net/ipv4/netfilter/ipt_MASQUERADE.c

   1 /* Masquerade.  Simple mapping which alters range to a local IP address
   2    (depending on route). */
   3
   4 /* (C) 1999-2001 Paul `Rusty' Russell
   5  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/config.h>
  13 #include <linux/types.h>
  14 #include <linux/inetdevice.h>
  15 #include <linux/ip.h>
  16 #include <linux/timer.h>
  17 #include <linux/module.h>
  18 #include <linux/netfilter.h>
  19 #include <net/protocol.h>
  20 #include <net/ip.h>
  21 #include <net/checksum.h>
  22 #include <net/route.h>
  23 #include <linux/netfilter_ipv4.h>
  24 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  25 #include <linux/netfilter_ipv4/ip_tables.h>
  26
  27 MODULE_LICENSE("GPL");
  28 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  29 MODULE_DESCRIPTION("iptables MASQUERADE target module");
  30
  31 #if 0
  32 #define DEBUGP printk
  33 #else
  34 #define DEBUGP(format, args...)
  35 #endif
  36
  37 /* Lock protects masq region inside conntrack */
  38 static DEFINE_RWLOCK(masq_lock);
  39
  40 /* FIXME: Multiple targets. --RR */
  41 static int
  42 masquerade_check(const char *tablename,
  43                  const void *e,
  44                  const struct xt_target *target,
  45                  void *targinfo,
  46                  unsigned int targinfosize,
  47                  unsigned int hook_mask)
  48 {
  49         const struct ip_nat_multi_range_compat *mr = targinfo;
  50
  51         if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  52                 DEBUGP("masquerade_check: bad MAP_IPS.\n");
  53                 return 0;
  54         }
  55         if (mr->rangesize != 1) {
  56                 DEBUGP("masquerade_check: bad rangesize %u.\n", mr->rangesize);
  57                 return 0;
  58         }
  59         return 1;
  60 }
  61
  62 static unsigned int
  63 masquerade_target(struct sk_buff **pskb,
  64                   const struct net_device *in,
  65                   const struct net_device *out,
  66                   unsigned int hooknum,
  67                   const struct xt_target *target,
  68                   const void *targinfo,
  69                   void *userinfo)
  70 {
  71         struct ip_conntrack *ct;
  72         enum ip_conntrack_info ctinfo;
  73         const struct ip_nat_multi_range_compat *mr;
  74         struct ip_nat_range newrange;
  75         struct rtable *rt;
  76         u_int32_t newsrc;
  77
  78         IP_NF_ASSERT(hooknum == NF_IP_POST_ROUTING);
  79
  80         ct = ip_conntrack_get(*pskb, &ctinfo);
  81         IP_NF_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
  82                             || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
  83
  84         /* Source address is 0.0.0.0 - locally generated packet that is
  85          * probably not supposed to be masqueraded.
  86          */
  87         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip == 0)
  88                 return NF_ACCEPT;
  89
  90         mr = targinfo;
  91         rt = (struct rtable *)(*pskb)->dst;
  92         newsrc = inet_select_addr(out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
  93         if (!newsrc) {
  94                 printk("MASQUERADE: %s ate my IP address\n", out->name);
  95                 return NF_DROP;
  96         }
  97
  98         write_lock_bh(&masq_lock);
  99         ct->nat.masq_index = out->ifindex;
 100         write_unlock_bh(&masq_lock);
 101
 102         /* Transfer from original range. */
 103         newrange = ((struct ip_nat_range)
 104                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
 105                   newsrc, newsrc,
 106                   mr->range[0].min, mr->range[0].max });
 107
 108         /* Hand modified range to generic setup. */
 109         return ip_nat_setup_info(ct, &newrange, hooknum);
 110 }
 111
 112 static inline int
 113 device_cmp(struct ip_conntrack *i, void *ifindex)
 114 {
 115         int ret;
 116
 117         read_lock_bh(&masq_lock);
 118         ret = (i->nat.masq_index == (int)(long)ifindex);
 119         read_unlock_bh(&masq_lock);
 120
 121         return ret;
 122 }
 123
 124 static int masq_device_event(struct notifier_block *this,
 125                              unsigned long event,
 126                              void *ptr)
 127 {
 128         struct net_device *dev = ptr;
 129
 130         if (event == NETDEV_DOWN) {
 131                 /* Device was downed.  Search entire table for
 132                    conntracks which were associated with that device,
 133                    and forget them. */
 134                 IP_NF_ASSERT(dev->ifindex != 0);
 135
 136                 ip_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 137         }
 138
 139         return NOTIFY_DONE;
 140 }
 141
 142 static int masq_inet_event(struct notifier_block *this,
 143                            unsigned long event,
 144                            void *ptr)
 145 {
 146         struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 147
 148         if (event == NETDEV_DOWN) {
 149                 /* IP address was deleted.  Search entire table for
 150                    conntracks which were associated with that device,
 151                    and forget them. */
 152                 IP_NF_ASSERT(dev->ifindex != 0);
 153
 154                 ip_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 155         }
 156
 157         return NOTIFY_DONE;
 158 }
 159
 160 static struct notifier_block masq_dev_notifier = {
 161         .notifier_call  = masq_device_event,
 162 };
 163
 164 static struct notifier_block masq_inet_notifier = {
 165         .notifier_call  = masq_inet_event,
 166 };
 167
 168 static struct ipt_target masquerade = {
 169         .name           = "MASQUERADE",
 170         .target         = masquerade_target,
 171         .targetsize     = sizeof(struct ip_nat_multi_range_compat),
 172         .table          = "nat",
 173         .hooks          = 1 << NF_IP_POST_ROUTING,
 174         .checkentry     = masquerade_check,
 175         .me             = THIS_MODULE,
 176 };
 177
 178 static int __init ipt_masquerade_init(void)
 179 {
 180         int ret;
 181
 182         ret = ipt_register_target(&masquerade);
 183
 184         if (ret == 0) {
 185                 /* Register for device down reports */
 186                 register_netdevice_notifier(&masq_dev_notifier);
 187                 /* Register IP address change reports */
 188                 register_inetaddr_notifier(&masq_inet_notifier);
 189         }
 190
 191         return ret;
 192 }
 193
 194 static void __exit ipt_masquerade_fini(void)
 195 {
 196         ipt_unregister_target(&masquerade);
 197         unregister_netdevice_notifier(&masq_dev_notifier);
 198         unregister_inetaddr_notifier(&masq_inet_notifier);
 199 }
 200
 201 module_init(ipt_masquerade_init);
 202 module_exit(ipt_masquerade_fini);