ebt_arp.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 *  ebt_arp
  4 *
  5 *	Authors:
  6 *	Bart De Schuymer <bdschuym@pandora.be>
  7 *	Tim Gardner <timg@tpi.com>
  8 *
  9 *  April, 2002
 10 *
 11 */
 12#include <linux/if_arp.h>
 13#include <linux/if_ether.h>
 14#include <linux/module.h>
 15#include <linux/netfilter/x_tables.h>
 16#include <linux/netfilter_bridge/ebtables.h>
 17#include <linux/netfilter_bridge/ebt_arp.h>
 18
 19static bool
 20ebt_arp_mt(const struct sk_buff *skb, struct xt_action_param *par)
 21{
 22	const struct ebt_arp_info *info = par->matchinfo;
 23	const struct arphdr *ah;
 24	struct arphdr _arph;
 25
 26	ah = skb_header_pointer(skb, 0, sizeof(_arph), &_arph);
 27	if (ah == NULL)
 28		return false;
 29	if ((info->bitmask & EBT_ARP_OPCODE) &&
 30	    NF_INVF(info, EBT_ARP_OPCODE, info->opcode != ah->ar_op))
 31		return false;
 32	if ((info->bitmask & EBT_ARP_HTYPE) &&
 33	    NF_INVF(info, EBT_ARP_HTYPE, info->htype != ah->ar_hrd))
 34		return false;
 35	if ((info->bitmask & EBT_ARP_PTYPE) &&
 36	    NF_INVF(info, EBT_ARP_PTYPE, info->ptype != ah->ar_pro))
 37		return false;
 38
 39	if (info->bitmask & (EBT_ARP_SRC_IP | EBT_ARP_DST_IP | EBT_ARP_GRAT)) {
 40		const __be32 *sap, *dap;
 41		__be32 saddr, daddr;
 42
 43		if (ah->ar_pln != sizeof(__be32) || ah->ar_pro != htons(ETH_P_IP))
 44			return false;
 45		sap = skb_header_pointer(skb, sizeof(struct arphdr) +
 46					ah->ar_hln, sizeof(saddr),
 47					&saddr);
 48		if (sap == NULL)
 49			return false;
 50		dap = skb_header_pointer(skb, sizeof(struct arphdr) +
 51					2*ah->ar_hln+sizeof(saddr),
 52					sizeof(daddr), &daddr);
 53		if (dap == NULL)
 54			return false;
 55		if ((info->bitmask & EBT_ARP_SRC_IP) &&
 56		    NF_INVF(info, EBT_ARP_SRC_IP,
 57			    info->saddr != (*sap & info->smsk)))
 58			return false;
 59		if ((info->bitmask & EBT_ARP_DST_IP) &&
 60		    NF_INVF(info, EBT_ARP_DST_IP,
 61			    info->daddr != (*dap & info->dmsk)))
 62			return false;
 63		if ((info->bitmask & EBT_ARP_GRAT) &&
 64		    NF_INVF(info, EBT_ARP_GRAT, *dap != *sap))
 65			return false;
 66	}
 67
 68	if (info->bitmask & (EBT_ARP_SRC_MAC | EBT_ARP_DST_MAC)) {
 69		const unsigned char *mp;
 70		unsigned char _mac[ETH_ALEN];
 71
 72		if (ah->ar_hln != ETH_ALEN || ah->ar_hrd != htons(ARPHRD_ETHER))
 73			return false;
 74		if (info->bitmask & EBT_ARP_SRC_MAC) {
 75			mp = skb_header_pointer(skb, sizeof(struct arphdr),
 76						sizeof(_mac), &_mac);
 77			if (mp == NULL)
 78				return false;
 79			if (NF_INVF(info, EBT_ARP_SRC_MAC,
 80				    !ether_addr_equal_masked(mp, info->smaddr,
 81							     info->smmsk)))
 82				return false;
 83		}
 84
 85		if (info->bitmask & EBT_ARP_DST_MAC) {
 86			mp = skb_header_pointer(skb, sizeof(struct arphdr) +
 87						ah->ar_hln + ah->ar_pln,
 88						sizeof(_mac), &_mac);
 89			if (mp == NULL)
 90				return false;
 91			if (NF_INVF(info, EBT_ARP_DST_MAC,
 92				    !ether_addr_equal_masked(mp, info->dmaddr,
 93							     info->dmmsk)))
 94				return false;
 95		}
 96	}
 97
 98	return true;
 99}
100
101static int ebt_arp_mt_check(const struct xt_mtchk_param *par)
102{
103	const struct ebt_arp_info *info = par->matchinfo;
104	const struct ebt_entry *e = par->entryinfo;
105
106	if ((e->ethproto != htons(ETH_P_ARP) &&
107	   e->ethproto != htons(ETH_P_RARP)) ||
108	   e->invflags & EBT_IPROTO)
109		return -EINVAL;
110	if (info->bitmask & ~EBT_ARP_MASK || info->invflags & ~EBT_ARP_MASK)
111		return -EINVAL;
112	return 0;
113}
114
115static struct xt_match ebt_arp_mt_reg __read_mostly = {
116	.name		= "arp",
117	.revision	= 0,
118	.family		= NFPROTO_BRIDGE,
119	.match		= ebt_arp_mt,
120	.checkentry	= ebt_arp_mt_check,
121	.matchsize	= sizeof(struct ebt_arp_info),
122	.me		= THIS_MODULE,
123};
124
125static int __init ebt_arp_init(void)
126{
127	return xt_register_match(&ebt_arp_mt_reg);
128}
129
130static void __exit ebt_arp_fini(void)
131{
132	xt_unregister_match(&ebt_arp_mt_reg);
133}
134
135module_init(ebt_arp_init);
136module_exit(ebt_arp_fini);
137MODULE_DESCRIPTION("Ebtables: ARP protocol packet match");
138MODULE_LICENSE("GPL");