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 }
134
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Linux/net/ipv4/ip_forward.c
