ip_fastfwd.c revision 254889
128021Sjoerg/*- 228021Sjoerg * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG 328021Sjoerg * All rights reserved. 428021Sjoerg * 528021Sjoerg * Redistribution and use in source and binary forms, with or without 628021Sjoerg * modification, are permitted provided that the following conditions 728021Sjoerg * are met: 828021Sjoerg * 1. Redistributions of source code must retain the above copyright 928021Sjoerg * notice, this list of conditions and the following disclaimer. 1028021Sjoerg * 2. Redistributions in binary form must reproduce the above copyright 1128021Sjoerg * notice, this list of conditions and the following disclaimer in the 1228021Sjoerg * documentation and/or other materials provided with the distribution. 1328021Sjoerg * 3. The name of the author may not be used to endorse or promote 1428021Sjoerg * products derived from this software without specific prior written 1528021Sjoerg * permission. 1628021Sjoerg * 1728021Sjoerg * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 1828021Sjoerg * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 1928021Sjoerg * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 2028021Sjoerg * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 2128021Sjoerg * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 2228021Sjoerg * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 2328021Sjoerg * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 2428021Sjoerg * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 2528021Sjoerg * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 2650476Speter * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 2728021Sjoerg * SUCH DAMAGE. 28272758Spfg */ 2928021Sjoerg 3028021Sjoerg/* 3128021Sjoerg * ip_fastforward gets its speed from processing the forwarded packet to 3228021Sjoerg * completion (if_output on the other side) without any queues or netisr's. 3328021Sjoerg * The receiving interface DMAs the packet into memory, the upper half of 3459460Sphantom * driver calls ip_fastforward, we do our routing table lookup and directly 3559460Sphantom * send it off to the outgoing interface, which DMAs the packet to the 3628021Sjoerg * network card. The only part of the packet we touch with the CPU is the 3784306Sru * IP header (unless there are complex firewall rules touching other parts 3839113Sdt * of the packet, but that is up to you). We are essentially limited by bus 39101936Srobert * bandwidth and how fast the network card/driver can set up receives and 40103012Stjr * transmits. 41103012Stjr * 42103012Stjr * We handle basic errors, IP header errors, checksum errors, 43101936Srobert * destination unreachable, fragmentation and fragmentation needed and 44237573Sissyl0 * report them via ICMP to the sender. 45237573Sissyl0 * 46237573Sissyl0 * Else if something is not pure IPv4 unicast forwarding we fall back to 47237573Sissyl0 * the normal ip_input processing path. We should only be called from 4828021Sjoerg * interfaces connected to the outside world. 4928021Sjoerg * 5028021Sjoerg * Firewalling is fully supported including divert, ipfw fwd and ipfilter 5128021Sjoerg * ipnat and address rewrite. 5228021Sjoerg * 5328021Sjoerg * IPSEC is not supported if this host is a tunnel broker. IPSEC is 5428021Sjoerg * supported for connections to/from local host. 5528021Sjoerg * 5628021Sjoerg * We try to do the least expensive (in CPU ops) checks and operations 5748550Sobrien * first to catch junk with as little overhead as possible. 5828021Sjoerg * 5928021Sjoerg * We take full advantage of hardware support for IP checksum and 60237573Sissyl0 * fragmentation offloading. 