ip_fastfwd.c

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    1 /*-
    2  * Copyright (c) 2003 Andre Oppermann, Internet Business Solutions AG
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. The name of the author may not be used to endorse or promote
   14  *    products derived from this software without specific prior written
   15  *    permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  */
   29 
   30 /*
   31  * ip_fastforward gets its speed from processing the forwarded packet to
   32  * completion (if_output on the other side) without any queues or netisr's.
   33  * The receiving interface DMAs the packet into memory, the upper half of
   34  * driver calls ip_fastforward, we do our routing table lookup and directly
   35  * send it off to the outgoing interface, which DMAs the packet to the
   36  * network card. The only part of the packet we touch with the CPU is the
   37  * IP header (unless there are complex firewall rules touching other parts
   38  * of the packet, but that is up to you). We are essentially limited by bus
   39  * bandwidth and how fast the network card/driver can set up receives and
   40  * transmits.
   41  *
   42  * We handle basic errors, IP header errors, checksum errors,
   43  * destination unreachable, fragmentation and fragmentation needed and
   44  * report them via ICMP to the sender.
   45  *
   46  * Else if something is not pure IPv4 unicast forwarding we fall back to
   47  * the normal ip_input processing path. We should only be called from
   48  * interfaces connected to the outside world.
   49  *
   50  * Firewalling is fully supported including divert, ipfw fwd and ipfilter
   51  * ipnat and address rewrite.
   52  *
   53  * IPSEC is not supported if this host is a tunnel broker. IPSEC is
   54  * supported for connections to/from local host.
   55  *
   56  * We try to do the least expensive (in CPU ops) checks and operations
   57  * first to catch junk with as little overhead as possible.
   58  * 
   59  * We take full advantage of hardware support for IP checksum and
   60  * fragmentation offloading.
   61  *
   62  * We don't do ICMP redirect in the fast forwarding path. I have had my own
   63  * cases where two core routers with Zebra routing suite would send millions
   64  * ICMP redirects to connected hosts if the destination router was not the
   65  * default gateway. In one case it was filling the routing table of a host
   66  * with approximately 300.000 cloned redirect entries until it ran out of
   67  * kernel memory. However the networking code proved very robust and it didn't
   68  * crash or fail in other ways.
   69  */
   70 
   71 /*
   72  * Many thanks to Matt Thomas of NetBSD for basic structure of ip_flow.c which
   73  * is being followed here.
   74  */
   75 
   76 #include <sys/cdefs.h>
   77 __FBSDID("$FreeBSD: releng/11.2/sys/netinet/ip_fastfwd.c 332513 2018-04-15 15:22:28Z kp $");
   78 
   79 #include "opt_ipstealth.h"
   80 
   81 #include <sys/param.h>
   82 #include <sys/systm.h>
   83 #include <sys/kernel.h>
   84 #include <sys/malloc.h>
   85 #include <sys/mbuf.h>
   86 #include <sys/protosw.h>
   87 #include <sys/sdt.h>
   88 #include <sys/socket.h>
   89 #include <sys/sysctl.h>
   90 
   91 #include <net/pfil.h>
   92 #include <net/if.h>
   93 #include <net/if_types.h>
   94 #include <net/if_var.h>
   95 #include <net/if_dl.h>
   96 #include <net/route.h>
   97 #include <net/vnet.h>
   98 
   99 #include <netinet/in.h>
  100 #include <netinet/in_fib.h>
  101 #include <netinet/in_kdtrace.h>
  102 #include <netinet/in_systm.h>
  103 #include <netinet/in_var.h>
  104 #include <netinet/ip.h>
  105 #include <netinet/ip_var.h>
  106 #include <netinet/ip_icmp.h>
  107 #include <netinet/ip_options.h>
  108 
  109 #include <machine/in_cksum.h>
  110 
  111 static int
  112 ip_findroute(struct nhop4_basic *pnh, struct in_addr dest, struct mbuf *m)
  113 {
  114 
  115         bzero(pnh, sizeof(*pnh));
  116         if (fib4_lookup_nh_basic(M_GETFIB(m), dest, 0, 0, pnh) != 0) {
  117                 IPSTAT_INC(ips_noroute);
  118                 IPSTAT_INC(ips_cantforward);
  119                 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
  120                 return (EHOSTUNREACH);
  121         }
  122         /*
  123          * Drop blackholed traffic and directed broadcasts.
