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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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 /* FIXME: Multiple targets. --RR */
  31 static int masquerade_tg_check(const struct xt_tgchk_param *par)
  32 {
  33         const struct nf_nat_multi_range_compat *mr = par->targinfo;
  34
  35         if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  36                 pr_debug("bad MAP_IPS.\n");
  37                 return -EINVAL;
  38         }
  39         if (mr->rangesize != 1) {
  40                 pr_debug("bad rangesize %u\n", mr->rangesize);
  41                 return -EINVAL;
  42         }
  43         return 0;
  44 }
  45
  46 static unsigned int
  47 masquerade_tg(struct sk_buff *skb, const struct xt_action_param *par)
  48 {
  49         struct nf_conn *ct;
  50         struct nf_conn_nat *nat;
  51         enum ip_conntrack_info ctinfo;
  52         struct nf_nat_range newrange;
  53         const struct nf_nat_multi_range_compat *mr;
  54         const struct rtable *rt;
  55         __be32 newsrc;
  56
  57         NF_CT_ASSERT(par->hooknum == NF_INET_POST_ROUTING);
  58
  59         ct = nf_ct_get(skb, &ctinfo);
  60         nat = nfct_nat(ct);
  61
  62         NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
  63                             ctinfo == IP_CT_RELATED_REPLY));
  64
  65         /* Source address is 0.0.0.0 - locally generated packet that is
  66          * probably not supposed to be masqueraded.
  67          */
  68         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
  69                 return NF_ACCEPT;
  70
  71         mr = par->targinfo;
  72         rt = skb_rtable(skb);
  73         newsrc = inet_select_addr(par->out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
  74         if (!newsrc) {
  75                 pr_info("%s ate my IP address\n", par->out->name);
  76                 return NF_DROP;
  77         }
  78
  79         nat->masq_index = par->out->ifindex;
  80
  81         /* Transfer from original range. */
  82         newrange = ((struct nf_nat_range)
  83                 { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  84                   newsrc, newsrc,
  85                   mr->range[0].min, mr->range[0].max });
  86
  87         /* Hand modified range to generic setup. */
  88         return nf_nat_setup_info(ct, &newrange, IP_NAT_MANIP_SRC);
  89 }
  90
  91 static int
  92 device_cmp(struct nf_conn *i, void *ifindex)
  93 {
  94         const struct nf_conn_nat *nat = nfct_nat(i);
  95
  96         if (!nat)
  97                 return 0;
  98
  99         return nat->masq_index == (int)(long)ifindex;
 100 }
 101
 102 static int masq_device_event(struct notifier_block *this,
 103                              unsigned long event,
 104                              void *ptr)
 105 {
 106         const struct net_device *dev = ptr;
 107         struct net *net = dev_net(dev);
 108
 109         if (event == NETDEV_DOWN) {
 110                 /* Device was downed.  Search entire table for
 111                    conntracks which were associated with that device,
 112                    and forget them. */
 113                 NF_CT_ASSERT(dev->ifindex != 0);
 114
 115                 nf_ct_iterate_cleanup(net, device_cmp,
 116                                       (void *)(long)dev->ifindex);
 117         }
 118
 119         return NOTIFY_DONE;
 120 }
 121
 122 static int masq_inet_event(struct notifier_block *this,
 123                            unsigned long event,
 124                            void *ptr)
 125 {
 126         struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 127         return masq_device_event(this, event, dev);
 128 }
 129
 130 static struct notifier_block masq_dev_notifier = {
 131         .notifier_call  = masq_device_event,
 132 };
 133
 134 static struct notifier_block masq_inet_notifier = {
 135         .notifier_call  = masq_inet_event,
 136 };
 137
 138 static struct xt_target masquerade_tg_reg __read_mostly = {
 139         .name           = "MASQUERADE",
 140         .family         = NFPROTO_IPV4,
 141         .target         = masquerade_tg,
 142         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
 143         .table          = "nat",
 144         .hooks          = 1 << NF_INET_POST_ROUTING,
 145         .checkentry     = masquerade_tg_check,
 146         .me             = THIS_MODULE,
 147 };
 148
 149 static int __init masquerade_tg_init(void)
 150 {
 151         int ret;
 152
 153         ret = xt_register_target(&masquerade_tg_reg);
 154
 155         if (ret == 0) {
 156                 /* Register for device down reports */
 157                 register_netdevice_notifier(&masq_dev_notifier);
 158                 /* Register IP address change reports */
 159                 register_inetaddr_notifier(&masq_inet_notifier);
 160         }
 161
 162         return ret;
 163 }
 164
 165 static void __exit masquerade_tg_exit(void)
 166 {
 167         xt_unregister_target(&masquerade_tg_reg);
 168         unregister_netdevice_notifier(&masq_dev_notifier);
 169         unregister_inetaddr_notifier(&masq_inet_notifier);
 170 }
 171
 172 module_init(masquerade_tg_init);
 173 module_exit(masquerade_tg_exit);