net/ipv4/ip_nat_dumb.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  *              Dumb Network Address Translation.
   7  *
   8  * Version:     $Id: ip_nat_dumb.c,v 1.7 1998/10/06 04:49:09 davem Exp $
   9  *
  10  * Authors:     Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
  11  *
  12  *              This program is free software; you can redistribute it and/or
  13  *              modify it under the terms of the GNU General Public License
  14  *              as published by the Free Software Foundation; either version
  15  *              2 of the License, or (at your option) any later version.
  16  *
  17  * Fixes:
  18  *              Rani Assaf      :       A zero checksum is a special case
  19  *                                      only in UDP
  20  *              Rani Assaf      :       Added ICMP messages rewriting
  21  *              Rani Assaf      :       Repaired wrong changes, made by ANK.
  22  *
  23  *
  24  * NOTE:        It is just working model of real NAT.
  25  */
  26
  27 #include <linux/config.h>
  28 #include <linux/types.h>
  29 #include <linux/mm.h>
  30 #include <linux/sched.h>
  31 #include <linux/skbuff.h>
  32 #include <linux/ip.h>
  33 #include <linux/icmp.h>
  34 #include <linux/netdevice.h>
  35 #include <net/sock.h>
  36 #include <net/ip.h>
  37 #include <net/icmp.h>
  38 #include <linux/tcp.h>
  39 #include <linux/udp.h>
  40 #include <linux/firewall.h>
  41 #include <linux/ip_fw.h>
  42 #include <net/checksum.h>
  43 #include <linux/route.h>
  44 #include <net/route.h>
  45 #include <net/ip_fib.h>
  46
  47
  48 int
  49 ip_do_nat(struct sk_buff *skb)
  50 {
  51         struct rtable *rt = (struct rtable*)skb->dst;
  52         struct iphdr *iph = skb->nh.iph;
  53         u32 odaddr = iph->daddr;
  54         u32 osaddr = iph->saddr;
  55         u16     check;
  56
  57         IPCB(skb)->flags |= IPSKB_TRANSLATED;
  58
  59         /* Rewrite IP header */
  60         iph->daddr = rt->rt_dst_map;
  61         iph->saddr = rt->rt_src_map;
  62         iph->check = 0;
  63         iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
  64
  65         /* If it is the first fragment, rewrite protocol headers */
  66
  67         if (!(iph->frag_off & htons(IP_OFFSET))) {
  68                 u16     *cksum;
  69
  70                 switch(iph->protocol) {
  71                 case IPPROTO_TCP:
  72                         cksum  = (u16*)&((struct tcphdr*)(((char*)iph) + (iph->ihl<<2)))->check;
  73                         if ((u8*)(cksum+1) > skb->tail)
  74                                 goto truncated;
  75                         check  = csum_tcpudp_magic(iph->saddr, iph->daddr, 0, 0, ~(*cksum));
  76                         *cksum = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0, ~check);
  77                         break;
  78                 case IPPROTO_UDP:
  79                         cksum  = (u16*)&((struct udphdr*)(((char*)iph) + (iph->ihl<<2)))->check;
  80                         if ((u8*)(cksum+1) > skb->tail)
  81                                 goto truncated;
  82                         if ((check = *cksum) != 0) {
  83                                 check = csum_tcpudp_magic(iph->saddr, iph->daddr, 0, 0, ~check);
  84                                 check = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0, ~check);
  85                                 *cksum = check ? : 0xFFFF;
  86                         }
  87                         break;
  88                 case IPPROTO_ICMP:
  89                 {
  90                         struct icmphdr *icmph = (struct icmphdr*)((char*)iph + (iph->ihl<<2));
  91                         struct   iphdr *ciph;
  92
  93                         if ((icmph->type != ICMP_DEST_UNREACH) &&
  94                             (icmph->type != ICMP_TIME_EXCEEDED) &&
  95                             (icmph->type != ICMP_PARAMETERPROB))
  96                                 break;
  97
  98                         ciph = (struct iphdr *) (icmph + 1);
  99
 100                         if ((u8*)(ciph+1) > skb->tail)
 101                                 goto truncated;
 102
 103                         if (rt->rt_flags&RTCF_DNAT && ciph->saddr == odaddr)
 104                                 ciph->saddr = iph->daddr;
 105                         if (rt->rt_flags&RTCF_SNAT) {
 106                                 if (ciph->daddr != osaddr) {
 107                                         struct   fib_result res;
 108                                         struct   rt_key key;
 109                                         unsigned flags = 0;
 110
 111                                         key.src = ciph->daddr;
 112                                         key.dst = ciph->saddr;
 113                                         key.iif = skb->dev->ifindex;
 114                                         key.oif = 0;
 115 #ifdef CONFIG_IP_ROUTE_TOS
 116                                         key.tos = RT_TOS(ciph->tos);
 117 #endif
 118                                         /* Use fib_lookup() until we get our own
 119                                          * hash table of NATed hosts -- Rani
 120                                          */
 121                                         if (fib_lookup(&key, &res) != 0)
 122                                                 return 0;
 123                                         if (res.r)
 124                                                 ciph->daddr = fib_rules_policy(ciph->daddr, &res, &flags);
 125                                 }
 126                                 else
 127                                         ciph->daddr = iph->saddr;
 128                         }
 129                         break;
 130                 }
 131                 default:
 132                         break;
 133                 }
 134         }
 135         return 0;
 136
 137 truncated:
 138         return -EINVAL;
 139 }