LXR linux-bk/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 * Version:     $Id: ip_forward.c,v 1.48 2000/12/13 18:31:48 davem Exp $
   9 *
  10 * Authors:     see ip.c
  11 *
  12 * Fixes:
  13 *              Many            :       Split from ip.c , see ip_input.c for 
  14 *                                      history.
  15 *              Dave Gregorich  :       NULL ip_rt_put fix for multicast 
  16 *                                      routing.
  17 *              Jos Vos         :       Add call_out_firewall before sending,
  18 *                                      use output device for accounting.
  19 *              Jos Vos         :       Call forward firewall after routing
  20 *                                      (always use output device).
  21 *              Mike McLagan    :       Routing by source
  22 */
  23
  24#include <linux/config.h>
  25#include <linux/types.h>
  26#include <linux/mm.h>
  27#include <linux/sched.h>
  28#include <linux/skbuff.h>
  29#include <linux/ip.h>
  30#include <linux/icmp.h>
  31#include <linux/netdevice.h>
  32#include <net/sock.h>
  33#include <net/ip.h>
  34#include <net/tcp.h>
  35#include <net/udp.h>
  36#include <net/icmp.h>
  37#include <linux/tcp.h>
  38#include <linux/udp.h>
  39#include <linux/netfilter_ipv4.h>
  40#include <net/checksum.h>
  41#include <linux/route.h>
  42#include <net/route.h>
  43#include <net/xfrm.h>
  44
  45static inline int ip_forward_finish(struct sk_buff *skb)
  46{
  47        struct ip_options * opt = &(IPCB(skb)->opt);
  48
  49        IP_INC_STATS_BH(IPSTATS_MIB_OUTFORWDATAGRAMS);
  50
  51        if (unlikely(opt->optlen))
  52                ip_forward_options(skb);
  53
  54        return dst_output(skb);
  55}
  56
  57int ip_forward(struct sk_buff *skb)
  58{
  59        struct iphdr *iph;      /* Our header */
  60        struct rtable *rt;      /* Route we use */
  61        struct ip_options * opt = &(IPCB(skb)->opt);
  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->ip_summed = CHECKSUM_NONE;
  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
  80        iph = skb->nh.iph;
  81
  82        if (iph->ttl <= 1)
  83                goto too_many_hops;
  84
  85        if (!xfrm4_route_forward(skb))
  86                goto drop;
  87
  88        iph = skb->nh.iph;
  89        rt = (struct rtable*)skb->dst;
  90
  91        if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
  92                goto sr_failed;
  93
  94        /* We are about to mangle packet. Copy it! */
  95        if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len))
  96                goto drop;
  97        iph = skb->nh.iph;
  98
  99        /* Decrease ttl after skb cow done */
 100        ip_decrease_ttl(iph);
 101
 102        /*
 103         *      We now generate an ICMP HOST REDIRECT giving the route
 104         *      we calculated.
 105         */
 106        if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)
 107                ip_rt_send_redirect(skb);
 108
 109        skb->priority = rt_tos2priority(iph->tos);
 110
 111        return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev,
 112                       ip_forward_finish);
 113
 114sr_failed:
 115        /*
 116         *      Strict routing permits no gatewaying
 117         */
 118         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
 119         goto drop;
 120
 121too_many_hops:
 122        /* Tell the sender its packet died... */
 123        icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
 124drop:
 125        kfree_skb(skb);
 126        return NET_RX_DROP;
 127}
 128