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                           (1 << NF_IP_LOCAL_OUT))) {
  51                 DEBUGP(MODULENAME":check: bad hooks %x.\n", hook_mask);
  52                 return 0;
  53         }
  54         if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
  55                 DEBUGP(MODULENAME":check: bad MAP_IPS.\n");
  56                 return 0;
  57         }
  58         if (mr->rangesize != 1) {
  59                 DEBUGP(MODULENAME":check: bad rangesize %u.\n", mr->rangesize);
  60                 return 0;
  61         }
  62         return 1;
  63 }
  64
  65 static unsigned int
  66 target(struct sk_buff **pskb,
  67        const struct net_device *in,
  68        const struct net_device *out,
  69        unsigned int hooknum,
  70        const void *targinfo,
  71        void *userinfo)
  72 {
  73         struct ip_conntrack *ct;
  74         enum ip_conntrack_info ctinfo;
  75         u_int32_t new_ip, netmask;
  76         const struct ip_nat_multi_range_compat *mr = targinfo;
  77         struct ip_nat_range newrange;
  78
  79         IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
  80                      || hooknum == NF_IP_POST_ROUTING
  81                      || hooknum == NF_IP_LOCAL_OUT);
  82         ct = ip_conntrack_get(*pskb, &ctinfo);
  83
  84         netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);
  85
  86         if (hooknum == NF_IP_PRE_ROUTING || hooknum == NF_IP_LOCAL_OUT)
  87                 new_ip = (*pskb)->nh.iph->daddr & ~netmask;
  88         else
  89                 new_ip = (*pskb)->nh.iph->saddr & ~netmask;
  90         new_ip |= mr->range[0].min_ip & netmask;
  91
  92         newrange = ((struct ip_nat_range)
  93                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  94                   new_ip, new_ip,
  95                   mr->range[0].min, mr->range[0].max });
  96
  97         /* Hand modified range to generic setup. */
  98         return ip_nat_setup_info(ct, &newrange, hooknum);
  99 }
 100
 101 static struct ipt_target target_module = {
 102         .name           = MODULENAME,
 103         .target         = target,
 104         .checkentry     = check,
 105         .me             = THIS_MODULE
 106 };
 107
 108 static int __init init(void)
 109 {
 110         return ipt_register_target(&target_module);
 111 }
 112
 113 static void __exit fini(void)
 114 {
 115         ipt_unregister_target(&target_module);
 116 }
 117
 118 module_init(init);
 119 module_exit(fini);