  124          */
  125         if ((pnh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) != 0) {
  126                 IPSTAT_INC(ips_cantforward);
  127                 m_freem(m);
  128                 return (EHOSTUNREACH);
  129         }
  130 
  131         if (pnh->nh_flags & NHF_REJECT) {
  132                 IPSTAT_INC(ips_cantforward);
  133                 icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
  134                 return (EHOSTUNREACH);
  135         }
  136 
  137         return (0);
  138 }
  139 
  140 /*
  141  * Try to forward a packet based on the destination address.
  142  * This is a fast path optimized for the plain forwarding case.
  143  * If the packet is handled (and consumed) here then we return NULL;
  144  * otherwise mbuf is returned and the packet should be delivered
  145  * to ip_input for full processing.
  146  */
  147 struct mbuf *
  148 ip_tryforward(struct mbuf *m)
  149 {
  150         struct ip *ip;
  151         struct mbuf *m0 = NULL;
  152         struct nhop4_basic nh;
  153         struct sockaddr_in dst;
  154         struct in_addr odest, dest;
  155         uint16_t ip_len, ip_off;
  156         int error = 0;
  157         struct m_tag *fwd_tag = NULL;
  158 
  159         /*
  160          * Are we active and forwarding packets?
  161          */
  162 
  163         M_ASSERTVALID(m);
  164         M_ASSERTPKTHDR(m);
  165 
  166 #ifdef ALTQ
  167         /*
  168          * Is packet dropped by traffic conditioner?
  169          */
  170         if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
  171                 goto drop;
  172 #endif
  173 
  174         /*
  175          * Only IP packets without options
  176          */
  177         ip = mtod(m, struct ip *);
  178 
  179         if (ip->ip_hl != (sizeof(struct ip) >> 2)) {
  180                 if (V_ip_doopts == 1)
  181                         return m;
  182                 else if (V_ip_doopts == 2) {
  183                         icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_FILTER_PROHIB,
  184                                 0, 0);
  185                         return NULL;    /* mbuf already free'd */
  186                 }
  187                 /* else ignore IP options and continue */
  188         }
  189 
  190         /*
  191          * Only unicast IP, not from loopback, no L2 or IP broadcast,
  192          * no multicast, no INADDR_ANY
  193          *
  194          * XXX: Probably some of these checks could be direct drop
  195          * conditions.  However it is not clear whether there are some
  196          * hacks or obscure behaviours which make it necessary to
  197          * let ip_input handle it.  We play safe here and let ip_input
  198          * deal with it until it is proven that we can directly drop it.
  199          */
  200         if ((m->m_flags & (M_BCAST|M_MCAST)) ||
  201             (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
  202             ntohl(ip->ip_src.s_addr) == (u_long)INADDR_BROADCAST ||
  203             ntohl(ip->ip_dst.s_addr) == (u_long)INADDR_BROADCAST ||
  204             IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
  205             IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
  206             IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
  207             IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
  208             ip->ip_src.s_addr == INADDR_ANY ||
  209             ip->ip_dst.s_addr == INADDR_ANY )
  210                 return m;
  211 
  212         /*
  213          * Is it for a local address on this host?
