/*- * SPDX-License-Identifier: BSD-3-Clause * * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote * products derived from this software without specific prior written * permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ /* * ip_fastforward gets its speed from processing the forwarded packet to * completion (if_output on the other side) without any queues or netisr's. * The receiving interface DMAs the packet into memory, the upper half of * driver calls ip_fastforward, we do our routing table lookup and directly * send it off to the outgoing interface, which DMAs the packet to the * network card. The only part of the packet we touch with the CPU is the * IP header (unless there are complex firewall rules touching other parts * of the packet, but that is up to you). We are essentially limited by bus * bandwidth and how fast the network card/driver can set up receives and * transmits. * * We handle basic errors, IP header errors, checksum errors, * destination unreachable, fragmentation and fragmentation needed and * report them via ICMP to the sender. * * Else if something is not pure IPv4 unicast forwarding we fall back to * the normal ip_input processing path. We should only be called from * interfaces connected to the outside world. * * Firewalling is fully supported including divert, ipfw fwd and ipfilter * ipnat and address rewrite. * * IPSEC is not supported if this host is a tunnel broker. IPSEC is * supported for connections to/from local host. * * We try to do the least expensive (in CPU ops) checks and operations * first to catch junk with as little overhead as possible. * * We take full advantage of hardware support for IP checksum and * fragmentation offloading. */ /* * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which * is being followed here. */ #include "opt_ipstealth.h" #include "opt_sctp.h" #include <sys/param.h> #include <sys/systm.h> #include <sys/kernel.h> #include <sys/malloc.h> #include <sys/mbuf.h> #include <sys/protosw.h> #include <sys/sdt.h> #include <sys/socket.h> #include <sys/sysctl.h> #include <net/if.h> #include <net/if_types.h> #include <net/if_var.h> #include <net/if_dl.h> #include <net/if_private.h> #include <net/pfil.h> #include <net/route.h> #include <net/route/nhop.h> #include <net/vnet.h> #include <netinet/in.h> #include <netinet/in_fib.h> #include <netinet/in_kdtrace.h> #include <netinet/in_systm.h> #include <netinet/in_var.h> #include <netinet/ip.h> #include <netinet/ip_var.h> #include <netinet/ip_icmp.h> #include <netinet/ip_options.h> #include <machine/in_cksum.h> #if defined(SCTP) || defined(SCTP_SUPPORT) #include <netinet/sctp_crc32.h> #endif #define V_ipsendredirects VNET(ipsendredirects) static struct mbuf * ip_redir_alloc(struct mbuf *m, struct nhop_object *nh, u_short ip_len, struct in_addr *osrc, struct in_addr *newgw) { struct in_ifaddr *nh_ia; struct mbuf *mcopy; KASSERT(nh != NULL, ("%s: m %p nh is NULL\n", __func__, m)); /* * Only send a redirect if: * - Redirects are not disabled (must be checked by caller), * - We have not applied NAT (must be checked by caller as possible), * - Neither a MCAST or BCAST packet (must be checked by caller) * [RFC1009 Appendix A.2]. * - The packet does not do IP source routing or having any other * IP options (this case was handled already by ip_input() calling * ip_dooptions() [RFC792, p13], * - The packet is being forwarded out the same physical interface * that it was received from [RFC1812, 5.2.7.2]. */ /* * - The forwarding route was not created