Broadcasting the Linux kernel, one source file at a time!

net/ipv4/ip_forward.c

net/ipv4/ip_forward.c (132 lines, 3379 bytes)
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/*
 * INET      An implementation of the TCP/IP protocol suite for the LINUX
 *       operating system.  INET is implemented using the  BSD Socket
 *       interface as the means of communication with the user level.
 *
 *       The IP forwarding functionality.
 *
 * Authors:  see ip.c
 *
 * Fixes:
 *       Many        :   Split from ip.c , see ip_input.c for
 *                   history.
 *       Dave Gregorich  :   NULL ip_rt_put fix for multicast
 *                   routing.
 *       Jos Vos     :   Add call_out_firewall before sending,
 *                   use output device for accounting.
 *       Jos Vos     :   Call forward firewall after routing
 *                   (always use output device).
 *       Mike McLagan    :   Routing by source
 */

#include <linux/types.h>
#include <linux/mm.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/icmp.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/netfilter_ipv4.h>
#include <net/checksum.h>
#include <linux/route.h>
#include <net/route.h>
#include <net/xfrm.h>

static int ip_forward_finish(struct sk_buff *skb)
{
  struct ip_options * opt = &(IPCB(skb)->opt);

  IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS);

  if (unlikely(opt->optlen))
      ip_forward_options(skb);

  return dst_output(skb);
}

int ip_forward(struct sk_buff *skb)
{
  struct iphdr *iph;   /* Our header */
  struct rtable *rt;   /* Route we use */
  struct ip_options * opt = &(IPCB(skb)->opt);

  if (skb_warn_if_lro(skb))
      goto drop;

  if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
      goto drop;

  if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
      return NET_RX_SUCCESS;

  if (skb->pkt_type != PACKET_HOST)
      goto drop;

  skb_forward_csum(skb);

  /*
  *  According to the RFC, we must first decrease the TTL field. If
  *  that reaches zero, we must reply an ICMP control message telling
  *  that the packet's lifetime expired.
  */
  if (ip_hdr(skb)->ttl <= 1)
      goto too_many_hops;

  if (!xfrm4_route_forward(skb))
      goto drop;

  rt = skb_rtable(skb);

  if (opt->is_strictroute && ip_hdr(skb)->daddr != rt->rt_gateway)
      goto sr_failed;

  if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) &&
           (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) {
      IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
      icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
            htonl(dst_mtu(&rt->dst)));
      goto drop;
  }

  /* We are about to mangle packet. Copy it! */
  if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
      goto drop;
  iph = ip_hdr(skb);

  /* Decrease ttl after skb cow done */
  ip_decrease_ttl(iph);

  /*
  *  We now generate an ICMP HOST REDIRECT giving the route
  *  we calculated.
  */
  if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb))
      ip_rt_send_redirect(skb);

  skb->priority = rt_tos2priority(iph->tos);

  return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev,
             rt->dst.dev, ip_forward_finish);

sr_failed:
  /*
  *  Strict routing permits no gatewaying
  */
   icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
   goto drop;

too_many_hops:
  /* Tell the sender its packet died... */
  IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS);
  icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
drop:
  kfree_skb(skb);
  return NET_RX_DROP;
}