1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote 16 * products derived from this software without specific prior written 17 * permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 /* 33 * ip_fastforward gets its speed from processing the forwarded packet to 34 * completion (if_output on the other side) without any queues or netisr's. 35 * The receiving interface DMAs the packet into memory, the upper half of 36 * driver calls ip_fastforward, we do our routing table lookup and directly 37 * send it off to the outgoing interface, which DMAs the packet to the 38 * network card. The only part of the packet we touch with the CPU is the 39 * IP header (unless there are complex firewall rules touching other parts 40 * of the packet, but that is up to you). We are essentially limited by bus 41 * bandwidth and how fast the network card/driver can set up receives and 42 * transmits. 43 * 44 * We handle basic errors, IP header errors, checksum errors, 45 * destination unreachable, fragmentation and fragmentation needed and 46 * report them via ICMP to the sender. 47 * 48 * Else if something is not pure IPv4 unicast forwarding we fall back to 49 * the normal ip_input processing path. We should only be called from 50 * interfaces connected to the outside world. 51 * 52 * Firewalling is fully supported including divert, ipfw fwd and ipfilter 53 * ipnat and address rewrite. 54 * 55 * IPSEC is not supported if this host is a tunnel broker. IPSEC is 56 * supported for connections to/from local host. 57 * 58 * We try to do the least expensive (in CPU ops) checks and operations 59 * first to catch junk with as little overhead as possible. 60 * 61 * We take full advantage of hardware support for IP checksum and 62 * fragmentation offloading. 63 */ 64 65 /* 66 * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 67 * is being followed here. 68 */ 69 70 #include <sys/cdefs.h> 71 __FBSDID("$FreeBSD$"); 72 73 #include "opt_ipstealth.h" 74 75 #include <sys/param.h> 76 #include <sys/systm.h> 77 #include <sys/kernel.h> 78 #include <sys/malloc.h> 79 #include <sys/mbuf.h> 80 #include <sys/protosw.h> 81 #include <sys/sdt.h> 82 #include <sys/socket.h> 83 #include <sys/sysctl.h> 84 85 #include <net/if.h> 86 #include <net/if_types.h> 87 #include <net/if_var.h> 88 #include <net/if_dl.h> 89 #include <net/if_private.h> 90 #include <net/pfil.h> 91 #include <net/route.h> 92 #include <net/route/nhop.h> 93 #include <net/vnet.h> 94 95 #include <netinet/in.h> 96 #include <netinet/in_fib.h> 97 #include <netinet/in_kdtrace.h> 98 #include <netinet/in_systm.h> 99 #include <netinet/in_var.h> 100 #include <netinet/ip.h> 101 #include <netinet/ip_var.h> 102 #include <netinet/ip_icmp.h> 103 #include <netinet/ip_options.h> 104 105 #include <machine/in_cksum.h> 106 107 #define V_ipsendredirects VNET(ipsendredirects) 108 109 static struct mbuf * 110 ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len, 111 struct in_addr *osrc, struct in_addr *newgw) 112 { 113 struct in_ifaddr *nh_ia; 114 struct mbuf *mcopy; 115 116 KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m)); 117 118 /* 119 * Only send a redirect if: 120 * - Redirects are not disabled (must be checked by caller), 121 * - We have not applied NAT (must be checked by caller as possible), 122 * - Neither a MCAST or BCAST packet (must be checked by caller) 123 * [RFC1009 Appendix A.2]. 124 * - The packet does not do IP source routing or having any other 125 * IP options (this case was handled already by ip_input() calling 126 * ip_dooptions() [RFC792, p13], 127 * - The packet is being forwarded out the same physical interface 128 * that it was received from [RFC1812, 5.2.7.2]. 129 */ 130 131 /* 132 * - The forwarding route was not created by a redirect 133 * [RFC1812, 5.2.7.2], or 134 * if it was to follow a default route (see below). 