  214          */
  215         if (in_localip(ip->ip_dst))
  216                 return m;
  217 
  218         IPSTAT_INC(ips_total);
  219 
  220         /*
  221          * Step 3: incoming packet firewall processing
  222          */
  223 
  224         odest.s_addr = dest.s_addr = ip->ip_dst.s_addr;
  225 
  226         /*
  227          * Run through list of ipfilter hooks for input packets
  228          */
  229         if (!PFIL_HOOKED(&V_inet_pfil_hook))
  230                 goto passin;
  231 
  232         if (pfil_run_hooks(
  233             &V_inet_pfil_hook, &m, m->m_pkthdr.rcvif, PFIL_IN, 0, NULL) ||
  234             m == NULL)
  235                 goto drop;
  236 
  237         M_ASSERTVALID(m);
  238         M_ASSERTPKTHDR(m);
  239 
  240         ip = mtod(m, struct ip *);      /* m may have changed by pfil hook */
  241         dest.s_addr = ip->ip_dst.s_addr;
  242 
  243         /*
  244          * Destination address changed?
  245          */
  246         if (odest.s_addr != dest.s_addr) {
  247                 /*
  248                  * Is it now for a local address on this host?
  249                  */
  250                 if (in_localip(dest))
  251                         goto forwardlocal;
  252                 /*
  253                  * Go on with new destination address
  254                  */
  255         }
  256 
  257         if (m->m_flags & M_FASTFWD_OURS) {
  258                 /*
  259                  * ipfw changed it for a local address on this host.
  260                  */
  261                 goto forwardlocal;
  262         }
  263 
  264 passin:
  265         /*
  266          * Step 4: decrement TTL and look up route
  267          */
  268 
  269         /*
  270          * Check TTL
  271          */
  272 #ifdef IPSTEALTH
  273         if (!V_ipstealth) {
  274 #endif
  275         if (ip->ip_ttl <= IPTTLDEC) {
  276                 icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, 0);
  277                 return NULL;    /* mbuf already free'd */
  278         }
  279 
  280         /*
  281          * Decrement the TTL and incrementally change the IP header checksum.
  282          * Don't bother doing this with hw checksum offloading, it's faster
  283          * doing it right here.
  284          */
  285         ip->ip_ttl -= IPTTLDEC;
  286         if (ip->ip_sum >= (u_int16_t) ~htons(IPTTLDEC << 8))
  287                 ip->ip_sum -= ~htons(IPTTLDEC << 8);
  288         else
  289                 ip->ip_sum += htons(IPTTLDEC << 8);
  290 #ifdef IPSTEALTH
  291         }
  292 #endif
  293 
  294         /*
  295          * Find route to destination.
  296          */
  297         if (ip_findroute(&nh, dest, m) != 0)
  298                 return (NULL);  /* icmp unreach already sent */
  299 
  300         /*
  301          * Step 5: outgoing firewall packet processing
  302          */
  303         if (!PFIL_HOOKED(&V_inet_pfil_hook))
  304                 goto passout;
  305 
  306         if (pfil_run_hooks(&V_inet_pfil_hook, &m, nh.nh_ifp, PFIL_OUT, PFIL_FWD,
  307             NULL) || m == NULL) {
  308                 goto drop;
  309         }
  310 
  311         M_ASSERTVALID(m);
  312         M_ASSERTPKTHDR(m);
  313 
  314         ip = mtod(m, struct ip *);
  315         dest.s_addr = ip->ip_dst.s_addr;
  316 
  317         /*
  318          * Destination address changed?
  319          */
  320         if (m->m_flags & M_IP_NEXTHOP)
  321                 fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
  322         if (odest.s_addr != dest.s_addr || fwd_tag != NULL) {
  323                 /*
  324                  * Is it now for a local address on this host?
  325                  */
  326                 if (m->m_flags & M_FASTFWD_OURS || in_localip(dest)) {
  327 forwardlocal:
  328                         /*
  329                          * Return packet for processing by ip_input().
