1/* module that allows mangling of the arp payload */
2#include <linux/module.h>
3#include <linux/netfilter.h>
4#include <linux/netfilter_arp/arpt_mangle.h>
5#include <net/sock.h>
6
7MODULE_LICENSE("GPL");
8MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
9MODULE_DESCRIPTION("arptables arp payload mangle target");
10
11static unsigned int
12target(struct sk_buff *skb, const struct xt_action_param *par)
13{
14	const struct arpt_mangle *mangle = par->targinfo;
15	const struct arphdr *arp;
16	unsigned char *arpptr;
17	int pln, hln;
18
19	if (!skb_make_writable(skb, skb->len))
20		return NF_DROP;
21
22	arp = arp_hdr(skb);
23	arpptr = skb_network_header(skb) + sizeof(*arp);
24	pln = arp->ar_pln;
25	hln = arp->ar_hln;
26	/* We assume that pln and hln were checked in the match */
27	if (mangle->flags & ARPT_MANGLE_SDEV) {
28		if (ARPT_DEV_ADDR_LEN_MAX < hln ||
29		   (arpptr + hln > skb_tail_pointer(skb)))
30			return NF_DROP;
31		memcpy(arpptr, mangle->src_devaddr, hln);
32	}
33	arpptr += hln;
34	if (mangle->flags & ARPT_MANGLE_SIP) {
35		if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
36		   (arpptr + pln > skb_tail_pointer(skb)))
37			return NF_DROP;
38		memcpy(arpptr, &mangle->u_s.src_ip, pln);
39	}
40	arpptr += pln;
41	if (mangle->flags & ARPT_MANGLE_TDEV) {
42		if (ARPT_DEV_ADDR_LEN_MAX < hln ||
43		   (arpptr + hln > skb_tail_pointer(skb)))
44			return NF_DROP;
45		memcpy(arpptr, mangle->tgt_devaddr, hln);
46	}
47	arpptr += hln;
48	if (mangle->flags & ARPT_MANGLE_TIP) {
49		if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
50		   (arpptr + pln > skb_tail_pointer(skb)))
51			return NF_DROP;
52		memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
53	}
54	return mangle->target;
55}
56
57static int checkentry(const struct xt_tgchk_param *par)
58{
59	const struct arpt_mangle *mangle = par->targinfo;
60
61	if (mangle->flags & ~ARPT_MANGLE_MASK ||
62	    !(mangle->flags & ARPT_MANGLE_MASK))
63		return -EINVAL;
64
65	if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
66	   mangle->target != XT_CONTINUE)
67		return -EINVAL;
68	return 0;
69}
70
71static struct xt_target arpt_mangle_reg __read_mostly = {
72	.name		= "mangle",
73	.family		= NFPROTO_ARP,
74	.target		= target,
75	.targetsize	= sizeof(struct arpt_mangle),
76	.checkentry	= checkentry,
77	.me		= THIS_MODULE,
78};
79
80static int __init arpt_mangle_init(void)
81{
82	return xt_register_target(&arpt_mangle_reg);
83}
84
85static void __exit arpt_mangle_fini(void)
86{
87	xt_unregister_target(&arpt_mangle_reg);
88}
89
90module_init(arpt_mangle_init);
91module_exit(arpt_mangle_fini);
92