSERT(sch); 1440 1441 /* 1442 * Pull information out of SYN-ACK/ACK and 1443 * revert sequence number advances. 1444 */ 1445 ack = th->th_ack - 1; 1446 seq = th->th_seq - 1; 1447 off = (ack >> 1) & 0x7; 1448 mss = (ack >> 4) & 0x7; 1449 flags = ack & 0x7f; 1450 1451 /* Which of the two secrets to use. */ 1452 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; 1453 1454 /* 1455 * The secret wasn't updated for the lifetime of a syncookie, 1456 * so this SYN-ACK/ACK is either too old (replay) or totally bogus. 1457 */ 1458 if (sch->sch_reseed < time_uptime) { 1459 return (NULL); 1460 } 1461 1462 /* Recompute the digest so we can compare it. */ 1463 MD5Init(&ctx); 1464 MD5Update(&ctx, ((u_int8_t *)secbits) + off, 1465 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); 1466 MD5Update(&ctx, secbits, off); 1467 MD5Update(&ctx, inc, sizeof(*inc)); 1468 MD5Update(&ctx, &seq, sizeof(seq)); 1469 MD5Update(&ctx, &flags, sizeof(flags)); 1470 MD5Final((u_int8_t *)&md5_buffer, &ctx); 1471 1472 /* Does the digest part of or ACK'ed ISS match? */ 1473 if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) 1474 return (NULL); 1475 1476 /* Does the digest part of our reflected timestamp match? */ 1477 if (to->to_flags & TOF_TS) { 1478 data = md5_buffer[3] ^ to->to_tsecr; 1479 if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) 1480 return (NULL); 1481 } 1482 1483 /* Fill in the syncache values. */ 1484 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); 1485 sc->sc_ipopts = NULL; 1486 1487 sc->sc_irs = seq; 1488 sc->sc_iss = ack; 1489 1490 #ifdef INET6 1491 if (inc->inc_isipv6) { 1492 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) 1493 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; 1494 } else 1495 #endif 1496 { 1497 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; 1498 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; 1499 } 1500 1501 /* Additional parameters that were encoded in the timestamp. */ 1502 if (data) { 1503 sc->sc_flags |= SCF_TIMESTAMP; 1504 sc->sc_tsreflect = to->to_tsval; 1505 sc->sc_tsoff = to->to_tsecr - ticks; 1506 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; 1507 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; 1508 sc->sc_requested_s_scale = min((data >> 2) & 0xf, 1509 TCP_MAX_WINSHIFT); 1510 sc->sc_requested_r_scale = min((data >> 6) & 0xf, 1511 TCP_MAX_WINSHIFT); 1512 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) 1513 sc->sc_flags |= SCF_WINSCALE; 1514 } else 1515 sc->sc_flags |= SCF_NOOPT; 1516 1517 wnd = sbspace(&so->so_rcv); 1518 wnd = imax(wnd, 0); 1519 wnd = imin(wnd, TCP_MAXWIN); 1520 sc->sc_wnd = wnd; 1521 1522 sc->sc_rxmits = 0; 1523 sc->sc_peer_mss = tcp_sc_msstab[mss]; 1524 1525 return (sc); 1526 } 1527