ip_fastfwd.c

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/*-
 * 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 <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include "opt_ipstealth.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/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>
 
#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);
 
#ifdef ALTQ
        /*
         * Is packet dropped by traffic conditioner?
         */
        if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
                goto drop;
#endif
 
        /*
         * 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) ||
            ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
            ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
            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)) ||
            ip->ip_src.s_addr == INADDR_ANY ||
            ip->ip_dst.s_addr == INADDR_ANY )
                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_run_hooks(V_inet_pfil_head, &m, m->m_pkthdr.rcvif, PFIL_IN,
            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 and incrementally change the IP header checksum.
         * Don't bother doing this with hw checksum offloading, it's faster
         * doing it right here.
         */
        ip->ip_ttl -= IPTTLDEC;
        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_run_hooks(V_inet_pfil_head, &m, nh->nh_ifp,
            PFIL_OUT | PFIL_FWD, 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;
 
        /* 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;
}