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("Xtables: automatic-address SNAT");
  29
  30 /* Lock protects masq region inside conntrack */
  31 static DEFINE_RWLOCK(masq_lock);
  32
  33 /* FIXME: Multiple targets. --RR */
  34 static bool
  35 masquerade_tg_check(const char *tablename, const void *e,
  36                     const struct xt_target *target, void *targinfo,
  37                     unsigned int hook_mask)
  38 {
  39         const struct nf_nat_multi_range_compat *mr = targinfo;
  40
  41         if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  42                 pr_debug("masquerade_check: bad MAP_IPS.\n");
  43                 return false;
  44         }
  45         if (mr->rangesize != 1) {
  46                 pr_debug("masquerade_check: bad rangesize %u\n", mr->rangesize);
  47                 return false;
  48         }
  49         return true;
  50 }
  51
  52 static unsigned int
  53 masquerade_tg(struct sk_buff *skb, const struct net_device *in,
  54               const struct net_device *out, unsigned int hooknum,
  55               const struct xt_target *target, const void *targinfo)
  56 {
  57         struct nf_conn *ct;
  58         struct nf_conn_nat *nat;
  59         enum ip_conntrack_info ctinfo;
  60         struct nf_nat_range newrange;
  61         const struct nf_nat_multi_range_compat *mr;
  62         const struct rtable *rt;
  63         __be32 newsrc;
  64
  65         NF_CT_ASSERT(hooknum == NF_INET_POST_ROUTING);
  66
  67         ct = nf_ct_get(skb, &ctinfo);
  68         nat = nfct_nat(ct);
  69
  70         NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
  71                             || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
  72
  73         /* Source address is 0.0.0.0 - locally generated packet that is
  74          * probably not supposed to be masqueraded.
  75          */
  76         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
  77                 return NF_ACCEPT;
  78
  79         mr = targinfo;
  80         rt = (struct rtable *)skb->dst;
  81         newsrc = inet_select_addr(out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
  82         if (!newsrc) {
  83                 printk("MASQUERADE: %s ate my IP address\n", out->name);
  84                 return NF_DROP;
  85         }
  86
  87         write_lock_bh(&masq_lock);
  88         nat->masq_index = out->ifindex;
  89         write_unlock_bh(&masq_lock);
  90
  91         /* Transfer from original range. */
  92         newrange = ((struct nf_nat_range)
  93                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  94                   newsrc, newsrc,
  95                   mr->range[0].min, mr->range[0].max });
  96
  97         /* Hand modified range to generic setup. */
  98         return nf_nat_setup_info(ct, &newrange, IP_NAT_MANIP_SRC);
  99 }
 100
 101 static int
 102 device_cmp(struct nf_conn *i, void *ifindex)
 103 {
 104         const struct nf_conn_nat *nat = nfct_nat(i);
 105         int ret;
 106
 107         if (!nat)
 108                 return 0;
 109
 110         read_lock_bh(&masq_lock);
 111         ret = (nat->masq_index == (int)(long)ifindex);
 112         read_unlock_bh(&masq_lock);
 113
 114         return ret;
 115 }
 116
 117 static int masq_device_event(struct notifier_block *this,
 118                              unsigned long event,
 119                              void *ptr)
 120 {
 121         const struct net_device *dev = ptr;
 122
 123         if (dev->nd_net != &init_net)
 124                 return NOTIFY_DONE;
 125
 126         if (event == NETDEV_DOWN) {
 127                 /* Device was downed.  Search entire table for
 128                    conntracks which were associated with that device,
 129                    and forget them. */
 130                 NF_CT_ASSERT(dev->ifindex != 0);
 131
 132                 nf_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 133         }
 134
 135         return NOTIFY_DONE;
 136 }
 137
 138 static int masq_inet_event(struct notifier_block *this,
 139                            unsigned long event,
 140                            void *ptr)
 141 {
 142         const struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 143
 144         if (event == NETDEV_DOWN) {
 145                 /* IP address was deleted.  Search entire table for
 146                    conntracks which were associated with that device,
 147                    and forget them. */
 148                 NF_CT_ASSERT(dev->ifindex != 0);
 149
 150                 nf_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
 151         }
 152
 153         return NOTIFY_DONE;
 154 }
 155
 156 static struct notifier_block masq_dev_notifier = {
 157         .notifier_call  = masq_device_event,
 158 };
 159
 160 static struct notifier_block masq_inet_notifier = {
 161         .notifier_call  = masq_inet_event,
 162 };
 163
 164 static struct xt_target masquerade_tg_reg __read_mostly = {
 165         .name           = "MASQUERADE",
 166         .family         = AF_INET,
 167         .target         = masquerade_tg,
 168         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
 169         .table          = "nat",
 170         .hooks          = 1 << NF_INET_POST_ROUTING,
 171         .checkentry     = masquerade_tg_check,
 172         .me             = THIS_MODULE,
 173 };
 174
 175 static int __init masquerade_tg_init(void)
 176 {
 177         int ret;
 178
 179         ret = xt_register_target(&masquerade_tg_reg);
 180
 181         if (ret == 0) {
 182                 /* Register for device down reports */
 183                 register_netdevice_notifier(&masq_dev_notifier);
 184                 /* Register IP address change reports */
 185                 register_inetaddr_notifier(&masq_inet_notifier);
 186         }
 187
 188         return ret;
 189 }
 190
 191 static void __exit masquerade_tg_exit(void)
 192 {
 193         xt_unregister_target(&masquerade_tg_reg);
 194         unregister_netdevice_notifier(&masq_dev_notifier);
 195         unregister_inetaddr_notifier(&masq_inet_notifier);
 196 }
 197
 198 module_init(masquerade_tg_init);
 199 module_exit(masquerade_tg_exit);