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("Xtables: 1:1 NAT mapping of IPv4 subnets");
  24
  25 static bool
  26 netmap_tg_check(const char *tablename, const void *e,
  27                 const struct xt_target *target, void *targinfo,
  28                 unsigned int hook_mask)
  29 {
  30         const struct nf_nat_multi_range_compat *mr = targinfo;
  31
  32         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  33                 pr_debug("NETMAP:check: bad MAP_IPS.\n");
  34                 return false;
  35         }
  36         if (mr->rangesize != 1) {
  37                 pr_debug("NETMAP:check: bad rangesize %u.\n", mr->rangesize);
  38                 return false;
  39         }
  40         return true;
  41 }
  42
  43 static unsigned int
  44 netmap_tg(struct sk_buff *skb, const struct net_device *in,
  45           const struct net_device *out, unsigned int hooknum,
  46           const struct xt_target *target, const void *targinfo)
  47 {
  48         struct nf_conn *ct;
  49         enum ip_conntrack_info ctinfo;
  50         __be32 new_ip, netmask;
  51         const struct nf_nat_multi_range_compat *mr = targinfo;
  52         struct nf_nat_range newrange;
  53
  54         NF_CT_ASSERT(hooknum == NF_INET_PRE_ROUTING
  55                      || hooknum == NF_INET_POST_ROUTING
  56                      || hooknum == NF_INET_LOCAL_OUT);
  57         ct = nf_ct_get(skb, &ctinfo);
  58
  59         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  60
  61         if (hooknum == NF_INET_PRE_ROUTING || hooknum == NF_INET_LOCAL_OUT)
  62                 new_ip = ip_hdr(skb)->daddr & ~netmask;
  63         else
  64                 new_ip = ip_hdr(skb)->saddr & ~netmask;
  65         new_ip |= mr->range[0].min_ip & netmask;
  66
  67         newrange = ((struct nf_nat_range)
  68                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  69                   new_ip, new_ip,
  70                   mr->range[0].min, mr->range[0].max });
  71
  72         /* Hand modified range to generic setup. */
  73         return nf_nat_setup_info(ct, &newrange, HOOK2MANIP(hooknum));
  74 }
  75
  76 static struct xt_target netmap_tg_reg __read_mostly = {
  77         .name           = "NETMAP",
  78         .family         = AF_INET,
  79         .target         = netmap_tg,
  80         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
  81         .table          = "nat",
  82         .hooks          = (1 << NF_INET_PRE_ROUTING) |
  83                           (1 << NF_INET_POST_ROUTING) |
  84                           (1 << NF_INET_LOCAL_OUT),
  85         .checkentry     = netmap_tg_check,
  86         .me             = THIS_MODULE
  87 };
  88
  89 static int __init netmap_tg_init(void)
  90 {
  91         return xt_register_target(&netmap_tg_reg);
  92 }
  93
  94 static void __exit netmap_tg_exit(void)
  95 {
  96         xt_unregister_target(&netmap_tg_reg);
  97 }
  98
  99 module_init(netmap_tg_init);
 100 module_exit(netmap_tg_exit);