1 /*
2  *  ebt_arpreply
3  *
4  *	Authors:
5  *	Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
6  *	Bart De Schuymer <bdschuym@pandora.be>
7  *
8  *  August, 2003
9  *
10  */
11 #include <linux/if_arp.h>
12 #include <net/arp.h>
13 #include <linux/module.h>
14 #include <linux/netfilter/x_tables.h>
15 #include <linux/netfilter_bridge/ebtables.h>
16 #include <linux/netfilter_bridge/ebt_arpreply.h>
17 
18 static unsigned int
19 ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
20 {
21 	const struct ebt_arpreply_info *info = par->targinfo;
22 	const __be32 *siptr, *diptr;
23 	__be32 _sip, _dip;
24 	const struct arphdr *ap;
25 	struct arphdr _ah;
26 	const unsigned char *shp;
27 	unsigned char _sha[ETH_ALEN];
28 
29 	ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
30 	if (ap == NULL)
31 		return EBT_DROP;
32 
33 	if (ap->ar_op != htons(ARPOP_REQUEST) ||
34 	    ap->ar_hln != ETH_ALEN ||
35 	    ap->ar_pro != htons(ETH_P_IP) ||
36 	    ap->ar_pln != 4)
37 		return EBT_CONTINUE;
38 
39 	shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
40 	if (shp == NULL)
41 		return EBT_DROP;
42 
43 	siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
44 				   sizeof(_sip), &_sip);
45 	if (siptr == NULL)
46 		return EBT_DROP;
47 
48 	diptr = skb_header_pointer(skb,
49 				   sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
50 				   sizeof(_dip), &_dip);
51 	if (diptr == NULL)
52 		return EBT_DROP;
53 
54 	arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr,
55 		 (struct net_device *)xt_in(par),
56 		 *diptr, shp, info->mac, shp);
57 
58 	return info->target;
59 }
60 
61 static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
62 {
63 	const struct ebt_arpreply_info *info = par->targinfo;
64 	const struct ebt_entry *e = par->entryinfo;
65 
66 	if (BASE_CHAIN && info->target == EBT_RETURN)
67 		return -EINVAL;
68 	if (e->ethproto != htons(ETH_P_ARP) ||
69 	    e->invflags & EBT_IPROTO)
70 		return -EINVAL;
71 	if (ebt_invalid_target(info->target))
72 		return -EINVAL;
73 
74 	return 0;
75 }
76 
77 static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
78 	.name		= "arpreply",
79 	.revision	= 0,
80 	.family		= NFPROTO_BRIDGE,
81 	.table		= "nat",
82 	.hooks		= (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
83 	.target		= ebt_arpreply_tg,
84 	.checkentry	= ebt_arpreply_tg_check,
85 	.targetsize	= sizeof(struct ebt_arpreply_info),
86 	.me		= THIS_MODULE,
87 };
88 
89 static int __init ebt_arpreply_init(void)
90 {
91 	return xt_register_target(&ebt_arpreply_tg_reg);
92 }
93 
94 static void __exit ebt_arpreply_fini(void)
95 {
96 	xt_unregister_target(&ebt_arpreply_tg_reg);
97 }
98 
99 module_init(ebt_arpreply_init);
100 module_exit(ebt_arpreply_fini);
101 MODULE_DESCRIPTION("Ebtables: ARP reply target");
102 MODULE_LICENSE("GPL");
103