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