by a redirect * [RFC1812, 5.2.7.2], or * if it was to follow a default route (see below). * - The next-hop is reachable by us [RFC1009 Appendix A.2]. */ if ((nh->nh_flags & (NHF_DEFAULT | NHF_REDIRECT | NHF_BLACKHOLE | NHF_REJECT)) != 0) return (NULL); /* Get the new gateway. */ if ((nh->nh_flags & NHF_GATEWAY) == 0 || nh->gw_sa.sa_family != AF_INET) return (NULL); newgw->s_addr = nh->gw4_sa.sin_addr.s_addr; /* * - The resulting forwarding destination is not "This host on this * network" [RFC1122, Section 3.2.1.3] (default route check above). */ if (newgw->s_addr == 0) return (NULL); /* * - We know how to reach the sender and the source address is * directly connected to us [RFC792, p13]. * + The new gateway address and the source address are on the same * subnet [RFC1009 Appendix A.2, RFC1122 3.2.2.2, RFC1812, 5.2.7.2]. * NB: if you think multiple logical subnets on the same wire should * receive redirects read [RFC1812, APPENDIX C (14->15)]. */ nh_ia = (struct in_ifaddr *)nh->nh_ifa; if ((ntohl(osrc->s_addr) & nh_ia->ia_subnetmask) != nh_ia->ia_subnet) return (NULL); /* Prepare for sending the redirect. */ /* * Make a copy of as much as we need of the packet as the original * one will be forwarded but we need (a portion) for icmp_error(). */ mcopy = m_gethdr(M_NOWAIT, m->m_type); if (mcopy == NULL) return (NULL); if (m_dup_pkthdr(mcopy, m, M_NOWAIT) == 0) { /* * It's probably ok if the pkthdr dup fails (because * the deep copy of the tag chain failed), but for now * be conservative and just discard the copy since * code below may some day want the tags. */ m_free(mcopy); return (NULL); } mcopy->m_len = min(ip_len, M_TRAILINGSPACE(mcopy)); mcopy->m_pkthdr.len = mcopy->m_len; m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t)); return (mcopy); } static int ip_findroute(struct nhop_object **pnh, struct in_addr dest, struct mbuf *m) { struct nhop_object *nh; nh = fib4_lookup(M_GETFIB(m), dest, 0, NHR_NONE, m->m_pkthdr.flowid); if (nh == NULL) { IPSTAT_INC(ips_noroute); IPSTAT_INC(ips_cantforward); icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); return (EHOSTUNREACH); } /* * Drop blackholed traffic and directed broadcasts. */ if ((nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) { IPSTAT_INC(ips_cantforward); m_freem(m); return (EHOSTUNREACH); } if (nh->nh_flags & NHF_REJECT) { IPSTAT_INC(ips_cantforward); icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0); return (EHOSTUNREACH); } *pnh = nh; return (0); } /* * Try to forward a packet based on the destination address. * This is a fast path optimized for the plain forwarding case. * If the packet is handled (and consumed) here then we return NULL; * otherwise mbuf is returned and the packet should be delivered * to ip_input for full processing. */ struct mbuf * ip_tryforward(struct mbuf *m) { struct ip *ip; struct mbuf *m0 = NULL; struct nhop_object *nh = NULL; struct route ro; struct sockaddr_in *dst; const struct sockaddr *gw; struct in_addr dest, odest, rtdest, osrc; uint16_t ip_len, ip_off; int error = 0; struct m_tag *fwd_tag = NULL; struct mbuf *mcopy = NULL; struct in_addr redest; /* * Are we active and forwarding packets? */ M_ASSERTVALID(m); M_ASSERTPKTHDR(m); /* * Only IP packets without options */ ip = mtod(m, struct ip *); if (ip->ip_hl != (sizeof(struct ip) >> 2)) { if (V_ip_doopts == 1) return m; else if (V_ip_doopts == 2) { icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB, 0, 0); return NULL; /* mbuf already free'd */ } /* else ignore IP options and