// SPDX-License-Identifier: GPL-2.0-only
/*
 *  ebt_arpreply
 *
 *	Authors:
 *	Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
 *	Bart De Schuymer <bdschuym@pandora.be>
 *
 *  August, 2003
 *
 */
#include <linux/if_arp.h>
#include <net/arp.h>
#include <linux/module.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_arpreply.h>

static unsigned int
ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
	const struct ebt_arpreply_info *info = par->targinfo;
	const __be32 *siptr, *diptr;
	__be32 _sip, _dip;
	const struct arphdr *ap;
	struct arphdr _ah;
	const unsigned char *shp;
	unsigned char _sha[ETH_ALEN];

	ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
	if (ap == NULL)
		return EBT_DROP;

	if (ap->ar_op != htons(ARPOP_REQUEST) ||
	    ap->ar_hln != ETH_ALEN ||
	    ap->ar_pro != htons(ETH_P_IP) ||
	    ap->ar_pln != 4)
		return EBT_CONTINUE;

	shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
	if (shp == NULL)
		return EBT_DROP;

	siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
				   sizeof(_sip), &_sip);
	if (siptr == NULL)
		return EBT_DROP;

	diptr = skb_header_pointer(skb,
				   sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
				   sizeof(_dip), &_dip);
	if (diptr == NULL)
		return EBT_DROP;

	arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr,
		 (struct net_device *)xt_in(par),
		 *diptr, shp, info->mac, shp);

	return info->target;
}

static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
{
	const struct ebt_arpreply_info *info = par->targinfo;
	const struct ebt_entry *e = par->entryinfo;

	if (BASE_CHAIN && info->target == EBT_RETURN)
		return -EINVAL;
	if (e->ethproto != htons(ETH_P_ARP) ||
	    e->invflags & EBT_IPROTO)
		return -EINVAL;
	if (ebt_invalid_target(info->target))
		return -EINVAL;

	return 0;
}

static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
	.name		= "arpreply",
	.revision	= 0,
	.family		= NFPROTO_BRIDGE,
	.table		= "nat",
	.hooks		= (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
	.target		= ebt_arpreply_tg,
	.checkentry	= ebt_arpreply_tg_check,
	.targetsize	= sizeof(struct ebt_arpreply_info),
	.me		= THIS_MODULE,
};

static int __init ebt_arpreply_init(void)
{
	return xt_register_target(&ebt_arpreply_tg_reg);
}

static void __exit ebt_arpreply_fini(void)
{
	xt_unregister_target(&ebt_arpreply_tg_reg);
}

module_init(ebt_arpreply_init);
module_exit(ebt_arpreply_fini);
MODULE_DESCRIPTION("Ebtables: ARP reply target");
MODULE_LICENSE("GPL");