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/config.h>
  14 #include <linux/ip.h>
  15 #include <linux/module.h>
  16 #include <linux/netdevice.h>
  17 #include <linux/netfilter.h>
  18 #include <linux/netfilter_ipv4.h>
  19 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  20
  21 #define MODULENAME "NETMAP"
  22 MODULE_LICENSE("GPL");
  23 MODULE_AUTHOR("Svenning Soerensen <svenning@post5.tele.dk>");
  24 MODULE_DESCRIPTION("iptables 1:1 NAT mapping of IP networks target");
  25
  26 #if 0
  27 #define DEBUGP printk
  28 #else
  29 #define DEBUGP(format, args...)
  30 #endif
  31
  32 static int
  33 check(const char *tablename,
  34       const void *e,
  35       const struct xt_target *target,
  36       void *targinfo,
  37       unsigned int targinfosize,
  38       unsigned int hook_mask)
  39 {
  40         const struct ip_nat_multi_range_compat *mr = targinfo;
  41
  42         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  43                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  44                 return 0;
  45         }
  46         if (mr->rangesize != 1) {
  47                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  48                 return 0;
  49         }
  50         return 1;
  51 }
  52
  53 static unsigned int
  54 target(struct sk_buff **pskb,
  55        const struct net_device *in,
  56        const struct net_device *out,
  57        unsigned int hooknum,
  58        const struct xt_target *target,
  59        const void *targinfo,
  60        void *userinfo)
  61 {
  62         struct ip_conntrack *ct;
  63         enum ip_conntrack_info ctinfo;
  64         u_int32_t new_ip, netmask;
  65         const struct ip_nat_multi_range_compat *mr = targinfo;
  66         struct ip_nat_range newrange;
  67
  68         IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
  69                      || hooknum == NF_IP_POST_ROUTING
  70                      || hooknum == NF_IP_LOCAL_OUT);
  71         ct = ip_conntrack_get(*pskb, &ctinfo);
  72
  73         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  74
  75         if (hooknum == NF_IP_PRE_ROUTING || hooknum == NF_IP_LOCAL_OUT)
  76                 new_ip = (*pskb)->nh.iph->daddr & ~netmask;
  77         else
  78                 new_ip = (*pskb)->nh.iph->saddr & ~netmask;
  79         new_ip |= mr->range[0].min_ip & netmask;
  80
  81         newrange = ((struct ip_nat_range)
  82                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  83                   new_ip, new_ip,
  84                   mr->range[0].min, mr->range[0].max });
  85
  86         /* Hand modified range to generic setup. */
  87         return ip_nat_setup_info(ct, &newrange, hooknum);
  88 }
  89
  90 static struct ipt_target target_module = {
  91         .name           = MODULENAME,
  92         .target         = target,
  93         .targetsize     = sizeof(struct ip_nat_multi_range_compat),
  94         .table          = "nat",
  95         .hooks          = (1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING) |
  96                           (1 << NF_IP_LOCAL_OUT),
  97         .checkentry     = check,
  98         .me             = THIS_MODULE
  99 };
 100
 101 static int __init ipt_netmap_init(void)
 102 {
 103         return ipt_register_target(&target_module);
 104 }
 105
 106 static void __exit ipt_netmap_fini(void)
 107 {
 108         ipt_unregister_target(&target_module);
 109 }
 110
 111 module_init(ipt_netmap_init);
 112 module_exit(ipt_netmap_fini);