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

     /*-
      * 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.
     *
     * $FreeBSD$
     */
    
    /*
     * 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 router to dest was not the default
     * gateway. In one case it was filling the routing table of a host with close
     * 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 went ill
     * otherwise.
     */
    
    /*
     * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which
     * is being followed here.
     */
    
    #include "opt_ipfw.h"
    #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/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 <netinet/in.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 <machine/in_cksum.h>
   
   static int ipfastforward_active = 0;
   SYSCTL_INT(_net_inet_ip, OID_AUTO, fastforwarding, CTLFLAG_RW,
       &ipfastforward_active, 0, "Enable fast IP forwarding");
   
   static struct sockaddr_in *
   ip_findroute(struct route *ro, struct in_addr dest, struct mbuf *m)
   {
           struct sockaddr_in *dst;
           struct rtentry *rt;
   
           /*
            * Find route to destination.
            */
           bzero(ro, sizeof(*ro));
           dst = (struct sockaddr_in *)&ro->ro_dst;
           dst->sin_family = AF_INET;
           dst->sin_len = sizeof(*dst);
           dst->sin_addr.s_addr = dest.s_addr;
           rtalloc_ign(ro, RTF_CLONING);
   
           /*
            * Route there and interface still up?
            */
           rt = ro->ro_rt;
           if (rt && (rt->rt_flags & RTF_UP) &&
               (rt->rt_ifp->if_flags & IFF_UP) &&
               (rt->rt_ifp->if_flags & IFF_RUNNING)) {
                   if (rt->rt_flags & RTF_GATEWAY)
                           dst = (struct sockaddr_in *)rt->rt_gateway;
           } else {
                   ipstat.ips_noroute++;
                   ipstat.ips_cantforward++;
                   if (rt)
                           RTFREE(rt);
                   icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, NULL);
                   return NULL;
           }
           return dst;
   }
   
   /*
    * 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 1;
    * otherwise 0 is returned and the packet should be delivered
    * to ip_input for full processing.
    */
   int
   ip_fastforward(struct mbuf *m)
   {
           struct ip *ip;
           struct mbuf *m0 = NULL;
           struct route ro;
           struct sockaddr_in *dst = NULL;
           struct ifnet *ifp;
           struct in_addr odest, dest;
           u_short sum, ip_len;
           int error = 0;
           int hlen, mtu;
   #ifdef IPFIREWALL_FORWARD
           struct m_tag *fwd_tag;
   #endif
   
           /*
            * Are we active and forwarding packets?
            */
           if (!ipfastforward_active || !ipforwarding)
                   return 0;
   
           M_ASSERTVALID(m);
           M_ASSERTPKTHDR(m);
   
           ro.ro_rt = NULL;
   
           /*
            * Step 1: check for packet drop conditions (and sanity checks)
            */
   
           /*
            * Is entire packet big enough?
            */
           if (m->m_pkthdr.len < sizeof(struct ip)) {
                   ipstat.ips_tooshort++;
                   goto drop;
           }
   
           /*
            * Is first mbuf large enough for ip header and is header present?
            */
           if (m->m_len < sizeof (struct ip) &&
              (m = m_pullup(m, sizeof (struct ip))) == NULL) {
                   ipstat.ips_toosmall++;
                   return 1;       /* mbuf already free'd */
           }
   
           ip = mtod(m, struct ip *);
   
           /*
            * Is it IPv4?
            */
           if (ip->ip_v != IPVERSION) {
                   ipstat.ips_badvers++;
                   goto drop;
           }
   
           /*
            * Is IP header length correct and is it in first mbuf?
            */
           hlen = ip->ip_hl << 2;
           if (hlen < sizeof(struct ip)) { /* minimum header length */
                   ipstat.ips_badlen++;
                   goto drop;
           }
           if (hlen > m->m_len) {
                   if ((m = m_pullup(m, hlen)) == 0) {
                           ipstat.ips_badhlen++;
                           return 1;       /* mbuf already free'd */
                   }
                   ip = mtod(m, struct ip *);
           }
   
           /*
            * Checksum correct?
            */
           if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED)
                   sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID);
           else {
                   if (hlen == sizeof(struct ip))
                           sum = in_cksum_hdr(ip);
                   else
                           sum = in_cksum(m, hlen);
           }
           if (sum) {
                   ipstat.ips_badsum++;
                   goto drop;
           }
           m->m_pkthdr.csum_flags |= (CSUM_IP_CHECKED | CSUM_IP_VALID);
   
           ip_len = ntohs(ip->ip_len);
   