continue */ } /* * Only unicast IP, not from loopback, no L2 or IP broadcast, * no multicast, no INADDR_ANY * * XXX: Probably some of these checks could be direct drop * conditions. However it is not clear whether there are some * hacks or obscure behaviours which make it necessary to * let ip_input handle it. We play safe here and let ip_input * deal with it until it is proven that we can directly drop it. */ if ((m->m_flags & (M_BCAST|M_MCAST)) || (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) || in_broadcast(ip->ip_src) || in_broadcast(ip->ip_dst) || IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) || IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ) return m; /* * Is it for a local address on this host? */ if (in_localip(ip->ip_dst)) return m; IPSTAT_INC(ips_total); /* * Step 3: incoming packet firewall processing */ odest.s_addr = dest.s_addr = ip->ip_dst.s_addr; osrc.s_addr = ip->ip_src.s_addr; /* * Run through list of ipfilter hooks for input packets */ if (!PFIL_HOOKED_IN(V_inet_pfil_head)) goto passin; if (pfil_mbuf_in(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, NULL) != PFIL_PASS) goto drop; M_ASSERTVALID(m); M_ASSERTPKTHDR(m); ip = mtod(m, struct ip *); /* m may have changed by pfil hook */ dest.s_addr = ip->ip_dst.s_addr; /* * Destination address changed? */ if (odest.s_addr != dest.s_addr) { /* * Is it now for a local address on this host? */ if (in_localip(dest)) goto forwardlocal; /* * Go on with new destination address */ } if (m->m_flags & M_FASTFWD_OURS) { /* * ipfw changed it for a local address on this host. */ goto forwardlocal; } passin: /* * Step 4: decrement TTL and look up route */ /* * Check TTL */ #ifdef IPSTEALTH if (!V_ipstealth) { #endif if (ip->ip_ttl <= IPTTLDEC) { icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0); return NULL; /* mbuf already free'd */ } /* * Decrement the TTL. * If the IP header checksum field contains a valid value, incrementally * change this value. Don't use hw checksum offloading, which would * recompute the checksum. It's faster to just change it here * according to the decremented TTL. * If the checksum still needs to be computed, don't touch it. */ ip->ip_ttl -= IPTTLDEC; if (__predict_true((m->m_pkthdr.csum_flags & CSUM_IP) == 0)) { if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8)) ip->ip_sum -= ~htons(IPTTLDEC << 8); else ip->ip_sum += htons(IPTTLDEC << 8); } #ifdef IPSTEALTH } #endif /* * Next hop forced by pfil(9) hook? */ if ((m->m_flags & M_IP_NEXTHOP) && ((fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL)) { /* * Now we will find route to forced destination. */ dest.s_addr = ((struct sockaddr_in *) (fwd_tag + 1))->sin_addr.s_addr; m_tag_delete(m, fwd_tag); m->m_flags &= ~M_IP_NEXTHOP; } /* * Find route to destination. */ if (ip_findroute(&nh, dest, m) != 0) return (NULL); /* icmp unreach already sent */ /* * Avoid second route lookup by caching destination. */ rtdest.s_addr = dest.s_addr; /* * Step 5: outgoing firewall packet processing */ if (!PFIL_HOOKED_OUT(V_inet_pfil_head)) goto passout; if (pfil_mbuf_fwd(V_inet_pfil_head, &m, nh->nh_ifp, NULL) != PFIL_PASS) goto drop; M_ASSERTVALID(m); M_ASSERTPKTHDR(m); ip = mtod(m, struct ip *); dest.s_addr = ip->ip_dst.s_addr; /* * Destination address changed? */ if (m->m_flags & M_IP_NEXTHOP) fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); else fwd_tag = NULL; if (odest.s_addr != dest.s_addr || fwd_tag != NULL) { /* * Is it now for a local address on this host? */ if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) { forwardlocal: /* * Return packet for processing by ip_input(). */ m->m_flags |= M_FASTFWD_OURS; return (m); } /* * Redo route lookup with new destination address */ if (fwd_tag) { dest.s_addr = ((struct sockaddr_in *) (fwd_tag + 1))->sin_addr.s_addr; m_tag_delete(m, fwd_tag); m->m_flags &= ~M_IP_NEXTHOP; } if (dest.s_addr != rtdest.s_addr && ip_findroute(&nh, dest, m) != 0) return (NULL); /* icmp unreach already sent */ } passout: /* * Step 6: send off the packet */ ip_len = ntohs(ip->ip_len); ip_off = ntohs(ip->ip_off); bzero(&ro, sizeof(ro)); dst = (struct sockaddr_in *)&ro.ro_dst; dst->sin_family = AF_INET; dst->sin_len = sizeof(*dst); dst->sin_addr = dest; if (nh->nh_flags & NHF_GATEWAY) { gw = &nh->gw_sa; ro.ro_flags |= RT_HAS_GW; } else gw = (const struct sockaddr *)dst; /* * If the IP/SCTP/TCP/UDP header still needs a valid checksum and the * interface will not calculate it for us, do it here. * Note that if we defer checksum calculation, we might send an ICMP * message later that reflects this packet, which still has an * invalid checksum. */ if (__predict_false(m->m_pkthdr.csum_flags & CSUM_IP & ~nh->nh_ifp->if_hwassist)) { ip->ip_sum = 0; ip->ip_sum = in_cksum(m, (ip->ip_hl << 2)); m->m_pkthdr.csum_flags &= ~CSUM_IP; } if (__predict_false(m->m_pkthdr.csum_flags & CSUM_DELAY_DATA & ~nh->nh_ifp->if_hwassist)) { in_delayed_cksum(m); m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA; } #if defined(SCTP) || defined(SCTP_SUPPORT) if (__predict_false(m->m_pkthdr.csum_flags & CSUM_IP_SCTP & ~nh->nh_ifp->if_hwassist)) { sctp_delayed_cksum(m, (uint32_t)(ip->ip_hl << 2)); m->m_pkthdr.csum_flags &= ~CSUM_IP_SCTP; } #endif /* Handle redirect case. */ redest.s_addr = 0; if (V_ipsendredirects && osrc.s_addr == ip->ip_src.s_addr && nh->nh_ifp == m->m_pkthdr.rcvif) mcopy = ip_redir_alloc(m, nh, ip_len, &osrc, &redest); /* * Check if packet fits MTU or if hardware will fragment for us */ if (ip_len <= nh->nh_mtu) { /* * Avoid confusing lower layers. */ m_clrprotoflags(m); /* * Send off the packet via outgoing interface */ IP_PROBE(send, NULL, NULL, ip, nh->nh_ifp, ip, NULL); error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); } else { /* * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery */ if (ip_off & IP_DF) { IPSTAT_INC(ips_cantfrag); icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG, 0, nh->nh_mtu); goto consumed; } else { /* * We have to fragment the packet */ m->m_pkthdr.csum_flags |= CSUM_IP; if (ip_fragment(ip, &m, nh->nh_mtu, nh->nh_ifp->if_hwassist) != 0) goto drop; KASSERT(m != NULL, ("null mbuf and no error")); /* * Send off the fragments via outgoing interface */ error = 0; do { m0 = m->m_nextpkt; m->m_nextpkt = NULL; /* * Avoid confusing lower layers. */ m_clrprotoflags(m); IP_PROBE(send, NULL, NULL, mtod(m, struct ip *), nh->nh_ifp, mtod(m, struct ip *), NULL); error = (*nh->nh_ifp->if_output)(nh->nh_ifp, m, gw, &ro); if (error) break; } while ((m = m0) != NULL); if (error) { /* Reclaim remaining fragments */ for (m = m0; m; m = m0) { m0 = m->m_nextpkt; m_freem(m); } } else IPSTAT_INC(ips_fragmented); } } if (error != 0) IPSTAT_INC(ips_odropped); else { IPSTAT_INC(ips_forward); IPSTAT_INC(ips_fastforward); } /* Send required redirect */ if (mcopy != NULL) { icmp_error(mcopy, ICMP_REDIRECT, ICMP_REDIRECT_HOST, redest.s_addr, 0); mcopy = NULL; /* Was consumed by callee. */ } consumed: if (mcopy != NULL) m_freem(mcopy); return NULL; drop: if (m) m_freem(m); return NULL; }
