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/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 <linux/netfilter_ipv4.h>
  22 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  23 #include <linux/netfilter_ipv4/ip_tables.h>
  24
  25 MODULE_LICENSE("GPL");
  26 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  27 MODULE_DESCRIPTION("iptables MASQUERADE target module");
  28
  29 #if 0
  30 #define DEBUGP printk
  31 #else
  32 #define DEBUGP(format, args...)
  33 #endif
  34
  35 /* Lock protects masq region inside conntrack */
  36 static DEFINE_RWLOCK(masq_lock);
  37
  38 /* FIXME: Multiple targets. --RR */
  39 static int
  40 masquerade_check(const char *tablename,
  41                  const struct ipt_entry *e,
  42                  void *targinfo,
  43                  unsigned int targinfosize,
  44                  unsigned int hook_mask)
  45 {
  46         const struct ip_nat_multi_range_compat *mr = targinfo;
  47
  48         if (strcmp(tablename, "nat") != 0) {
  49                 DEBUGP("masquerade_check: bad table `%s'.\n", tablename);
  50                 return 0;
  51         }
  52         if (targinfosize != IPT_ALIGN(sizeof(*mr))) {
  53                 DEBUGP("masquerade_check: size %u != %u.\n",
  54                        targinfosize, sizeof(*mr));
  55                 return 0;
  56         }
  57         if (hook_mask & ~(1 << NF_IP_POST_ROUTING)) {
  58                 DEBUGP("masquerade_check: bad hooks %x.\n", hook_mask);
  59                 return 0;
  60         }
  61         if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  62                 DEBUGP("masquerade_check: bad MAP_IPS.\n");
  63                 return 0;
  64         }
  65         if (mr->rangesize != 1) {
  66                 DEBUGP("masquerade_check: bad rangesize %u.\n", mr->rangesize);
  67                 return 0;
  68         }
  69         return 1;
  70 }
  71
  72 static unsigned int
  73 masquerade_target(struct sk_buff **pskb,
  74                   const struct net_device *in,
  75                   const struct net_device *out,
  76                   unsigned int hooknum,
  77                   const void *targinfo,
  78                   void *userinfo)
  79 {
  80         struct ip_conntrack *ct;
  81         enum ip_conntrack_info ctinfo;
  82         const struct ip_nat_multi_range_compat *mr;
  83         struct ip_nat_range newrange;
  84         struct rtable *rt;
  85         u_int32_t newsrc;
  86
  87         IP_NF_ASSERT(hooknum == NF_IP_POST_ROUTING);
  88
  89         ct = ip_conntrack_get(*pskb, &ctinfo);
  90         IP_NF_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
  91                             || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
  92
  93         /* Source address is 0.0.0.0 - locally generated packet that is
  94          * probably not supposed to be masqueraded.
  95          */
  96         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip == 0)
  97                 return NF_ACCEPT;
  98
  99         mr = targinfo;
 100         rt = (struct rtable *)(*pskb)->dst;
 101         newsrc = inet_select_addr(out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
 102         if (!newsrc) {
 103                 printk("MASQUERADE: %s ate my IP address\n", out->name);
 104                 return NF_DROP;
 105         }
 106
 107         write_lock_bh(&masq_lock);
 108         ct->nat.masq_index = out->ifindex;
 109         write_unlock_bh(&masq_lock);
 110
 111         /* Transfer from original range. */
 112         newrange = ((struct ip_nat_range)
 113                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
 114                   newsrc, newsrc,
 115                   mr->range[0].min, mr->range[0].max });
 116
 117         /* Hand modified range to generic setup. */
 118         return ip_nat_setup_info(ct, &newrange, hooknum);
 119 }
 120
 121 static inline int
 122 device_cmp(struct ip_conntrack *i, void *ifindex)
 123 {
 124         int ret;
 125
 126         read_lock_bh(&masq_lock);
 127         ret = (i->nat.masq_index == (int)(long)ifindex);
 128         read_unlock_bh(&masq_lock);
 129
 130         return ret;
 131 }
 132
 133 static int masq_device_event(struct notifier_block *this,
 134                              unsigned long event,
 135                              void *ptr)
 136 {
 137         struct net_device *dev = ptr;
 138
 139         if (event == NETDEV_DOWN) {
 140                 /* Device was downed.  Search entire table for
 141                    conntracks which were associated with that device,
 142                    and forget them. */
 143                 IP_NF_ASSERT(dev->ifindex != 0);
 144
 145                 ip_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 146         }
 147
 148         return NOTIFY_DONE;
 149 }
 150
 151 static int masq_inet_event(struct notifier_block *this,
 152                            unsigned long event,
 153                            void *ptr)
 154 {
 155         struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 156
 157         if (event == NETDEV_DOWN) {
 158                 /* IP address was deleted.  Search entire table for
 159                    conntracks which were associated with that device,
 160                    and forget them. */
 161                 IP_NF_ASSERT(dev->ifindex != 0);
 162
 163                 ip_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 164         }
 165
 166         return NOTIFY_DONE;
 167 }
 168
 169 static struct notifier_block masq_dev_notifier = {
 170         .notifier_call  = masq_device_event,
 171 };
 172
 173 static struct notifier_block masq_inet_notifier = {
 174         .notifier_call  = masq_inet_event,
 175 };
 176
 177 static struct ipt_target masquerade = {
 178         .name           = "MASQUERADE",
 179         .target         = masquerade_target,
 180         .checkentry     = masquerade_check,
 181         .me             = THIS_MODULE,
 182 };
 183
 184 static int __init init(void)
 185 {
 186         int ret;
 187
 188         ret = ipt_register_target(&masquerade);
 189
 190         if (ret == 0) {
 191                 /* Register for device down reports */
 192                 register_netdevice_notifier(&masq_dev_notifier);
 193                 /* Register IP address change reports */
 194                 register_inetaddr_notifier(&masq_inet_notifier);
 195         }
 196
 197         return ret;
 198 }
 199
 200 static void __exit fini(void)
 201 {
 202         ipt_unregister_target(&masquerade);
 203         unregister_netdevice_notifier(&masq_dev_notifier);
 204         unregister_inetaddr_notifier(&masq_inet_notifier);
 205 }
 206
 207 module_init(init);
 208 module_exit(fini);