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) 2002-2006 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 <net/netfilter/nf_nat_rule.h>
  23 #include <linux/netfilter_ipv4.h>
  24 #include <linux/netfilter/x_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 bool
  41 masquerade_check(const char *tablename,
  42                  const void *e,
  43                  const struct xt_target *target,
  44                  void *targinfo,
  45                  unsigned int hook_mask)
  46 {
  47         const struct nf_nat_multi_range_compat *mr = targinfo;
  48
  49         if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  50                 DEBUGP("masquerade_check: bad MAP_IPS.\n");
  51                 return false;
  52         }
  53         if (mr->rangesize != 1) {
  54                 DEBUGP("masquerade_check: bad rangesize %u.\n", mr->rangesize);
  55                 return false;
  56         }
  57         return true;
  58 }
  59
  60 static unsigned int
  61 masquerade_target(struct sk_buff **pskb,
  62                   const struct net_device *in,
  63                   const struct net_device *out,
  64                   unsigned int hooknum,
  65                   const struct xt_target *target,
  66                   const void *targinfo)
  67 {
  68         struct nf_conn *ct;
  69         struct nf_conn_nat *nat;
  70         enum ip_conntrack_info ctinfo;
  71         struct nf_nat_range newrange;
  72         const struct nf_nat_multi_range_compat *mr;
  73         const struct rtable *rt;
  74         __be32 newsrc;
  75
  76         NF_CT_ASSERT(hooknum == NF_IP_POST_ROUTING);
  77
  78         ct = nf_ct_get(*pskb, &ctinfo);
  79         nat = nfct_nat(ct);
  80
  81         NF_CT_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.u3.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         nat->masq_index = out->ifindex;
 100         write_unlock_bh(&masq_lock);
 101
 102         /* Transfer from original range. */
 103         newrange = ((struct nf_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 nf_nat_setup_info(ct, &newrange, hooknum);
 110 }
 111
 112 static int
 113 device_cmp(struct nf_conn *i, void *ifindex)
 114 {
 115         const struct nf_conn_nat *nat = nfct_nat(i);
 116         int ret;
 117
 118         if (!nat)
 119                 return 0;
 120
 121         read_lock_bh(&masq_lock);
 122         ret = (nat->masq_index == (int)(long)ifindex);
 123         read_unlock_bh(&masq_lock);
 124
 125         return ret;
 126 }
 127
 128 static int masq_device_event(struct notifier_block *this,
 129                              unsigned long event,
 130                              void *ptr)
 131 {
 132         const struct net_device *dev = ptr;
 133
 134         if (event == NETDEV_DOWN) {
 135                 /* Device was downed.  Search entire table for
 136                    conntracks which were associated with that device,
 137                    and forget them. */
 138                 NF_CT_ASSERT(dev->ifindex != 0);
 139
 140                 nf_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 141         }
 142
 143         return NOTIFY_DONE;
 144 }
 145
 146 static int masq_inet_event(struct notifier_block *this,
 147                            unsigned long event,
 148                            void *ptr)
 149 {
 150         const struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 151
 152         if (event == NETDEV_DOWN) {
 153                 /* IP address was deleted.  Search entire table for
 154                    conntracks which were associated with that device,
 155                    and forget them. */
 156                 NF_CT_ASSERT(dev->ifindex != 0);
 157
 158                 nf_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 159         }
 160
 161         return NOTIFY_DONE;
 162 }
 163
 164 static struct notifier_block masq_dev_notifier = {
 165         .notifier_call  = masq_device_event,
 166 };
 167
 168 static struct notifier_block masq_inet_notifier = {
 169         .notifier_call  = masq_inet_event,
 170 };
 171
 172 static struct xt_target masquerade __read_mostly = {
 173         .name           = "MASQUERADE",
 174         .family         = AF_INET,
 175         .target         = masquerade_target,
 176         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
 177         .table          = "nat",
 178         .hooks          = 1 << NF_IP_POST_ROUTING,
 179         .checkentry     = masquerade_check,
 180         .me             = THIS_MODULE,
 181 };
 182
 183 static int __init ipt_masquerade_init(void)
 184 {
 185         int ret;
 186
 187         ret = xt_register_target(&masquerade);
 188
 189         if (ret == 0) {
 190                 /* Register for device down reports */
 191                 register_netdevice_notifier(&masq_dev_notifier);
 192                 /* Register IP address change reports */
 193                 register_inetaddr_notifier(&masq_inet_notifier);
 194         }
 195
 196         return ret;
 197 }
 198
 199 static void __exit ipt_masquerade_fini(void)
 200 {
 201         xt_unregister_target(&masquerade);
 202         unregister_netdevice_notifier(&masq_dev_notifier);
 203         unregister_inetaddr_notifier(&masq_inet_notifier);
 204 }
 205
 206 module_init(ipt_masquerade_init);
 207 module_exit(ipt_masquerade_fini);