61237573Sissyl0 * 62237573Sissyl0 * We don't do ICMP redirect in the fast forwarding path. I have had my own 63237573Sissyl0 * cases where two core routers with Zebra routing suite would send millions 64237573Sissyl0 * ICMP redirects to connected hosts if the destination router was not the 6528021Sjoerg * default gateway. In one case it was filling the routing table of a host 6628021Sjoerg * with approximately 300.000 cloned redirect entries until it ran out of 6728021Sjoerg * kernel memory. However the networking code proved very robust and it didn't 6828021Sjoerg * crash or fail in other ways. 6928021Sjoerg */ 7028021Sjoerg 7128021Sjoerg/* 7228021Sjoerg * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which 7328021Sjoerg * is being followed here. 7428021Sjoerg */ 7546042Swes 7646042Swes#include <sys/cdefs.h> 7746051Swes__FBSDID("$FreeBSD: head/sys/netinet/ip_fastfwd.c 254889 2013-08-25 21:54:41Z markj $"); 7879754Sdd 7970481Sru#include "opt_ipfw.h" 8046051Swes#include "opt_ipstealth.h" 8146051Swes#include "opt_kdtrace.h" 8246051Swes 83272758Spfg#include <sys/param.h> 84272758Spfg#include <sys/systm.h> 85272758Spfg#include <sys/kernel.h> 86272758Spfg#include <sys/malloc.h> 87272758Spfg#include <sys/mbuf.h> 88108013Stjr#include <sys/protosw.h> 89108013Stjr#include <sys/sdt.h> 90108013Stjr#include <sys/socket.h> 91108013Stjr#include <sys/sysctl.h> 92108013Stjr 93108013Stjr#include <net/pfil.h> 94108013Stjr#include <net/if.h> 95108013Stjr#include <net/if_types.h> 96108013Stjr#include <net/if_var.h> 97108013Stjr#include <net/if_dl.h> 98108013Stjr#include <net/route.h> 99108013Stjr#include <net/vnet.h> 100108083Sru 101108013Stjr#include <netinet/in.h> 102108013Stjr#include <netinet/in_kdtrace.h> 103108013Stjr#include <netinet/in_systm.h> 104108013Stjr#include <netinet/in_var.h> 105108013Stjr#include <netinet/ip.h> 106108013Stjr#include <netinet/ip_var.h> 107108013Stjr#include <netinet/ip_icmp.h> 108108013Stjr#include <netinet/ip_options.h> 109108013Stjr 110108013Stjr#include <machine/in_cksum.h> 11128021Sjoerg 11228021Sjoergstatic VNET_DEFINE(int, ipfastforward_active); 11328021Sjoerg#define V_ipfastforward_active VNET(ipfastforward_active) 11428021Sjoerg 11528021SjoergSYSCTL_VNET_INT(_net_inet_ip, OID_AUTO, fastforwarding, CTLFLAG_RW, 11628021Sjoerg &VNET_NAME(ipfastforward_active), 0, "Enable fast IP forwarding"); 11728021Sjoerg 11828021Sjoergstatic struct sockaddr_in * 11928021Sjoergip_findroute(struct route *ro, struct in_addr dest, struct mbuf *m) 12028021Sjoerg{ 121237573Sissyl0 struct sockaddr_in *dst; 122237573Sissyl0 struct rtentry *rt; 123237573Sissyl0 12428021Sjoerg /* 12528021Sjoerg * Find route to destination. 12628021Sjoerg */ 12728021Sjoerg bzero(ro, sizeof(*ro)); 128140505Sru dst = (struct sockaddr_in *)&ro->ro_dst; 129140505Sru dst->sin_family = AF_INET; 130140505Sru dst->sin_len = sizeof(*dst); 131140505Sru dst->sin_addr.s_addr = dest.s_addr; 132140505Sru in_rtalloc_ign(ro, 0, M_GETFIB(m)); 13328021Sjoerg 13428021Sjoerg /* 13528021Sjoerg * Route there and interface still up? 13628021Sjoerg */ 13728021Sjoerg rt = ro->ro_rt; 13828021Sjoerg if (rt && (rt->rt_flags & RTF_UP) && 13968575Sru (rt->rt_ifp->if_flags & IFF_UP) && 14048550Sobrien (rt->rt_ifp->if_drv_flags & IFF_DRV_RUNNING)) { 14154316Ssheldonh if (rt->rt_flags & RTF_GATEWAY) 14254316Ssheldonh dst = (struct sockaddr_in *)rt->rt_gateway; 14354316Ssheldonh } else { 14454316Ssheldonh IPSTAT_INC(ips_noroute); 14554316Ssheldonh IPSTAT_INC(ips_cantforward); 14654316Ssheldonh if (rt) 14754316Ssheldonh RTFREE(rt); 14854316Ssheldonh icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 14954316Ssheldonh return NULL; 15054316Ssheldonh } 15154316Ssheldonh return dst; 15254316Ssheldonh} 15354316Ssheldonh 15454316Ssheldonh/* 15554316Ssheldonh * Try to forward a packet based on the destination address. 