1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * IP tables module for matching the value of the TTL
4 * (C) 2000,2001 by Harald Welte <laforge@netfilter.org>
5 *
6 * Hop Limit matching module
7 * (C) 2001-2002 Maciej Soltysiak <solt@dns.toxicfilms.tv>
8 */
9
10#include <linux/ip.h>
11#include <linux/ipv6.h>
12#include <linux/module.h>
13#include <linux/skbuff.h>
14
15#include <linux/netfilter/x_tables.h>
16#include <linux/netfilter_ipv4/ipt_ttl.h>
17#include <linux/netfilter_ipv6/ip6t_hl.h>
18
19MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
20MODULE_DESCRIPTION("Xtables: Hoplimit/TTL field match");
21MODULE_LICENSE("GPL");
22MODULE_ALIAS("ipt_ttl");
23MODULE_ALIAS("ip6t_hl");
24
25static bool ttl_mt(const struct sk_buff *skb, struct xt_action_param *par)
26{
27 const struct ipt_ttl_info *info = par->matchinfo;
28 const u8 ttl = ip_hdr(skb)->ttl;
29
30 switch (info->mode) {
31 case IPT_TTL_EQ:
32 return ttl == info->ttl;
33 case IPT_TTL_NE:
34 return ttl != info->ttl;
35 case IPT_TTL_LT:
36 return ttl < info->ttl;
37 case IPT_TTL_GT:
38 return ttl > info->ttl;
39 }
40
41 return false;
42}
43
44static bool hl_mt6(const struct sk_buff *skb, struct xt_action_param *par)
45{
46 const struct ip6t_hl_info *info = par->matchinfo;
47 const struct ipv6hdr *ip6h = ipv6_hdr(skb);
48
49 switch (info->mode) {
50 case IP6T_HL_EQ:
51 return ip6h->hop_limit == info->hop_limit;
52 case IP6T_HL_NE:
53 return ip6h->hop_limit != info->hop_limit;
54 case IP6T_HL_LT:
55 return ip6h->hop_limit < info->hop_limit;
56 case IP6T_HL_GT:
57 return ip6h->hop_limit > info->hop_limit;
58 }
59
60 return false;
61}
62
63static struct xt_match hl_mt_reg[] __read_mostly = {
64 {
65 .name = "ttl",
66 .revision = 0,
67 .family = NFPROTO_IPV4,
68 .match = ttl_mt,
69 .matchsize = sizeof(struct ipt_ttl_info),
70 .me = THIS_MODULE,
71 },
72 {
73 .name = "hl",
74 .revision = 0,
75 .family = NFPROTO_IPV6,
76 .match = hl_mt6,
77 .matchsize = sizeof(struct ip6t_hl_info),
78 .me = THIS_MODULE,
79 },
80};
81
82static int __init hl_mt_init(void)
83{
84 return xt_register_matches(match: hl_mt_reg, ARRAY_SIZE(hl_mt_reg));
85}
86
87static void __exit hl_mt_exit(void)
88{
89 xt_unregister_matches(match: hl_mt_reg, ARRAY_SIZE(hl_mt_reg));
90}
91
92module_init(hl_mt_init);
93module_exit(hl_mt_exit);
94

source code of linux/net/netfilter/xt_hl.c