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/net/ipv4/netfilter/arpt_mangle.c

http://github.com/mirrors/linux
C | 92 lines | 78 code | 11 blank | 3 comment | 15 complexity | ad9c10accdcbceadf7e3923549230a33 MD5 | raw file
 1// SPDX-License-Identifier: GPL-2.0-only
 2/* module that allows mangling of the arp payload */
 3#include <linux/module.h>
 4#include <linux/netfilter.h>
 5#include <linux/netfilter_arp/arpt_mangle.h>
 6#include <net/sock.h>
 7
 8MODULE_LICENSE("GPL");
 9MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
10MODULE_DESCRIPTION("arptables arp payload mangle target");
11
12static unsigned int
13target(struct sk_buff *skb, const struct xt_action_param *par)
14{
15	const struct arpt_mangle *mangle = par->targinfo;
16	const struct arphdr *arp;
17	unsigned char *arpptr;
18	int pln, hln;
19
20	if (skb_ensure_writable(skb, skb->len))
21		return NF_DROP;
22
23	arp = arp_hdr(skb);
24	arpptr = skb_network_header(skb) + sizeof(*arp);
25	pln = arp->ar_pln;
26	hln = arp->ar_hln;
27	/* We assume that pln and hln were checked in the match */
28	if (mangle->flags & ARPT_MANGLE_SDEV) {
29		if (ARPT_DEV_ADDR_LEN_MAX < hln ||
30		   (arpptr + hln > skb_tail_pointer(skb)))
31			return NF_DROP;
32		memcpy(arpptr, mangle->src_devaddr, hln);
33	}
34	arpptr += hln;
35	if (mangle->flags & ARPT_MANGLE_SIP) {
36		if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
37		   (arpptr + pln > skb_tail_pointer(skb)))
38			return NF_DROP;
39		memcpy(arpptr, &mangle->u_s.src_ip, pln);
40	}
41	arpptr += pln;
42	if (mangle->flags & ARPT_MANGLE_TDEV) {
43		if (ARPT_DEV_ADDR_LEN_MAX < hln ||
44		   (arpptr + hln > skb_tail_pointer(skb)))
45			return NF_DROP;
46		memcpy(arpptr, mangle->tgt_devaddr, hln);
47	}
48	arpptr += hln;
49	if (mangle->flags & ARPT_MANGLE_TIP) {
50		if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
51		   (arpptr + pln > skb_tail_pointer(skb)))
52			return NF_DROP;
53		memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
54	}
55	return mangle->target;
56}
57
58static int checkentry(const struct xt_tgchk_param *par)
59{
60	const struct arpt_mangle *mangle = par->targinfo;
61
62	if (mangle->flags & ~ARPT_MANGLE_MASK ||
63	    !(mangle->flags & ARPT_MANGLE_MASK))
64		return -EINVAL;
65
66	if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
67	   mangle->target != XT_CONTINUE)
68		return -EINVAL;
69	return 0;
70}
71
72static struct xt_target arpt_mangle_reg __read_mostly = {
73	.name		= "mangle",
74	.family		= NFPROTO_ARP,
75	.target		= target,
76	.targetsize	= sizeof(struct arpt_mangle),
77	.checkentry	= checkentry,
78	.me		= THIS_MODULE,
79};
80
81static int __init arpt_mangle_init(void)
82{
83	return xt_register_target(&arpt_mangle_reg);
84}
85
86static void __exit arpt_mangle_fini(void)
87{
88	xt_unregister_target(&arpt_mangle_reg);
89}
90
91module_init(arpt_mangle_init);
92module_exit(arpt_mangle_fini);