15654316Ssheldonh * This is a fast path optimized for the plain forwarding case. 15754316Ssheldonh * If the packet is handled (and consumed) here then we return NULL; 15854316Ssheldonh * otherwise mbuf is returned and the packet should be delivered 15954316Ssheldonh * to ip_input for full processing. 16054316Ssheldonh */ 16154316Ssheldonhstruct mbuf * 16281251Sruip_fastforward(struct mbuf *m) 16354316Ssheldonh{ 16454316Ssheldonh struct ip *ip; 16581251Sru struct mbuf *m0 = NULL; 16654316Ssheldonh struct route ro; 16754316Ssheldonh struct sockaddr_in *dst = NULL; 16854316Ssheldonh struct ifnet *ifp; 16948550Sobrien struct in_addr odest, dest; 17048550Sobrien uint16_t sum, ip_len, ip_off; 17148550Sobrien int error = 0; 17248550Sobrien int hlen, mtu; 173131504Sru struct m_tag *fwd_tag = NULL; 174131504Sru 17548550Sobrien /* 17648550Sobrien * Are we active and forwarding packets? 177108653Stjr */ 178108653Stjr if (!V_ipfastforward_active || !V_ipforwarding) 179108653Stjr return m; 180108653Stjr 181108653Stjr M_ASSERTVALID(m); 182108653Stjr M_ASSERTPKTHDR(m); 183 184 bzero(&ro, sizeof(ro)); 185 186 /* 187 * Step 1: check for packet drop conditions (and sanity checks) 188 */ 189 190 /* 191 * Is entire packet big enough? 192 */ 193 if (m->m_pkthdr.len < sizeof(struct ip)) { 194 IPSTAT_INC(ips_tooshort); 195 goto drop; 196 } 197 198 /* 199 * Is first mbuf large enough for ip header and is header present? 200 */ 201 if (m->m_len < sizeof (struct ip) && 202 (m = m_pullup(m, sizeof (struct ip))) == NULL) { 203 IPSTAT_INC(ips_toosmall); 204 return NULL; /* mbuf already free'd */ 205 } 206 207 ip = mtod(m, struct ip *); 208 209 /* 210 * Is it IPv4? 211 */ 212 if (ip->ip_v != IPVERSION) { 213 IPSTAT_INC(ips_badvers); 214 goto drop; 215 } 216 217 /* 218 * Is IP header length correct and is it in first mbuf? 219 */ 220 hlen = ip->ip_hl << 2; 221 if (hlen < sizeof(struct ip)) { /* minimum header length */ 222 IPSTAT_INC(ips_badhlen); 223 goto drop; 224 } 225 if (hlen > m->m_len) { 226 if ((m = m_pullup(m, hlen)) == NULL) { 227 IPSTAT_INC(ips_badhlen); 228 return NULL; /* mbuf already free'd */ 229 } 230 ip = mtod(m, struct ip *); 231 } 232 233 /* 234 * Checksum correct? 235 */ 236 if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED) 237 sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID); 238 else { 239 if (hlen == sizeof(struct ip)) 240 sum = in_cksum_hdr(ip); 241 else 242 sum = in_cksum(m, hlen); 243 } 244 if (sum) { 245 IPSTAT_INC(ips_badsum); 246 goto drop; 247 } 248 249 /* 250 * Remember that we have checked the IP header and found it valid. 251 */ 252 m->m_pkthdr.csum_flags |= (CSUM_IP_CHECKED | CSUM_IP_VALID); 253 254 ip_len = ntohs(ip->ip_len); 255 256 /* 257 * Is IP length longer than packet we have got? 258 */ 259 if (m->m_pkthdr.len < ip_len) { 260 IPSTAT_INC(ips_tooshort); 261 goto drop; 262 } 263 264 /* 265 * Is packet longer than IP header tells us? If yes, truncate packet. 266 */ 267 if (m->m_pkthdr.len > ip_len) { 268 if (m->m_len == m->m_pkthdr.len) { 269 m->m_len = ip_len; 270 m->m_pkthdr.len = ip_len; 271 } else 272 m_adj(m, ip_len - m->m_pkthdr.len); 273 } 274 275 /* 276 * Is packet from or to 127/8? 277 */ 278 if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET || 279 (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) { 280 IPSTAT_INC(ips_badaddr); 281 goto drop; 282 } 283 284#ifdef ALTQ 285 /* 286 * Is packet dropped by traffic conditioner? 