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 <linux/netfilter_ipv4.h>
  23 #include <linux/netfilter/x_tables.h>
  24 #include <net/netfilter/nf_nat.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_ipv4_multi_range_compat *mr = par->targinfo;
  34
  35         if (mr->range[0].flags & NF_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_ipv4_multi_range_compat *mr;
  54         const struct rtable *rt;
  55         __be32 newsrc, nh;
  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         nh = rt_nexthop(rt, ip_hdr(skb)->daddr);
  74         newsrc = inet_select_addr(par->out, nh, RT_SCOPE_UNIVERSE);
  75         if (!newsrc) {
  76                 pr_info("%s ate my IP address\n", par->out->name);
  77                 return NF_DROP;
  78         }
  79
  80         nat->masq_index = par->out->ifindex;
  81
  82         /* Transfer from original range. */
  83         memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
  84         memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
  85         newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
  86         newrange.min_addr.ip = newsrc;
  87         newrange.max_addr.ip = newsrc;
  88         newrange.min_proto   = mr->range[0].min;
  89         newrange.max_proto   = mr->range[0].max;
  90
  91         /* Hand modified range to generic setup. */
  92         return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
  93 }
  94
  95 static int
  96 device_cmp(struct nf_conn *i, void *ifindex)
  97 {
  98         const struct nf_conn_nat *nat = nfct_nat(i);
  99
 100         if (!nat)
 101                 return 0;
 102         if (nf_ct_l3num(i) != NFPROTO_IPV4)
 103                 return 0;
 104         return nat->masq_index == (int)(long)ifindex;
 105 }
 106
 107 static int masq_device_event(struct notifier_block *this,
 108                              unsigned long event,
 109                              void *ptr)
 110 {
 111         const struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 112         struct net *net = dev_net(dev);
 113
 114         if (event == NETDEV_DOWN) {
 115                 /* Device was downed.  Search entire table for
 116                    conntracks which were associated with that device,
 117                    and forget them. */
 118                 NF_CT_ASSERT(dev->ifindex != 0);
 119
 120                 nf_ct_iterate_cleanup(net, device_cmp,
 121                                       (void *)(long)dev->ifindex);
 122         }
 123
 124         return NOTIFY_DONE;
 125 }
 126
 127 static int masq_inet_event(struct notifier_block *this,
 128                            unsigned long event,
 129                            void *ptr)
 130 {
 131         struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
 132         return masq_device_event(this, event, dev);
 133 }
 134
 135 static struct notifier_block masq_dev_notifier = {
 136         .notifier_call  = masq_device_event,
 137 };
 138
 139 static struct notifier_block masq_inet_notifier = {
 140         .notifier_call  = masq_inet_event,
 141 };
 142
 143 static struct xt_target masquerade_tg_reg __read_mostly = {
 144         .name           = "MASQUERADE",
 145         .family         = NFPROTO_IPV4,
 146         .target         = masquerade_tg,
 147         .targetsize     = sizeof(struct nf_nat_ipv4_multi_range_compat),
 148         .table          = "nat",
 149         .hooks          = 1 << NF_INET_POST_ROUTING,
 150         .checkentry     = masquerade_tg_check,
 151         .me             = THIS_MODULE,
 152 };
 153
 154 static int __init masquerade_tg_init(void)
 155 {
 156         int ret;
 157
 158         ret = xt_register_target(&masquerade_tg_reg);
 159
 160         if (ret == 0) {
 161                 /* Register for device down reports */
 162                 register_netdevice_notifier(&masq_dev_notifier);
 163                 /* Register IP address change reports */
 164                 register_inetaddr_notifier(&masq_inet_notifier);
 165         }
 166
 167         return ret;
 168 }
 169
 170 static void __exit masquerade_tg_exit(void)
 171 {
 172         xt_unregister_target(&masquerade_tg_reg);
 173         unregister_netdevice_notifier(&masq_dev_notifier);
 174         unregister_inetaddr_notifier(&masq_inet_notifier);
 175 }
 176
 177 module_init(masquerade_tg_init);
 178 module_exit(masquerade_tg_exit);