FreeBSD/Linux Kernel Cross Reference
sys/netinet/ip_fastfwd.c

     /*-
      * 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.
     *
     * We don't do ICMP redirect in the fast forwarding path. I have had my own
     * cases where two core routers with Zebra routing suite would send millions
     * ICMP redirects to connected hosts if the destination router was not the
     * default gateway. In one case it was filling the routing table of a host
     * with approximately 300.000 cloned redirect entries until it ran out of
     * kernel memory. However the networking code proved very robust and it didn't
     * crash or fail in other ways.
     */
    
    /*
     * 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/pfil.h>
    #include <net/if.h>
    #include <net/if_types.h>
    #include <net/if_var.h>
    #include <net/if_dl.h>
    #include <net/route.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)
   
   struct mbuf *
   ip_redir_alloc(struct mbuf *m, struct ip *ip, struct in_addr dest,
       in_addr_t *addr);
   
   
   struct mbuf *
   ip_redir_alloc(struct mbuf *m, struct ip *ip, struct in_addr dest,
       in_addr_t *addr)
   {
           struct sockaddr_in s;
           struct nhop4_extended nh;
           struct mbuf *mcopy = m_gethdr(M_NOWAIT, m->m_type);
   
           if (mcopy == NULL)
                   return (NULL);
   
           if (fib4_lookup_nh_ext(M_GETFIB(m), dest, 0, 0, &nh) != 0)
                   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(ntohs(ip->ip_len), M_TRAILINGSPACE(mcopy));
           mcopy->m_pkthdr.len = mcopy->m_len;
           m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
   
           s.sin_len = sizeof(struct sockaddr_in);
           s.sin_family= AF_INET;
           s.sin_addr = nh.nh_src;
   
           if (((nh.nh_flags & (NHF_REDIRECT|NHF_DEFAULT)) == 0)) {
                   struct in_ifaddr *nh_ia = (struct in_ifaddr *)ifaof_ifpforaddr((struct sockaddr *)&s, nh.nh_ifp);
                   u_long src = ntohl(ip->ip_src.s_addr);
                   
                   if (nh_ia != NULL && (src & nh_ia->ia_subnetmask) == nh_ia->ia_subnet) {
                           if (nh.nh_flags & NHF_GATEWAY)
                                   *addr = nh.nh_addr.s_addr;
                           else
                                   *addr = ip->ip_dst.s_addr;
                   }
           }
   
   
           return (mcopy);
   }
   
   
   static int
   ip_findroute(struct nhop4_basic *pnh, struct in_addr dest, struct mbuf *m)
   {
   
           bzero(pnh, sizeof(*pnh));
           if (fib4_lookup_nh_basic(M_GETFIB(m), dest, 0, 0, pnh) != 0) {
                   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 ((pnh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
                   IPSTAT_INC(ips_cantforward);
                   m_freem(m);
                   return (EHOSTUNREACH);
           }
   
           if (pnh->nh_flags & NHF_REJECT) {
                   IPSTAT_INC(ips_cantforward);
                   icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
                   return (EHOSTUNREACH);
           }
   
           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 nhop4_basic nh;
           struct sockaddr_in dst;
           struct in_addr dest, odest, rtdest;
           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;
   
           /*
            * Run through list of ipfilter hooks for input packets
            */
           if (!PFIL_HOOKED(&V_inet_pfil_hook))
                   goto passin;
   
           if (pfil_run_hooks(
               &V_inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, 0, NULL) ||
               m == NULL)
                   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(&V_inet_pfil_hook))
                   goto passout;
   
           if (pfil_run_hooks(&V_inet_pfil_hook, &m, nh.nh_ifp, PFIL_OUT, PFIL_FWD,
               NULL) || m == NULL) {
                   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(&dst, sizeof(dst));
           dst.sin_family = AF_INET;
           dst.sin_len = sizeof(dst);
           dst.sin_addr = nh.nh_addr;
   
           /*
            * Handle redirect case.
            */
           redest.s_addr = 0;
           if (V_ipsendredirects && (nh.nh_ifp == m->m_pkthdr.rcvif))
                   mcopy = ip_redir_alloc(m, ip, dest, &redest.s_addr);
   
           /*
            * 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,
                       (struct sockaddr *)&dst, NULL);
           } 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);
                                   /* XXX: we can use cached route here */
                                   error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m,
                                       (struct sockaddr *)&dst, NULL);
                                   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; /* Freed by caller */
           }
   
   consumed:
           if (mcopy != NULL)
                   m_freem(mcopy);
           return NULL;
   drop:
           if (m)
                   m_freem(m);
           return NULL;
   }

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