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.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_ipv4_multi_range_compat *mr = par->targinfo;
  28
  29         if (!(mr->range[0].flags & NF_NAT_RANGE_MAP_IPS)) {
  30                 pr_debug("bad MAP_IPS.\n");
  31                 return -EINVAL;
  32         }
  33         if (mr->rangesize != 1) {
  34                 pr_debug("bad rangesize %u.\n", mr->rangesize);
  35                 return -EINVAL;
  36         }
  37         return 0;
  38 }
  39
  40 static unsigned int
  41 netmap_tg(struct sk_buff *skb, const struct xt_action_param *par)
  42 {
  43         struct nf_conn *ct;
  44         enum ip_conntrack_info ctinfo;
  45         __be32 new_ip, netmask;
  46         const struct nf_nat_ipv4_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                      par->hooknum == NF_INET_LOCAL_IN);
  53         ct = nf_ct_get(skb, &ctinfo);
  54
  55         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  56
  57         if (par->hooknum == NF_INET_PRE_ROUTING ||
  58             par->hooknum == NF_INET_LOCAL_OUT)
  59                 new_ip = ip_hdr(skb)->daddr & ~netmask;
  60         else
  61                 new_ip = ip_hdr(skb)->saddr & ~netmask;
  62         new_ip |= mr->range[0].min_ip & netmask;
  63
  64         memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
  65         memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
  66         newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
  67         newrange.min_addr.ip = new_ip;
  68         newrange.max_addr.ip = new_ip;
  69         newrange.min_proto   = mr->range[0].min;
  70         newrange.max_proto   = mr->range[0].max;
  71
  72         /* Hand modified range to generic setup. */
  73         return nf_nat_setup_info(ct, &newrange, HOOK2MANIP(par->hooknum));
  74 }
  75
  76 static struct xt_target netmap_tg_reg __read_mostly = {
  77         .name           = "NETMAP",
  78         .family         = NFPROTO_IPV4,
  79         .target         = netmap_tg,
  80         .targetsize     = sizeof(struct nf_nat_ipv4_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                           (1 << NF_INET_LOCAL_IN),
  86         .checkentry     = netmap_tg_check,
  87         .me             = THIS_MODULE
  88 };
  89
  90 static int __init netmap_tg_init(void)
  91 {
  92         return xt_register_target(&netmap_tg_reg);
  93 }
  94
  95 static void __exit netmap_tg_exit(void)
  96 {
  97         xt_unregister_target(&netmap_tg_reg);
  98 }
  99
 100 module_init(netmap_tg_init);
 101 module_exit(netmap_tg_exit);