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 masquerade_tg_check(const struct xt_tgchk_param *par)
  35 {
  36         const struct nf_nat_multi_range_compat *mr = par->targinfo;
  37
  38         if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  39                 pr_debug("masquerade_check: bad MAP_IPS.\n");
  40                 return false;
  41         }
  42         if (mr->rangesize != 1) {
  43                 pr_debug("masquerade_check: bad rangesize %u\n", mr->rangesize);
  44                 return false;
  45         }
  46         return true;
  47 }
  48
  49 static unsigned int
  50 masquerade_tg(struct sk_buff *skb, const struct xt_target_param *par)
  51 {
  52         struct nf_conn *ct;
  53         struct nf_conn_nat *nat;
  54         enum ip_conntrack_info ctinfo;
  55         struct nf_nat_range newrange;
  56         const struct nf_nat_multi_range_compat *mr;
  57         const struct rtable *rt;
  58         __be32 newsrc;
  59
  60         NF_CT_ASSERT(par->hooknum == NF_INET_POST_ROUTING);
  61
  62         ct = nf_ct_get(skb, &ctinfo);
  63         nat = nfct_nat(ct);
  64
  65         NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
  66                             || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
  67
  68         /* Source address is 0.0.0.0 - locally generated packet that is
  69          * probably not supposed to be masqueraded.
  70          */
  71         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
  72                 return NF_ACCEPT;
  73
  74         mr = par->targinfo;
  75         rt = skb->rtable;
  76         newsrc = inet_select_addr(par->out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
  77         if (!newsrc) {
  78                 printk("MASQUERADE: %s ate my IP address\n", par->out->name);
  79                 return NF_DROP;
  80         }
  81
  82         write_lock_bh(&masq_lock);
  83         nat->masq_index = par->out->ifindex;
  84         write_unlock_bh(&masq_lock);
  85
  86         /* Transfer from original range. */
  87         newrange = ((struct nf_nat_range)
  88                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  89                   newsrc, newsrc,
  90                   mr->range[0].min, mr->range[0].max });
  91
  92         /* Hand modified range to generic setup. */
  93         return nf_nat_setup_info(ct, &newrange, IP_NAT_MANIP_SRC);
  94 }
  95
  96 static int
  97 device_cmp(struct nf_conn *i, void *ifindex)
  98 {
  99         const struct nf_conn_nat *nat = nfct_nat(i);
 100         int ret;
 101
 102         if (!nat)
 103                 return 0;
 104
 105         read_lock_bh(&masq_lock);
 106         ret = (nat->masq_index == (int)(long)ifindex);
 107         read_unlock_bh(&masq_lock);
 108
 109         return ret;
 110 }
 111
 112 static int masq_device_event(struct notifier_block *this,
 113                              unsigned long event,
 114                              void *ptr)
 115 {
 116         const struct net_device *dev = ptr;
 117         struct net *net = dev_net(dev);
 118
 119         if (event == NETDEV_DOWN) {
 120                 /* Device was downed.  Search entire table for
 121                    conntracks which were associated with that device,
 122                    and forget them. */
 123                 NF_CT_ASSERT(dev->ifindex != 0);
 124
 125                 nf_ct_iterate_cleanup(net, device_cmp,
 126                                       (void *)(long)dev->ifindex);
 127         }
 128
 129         return NOTIFY_DONE;
 130 }
 131
 132 static int masq_inet_event(struct notifier_block *this,
 133                            unsigned long event,
 134                            void *ptr)
 135 {
 136         struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 137         return masq_device_event(this, event, dev);
 138 }
 139
 140 static struct notifier_block masq_dev_notifier = {
 141         .notifier_call  = masq_device_event,
 142 };
 143
 144 static struct notifier_block masq_inet_notifier = {
 145         .notifier_call  = masq_inet_event,
 146 };
 147
 148 static struct xt_target masquerade_tg_reg __read_mostly = {
 149         .name           = "MASQUERADE",
 150         .family         = NFPROTO_IPV4,
 151         .target         = masquerade_tg,
 152         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
 153         .table          = "nat",
 154         .hooks          = 1 << NF_INET_POST_ROUTING,
 155         .checkentry     = masquerade_tg_check,
 156         .me             = THIS_MODULE,
 157 };
 158
 159 static int __init masquerade_tg_init(void)
 160 {
 161         int ret;
 162
 163         ret = xt_register_target(&masquerade_tg_reg);
 164
 165         if (ret == 0) {
 166                 /* Register for device down reports */
 167                 register_netdevice_notifier(&masq_dev_notifier);
 168                 /* Register IP address change reports */
 169                 register_inetaddr_notifier(&masq_inet_notifier);
 170         }
 171
 172         return ret;
 173 }
 174
 175 static void __exit masquerade_tg_exit(void)
 176 {
 177         xt_unregister_target(&masquerade_tg_reg);
 178         unregister_netdevice_notifier(&masq_dev_notifier);
 179         unregister_inetaddr_notifier(&masq_inet_notifier);
 180 }
 181
 182 module_init(masquerade_tg_init);
 183 module_exit(masquerade_tg_exit);