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_ipv4/ip_nat_rule.h>
  19
  20 #define MODULENAME "NETMAP"
  21 MODULE_LICENSE("GPL");
  22 MODULE_AUTHOR("Svenning Soerensen <svenning@post5.tele.dk>");
  23 MODULE_DESCRIPTION("iptables 1:1 NAT mapping of IP networks target");
  24
  25 #if 0
  26 #define DEBUGP printk
  27 #else
  28 #define DEBUGP(format, args...)
  29 #endif
  30
  31 static int
  32 check(const char *tablename,
  33       const void *e,
  34       const struct xt_target *target,
  35       void *targinfo,
  36       unsigned int hook_mask)
  37 {
  38         const struct ip_nat_multi_range_compat *mr = targinfo;
  39
  40         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  41                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  42                 return 0;
  43         }
  44         if (mr->rangesize != 1) {
  45                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  46                 return 0;
  47         }
  48         return 1;
  49 }
  50
  51 static unsigned int
  52 target(struct sk_buff **pskb,
  53        const struct net_device *in,
  54        const struct net_device *out,
  55        unsigned int hooknum,
  56        const struct xt_target *target,
  57        const void *targinfo)
  58 {
  59         struct ip_conntrack *ct;
  60         enum ip_conntrack_info ctinfo;
  61         u_int32_t new_ip, netmask;
  62         const struct ip_nat_multi_range_compat *mr = targinfo;
  63         struct ip_nat_range newrange;
  64
  65         IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
  66                      || hooknum == NF_IP_POST_ROUTING
  67                      || hooknum == NF_IP_LOCAL_OUT);
  68         ct = ip_conntrack_get(*pskb, &ctinfo);
  69
  70         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  71
  72         if (hooknum == NF_IP_PRE_ROUTING || hooknum == NF_IP_LOCAL_OUT)
  73                 new_ip = (*pskb)->nh.iph->daddr & ~netmask;
  74         else
  75                 new_ip = (*pskb)->nh.iph->saddr & ~netmask;
  76         new_ip |= mr->range[0].min_ip & netmask;
  77
  78         newrange = ((struct ip_nat_range)
  79                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  80                   new_ip, new_ip,
  81                   mr->range[0].min, mr->range[0].max });
  82
  83         /* Hand modified range to generic setup. */
  84         return ip_nat_setup_info(ct, &newrange, hooknum);
  85 }
  86
  87 static struct ipt_target target_module = {
  88         .name           = MODULENAME,
  89         .target         = target,
  90         .targetsize     = sizeof(struct ip_nat_multi_range_compat),
  91         .table          = "nat",
  92         .hooks          = (1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING) |
  93                           (1 << NF_IP_LOCAL_OUT),
  94         .checkentry     = check,
  95         .me             = THIS_MODULE
  96 };
  97
  98 static int __init ipt_netmap_init(void)
  99 {
 100         return ipt_register_target(&target_module);
 101 }
 102
 103 static void __exit ipt_netmap_fini(void)
 104 {
 105         ipt_unregister_target(&target_module);
 106 }
 107
 108 module_init(ipt_netmap_init);
 109 module_exit(ipt_netmap_fini);