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/config.h>
  14 #include <linux/ip.h>
  15 #include <linux/module.h>
  16 #include <linux/netdevice.h>
  17 #include <linux/netfilter.h>
  18 #include <linux/netfilter_ipv4.h>
  19 #include <linux/netfilter_ipv4/ip_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 int
  33 check(const char *tablename,
  34       const struct ipt_entry *e,
  35       void *targinfo,
  36       unsigned int targinfosize,
  37       unsigned int hook_mask)
  38 {
  39         const struct ip_nat_multi_range_compat *mr = targinfo;
  40
  41         if (strcmp(tablename, "nat") != 0) {
  42                 DEBUGP(MODULENAME":check: bad table `%s'.\n", tablename);
  43                 return 0;
  44         }
  45         if (targinfosize != IPT_ALIGN(sizeof(*mr))) {
  46                 DEBUGP(MODULENAME":check: size %u.\n", targinfosize);
  47                 return 0;
  48         }
  49         if (hook_mask & ~((1 << NF_IP_PRE_ROUTING) | (1 << NF_IP_POST_ROUTING))) {
  50                 DEBUGP(MODULENAME":check: bad hooks %x.\n", hook_mask);
  51                 return 0;
  52         }
  53         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  54                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  55                 return 0;
  56         }
  57         if (mr->rangesize != 1) {
  58                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  59                 return 0;
  60         }
  61         return 1;
  62 }
  63
  64 static unsigned int
  65 target(struct sk_buff **pskb,
  66        const struct net_device *in,
  67        const struct net_device *out,
  68        unsigned int hooknum,
  69        const void *targinfo,
  70        void *userinfo)
  71 {
  72         struct ip_conntrack *ct;
  73         enum ip_conntrack_info ctinfo;
  74         u_int32_t new_ip, netmask;
  75         const struct ip_nat_multi_range_compat *mr = targinfo;
  76         struct ip_nat_range newrange;
  77
  78         IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
  79                      || hooknum == NF_IP_POST_ROUTING);
  80         ct = ip_conntrack_get(*pskb, &ctinfo);
  81
  82         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  83
  84         if (hooknum == NF_IP_PRE_ROUTING)
  85                 new_ip = (*pskb)->nh.iph->daddr & ~netmask;
  86         else
  87                 new_ip = (*pskb)->nh.iph->saddr & ~netmask;
  88         new_ip |= mr->range[0].min_ip & netmask;
  89
  90         newrange = ((struct ip_nat_range)
  91                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  92                   new_ip, new_ip,
  93                   mr->range[0].min, mr->range[0].max });
  94
  95         /* Hand modified range to generic setup. */
  96         return ip_nat_setup_info(ct, &newrange, hooknum);
  97 }
  98
  99 static struct ipt_target target_module = {
 100         .name           = MODULENAME,
 101         .target         = target,
 102         .checkentry     = check,
 103         .me             = THIS_MODULE
 104 };
 105
 106 static int __init init(void)
 107 {
 108         return ipt_register_target(&target_module);
 109 }
 110
 111 static void __exit fini(void)
 112 {
 113         ipt_unregister_target(&target_module);
 114 }
 115
 116 module_init(init);
 117 module_exit(fini);