/* (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/module.h>
#include <linux/atomic.h>
#include <linux/inetdevice.h>
#include <linux/ip.h>
#include <linux/timer.h>
#include <linux/netfilter.h>
#include <net/protocol.h>
#include <net/ip.h>
#include <net/checksum.h>
#include <net/route.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter/x_tables.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/ipv4/nf_nat_masquerade.h>

unsigned int
nf_nat_masquerade_ipv4(struct sk_buff *skb, unsigned int hooknum,
		       const struct nf_nat_range *range,
		       const struct net_device *out)
{
	struct nf_conn *ct;
	struct nf_conn_nat *nat;
	enum ip_conntrack_info ctinfo;
	struct nf_nat_range newrange;
	const struct rtable *rt;
	__be32 newsrc, nh;

	NF_CT_ASSERT(hooknum == NF_INET_POST_ROUTING);

	ct = nf_ct_get(skb, &ctinfo);

	NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
			    ctinfo == IP_CT_RELATED_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;

	rt = skb_rtable(skb);
	nh = rt_nexthop(rt, ip_hdr(skb)->daddr);
	newsrc = inet_select_addr(out, nh, RT_SCOPE_UNIVERSE);
	if (!newsrc) {
		pr_info("%s ate my IP address\n", out->name);
		return NF_DROP;
	}

	nat = nf_ct_nat_ext_add(ct);
	if (nat)
		nat->masq_index = out->ifindex;

	/* Transfer from original range. */
	memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
	memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
	newrange.flags       = range->flags | NF_NAT_RANGE_MAP_IPS;
	newrange.min_addr.ip = newsrc;
	newrange.max_addr.ip = newsrc;
	newrange.min_proto   = range->min_proto;
	newrange.max_proto   = range->max_proto;

	/* Hand modified range to generic setup. */
	return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
}
EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv4);

static int device_cmp(struct nf_conn *i, void *ifindex)
{
	const struct nf_conn_nat *nat = nfct_nat(i);

	if (!nat)
		return 0;
	if (nf_ct_l3num(i) != NFPROTO_IPV4)
		return 0;
	return nat->masq_index == (int)(long)ifindex;
}

static int masq_device_event(struct notifier_block *this,
			     unsigned long event,
			     void *ptr)
{
	const struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct net *net = dev_net(dev);

	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(net, device_cmp,
				      (void *)(long)dev->ifindex, 0, 0);
	}

	return NOTIFY_DONE;
}

static int masq_inet_event(struct notifier_block *this,
			   unsigned long event,
			   void *ptr)
{
	struct in_device *idev = ((struct in_ifaddr *)ptr)->ifa_dev;
	struct netdev_notifier_info info;

	/* The masq_dev_notifier will catch the case of the device going
	 * down.  So if the inetdev is dead and being destroyed we have
	 * no work to do.  Otherwise this is an individual address removal
	 * and we have to perform the flush.
	 */
	if (idev->dead)
		return NOTIFY_DONE;

	netdev_notifier_info_init(&info, idev->dev);
	return masq_device_event(this, event, &info);
}

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 atomic_t masquerade_notifier_refcount = ATOMIC_INIT(0);

void nf_nat_masquerade_ipv4_register_notifier(void)
{
	/* check if the notifier was already set */
	if (atomic_inc_return(&masquerade_notifier_refcount) > 1)
		return;

	/* Register for device down reports */
	register_netdevice_notifier(&masq_dev_notifier);
	/* Register IP address change reports */
	register_inetaddr_notifier(&masq_inet_notifier);
}
EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv4_register_notifier);

void nf_nat_masquerade_ipv4_unregister_notifier(void)
{
	/* check if the notifier still has clients */
	if (atomic_dec_return(&masquerade_notifier_refcount) > 0)
		return;

	unregister_netdevice_notifier(&masq_dev_notifier);
	unregister_inetaddr_notifier(&masq_inet_notifier);
}
EXPORT_SYMBOL_GPL(nf_nat_masquerade_ipv4_unregister_notifier);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");