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 #ifdef CONFIG_NF_NAT_NEEDED
  19 #include <net/netfilter/nf_nat_rule.h>
  20 #else
  21 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  22 #endif
  23
  24 #define MODULENAME "NETMAP"
  25 MODULE_LICENSE("GPL");
  26 MODULE_AUTHOR("Svenning Soerensen <svenning@post5.tele.dk>");
  27 MODULE_DESCRIPTION("iptables 1:1 NAT mapping of IP networks target");
  28
  29 #if 0
  30 #define DEBUGP printk
  31 #else
  32 #define DEBUGP(format, args...)
  33 #endif
  34
  35 static int
  36 check(const char *tablename,
  37       const void *e,
  38       const struct xt_target *target,
  39       void *targinfo,
  40       unsigned int hook_mask)
  41 {
  42         const struct ip_nat_multi_range_compat *mr = targinfo;
  43
  44         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  45                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  46                 return 0;
  47         }
  48         if (mr->rangesize != 1) {
  49                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  50                 return 0;
  51         }
  52         return 1;
  53 }
  54
  55 static unsigned int
  56 target(struct sk_buff **pskb,
  57        const struct net_device *in,
  58        const struct net_device *out,
  59        unsigned int hooknum,
  60        const struct xt_target *target,
  61        const void *targinfo)
  62 {
  63         struct ip_conntrack *ct;
  64         enum ip_conntrack_info ctinfo;
  65         __be32 new_ip, netmask;
  66         const struct ip_nat_multi_range_compat *mr = targinfo;
  67         struct ip_nat_range newrange;
  68
  69         IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
  70                      || hooknum == NF_IP_POST_ROUTING
  71                      || hooknum == NF_IP_LOCAL_OUT);
  72         ct = ip_conntrack_get(*pskb, &ctinfo);
  73
  74         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  75
  76         if (hooknum == NF_IP_PRE_ROUTING || hooknum == NF_IP_LOCAL_OUT)
  77                 new_ip = (*pskb)->nh.iph->daddr & ~netmask;
  78         else
  79                 new_ip = (*pskb)->nh.iph->saddr & ~netmask;
  80         new_ip |= mr->range[0].min_ip & netmask;
  81
  82         newrange = ((struct ip_nat_range)
  83                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  84                   new_ip, new_ip,
  85                   mr->range[0].min, mr->range[0].max });
  86
  87         /* Hand modified range to generic setup. */
  88         return ip_nat_setup_info(ct, &newrange, hooknum);
  89 }
  90
  91 static struct ipt_target target_module = {
  92         .name           = MODULENAME,
  93         .target         = target,
  94         .targetsize     = sizeof(struct ip_nat_multi_range_compat),
  95         .table          = "nat",
  96         .hooks          = (1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING) |
  97                           (1 << NF_IP_LOCAL_OUT),
  98         .checkentry     = check,
  99         .me             = THIS_MODULE
 100 };
 101
 102 static int __init ipt_netmap_init(void)
 103 {
 104         return ipt_register_target(&target_module);
 105 }
 106
 107 static void __exit ipt_netmap_fini(void)
 108 {
 109         ipt_unregister_target(&target_module);
 110 }
 111
 112 module_init(ipt_netmap_init);
 113 module_exit(ipt_netmap_fini);