135 * - The next-hop is reachable by us [RFC1009 Appendix A.2]. 136 */ 137 if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT | 138 NHF_BLACKHOLE | NHF_REJECT)) != 0) 139 return (NULL); 140 141 /* Get the new gateway. */ 142 if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET) 143 return (NULL); 144 newgw->s_addr = nh->gw4_sa.sin_addr.s_addr; 145 146 /* 147 * - The resulting forwarding destination is not "This host on this 148 * network" [RFC1122, Section 3.2.1.3] (default route check above). 149 */ 150 if (newgw->s_addr == 0) 151 return (NULL); 152 153 /* 154 * - We know how to reach the sender and the source address is 155 * directly connected to us [RFC792, p13]. 156 * + The new gateway address and the source address are on the same 157 * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2]. 158 * NB: if you think multiple logical subnets on the same wire should 159 * receive redirects read [RFC1812, APPENDIX C (14->15)]. 160 */ 161 nh_ia = (struct in_ifaddr *)nh->nh_ifa; 162 if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet) 163 return (NULL); 164 165 /* Prepare for sending the redirect. */ 166 167 /* 168 * Make a copy of as much as we need of the packet as the original 169 * one will be forwarded but we need (a portion) for icmp_error(). 170 */ 171 mcopy = m_gethdr(M_NOWAIT, m->m_type); 172 if (mcopy == NULL) 173 return (NULL); 174 175 if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) { 176 /* 177 * It's probably ok if the pkthdr dup fails (because 178 * the deep copy of the tag chain failed), but for now 179 * be conservative and just discard the copy since 180 * code below may some day want the tags. 181 */ 182 m_free(mcopy); 183 return (NULL); 184 } 185 mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy)); 186 mcopy->m_pkthdr.len = mcopy->m_len; 187 m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t)); 188 189 return (mcopy); 190 } 191 192 193 static int 194 ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m) 195 { 196 struct nhop_object *nh; 197 198 nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE, 199 m->m_pkthdr.flowid); 200 if (nh == NULL) { 201 IPSTAT_INC(ips_noroute); 202 IPSTAT_INC(ips_cantforward); 203 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 204 return (EHOSTUNREACH); 205 } 206 /* 207 * Drop blackholed traffic and directed broadcasts. 208 */ 209 if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { 210 IPSTAT_INC(ips_cantforward); 211 m_freem(m); 212 return (EHOSTUNREACH); 213 } 214 215 if (nh->nh_flags & NHF_REJECT) { 216 IPSTAT_INC(ips_cantforward); 217 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 218 return (EHOSTUNREACH); 219 } 220 221 *pnh = nh; 222 223 return (0); 224 } 225 226 /* 227 * Try to forward a packet based on the destination address. 228 * This is a fast path optimized for the plain forwarding case. 229 * If the packet is handled (and consumed) here then we return NULL; 230 * otherwise mbuf is returned and the packet should be delivered 231 * to ip_input for full processing. 232 */ 233 struct mbuf * 234 ip_tryforward(struct mbuf *m) 235 { 236 struct ip *ip; 237 struct mbuf *m0 = NULL; 238 struct nhop_object *nh = NULL; 239 struct route ro; 240 struct sockaddr_in *dst; 241 const struct sockaddr *gw; 242 struct in_addr dest, odest, rtdest, osrc; 243 uint16_t ip_len, ip_off; 244 int error = 0; 245 struct m_tag *fwd_tag = NULL; 246 struct mbuf *mcopy = NULL; 247 struct in_addr redest; 248 /* 249 * Are we active and forwarding packets? 