net/ipv4/netfilter/ipt_NETMAP.c

   1 /* NETMAP - static NAT mapping of IP network addresses (1:1).
   2  * The mapping can be applied to source (POSTROUTING),
   3  * destination (PREROUTING), or both (with separate rules).
   4  */
   5
   6 /* (C) 2000-2001 Svenning Soerensen <svenning@post5.tele.dk>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/ip.h>
  14 #include <linux/module.h>
  15 #include <linux/netdevice.h>
  16 #include <linux/netfilter.h>
  17 #include <linux/netfilter_ipv4.h>
  18 #include <linux/netfilter/x_tables.h>
  19 #ifdef CONFIG_NF_NAT_NEEDED
  20 #include <net/netfilter/nf_nat_rule.h>
  21 #else
  22 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  23 #endif
  24
  25 #define MODULENAME "NETMAP"
  26 MODULE_LICENSE("GPL");
  27 MODULE_AUTHOR("Svenning Soerensen <svenning@post5.tele.dk>");
  28 MODULE_DESCRIPTION("iptables 1:1 NAT mapping of IP networks target");
  29
  30 #if 0
  31 #define DEBUGP printk
  32 #else
  33 #define DEBUGP(format, args...)
  34 #endif
  35
  36 static int
  37 check(const char *tablename,
  38       const void *e,
  39       const struct xt_target *target,
  40       void *targinfo,
  41       unsigned int hook_mask)
  42 {
  43         const struct ip_nat_multi_range_compat *mr = targinfo;
  44
  45         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  46                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  47                 return 0;
  48         }
  49         if (mr->rangesize != 1) {
  50                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  51                 return 0;
  52         }
  53         return 1;
  54 }
  55
  56 static unsigned int
  57 target(struct sk_buff **pskb,
  58        const struct net_device *in,
  59        const struct net_device *out,
  60        unsigned int hooknum,
  61        const struct xt_target *target,
  62        const void *targinfo)
  63 {
  64         struct ip_conntrack *ct;
  65         enum ip_conntrack_info ctinfo;
  66         __be32 new_ip, netmask;
  67         const struct ip_nat_multi_range_compat *mr = targinfo;
  68         struct ip_nat_range newrange;
  69
  70         IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
  71                      || hooknum == NF_IP_POST_ROUTING
  72                      || hooknum == NF_IP_LOCAL_OUT);
  73         ct = ip_conntrack_get(*pskb, &ctinfo);
  74
  75         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  76
  77         if (hooknum == NF_IP_PRE_ROUTING || hooknum == NF_IP_LOCAL_OUT)
  78                 new_ip = (*pskb)->nh.iph->daddr & ~netmask;
  79         else
  80                 new_ip = (*pskb)->nh.iph->saddr & ~netmask;
  81         new_ip |= mr->range[0].min_ip & netmask;
  82
  83         newrange = ((struct ip_nat_range)
  84                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  85                   new_ip, new_ip,
  86                   mr->range[0].min, mr->range[0].max });
  87
  88         /* Hand modified range to generic setup. */
  89         return ip_nat_setup_info(ct, &newrange, hooknum);
  90 }
  91
  92 static struct xt_target target_module = {
  93         .name           = MODULENAME,
  94         .family         = AF_INET,
  95         .target         = target,
  96         .targetsize     = sizeof(struct ip_nat_multi_range_compat),
  97         .table          = "nat",
  98         .hooks          = (1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING) |
  99                           (1 << NF_IP_LOCAL_OUT),
 100         .checkentry     = check,
 101         .me             = THIS_MODULE
 102 };
 103
 104 static int __init ipt_netmap_init(void)
 105 {
 106         return xt_register_target(&target_module);
 107 }
 108
 109 static void __exit ipt_netmap_fini(void)
 110 {
 111         xt_unregister_target(&target_module);
 112 }
 113
 114 module_init(ipt_netmap_init);
 115 module_exit(ipt_netmap_fini);