LXR linux/net/ipv4/ip

   1/*
   2 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3 *              operating system.  INET is implemented using the  BSD Socket
   4 *              interface as the means of communication with the user level.
   5 *
   6 *              The IP forwarding functionality.
   7 *
   8 * Authors:     see ip.c
   9 *
  10 * Fixes:
  11 *              Many            :       Split from ip.c , see ip_input.c for
  12 *                                      history.
  13 *              Dave Gregorich  :       NULL ip_rt_put fix for multicast
  14 *                                      routing.
  15 *              Jos Vos         :       Add call_out_firewall before sending,
  16 *                                      use output device for accounting.
  17 *              Jos Vos         :       Call forward firewall after routing
  18 *                                      (always use output device).
  19 *              Mike McLagan    :       Routing by source
  20 */
  21
  22#include <linux/types.h>
  23#include <linux/mm.h>
  24#include <linux/skbuff.h>
  25#include <linux/ip.h>
  26#include <linux/icmp.h>
  27#include <linux/netdevice.h>
  28#include <linux/slab.h>
  29#include <net/sock.h>
  30#include <net/ip.h>
  31#include <net/tcp.h>
  32#include <net/udp.h>
  33#include <net/icmp.h>
  34#include <linux/tcp.h>
  35#include <linux/udp.h>
  36#include <linux/netfilter_ipv4.h>
  37#include <net/checksum.h>
  38#include <linux/route.h>
  39#include <net/route.h>
  40#include <net/xfrm.h>
  41
  42static int ip_forward_finish(struct sk_buff *skb)
  43{
  44        struct ip_options * opt = &(IPCB(skb)->opt);
  45
  46        IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS);
  47
  48        if (unlikely(opt->optlen))
  49                ip_forward_options(skb);
  50
  51        return dst_output(skb);
  52}
  53
  54int ip_forward(struct sk_buff *skb)
  55{
  56        struct iphdr *iph;      /* Our header */
  57        struct rtable *rt;      /* Route we use */
  58        struct ip_options * opt = &(IPCB(skb)->opt);
  59
  60        if (skb_warn_if_lro(skb))
  61                goto drop;
  62
  63        if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
  64                goto drop;
  65
  66        if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
  67                return NET_RX_SUCCESS;
  68
  69        if (skb->pkt_type != PACKET_HOST)
  70                goto drop;
  71
  72        skb_forward_csum(skb);
  73
  74        /*
  75         *      According to the RFC, we must first decrease the TTL field. If
  76         *      that reaches zero, we must reply an ICMP control message telling
  77         *      that the packet's lifetime expired.
  78         */
  79        if (ip_hdr(skb)->ttl <= 1)
  80                goto too_many_hops;
  81
  82        if (!xfrm4_route_forward(skb))
  83                goto drop;
  84
  85        rt = skb_rtable(skb);
  86
  87        if (opt->is_strictroute && opt->nexthop != rt->rt_gateway)
  88                goto sr_failed;
  89
  90        if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) &&
  91                     (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) {
  92                IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
  93                icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
  94                          htonl(dst_mtu(&rt->dst)));
  95                goto drop;
  96        }
  97
  98        /* We are about to mangle packet. Copy it! */
  99        if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
 100                goto drop;
 101        iph = ip_hdr(skb);
 102
 103        /* Decrease ttl after skb cow done */
 104        ip_decrease_ttl(iph);
 105
 106        /*
 107         *      We now generate an ICMP HOST REDIRECT giving the route
 108         *      we calculated.
 109         */
 110        if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb))
 111                ip_rt_send_redirect(skb);
 112
 113        skb->priority = rt_tos2priority(iph->tos);
 114
 115        return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev,
 116                       rt->dst.dev, ip_forward_finish);
 117
 118sr_failed:
 119        /*
 120         *      Strict routing permits no gatewaying
 121         */
 122         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
 123         goto drop;
 124
 125too_many_hops:
 126        /* Tell the sender its packet died... */
 127        IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS);
 128        icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
 129drop:
 130        kfree_skb(skb);
 131        return NET_RX_DROP;
 132}
 133