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 
19 static unsigned int
20 ebt_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 
62 static 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 
78 static 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 
90 static int __init ebt_arpreply_init(void)
91 {
92 	return xt_register_target(&ebt_arpreply_tg_reg);
93 }
94 
95 static void __exit ebt_arpreply_fini(void)
96 {
97 	xt_unregister_target(&ebt_arpreply_tg_reg);
98 }
99 
100 module_init(ebt_arpreply_init);
101 module_exit(ebt_arpreply_fini);
102 MODULE_DESCRIPTION("Ebtables: ARP reply target");
103 MODULE_LICENSE("GPL");
104