  330                          */
  331                         m->m_flags |= M_FASTFWD_OURS;
  332                         return (m);
  333                 }
  334                 /*
  335                  * Redo route lookup with new destination address
  336                  */
  337                 if (fwd_tag) {
  338                         dest.s_addr = ((struct sockaddr_in *)
  339                                     (fwd_tag + 1))->sin_addr.s_addr;
  340                         m_tag_delete(m, fwd_tag);
  341                         m->m_flags &= ~M_IP_NEXTHOP;
  342                 }
  343                 if (ip_findroute(&nh, dest, m) != 0)
  344                         return (NULL);  /* icmp unreach already sent */
  345         }
  346 
  347 passout:
  348         /*
  349          * Step 6: send off the packet
  350          */
  351         ip_len = ntohs(ip->ip_len);
  352         ip_off = ntohs(ip->ip_off);
  353 
  354         bzero(&dst, sizeof(dst));
  355         dst.sin_family = AF_INET;
  356         dst.sin_len = sizeof(dst);
  357         dst.sin_addr = nh.nh_addr;
  358 
  359         /*
  360          * Check if packet fits MTU or if hardware will fragment for us
  361          */
  362         if (ip_len <= nh.nh_mtu) {
  363                 /*
  364                  * Avoid confusing lower layers.
  365                  */
  366                 m_clrprotoflags(m);
  367                 /*
  368                  * Send off the packet via outgoing interface
  369                  */
  370                 IP_PROBE(send, NULL, NULL, ip, nh.nh_ifp, ip, NULL);
  371                 error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m,
  372                     (struct sockaddr *)&dst, NULL);
  373         } else {
  374                 /*
  375                  * Handle EMSGSIZE with icmp reply needfrag for TCP MTU discovery
  376                  */
  377                 if (ip_off & IP_DF) {
  378                         IPSTAT_INC(ips_cantfrag);
  379                         icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
  380                                 0, nh.nh_mtu);
  381                         goto consumed;
  382                 } else {
  383                         /*
  384                          * We have to fragment the packet
  385                          */
  386                         m->m_pkthdr.csum_flags |= CSUM_IP;
  387                         if (ip_fragment(ip, &m, nh.nh_mtu,
  388                             nh.nh_ifp->if_hwassist) != 0)
  389                                 goto drop;
  390                         KASSERT(m != NULL, ("null mbuf and no error"));
  391                         /*
  392                          * Send off the fragments via outgoing interface
  393                          */
  394                         error = 0;
  395                         do {
  396                                 m0 = m->m_nextpkt;
  397                                 m->m_nextpkt = NULL;
  398                                 /*
  399                                  * Avoid confusing lower layers.
  400                                  */
  401                                 m_clrprotoflags(m);
  402 
  403                                 IP_PROBE(send, NULL, NULL,
  404                                     mtod(m, struct ip *), nh.nh_ifp,
  405                                     mtod(m, struct ip *), NULL);
  406                                 /* XXX: we can use cached route here */
  407                                 error = (*nh.nh_ifp->if_output)(nh.nh_ifp, m,
  408                                     (struct sockaddr *)&dst, NULL);
  409                                 if (error)
  410                                         break;
  411                         } while ((m = m0) != NULL);
  412                         if (error) {
  413                                 /* Reclaim remaining fragments */
  414                                 for (m = m0; m; m = m0) {
  415                                         m0 = m->m_nextpkt;
  416                                         m_freem(m);
  417                                 }
  418                         } else
  419                                 IPSTAT_INC(ips_fragmented);
  420                 }
  421         }
  422 
  423         if (error != 0)
  424                 IPSTAT_INC(ips_odropped);
  425         else {
  426                 IPSTAT_INC(ips_forward);
  427                 IPSTAT_INC(ips_fastforward);
  428         }
  429 consumed:
  430         return NULL;
  431 drop:
  432         if (m)
  433                 m_freem(m);
  434         return NULL;
  435 }
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FreeBSD/Linux Kernel Cross Reference sys/netinet/ip_fastfwd.c

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