net/netfilter/xt_MASQUERADE.c

// SPDX-License-Identifier: GPL-2.0-only
/* 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>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/netfilter/x_tables.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/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 nf_ct_netns_get(par->net, par->family);
}

static unsigned int
masquerade_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
	struct nf_nat_range2 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, xt_hooknum(par), &range,
				      xt_out(par));
}

static void masquerade_tg_destroy(const struct xt_tgdtor_param *par)
{
	nf_ct_netns_put(par->net, par->family);
}

#if IS_ENABLED(CONFIG_IPV6)
static unsigned int
masquerade_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
	return nf_nat_masquerade_ipv6(skb, par->targinfo, xt_out(par));
}

static int masquerade_tg6_checkentry(const struct xt_tgchk_param *par)
{
	const struct nf_nat_range2 *range = par->targinfo;

	if (range->flags & NF_NAT_RANGE_MAP_IPS)
		return -EINVAL;

	return nf_ct_netns_get(par->net, par->family);
}
#endif

static struct xt_target masquerade_tg_reg[] __read_mostly = {
	{
#if IS_ENABLED(CONFIG_IPV6)
		.name		= "MASQUERADE",
		.family		= NFPROTO_IPV6,
		.target		= masquerade_tg6,
		.targetsize	= sizeof(struct nf_nat_range),
		.table		= "nat",
		.hooks		= 1 << NF_INET_POST_ROUTING,
		.checkentry	= masquerade_tg6_checkentry,
		.destroy	= masquerade_tg_destroy,
		.me		= THIS_MODULE,
	}, {
#endif
		.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,
		.destroy	= masquerade_tg_destroy,
		.me		= THIS_MODULE,
	}
};

static int __init masquerade_tg_init(void)
{
	int ret;

	ret = xt_register_targets(masquerade_tg_reg,
				  ARRAY_SIZE(masquerade_tg_reg));
	if (ret)
		return ret;

	ret = nf_nat_masquerade_inet_register_notifiers();
	if (ret) {
		xt_unregister_targets(masquerade_tg_reg,
				      ARRAY_SIZE(masquerade_tg_reg));
		return ret;
	}

	return ret;
}

static void __exit masquerade_tg_exit(void)
{
	xt_unregister_targets(masquerade_tg_reg, ARRAY_SIZE(masquerade_tg_reg));
	nf_nat_masquerade_inet_unregister_notifiers();
}

module_init(masquerade_tg_init);
module_exit(masquerade_tg_exit);
#if IS_ENABLED(CONFIG_IPV6)
MODULE_ALIAS("ip6t_MASQUERADE");
#endif
MODULE_ALIAS("ipt_MASQUERADE");