           /*
            * Is IP length longer than packet we have got?
            */
           if (m->m_pkthdr.len < ip_len) {
                   ipstat.ips_tooshort++;
                   goto drop;
           }
   
           /*
            * Is packet longer than IP header tells us? If yes, truncate packet.
            */
           if (m->m_pkthdr.len > ip_len) {
                   if (m->m_len == m->m_pkthdr.len) {
                           m->m_len = ip_len;
                           m->m_pkthdr.len = ip_len;
                   } else
                           m_adj(m, ip_len - m->m_pkthdr.len);
           }
   
           /*
            * Is packet from or to 127/8?
            */
           if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
               (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
                   ipstat.ips_badaddr++;
                   goto drop;
           }
   
   #ifdef ALTQ
           /*
            * Is packet dropped by traffic conditioner?
            */
           if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
                   return 1;
   #endif
   
           /*
            * Step 2: fallback conditions to normal ip_input path processing
            */
   
           /*
            * Only IP packets without options
            */
           if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
                   if (ip_doopts == 1)
                           return 0;
                   else if (ip_doopts == 2) {
                           icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
                                   0, NULL);
                           return 1;
                   }
                   /* 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 neccessary 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)) ||
               ip->ip_src.s_addr == INADDR_ANY ||
               ip->ip_dst.s_addr == INADDR_ANY )
                   return 0;
   
           /*
            * Is it for a local address on this host?
            */
           if (in_localip(ip->ip_dst))
                   return 0;
   
           ipstat.ips_total++;
   
           /*
            * Step 3: incoming packet firewall processing
            */
   
           /*
            * Convert to host representation
            */
           ip->ip_len = ntohs(ip->ip_len);
           ip->ip_off = ntohs(ip->ip_off);
   
           odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
   
           /*
            * Run through list of ipfilter hooks for input packets
            */
           if (inet_pfil_hook.ph_busy_count == -1)
                   goto passin;
   
           if (pfil_run_hooks(&inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, NULL) ||
               m == NULL)
                   return 1;
   
           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
                    */
           }
   #ifdef IPFIREWALL_FORWARD
           if (m->m_flags & M_FASTFWD_OURS) {
                   /*
                    * ipfw changed it for a local address on this host.
                    */
                   goto forwardlocal;
           }
   #endif /* IPFIREWALL_FORWARD */
   
   passin:
           /*
            * Step 4: decrement TTL and look up route
            */
   
           /*
            * Check TTL
            */
   #ifdef IPSTEALTH
           if (!ipstealth) {
   #endif
           if (ip->ip_ttl <= IPTTLDEC) {
                   icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, NULL);
                   return 1;
           }
   
           /*
            * Decrement the TTL and incrementally change the checksum.
            * Don't bother doing this with hw checksum offloading.
            */
           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
   
           /*
            * Find route to destination.
            */
           if ((dst = ip_findroute(&ro, dest, m)) == NULL)
                   return 1;       /* icmp unreach already sent */
           ifp = ro.ro_rt->rt_ifp;
   
           /*
            * Immediately drop blackholed traffic.
            */
           if (ro.ro_rt->rt_flags & RTF_BLACKHOLE)
                   goto drop;
   
           /*
            * Step 5: outgoing firewall packet processing
            */
   
           /*
            * Run through list of hooks for output packets.
            */
           if (inet_pfil_hook.ph_busy_count == -1)
                   goto passout;
   
           if (pfil_run_hooks(&inet_pfil_hook, &m, ifp, PFIL_OUT, NULL) || m == NULL) {
                   goto consumed;
           }
   
           M_ASSERTVALID(m);
           M_ASSERTPKTHDR(m);
   
           ip = mtod(m, struct ip *);
           dest.s_addr = ip->ip_dst.s_addr;
   