250 */ 251 252 M_ASSERTVALID(m); 253 M_ASSERTPKTHDR(m); 254 255 /* 256 * Only IP packets without options 257 */ 258 ip = mtod(m, struct ip *); 259 260 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 261 if (V_ip_doopts == 1) 262 return m; 263 else if (V_ip_doopts == 2) { 264 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 265 0, 0); 266 return NULL; /* mbuf already free'd */ 267 } 268 /* else ignore IP options and continue */ 269 } 270 271 /* 272 * Only unicast IP, not from loopback, no L2 or IP broadcast, 273 * no multicast, no INADDR_ANY 274 * 275 * XXX: Probably some of these checks could be direct drop 276 * conditions. However it is not clear whether there are some 277 * hacks or obscure behaviours which make it necessary to 278 * let ip_input handle it. We play safe here and let ip_input 279 * deal with it until it is proven that we can directly drop it. 280 */ 281 if ((m->m_flags & (M_BCAST|M_MCAST)) || 282 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 283 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 284 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 285 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 286 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 287 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 288 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 289 ip->ip_src.s_addr == INADDR_ANY || 290 ip->ip_dst.s_addr == INADDR_ANY ) 291 return m; 292 293 /* 294 * Is it for a local address on this host? 295 */ 296 if (in_localip(ip->ip_dst)) 297 return m; 298 299 IPSTAT_INC(ips_total); 300 301 /* 302 * Step 3: incoming packet firewall processing 303 */ 304 305 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 306 osrc.s_addr = ip->ip_src.s_addr; 307 308 /* 309 * Run through list of ipfilter hooks for input packets 310 */ 311 if (!PFIL_HOOKED_IN(V_inet_pfil_head)) 312 goto passin; 313 314 if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, 315 NULL) != PFIL_PASS) 316 goto drop; 317 318 M_ASSERTVALID(m); 319 M_ASSERTPKTHDR(m); 320 321 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 322 dest.s_addr = ip->ip_dst.s_addr; 323 324 /* 325 * Destination address changed? 326 */ 327 if (odest.s_addr != dest.s_addr) { 328 /* 329 * Is it now for a local address on this host? 330 */ 331 if (in_localip(dest)) 332 goto forwardlocal; 333 /* 334 * Go on with new destination address 335 */ 336 } 337 338 if (m->m_flags & M_FASTFWD_OURS) { 339 /* 340 * ipfw changed it for a local address on this host. 341 */ 342 goto forwardlocal; 343 } 344 345 passin: 346 /* 347 * Step 4: decrement TTL and look up route 348 */ 349 350 /* 351 * Check TTL 352 */ 353 #ifdef IPSTEALTH 354 if (!V_ipstealth) { 355 #endif 356 if (ip->ip_ttl <= IPTTLDEC) { 357 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 358 return NULL; /* mbuf already free'd */ 359 } 360 361 /* 362 * Decrement the TTL and incrementally change the IP header checksum. 363 * Don't bother doing this with hw checksum offloading, it's faster 364 * doing it right here. 365 */ 366 ip->ip_ttl -= IPTTLDEC; 367 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 368 ip->ip_sum -= ~htons(IPTTLDEC << 8); 369 else 370 ip->ip_sum += htons(IPTTLDEC << 8); 371 #ifdef IPSTEALTH 372 } 373 #endif 374 375 /* 376 * Next hop forced by pfil(9) hook? 377 */ 378 if ((m->m_flags & M_IP_NEXTHOP) && 379 ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) { 380 /* 381 * Now we will find route to forced destination. 382 */ 383 dest.s_addr = ((struct sockaddr_in *) 384 (fwd_tag + 1))->sin_addr.s_addr; 385 m_tag_delete(m, fwd_tag); 386 m->m_flags &= ~M_IP_NEXTHOP; 387 } 388 389 /* 390 * Find route to destination. 391 */ 392 if (ip_findroute(&nh, dest, m) != 0) 393 return (NULL); /* icmp unreach already sent */ 394 395 /* 396 * Avoid second route lookup by caching destination. 