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 #include <net/netfilter/nf_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 bool
  33 check(const char *tablename,
  34       const void *e,
  35       const struct xt_target *target,
  36       void *targinfo,
  37       unsigned int hook_mask)
  38 {
  39         const struct nf_nat_multi_range_compat *mr = targinfo;
  40
  41         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  42                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  43                 return false;
  44         }
  45         if (mr->rangesize != 1) {
  46                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  47                 return false;
  48         }
  49         return true;
  50 }
  51
  52 static unsigned int
  53 target(struct sk_buff **pskb,
  54        const struct net_device *in,
  55        const struct net_device *out,
  56        unsigned int hooknum,
  57        const struct xt_target *target,
  58        const void *targinfo)
  59 {
  60         struct nf_conn *ct;
  61         enum ip_conntrack_info ctinfo;
  62         __be32 new_ip, netmask;
  63         const struct nf_nat_multi_range_compat *mr = targinfo;
  64         struct nf_nat_range newrange;
  65
  66         NF_CT_ASSERT(hooknum == NF_IP_PRE_ROUTING
  67                      || hooknum == NF_IP_POST_ROUTING
  68                      || hooknum == NF_IP_LOCAL_OUT);
  69         ct = nf_ct_get(*pskb, &ctinfo);
  70
  71         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  72
  73         if (hooknum == NF_IP_PRE_ROUTING || hooknum == NF_IP_LOCAL_OUT)
  74                 new_ip = ip_hdr(*pskb)->daddr & ~netmask;
  75         else
  76                 new_ip = ip_hdr(*pskb)->saddr & ~netmask;
  77         new_ip |= mr->range[0].min_ip & netmask;
  78
  79         newrange = ((struct nf_nat_range)
  80                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  81                   new_ip, new_ip,
  82                   mr->range[0].min, mr->range[0].max });
  83
  84         /* Hand modified range to generic setup. */
  85         return nf_nat_setup_info(ct, &newrange, hooknum);
  86 }
  87
  88 static struct xt_target target_module = {
  89         .name           = MODULENAME,
  90         .family         = AF_INET,
  91         .target         = target,
  92         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
  93         .table          = "nat",
  94         .hooks          = (1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING) |
  95                           (1 << NF_IP_LOCAL_OUT),
  96         .checkentry     = check,
  97         .me             = THIS_MODULE
  98 };
  99
 100 static int __init ipt_netmap_init(void)
 101 {
 102         return xt_register_target(&target_module);
 103 }
 104
 105 static void __exit ipt_netmap_fini(void)
 106 {
 107         xt_unregister_target(&target_module);
 108 }
 109
 110 module_init(ipt_netmap_init);
 111 module_exit(ipt_netmap_fini);