text: /* Masquerade.  Simple mapping which alters range to a local IP address
     (depending on route). */
  
  /* (C) 1999-2001 Paul `Rusty' Russell
   * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   */
  
  #include <linux/types.h>
  #include <linux/inetdevice.h>
  #include <linux/ip.h>
  #include <linux/timer.h>
  #include <linux/module.h>
  #include <linux/netfilter.h>
  #include <net/protocol.h>
  #include <net/ip.h>
  #include <net/checksum.h>
  #include <net/route.h>
  #include <net/netfilter/nf_nat_rule.h>
  #include <linux/netfilter_ipv4.h>
  #include <linux/netfilter/x_tables.h>
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  MODULE_DESCRIPTION("iptables MASQUERADE target module");
  
  /* Lock protects masq region inside conntrack */
  static DEFINE_RWLOCK(masq_lock);
  
  /* FIXME: Multiple targets. --RR */
  static bool
  masquerade_check(const char *tablename,
  		 const void *e,
  		 const struct xt_target *target,
  		 void *targinfo,
  		 unsigned int hook_mask)
  {
  	const struct nf_nat_multi_range_compat *mr = targinfo;
  
  	if (mr->range[0].flags & IP_NAT_RANGE_MAP_IPS) {
  		pr_debug("masquerade_check: bad MAP_IPS.\n");
  		return false;
  	}
  	if (mr->rangesize != 1) {
  		pr_debug("masquerade_check: bad rangesize %u\n", mr->rangesize);
  		return false;
  	}
  	return true;
  }
  
  static unsigned int
  masquerade_target(struct sk_buff *skb,
  		  const struct net_device *in,
  		  const struct net_device *out,
  		  unsigned int hooknum,
  		  const struct xt_target *target,
  		  const void *targinfo)
  {
  	struct nf_conn *ct;
  	struct nf_conn_nat *nat;
  	enum ip_conntrack_info ctinfo;
  	struct nf_nat_range newrange;
  	const struct nf_nat_multi_range_compat *mr;
  	const struct rtable *rt;
  	__be32 newsrc;
  
  	NF_CT_ASSERT(hooknum == NF_IP_POST_ROUTING);
  
  	ct = nf_ct_get(skb, &ctinfo);
  	nat = nfct_nat(ct);
  
  	NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
  			    || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
  
  	/* Source address is 0.0.0.0 - locally generated packet that is
  	 * probably not supposed to be masqueraded.
  	 */
  	if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
  		return NF_ACCEPT;
  
  	mr = targinfo;
  	rt = (struct rtable *)skb->dst;
  	newsrc = inet_select_addr(out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
  	if (!newsrc) {
  		printk("MASQUERADE: %s ate my IP address\n", out->name);
  		return NF_DROP;
  	}
  
  	write_lock_bh(&masq_lock);
  	nat->masq_index = out->ifindex;
  	write_unlock_bh(&masq_lock);
  
  	/* Transfer from original range. */
  	newrange = ((struct nf_nat_range)
  		{ mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
  		  newsrc, newsrc,
  		  mr->range[0].min, mr->range[0].max });
  
  	/* Hand modified range to generic setup. */
  	return nf_nat_setup_info(ct, &newrange, hooknum);
  }
  
  static int
  device_cmp(struct nf_conn *i, void *ifindex)
  {
  	const struct nf_conn_nat *nat = nfct_nat(i);
  	int ret;
  
  	if (!nat)
  		return 0;
  
  	read_lock_bh(&masq_lock);
  	ret = (nat->masq_index == (int)(long)ifindex);
  	read_unlock_bh(&masq_lock);
  
  	return ret;
  }
  
  static int masq_device_event(struct notifier_block *this,
  			     unsigned long event,
  			     void *ptr)
  {
  	const struct net_device *dev = ptr;
  
  	if (dev->nd_net != &init_net)
  		return NOTIFY_DONE;
  
  	if (event == NETDEV_DOWN) {
  		/* Device was downed.  Search entire table for
  		   conntracks which were associated with that device,
  		   and forget them. */
  		NF_CT_ASSERT(dev->ifindex != 0);
  
  		nf_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
  	}
  
  	return NOTIFY_DONE;
  }
  
  static int masq_inet_event(struct notifier_block *this,
  			   unsigned long event,
  			   void *ptr)
  {
  	const struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
  
  	if (event == NETDEV_DOWN) {
  		/* IP address was deleted.  Search entire table for
  		   conntracks which were associated with that device,
  		   and forget them. */
  		NF_CT_ASSERT(dev->ifindex != 0);
  
  		nf_ct_iterate_cleanup(device_cmp, (void *)(long)dev->ifindex);
  	}
  
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block masq_dev_notifier = {
  	.notifier_call	= masq_device_event,
  };
  
  static struct notifier_block masq_inet_notifier = {
  	.notifier_call	= masq_inet_event,
  };
  
  static struct xt_target masquerade __read_mostly = {
  	.name		= "MASQUERADE",
  	.family		= AF_INET,
  	.target		= masquerade_target,
  	.targetsize	= sizeof(struct nf_nat_multi_range_compat),
  	.table		= "nat",
  	.hooks		= 1 << NF_IP_POST_ROUTING,
  	.checkentry	= masquerade_check,
  	.me		= THIS_MODULE,
  };
  
  static int __init ipt_masquerade_init(void)
  {
  	int ret;
  
  	ret = xt_register_target(&masquerade);
  
  	if (ret == 0) {
  		/* Register for device down reports */
  		register_netdevice_notifier(&masq_dev_notifier);
  		/* Register IP address change reports */
  		register_inetaddr_notifier(&masq_inet_notifier);
  	}
  
  	return ret;
  }
  
  static void __exit ipt_masquerade_fini(void)
  {
  	xt_unregister_target(&masquerade);
  	unregister_netdevice_notifier(&masq_dev_notifier);
  	unregister_inetaddr_notifier(&masq_inet_notifier);
  }
  
  module_init(ipt_masquerade_init);
  module_exit(ipt_masquerade_fini);
  