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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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 int netmap_tg_check(const struct xt_tgchk_param *par)
  26 {
  27         const struct nf_nat_multi_range_compat *mr = par->targinfo;
  28
  29         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  30                 pr_debug("bad MAP_IPS.\n");
  31                 return false;
  32         }
  33         if (mr->rangesize != 1) {
  34                 pr_debug("bad rangesize %u.\n", mr->rangesize);
  35                 return false;
  36         }
  37         return true;
  38 }
  39
  40 static unsigned int
  41 netmap_tg(struct sk_buff *skb, const struct xt_target_param *par)
  42 {
  43         struct nf_conn *ct;
  44         enum ip_conntrack_info ctinfo;
  45         __be32 new_ip, netmask;
  46         const struct nf_nat_multi_range_compat *mr = par->targinfo;
  47         struct nf_nat_range newrange;
  48
  49         NF_CT_ASSERT(par->hooknum == NF_INET_PRE_ROUTING ||
  50                      par->hooknum == NF_INET_POST_ROUTING ||
  51                      par->hooknum == NF_INET_LOCAL_OUT);
  52         ct = nf_ct_get(skb, &ctinfo);
  53
  54         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  55
  56         if (par->hooknum == NF_INET_PRE_ROUTING ||
  57             par->hooknum == NF_INET_LOCAL_OUT)
  58                 new_ip = ip_hdr(skb)->daddr & ~netmask;
  59         else
  60                 new_ip = ip_hdr(skb)->saddr & ~netmask;
  61         new_ip |= mr->range[0].min_ip & netmask;
  62
  63         newrange = ((struct nf_nat_range)
  64                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  65                   new_ip, new_ip,
  66                   mr->range[0].min, mr->range[0].max });
  67
  68         /* Hand modified range to generic setup. */
  69         return nf_nat_setup_info(ct, &newrange, HOOK2MANIP(par->hooknum));
  70 }
  71
  72 static struct xt_target netmap_tg_reg __read_mostly = {
  73         .name           = "NETMAP",
  74         .family         = NFPROTO_IPV4,
  75         .target         = netmap_tg,
  76         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
  77         .table          = "nat",
  78         .hooks          = (1 << NF_INET_PRE_ROUTING) |
  79                           (1 << NF_INET_POST_ROUTING) |
  80                           (1 << NF_INET_LOCAL_OUT),
  81         .checkentry     = netmap_tg_check,
  82         .me             = THIS_MODULE
  83 };
  84
  85 static int __init netmap_tg_init(void)
  86 {
  87         return xt_register_target(&netmap_tg_reg);
  88 }
  89
  90 static void __exit netmap_tg_exit(void)
  91 {
  92         xt_unregister_target(&netmap_tg_reg);
  93 }
  94
  95 module_init(netmap_tg_init);
  96 module_exit(netmap_tg_exit);