397 */ 398 rtdest.s_addr = dest.s_addr; 399 400 /* 401 * Step 5: outgoing firewall packet processing 402 */ 403 if (!PFIL_HOOKED_OUT(V_inet_pfil_head)) 404 goto passout; 405 406 if (pfil_mbuf_out(V_inet_pfil_head, &m, nh->nh_ifp, 407 NULL) != PFIL_PASS) 408 goto drop; 409 410 M_ASSERTVALID(m); 411 M_ASSERTPKTHDR(m); 412 413 ip = mtod(m, struct ip *); 414 dest.s_addr = ip->ip_dst.s_addr; 415 416 /* 417 * Destination address changed? 418 */ 419 if (m->m_flags & M_IP_NEXTHOP) 420 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 421 else 422 fwd_tag = NULL; 423 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 424 /* 425 * Is it now for a local address on this host? 426 */ 427 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 428 forwardlocal: 429 /* 430 * Return packet for processing by ip_input(). 431 */ 432 m->m_flags |= M_FASTFWD_OURS; 433 return (m); 434 } 435 /* 436 * Redo route lookup with new destination address 437 */ 438 if (fwd_tag) { 439 dest.s_addr = ((struct sockaddr_in *) 440 (fwd_tag + 1))->sin_addr.s_addr; 441 m_tag_delete(m, fwd_tag); 442 m->m_flags &= ~M_IP_NEXTHOP; 443 } 444 if (dest.s_addr != rtdest.s_addr && 445 ip_findroute(&nh, dest, m) != 0) 446 return (NULL); /* icmp unreach already sent */ 447 } 448 449 passout: 450 /* 451 * Step 6: send off the packet 452 */ 453 ip_len = ntohs(ip->ip_len); 454 ip_off = ntohs(ip->ip_off); 455 456 bzero(&ro, sizeof(ro)); 457 dst = (struct sockaddr_in *)&ro.ro_dst; 458 dst->sin_family = AF_INET; 459 dst->sin_len = sizeof(*dst); 460 dst->sin_addr = dest; 461 if (nh->nh_flags & NHF_GATEWAY) { 462 gw = &nh->gw_sa; 463 ro.ro_flags |= RT_HAS_GW; 464 } else 465 gw = (const struct sockaddr *)dst; 466 467 /* Handle redirect case. */ 468 redest.s_addr = 0; 469 if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr && 470 nh->nh_ifp == m->m_pkthdr.rcvif) 471 mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest); 472 473 /* 474 * Check if packet fits MTU or if hardware will fragment for us 475 */ 476 if (ip_len <= nh->nh_mtu) { 477 /* 478 * Avoid confusing lower layers. 479 */ 480 m_clrprotoflags(m); 481 /* 482 * Send off the packet via outgoing interface 483 */ 484 IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL); 485 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); 486 } else { 487 /* 488 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 489 */ 490 if (ip_off & IP_DF) { 491 IPSTAT_INC(ips_cantfrag); 492 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 493 0, nh->nh_mtu); 494 goto consumed; 495 } else { 496 /* 497 * We have to fragment the packet 498 */ 499 m->m_pkthdr.csum_flags |= CSUM_IP; 500 if (ip_fragment(ip, &m, nh->nh_mtu, 501 nh->nh_ifp->if_hwassist) != 0) 502 goto drop; 503 KASSERT(m != NULL, ("null mbuf and no error")); 504 /* 505 * Send off the fragments via outgoing interface 506 */ 507 error = 0; 508 do { 509 m0 = m->m_nextpkt; 510 m->m_nextpkt = NULL; 511 /* 512 * Avoid confusing lower layers. 513 */ 514 m_clrprotoflags(m); 515 516 IP_PROBE(send, NULL, NULL, 517 mtod(m, struct ip *), nh->nh_ifp, 518 mtod(m, struct ip *), NULL); 519 error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, 520 gw, &ro); 521 if (error) 522 break; 523 } while ((m = m0) != NULL); 524 if (error) { 525 /* Reclaim remaining fragments */ 526 for (m = m0; m; m = m0) { 527 m0 = m->m_nextpkt; 528 m_freem(m); 529 } 530 } else 531 IPSTAT_INC(ips_fragmented); 532 } 533 } 534 535 if (error != 0) 536 IPSTAT_INC(ips_odropped); 537 else { 538 IPSTAT_INC(ips_forward); 539 IPSTAT_INC(ips_fastforward); 540 } 541 542 /* Send required redirect */ 543 if (mcopy != NULL) { 544 icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0); 545 mcopy = NULL; /* Was consumed by callee. */ 546 } 547 548 consumed: 549 if (mcopy != NULL) 550 m_freem(mcopy); 551 return NULL; 552 drop: 553 if (m) 554 m_freem(m); 555 return NULL; 556 } 557