net/ipv4/netfilter/ipt_MASQUERADE.c

/* 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.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#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 <linux/netfilter_ipv4.h>
#include <linux/netfilter/x_tables.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/ipv4/nf_nat_masquerade.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("Xtables: automatic-address SNAT");

/* FIXME: Multiple targets. --RR */
static int masquerade_tg_check(const struct xt_tgchk_param *par)
{
	const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;

	if (mr->range[0].flags & NF_NAT_RANGE_MAP_IPS) {
		pr_debug("bad MAP_IPS.\n");
		return -EINVAL;
	}
	if (mr->rangesize != 1) {
		pr_debug("bad rangesize %u\n", mr->rangesize);
		return -EINVAL;
	}
	return 0;
}

static unsigned int
masquerade_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
	struct nf_nat_range range;
	const struct nf_nat_ipv4_multi_range_compat *mr;

	mr = par->targinfo;
	range.flags = mr->range[0].flags;
	range.min_proto = mr->range[0].min;
	range.max_proto = mr->range[0].max;

	return nf_nat_masquerade_ipv4(skb, par->hooknum, &range, par->out);
}

static struct xt_target masquerade_tg_reg __read_mostly = {
	.name		= "MASQUERADE",
	.family		= NFPROTO_IPV4,
	.target		= masquerade_tg,
	.targetsize	= sizeof(struct nf_nat_ipv4_multi_range_compat),
	.table		= "nat",
	.hooks		= 1 << NF_INET_POST_ROUTING,
	.checkentry	= masquerade_tg_check,
	.me		= THIS_MODULE,
};

static int __init masquerade_tg_init(void)
{
	int ret;

	ret = xt_register_target(&masquerade_tg_reg);

	if (ret == 0)
		nf_nat_masquerade_ipv4_register_notifier();

	return ret;
}

static void __exit masquerade_tg_exit(void)
{
	xt_unregister_target(&masquerade_tg_reg);
	nf_nat_masquerade_ipv4_unregister_notifier();
}

module_init(masquerade_tg_init);
module_exit(masquerade_tg_exit);