287 */ 288 if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0) 289 goto drop; 290#endif 291 292 /* 293 * Step 2: fallback conditions to normal ip_input path processing 294 */ 295 296 /* 297 * Only IP packets without options 298 */ 299 if (ip->ip_hl != (sizeof(struct ip) >> 2)) { 300 if (ip_doopts == 1) 301 return m; 302 else if (ip_doopts == 2) { 303 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 304 0, 0); 305 return NULL; /* mbuf already free'd */ 306 } 307 /* else ignore IP options and continue */ 308 } 309 310 /* 311 * Only unicast IP, not from loopback, no L2 or IP broadcast, 312 * no multicast, no INADDR_ANY 313 * 314 * XXX: Probably some of these checks could be direct drop 315 * conditions. However it is not clear whether there are some 316 * hacks or obscure behaviours which make it neccessary to 317 * let ip_input handle it. We play safe here and let ip_input 318 * deal with it until it is proven that we can directly drop it. 319 */ 320 if ((m->m_flags & (M_BCAST|M_MCAST)) || 321 (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || 322 ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST || 323 ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST || 324 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 325 IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 326 IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || 327 IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) || 328 ip->ip_src.s_addr == INADDR_ANY || 329 ip->ip_dst.s_addr == INADDR_ANY ) 330 return m; 331 332 /* 333 * Is it for a local address on this host? 334 */ 335 if (in_localip(ip->ip_dst)) 336 return m; 337 338 IPSTAT_INC(ips_total); 339 340 /* 341 * Step 3: incoming packet firewall processing 342 */ 343 344 odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; 345 346 /* 347 * Run through list of ipfilter hooks for input packets 348 */ 349 if (!PFIL_HOOKED(&V_inet_pfil_hook)) 350 goto passin; 351 352 if (pfil_run_hooks( 353 &V_inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, NULL) || 354 m == NULL) 355 goto drop; 356 357 M_ASSERTVALID(m); 358 M_ASSERTPKTHDR(m); 359 360 ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ 361 dest.s_addr = ip->ip_dst.s_addr; 362 363 /* 364 * Destination address changed? 365 */ 366 if (odest.s_addr != dest.s_addr) { 367 /* 368 * Is it now for a local address on this host? 369 */ 370 if (in_localip(dest)) 371 goto forwardlocal; 372 /* 373 * Go on with new destination address 374 */ 375 } 376 377 if (m->m_flags & M_FASTFWD_OURS) { 378 /* 379 * ipfw changed it for a local address on this host. 380 */ 381 goto forwardlocal; 382 } 383 384passin: 385 /* 386 * Step 4: decrement TTL and look up route 387 */ 388 389 /* 390 * Check TTL 391 */ 392#ifdef IPSTEALTH 393 if (!V_ipstealth) { 394#endif 395 if (ip->ip_ttl <= IPTTLDEC) { 396 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); 397 return NULL; /* mbuf already free'd */ 398 } 399 400 /* 401 * Decrement the TTL and incrementally change the IP header checksum. 402 * Don't bother doing this with hw checksum offloading, it's faster 403 * doing it right here. 404 */ 405 ip->ip_ttl -= IPTTLDEC; 406 if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) 407 ip->ip_sum -= ~htons(IPTTLDEC << 8); 408 else 409 ip->ip_sum += htons(IPTTLDEC << 8); 410#ifdef IPSTEALTH 411 } 412#endif 413 414 /* 415 * Find route to destination. 416 */ 417 if ((dst = ip_findroute(&ro, dest, m)) == NULL) 418 return NULL; /* icmp unreach already sent */ 419 ifp = ro.ro_rt->rt_ifp; 420 421 /* 422 * Immediately drop blackholed traffic, and directed broadcasts 423 * for either the all-ones or all-zero subnet addresses on 424 * locally attached networks. 425 */ 426 if ((ro.ro_rt->rt_flags & (RTF_BLACKHOLE|RTF_BROADCAST)) != 0) 427 goto drop; 428 429 /* 430 * Step 5: outgoing firewall packet processing 431 */ 432 433 /* 434 * Run through list of hooks for output packets. 435 */ 436 if (!PFIL_HOOKED(&V_inet_pfil_hook)) 437 goto passout; 438 439 if (pfil_run_hooks(&V_inet_pfil_hook, &m, ifp, PFIL_OUT, NULL) || m == NULL) { 440 goto drop; 441 } 442 443 M_ASSERTVALID(m); 444 M_ASSERTPKTHDR(m); 445 446 ip = mtod(m, struct ip *); 447 dest.s_addr = ip->ip_dst.s_addr; 448 449 /* 450 * Destination address changed? 