           /*
            * Destination address changed?
            */
   #ifndef IPFIREWALL_FORWARD
           if (odest.s_addr != dest.s_addr) {
   #else
           fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
           if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
   #endif /* IPFIREWALL_FORWARD */
                   /*
                    * Is it now for a local address on this host?
                    */
   #ifndef IPFIREWALL_FORWARD
                   if (in_localip(dest)) {
   #else
                   if (in_localip(dest) || m->m_flags & M_FASTFWD_OURS) {
   #endif /* IPFIREWALL_FORWARD */
   forwardlocal:
                           /*
                            * Return packet for processing by ip_input().
                            * Keep host byte order as expected at ip_input's
                            * "ours"-label.
                            */
                           m->m_flags |= M_FASTFWD_OURS;
                           if (ro.ro_rt)
                                   RTFREE(ro.ro_rt);
                           return 0;
                   }
                   /*
                    * Redo route lookup with new destination address
                    */
   #ifdef IPFIREWALL_FORWARD
                   if (fwd_tag) {
                           if (!in_localip(ip->ip_src) && !in_localaddr(ip->ip_dst))
                                   dest.s_addr = ((struct sockaddr_in *)(fwd_tag+1))->sin_addr.s_addr;
                           m_tag_delete(m, fwd_tag);
                   }
   #endif /* IPFIREWALL_FORWARD */
                   RTFREE(ro.ro_rt);
                   if ((dst = ip_findroute(&ro, dest, m)) == NULL)
                           return 1;       /* icmp unreach already sent */
                   ifp = ro.ro_rt->rt_ifp;
           }
   
   passout:
           /*
            * Step 6: send off the packet
            */
   
           /*
            * Check if route is dampned (when ARP is unable to resolve)
            */
           if ((ro.ro_rt->rt_flags & RTF_REJECT) &&
               ro.ro_rt->rt_rmx.rmx_expire >= time_second) {
                   icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, NULL);
                   goto consumed;
           }
   
   #ifndef ALTQ
           /*
            * Check if there is enough space in the interface queue
            */
           if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >=
               ifp->if_snd.ifq_maxlen) {
                   ipstat.ips_odropped++;
                   /* would send source quench here but that is depreciated */
                   goto drop;
           }
   #endif
   
           /*
            * Check if media link state of interface is not down
            */
           if (ifp->if_link_state == LINK_STATE_DOWN) {
                   icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, NULL);
                   goto consumed;
           }
   
           /*
            * Check if packet fits MTU or if hardware will fragement for us
            */
           if (ro.ro_rt->rt_rmx.rmx_mtu)
                   mtu = min(ro.ro_rt->rt_rmx.rmx_mtu, ifp->if_mtu);
           else
                   mtu = ifp->if_mtu;
   
           if (ip->ip_len <= mtu ||
               (ifp->if_hwassist & CSUM_FRAGMENT && (ip->ip_off & IP_DF) == 0)) {
                   /*
                    * Restore packet header fields to original values
                    */
                   ip->ip_len = htons(ip->ip_len);
                   ip->ip_off = htons(ip->ip_off);
                   /*
                    * Send off the packet via outgoing interface
                    */
                   error = (*ifp->if_output)(ifp, m,
                                   (struct sockaddr *)dst, ro.ro_rt);
           } else {
                   /*
                    * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
                    */
                   if (ip->ip_off & IP_DF) {
                           ipstat.ips_cantfrag++;
                           icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
                                   0, ifp);
                           goto consumed;
                   } else {
                           /*
                            * We have to fragement the packet
                            */
                           m->m_pkthdr.csum_flags |= CSUM_IP;
                           /*
                            * ip_fragment expects ip_len and ip_off in host byte
                            * order but returns all packets in network byte order
                            */
                           if (ip_fragment(ip, &m, mtu, ifp->if_hwassist,
                                           (~ifp->if_hwassist & CSUM_DELAY_IP))) {
                                   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;
   
                                   error = (*ifp->if_output)(ifp, m,
                                           (struct sockaddr *)dst, ro.ro_rt);
                                   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.ips_fragmented++;
                   }
           }
   
           if (error != 0)
                   ipstat.ips_odropped++;
           else {
                   ro.ro_rt->rt_rmx.rmx_pksent++;
                   ipstat.ips_forward++;
                   ipstat.ips_fastforward++;
           }
   consumed:
           RTFREE(ro.ro_rt);
           return 1;
   drop:
           if (m)
                   m_freem(m);
           if (ro.ro_rt)
                   RTFREE(ro.ro_rt);
           return 1;
   }

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