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 1.11 2000/12/13 18:31:48 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 <net/checksum.h>
  41 #include <linux/route.h>
  42 #include <net/route.h>
  43 #include <net/ip_fib.h>
  44
  45
  46 int
  47 ip_do_nat(struct sk_buff *skb)
  48 {
  49         struct rtable *rt = (struct rtable*)skb->dst;
  50         struct iphdr *iph = skb->nh.iph;
  51         u32 odaddr = iph->daddr;
  52         u32 osaddr = iph->saddr;
  53         u16     check;
  54
  55         IPCB(skb)->flags |= IPSKB_TRANSLATED;
  56
  57         /* Rewrite IP header */
  58         iph->daddr = rt->rt_dst_map;
  59         iph->saddr = rt->rt_src_map;
  60         iph->check = 0;
  61         iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
  62
  63         /* If it is the first fragment, rewrite protocol headers */
  64
  65         if (!(iph->frag_off & htons(IP_OFFSET))) {
  66                 u16     *cksum;
  67
  68                 switch(iph->protocol) {
  69                 case IPPROTO_TCP:
  70                         cksum  = (u16*)&((struct tcphdr*)(((char*)iph) + (iph->ihl<<2)))->check;
  71                         if ((u8*)(cksum+1) > skb->tail)
  72                                 goto truncated;
  73                         check = *cksum;
  74                         if (skb->ip_summed != CHECKSUM_HW)
  75                                 check = ~check;
  76                         check = csum_tcpudp_magic(iph->saddr, iph->daddr, 0, 0, check);
  77                         check = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0, ~check);
  78                         if (skb->ip_summed == CHECKSUM_HW)
  79                                 check = ~check;
  80                         *cksum = check;
  81                         break;
  82                 case IPPROTO_UDP:
  83                         cksum  = (u16*)&((struct udphdr*)(((char*)iph) + (iph->ihl<<2)))->check;
  84                         if ((u8*)(cksum+1) > skb->tail)
  85                                 goto truncated;
  86                         if ((check = *cksum) != 0) {
  87                                 check = csum_tcpudp_magic(iph->saddr, iph->daddr, 0, 0, ~check);
  88                                 check = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0, ~check);
  89                                 *cksum = check ? : 0xFFFF;
  90                         }
  91                         break;
  92                 case IPPROTO_ICMP:
  93                 {
  94                         struct icmphdr *icmph = (struct icmphdr*)((char*)iph + (iph->ihl<<2));
  95                         struct   iphdr *ciph;
  96                         u32 idaddr, isaddr;
  97                         int updated;
  98
  99                         if ((icmph->type != ICMP_DEST_UNREACH) &&
 100                             (icmph->type != ICMP_TIME_EXCEEDED) &&
 101                             (icmph->type != ICMP_PARAMETERPROB))
 102                                 break;
 103
 104                         ciph = (struct iphdr *) (icmph + 1);
 105
 106                         if ((u8*)(ciph+1) > skb->tail)
 107                                 goto truncated;
 108
 109                         isaddr = ciph->saddr;
 110                         idaddr = ciph->daddr;
 111                         updated = 0;
 112
 113                         if (rt->rt_flags&RTCF_DNAT && ciph->saddr == odaddr) {
 114                                 ciph->saddr = iph->daddr;
 115                                 updated = 1;
 116                         }
 117                         if (rt->rt_flags&RTCF_SNAT) {
 118                                 if (ciph->daddr != osaddr) {
 119                                         struct   fib_result res;
 120                                         struct   rt_key key;
 121                                         unsigned flags = 0;
 122
 123                                         key.src = ciph->daddr;
 124                                         key.dst = ciph->saddr;
 125                                         key.iif = skb->dev->ifindex;
 126                                         key.oif = 0;
 127 #ifdef CONFIG_IP_ROUTE_TOS
 128                                         key.tos = RT_TOS(ciph->tos);
 129 #endif
 130 #ifdef CONFIG_IP_ROUTE_FWMARK
 131                                         key.fwmark = 0;
 132 #endif
 133                                         /* Use fib_lookup() until we get our own
 134                                          * hash table of NATed hosts -- Rani
 135                                          */
 136                                         if (fib_lookup(&key, &res) == 0) {
 137                                                 if (res.r) {
 138                                                         ciph->daddr = fib_rules_policy(ciph->daddr, &res, &flags);
 139                                                         if (ciph->daddr != idaddr)
 140                                                                 updated = 1;
 141                                                 }
 142                                                 fib_res_put(&res);
 143                                         }
 144                                 } else {
 145                                         ciph->daddr = iph->saddr;
 146                                         updated = 1;
 147                                 }
 148                         }
 149                         if (updated) {
 150                                 cksum  = &icmph->checksum;
 151                                 /* Using tcpudp primitive. Why not? */
 152                                 check  = csum_tcpudp_magic(ciph->saddr, ciph->daddr, 0, 0, ~(*cksum));
 153                                 *cksum = csum_tcpudp_magic(~isaddr, ~idaddr, 0, 0, ~check);
 154                         }
 155                         break;
 156                 }
 157                 default:
 158                         break;
 159                 }
 160         }
 161         return NET_RX_SUCCESS;
 162
 163 truncated:
 164         /* should be return NET_RX_BAD; */
 165         return -EINVAL;
 166 }