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 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 static bool
  26 check(const char *tablename,
  27       const void *e,
  28       const struct xt_target *target,
  29       void *targinfo,
  30       unsigned int hook_mask)
  31 {
  32         const struct nf_nat_multi_range_compat *mr = targinfo;
  33
  34         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  35                 pr_debug("NETMAP:check: bad MAP_IPS.\n");
  36                 return false;
  37         }
  38         if (mr->rangesize != 1) {
  39                 pr_debug("NETMAP:check: bad rangesize %u.\n", mr->rangesize);
  40                 return false;
  41         }
  42         return true;
  43 }
  44
  45 static unsigned int
  46 target(struct sk_buff *skb,
  47        const struct net_device *in,
  48        const struct net_device *out,
  49        unsigned int hooknum,
  50        const struct xt_target *target,
  51        const void *targinfo)
  52 {
  53         struct nf_conn *ct;
  54         enum ip_conntrack_info ctinfo;
  55         __be32 new_ip, netmask;
  56         const struct nf_nat_multi_range_compat *mr = targinfo;
  57         struct nf_nat_range newrange;
  58
  59         NF_CT_ASSERT(hooknum == NF_INET_PRE_ROUTING
  60                      || hooknum == NF_INET_POST_ROUTING
  61                      || hooknum == NF_INET_LOCAL_OUT);
  62         ct = nf_ct_get(skb, &ctinfo);
  63
  64         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  65
  66         if (hooknum == NF_INET_PRE_ROUTING || hooknum == NF_INET_LOCAL_OUT)
  67                 new_ip = ip_hdr(skb)->daddr & ~netmask;
  68         else
  69                 new_ip = ip_hdr(skb)->saddr & ~netmask;
  70         new_ip |= mr->range[0].min_ip & netmask;
  71
  72         newrange = ((struct nf_nat_range)
  73                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  74                   new_ip, new_ip,
  75                   mr->range[0].min, mr->range[0].max });
  76
  77         /* Hand modified range to generic setup. */
  78         return nf_nat_setup_info(ct, &newrange, hooknum);
  79 }
  80
  81 static struct xt_target target_module __read_mostly = {
  82         .name           = "NETMAP",
  83         .family         = AF_INET,
  84         .target         = target,
  85         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
  86         .table          = "nat",
  87         .hooks          = (1 << NF_INET_PRE_ROUTING) |
  88                           (1 << NF_INET_POST_ROUTING) |
  89                           (1 << NF_INET_LOCAL_OUT),
  90         .checkentry     = check,
  91         .me             = THIS_MODULE
  92 };
  93
  94 static int __init ipt_netmap_init(void)
  95 {
  96         return xt_register_target(&target_module);
  97 }
  98
  99 static void __exit ipt_netmap_fini(void)
 100 {
 101         xt_unregister_target(&target_module);
 102 }
 103
 104 module_init(ipt_netmap_init);
 105 module_exit(ipt_netmap_fini);