net/ipv4/ip_forward.c

   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
  42 static 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         IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len);
  48
  49         if (unlikely(opt->optlen))
  50                 ip_forward_options(skb);
  51
  52         return dst_output(skb);
  53 }
  54
  55 int ip_forward(struct sk_buff *skb)
  56 {
  57         struct iphdr *iph;      /* Our header */
  58         struct rtable *rt;      /* Route we use */
  59         struct ip_options *opt  = &(IPCB(skb)->opt);
  60
  61         if (skb_warn_if_lro(skb))
  62                 goto drop;
  63
  64         if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
  65                 goto drop;
  66
  67         if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
  68                 return NET_RX_SUCCESS;
  69
  70         if (skb->pkt_type != PACKET_HOST)
  71                 goto drop;
  72
  73         skb_forward_csum(skb);
  74
  75         /*
  76          *      According to the RFC, we must first decrease the TTL field. If
  77          *      that reaches zero, we must reply an ICMP control message telling
  78          *      that the packet's lifetime expired.
  79          */
  80         if (ip_hdr(skb)->ttl <= 1)
  81                 goto too_many_hops;
  82
  83         if (!xfrm4_route_forward(skb))
  84                 goto drop;
  85
  86         rt = skb_rtable(skb);
  87
  88         if (opt->is_strictroute && rt->rt_uses_gateway)
  89                 goto sr_failed;
  90
  91         if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) &&
  92                      (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) {
  93                 IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
  94                 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
  95                           htonl(dst_mtu(&rt->dst)));
  96                 goto drop;
  97         }
  98
  99         /* We are about to mangle packet. Copy it! */
 100         if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
 101                 goto drop;
 102         iph = ip_hdr(skb);
 103
 104         /* Decrease ttl after skb cow done */
 105         ip_decrease_ttl(iph);
 106
 107         /*
 108          *      We now generate an ICMP HOST REDIRECT giving the route
 109          *      we calculated.
 110          */
 111         if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb))
 112                 ip_rt_send_redirect(skb);
 113
 114         skb->priority = rt_tos2priority(iph->tos);
 115
 116         return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev,
 117                        rt->dst.dev, ip_forward_finish);
 118
 119 sr_failed:
 120         /*
 121          *      Strict routing permits no gatewaying
 122          */
 123          icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
 124          goto drop;
 125
 126 too_many_hops:
 127         /* Tell the sender its packet died... */
 128         IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS);
 129         icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
 130 drop:
 131         kfree_skb(skb);
 132         return NET_RX_DROP;
 133 }