// SPDX-License-Identifier: GPL-2.0-only
/*
 *  ebt_arp
 *
 *	Authors:
 *	Bart De Schuymer <bdschuym@pandora.be>
 *	Tim Gardner <timg@tpi.com>
 *
 *  April, 2002
 *
 */
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/module.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_arp.h>

static bool
ebt_arp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct ebt_arp_info *info = par->matchinfo;
	const struct arphdr *ah;
	struct arphdr _arph;

	ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
	if (ah == NULL)
		return false;
	if ((info->bitmask & EBT_ARP_OPCODE) &&
	    NF_INVF(info, EBT_ARP_OPCODE, info->opcode != ah->ar_op))
		return false;
	if ((info->bitmask & EBT_ARP_HTYPE) &&
	    NF_INVF(info, EBT_ARP_HTYPE, info->htype != ah->ar_hrd))
		return false;
	if ((info->bitmask & EBT_ARP_PTYPE) &&
	    NF_INVF(info, EBT_ARP_PTYPE, info->ptype != ah->ar_pro))
		return false;

	if (info->bitmask & (EBT_ARP_SRC_IP | EBT_ARP_DST_IP | EBT_ARP_GRAT)) {
		const __be32 *sap, *dap;
		__be32 saddr, daddr;

		if (ah->ar_pln != sizeof(__be32) || ah->ar_pro != htons(ETH_P_IP))
			return false;
		sap = skb_header_pointer(skb, sizeof(struct arphdr) +
					ah->ar_hln, sizeof(saddr),
					&saddr);
		if (sap == NULL)
			return false;
		dap = skb_header_pointer(skb, sizeof(struct arphdr) +
					2*ah->ar_hln+sizeof(saddr),
					sizeof(daddr), &daddr);
		if (dap == NULL)
			return false;
		if ((info->bitmask & EBT_ARP_SRC_IP) &&
		    NF_INVF(info, EBT_ARP_SRC_IP,
			    info->saddr != (*sap & info->smsk)))
			return false;
		if ((info->bitmask & EBT_ARP_DST_IP) &&
		    NF_INVF(info, EBT_ARP_DST_IP,
			    info->daddr != (*dap & info->dmsk)))
			return false;
		if ((info->bitmask & EBT_ARP_GRAT) &&
		    NF_INVF(info, EBT_ARP_GRAT, *dap != *sap))
			return false;
	}

	if (info->bitmask & (EBT_ARP_SRC_MAC | EBT_ARP_DST_MAC)) {
		const unsigned char *mp;
		unsigned char _mac[ETH_ALEN];

		if (ah->ar_hln != ETH_ALEN || ah->ar_hrd != htons(ARPHRD_ETHER))
			return false;
		if (info->bitmask & EBT_ARP_SRC_MAC) {
			mp = skb_header_pointer(skb, sizeof(struct arphdr),
						sizeof(_mac), &_mac);
			if (mp == NULL)
				return false;
			if (NF_INVF(info, EBT_ARP_SRC_MAC,
				    !ether_addr_equal_masked(mp, info->smaddr,
							     info->smmsk)))
				return false;
		}

		if (info->bitmask & EBT_ARP_DST_MAC) {
			mp = skb_header_pointer(skb, sizeof(struct arphdr) +
						ah->ar_hln + ah->ar_pln,
						sizeof(_mac), &_mac);
			if (mp == NULL)
				return false;
			if (NF_INVF(info, EBT_ARP_DST_MAC,
				    !ether_addr_equal_masked(mp, info->dmaddr,
							     info->dmmsk)))
				return false;
		}
	}

	return true;
}

static int ebt_arp_mt_check(const struct xt_mtchk_param *par)
{
	const struct ebt_arp_info *info = par->matchinfo;
	const struct ebt_entry *e = par->entryinfo;

	if ((e->ethproto != htons(ETH_P_ARP) &&
	   e->ethproto != htons(ETH_P_RARP)) ||
	   e->invflags & EBT_IPROTO)
		return -EINVAL;
	if (info->bitmask & ~EBT_ARP_MASK || info->invflags & ~EBT_ARP_MASK)
		return -EINVAL;
	return 0;
}

static struct xt_match ebt_arp_mt_reg __read_mostly = {
	.name		= "arp",
	.revision	= 0,
	.family		= NFPROTO_BRIDGE,
	.match		= ebt_arp_mt,
	.checkentry	= ebt_arp_mt_check,
	.matchsize	= sizeof(struct ebt_arp_info),
	.me		= THIS_MODULE,
};

static int __init ebt_arp_init(void)
{
	return xt_register_match(&ebt_arp_mt_reg);
}

static void __exit ebt_arp_fini(void)
{
	xt_unregister_match(&ebt_arp_mt_reg);
}

module_init(ebt_arp_init);
module_exit(ebt_arp_fini);
MODULE_DESCRIPTION("Ebtables: ARP protocol packet match");
MODULE_LICENSE("GPL"