451 */ 452 if (m->m_flags & M_IP_NEXTHOP) 453 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); 454 if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { 455 /* 456 * Is it now for a local address on this host? 457 */ 458 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { 459forwardlocal: 460 /* 461 * Return packet for processing by ip_input(). 462 */ 463 m->m_flags |= M_FASTFWD_OURS; 464 if (ro.ro_rt) 465 RTFREE(ro.ro_rt); 466 return m; 467 } 468 /* 469 * Redo route lookup with new destination address 470 */ 471 if (fwd_tag) { 472 dest.s_addr = ((struct sockaddr_in *) 473 (fwd_tag + 1))->sin_addr.s_addr; 474 m_tag_delete(m, fwd_tag); 475 m->m_flags &= ~M_IP_NEXTHOP; 476 } 477 RTFREE(ro.ro_rt); 478 if ((dst = ip_findroute(&ro, dest, m)) == NULL) 479 return NULL; /* icmp unreach already sent */ 480 ifp = ro.ro_rt->rt_ifp; 481 } 482 483passout: 484 /* 485 * Step 6: send off the packet 486 */ 487 ip_len = ntohs(ip->ip_len); 488 ip_off = ntohs(ip->ip_off); 489 490 /* 491 * Check if route is dampned (when ARP is unable to resolve) 492 */ 493 if ((ro.ro_rt->rt_flags & RTF_REJECT) && 494 (ro.ro_rt->rt_rmx.rmx_expire == 0 || 495 time_uptime < ro.ro_rt->rt_rmx.rmx_expire)) { 496 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 497 goto consumed; 498 } 499 500#ifndef ALTQ 501 /* 502 * Check if there is enough space in the interface queue 503 */ 504 if ((ifp->if_snd.ifq_len + ip_len / ifp->if_mtu + 1) >= 505 ifp->if_snd.ifq_maxlen) { 506 IPSTAT_INC(ips_odropped); 507 /* would send source quench here but that is depreciated */ 508 goto drop; 509 } 510#endif 511 512 /* 513 * Check if media link state of interface is not down 514 */ 515 if (ifp->if_link_state == LINK_STATE_DOWN) { 516 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); 517 goto consumed; 518 } 519 520 /* 521 * Check if packet fits MTU or if hardware will fragment for us 522 */ 523 if (ro.ro_rt->rt_rmx.rmx_mtu) 524 mtu = min(ro.ro_rt->rt_rmx.rmx_mtu, ifp->if_mtu); 525 else 526 mtu = ifp->if_mtu; 527 528 if (ip_len <= mtu || 529 (ifp->if_hwassist & CSUM_FRAGMENT && (ip_off & IP_DF) == 0)) { 530 /* 531 * Avoid confusing lower layers. 532 */ 533 m_clrprotoflags(m); 534 /* 535 * Send off the packet via outgoing interface 536 */ 537 IP_PROBE(send, NULL, NULL, ip, ifp, ip, NULL); 538 error = (*ifp->if_output)(ifp, m, 539 (struct sockaddr *)dst, &ro); 540 } else { 541 /* 542 * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery 543 */ 544 if (ip_off & IP_DF) { 545 IPSTAT_INC(ips_cantfrag); 546 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 547 0, mtu); 548 goto consumed; 549 } else { 550 /* 551 * We have to fragment the packet 552 */ 553 m->m_pkthdr.csum_flags |= CSUM_IP; 554 if (ip_fragment(ip, &m, mtu, ifp->if_hwassist)) 555 goto drop; 556 KASSERT(m != NULL, ("null mbuf and no error")); 557 /* 558 * Send off the fragments via outgoing interface 559 */ 560 error = 0; 561 do { 562 m0 = m->m_nextpkt; 563 m->m_nextpkt = NULL; 564 /* 565 * Avoid confusing lower layers. 566 */ 567 m_clrprotoflags(m); 568 569 IP_PROBE(send, NULL, NULL, ip, ifp, ip, NULL); 570 error = (*ifp->if_output)(ifp, m, 571 (struct sockaddr *)dst, &ro); 572 if (error) 573 break; 574 } while ((m = m0) != NULL); 575 if (error) { 576 /* Reclaim remaining fragments */ 577 for (m = m0; m; m = m0) { 578 m0 = m->m_nextpkt; 579 m_freem(m); 580 } 581 } else 582 IPSTAT_INC(ips_fragmented); 583 } 584 } 585 586 if (error != 0) 587 IPSTAT_INC(ips_odropped); 588 else { 589 ro.ro_rt->rt_rmx.rmx_pksent++; 590 IPSTAT_INC(ips_forward); 591 IPSTAT_INC(ips_fastforward); 592 } 593consumed: 594 RTFREE(ro.ro_rt); 595 return NULL; 596drop: 597 if (m) 598 m_freem(m); 599 if (ro.ro_rt) 600 RTFREE(ro.ro_rt); 601 return NULL; 602} 603