1 // SPDX-License-Identifier: GPL-2.0-only
2 /* Kernel module to match packet length. */
3 /* (C) 1999-2001 James Morris <jmorros@intercode.com.au>
4  */
5 
6 #include <linux/module.h>
7 #include <linux/skbuff.h>
8 #include <linux/ipv6.h>
9 #include <net/ip.h>
10 
11 #include <linux/netfilter/xt_length.h>
12 #include <linux/netfilter/x_tables.h>
13 
14 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
15 MODULE_DESCRIPTION("Xtables: Packet length (Layer3,4,5) match");
16 MODULE_LICENSE("GPL");
17 MODULE_ALIAS("ipt_length");
18 MODULE_ALIAS("ip6t_length");
19 
20 static bool
length_mt(const struct sk_buff * skb,struct xt_action_param * par)21 length_mt(const struct sk_buff *skb, struct xt_action_param *par)
22 {
23 	const struct xt_length_info *info = par->matchinfo;
24 	u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);
25 
26 	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
27 }
28 
29 static bool
length_mt6(const struct sk_buff * skb,struct xt_action_param * par)30 length_mt6(const struct sk_buff *skb, struct xt_action_param *par)
31 {
32 	const struct xt_length_info *info = par->matchinfo;
33 	const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
34 				 sizeof(struct ipv6hdr);
35 
36 	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
37 }
38 
39 static struct xt_match length_mt_reg[] __read_mostly = {
40 	{
41 		.name		= "length",
42 		.family		= NFPROTO_IPV4,
43 		.match		= length_mt,
44 		.matchsize	= sizeof(struct xt_length_info),
45 		.me		= THIS_MODULE,
46 	},
47 	{
48 		.name		= "length",
49 		.family		= NFPROTO_IPV6,
50 		.match		= length_mt6,
51 		.matchsize	= sizeof(struct xt_length_info),
52 		.me		= THIS_MODULE,
53 	},
54 };
55 
length_mt_init(void)56 static int __init length_mt_init(void)
57 {
58 	return xt_register_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
59 }
60 
length_mt_exit(void)61 static void __exit length_mt_exit(void)
62 {
63 	xt_unregister_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
64 }
65 
66 module_init(length_mt_init);
67 module_exit(length_mt_exit);
68