1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  ebt_arpreply
4 *
5 *	Authors:
6 *	Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
7 *	Bart De Schuymer <bdschuym@pandora.be>
8 *
9 *  August, 2003
10 *
11 */
12#include <linux/if_arp.h>
13#include <net/arp.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_arpreply.h>
18
19static unsigned int
20ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
21{
22	const struct ebt_arpreply_info *info = par->targinfo;
23	const __be32 *siptr, *diptr;
24	__be32 _sip, _dip;
25	const struct arphdr *ap;
26	struct arphdr _ah;
27	const unsigned char *shp;
28	unsigned char _sha[ETH_ALEN];
29
30	ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
31	if (ap == NULL)
32		return EBT_DROP;
33
34	if (ap->ar_op != htons(ARPOP_REQUEST) ||
35	    ap->ar_hln != ETH_ALEN ||
36	    ap->ar_pro != htons(ETH_P_IP) ||
37	    ap->ar_pln != 4)
38		return EBT_CONTINUE;
39
40	shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
41	if (shp == NULL)
42		return EBT_DROP;
43
44	siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
45				   sizeof(_sip), &_sip);
46	if (siptr == NULL)
47		return EBT_DROP;
48
49	diptr = skb_header_pointer(skb,
50				   sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
51				   sizeof(_dip), &_dip);
52	if (diptr == NULL)
53		return EBT_DROP;
54
55	arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr,
56		 (struct net_device *)xt_in(par),
57		 *diptr, shp, info->mac, shp);
58
59	return info->target;
60}
61
62static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
63{
64	const struct ebt_arpreply_info *info = par->targinfo;
65	const struct ebt_entry *e = par->entryinfo;
66
67	if (BASE_CHAIN && info->target == EBT_RETURN)
68		return -EINVAL;
69	if (e->ethproto != htons(ETH_P_ARP) ||
70	    e->invflags & EBT_IPROTO)
71		return -EINVAL;
72	if (ebt_invalid_target(info->target))
73		return -EINVAL;
74
75	return 0;
76}
77
78static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
79	.name		= "arpreply",
80	.revision	= 0,
81	.family		= NFPROTO_BRIDGE,
82	.table		= "nat",
83	.hooks		= (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
84	.target		= ebt_arpreply_tg,
85	.checkentry	= ebt_arpreply_tg_check,
86	.targetsize	= sizeof(struct ebt_arpreply_info),
87	.me		= THIS_MODULE,
88};
89
90static int __init ebt_arpreply_init(void)
91{
92	return xt_register_target(&ebt_arpreply_tg_reg);
93}
94
95static void __exit ebt_arpreply_fini(void)
96{
97	xt_unregister_target(&ebt_arpreply_tg_reg);
98}
99
100module_init(ebt_arpreply_init);
101module_exit(ebt_arpreply_fini);
102MODULE_DESCRIPTION("Ebtables: ARP reply target");
103MODULE_LICENSE("GPL");
104