1/*
2 * TTL modification target for IP tables
3 * (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
4 *
5 * Hop Limit modification target for ip6tables
6 * Maciej Soltysiak <solt@dns.toxicfilms.tv>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
11 */
12#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13#include <linux/module.h>
14#include <linux/skbuff.h>
15#include <linux/ip.h>
16#include <linux/ipv6.h>
17#include <net/checksum.h>
18
19#include <linux/netfilter/x_tables.h>
20#include <linux/netfilter_ipv4/ipt_TTL.h>
21#include <linux/netfilter_ipv6/ip6t_HL.h>
22
23MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
24MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
25MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
26MODULE_LICENSE("GPL");
27
28static unsigned int
29ttl_tg(struct sk_buff *skb, const struct xt_action_param *par)
30{
31	struct iphdr *iph;
32	const struct ipt_TTL_info *info = par->targinfo;
33	int new_ttl;
34
35	if (!skb_make_writable(skb, skb->len))
36		return NF_DROP;
37
38	iph = ip_hdr(skb);
39
40	switch (info->mode) {
41	case IPT_TTL_SET:
42		new_ttl = info->ttl;
43		break;
44	case IPT_TTL_INC:
45		new_ttl = iph->ttl + info->ttl;
46		if (new_ttl > 255)
47			new_ttl = 255;
48		break;
49	case IPT_TTL_DEC:
50		new_ttl = iph->ttl - info->ttl;
51		if (new_ttl < 0)
52			new_ttl = 0;
53		break;
54	default:
55		new_ttl = iph->ttl;
56		break;
57	}
58
59	if (new_ttl != iph->ttl) {
60		csum_replace2(&iph->check, htons(iph->ttl << 8),
61					   htons(new_ttl << 8));
62		iph->ttl = new_ttl;
63	}
64
65	return XT_CONTINUE;
66}
67
68static unsigned int
69hl_tg6(struct sk_buff *skb, const struct xt_action_param *par)
70{
71	struct ipv6hdr *ip6h;
72	const struct ip6t_HL_info *info = par->targinfo;
73	int new_hl;
74
75	if (!skb_make_writable(skb, skb->len))
76		return NF_DROP;
77
78	ip6h = ipv6_hdr(skb);
79
80	switch (info->mode) {
81	case IP6T_HL_SET:
82		new_hl = info->hop_limit;
83		break;
84	case IP6T_HL_INC:
85		new_hl = ip6h->hop_limit + info->hop_limit;
86		if (new_hl > 255)
87			new_hl = 255;
88		break;
89	case IP6T_HL_DEC:
90		new_hl = ip6h->hop_limit - info->hop_limit;
91		if (new_hl < 0)
92			new_hl = 0;
93		break;
94	default:
95		new_hl = ip6h->hop_limit;
96		break;
97	}
98
99	ip6h->hop_limit = new_hl;
100
101	return XT_CONTINUE;
102}
103
104static int ttl_tg_check(const struct xt_tgchk_param *par)
105{
106	const struct ipt_TTL_info *info = par->targinfo;
107
108	if (info->mode > IPT_TTL_MAXMODE) {
109		pr_info("TTL: invalid or unknown mode %u\n", info->mode);
110		return -EINVAL;
111	}
112	if (info->mode != IPT_TTL_SET && info->ttl == 0)
113		return -EINVAL;
114	return 0;
115}
116
117static int hl_tg6_check(const struct xt_tgchk_param *par)
118{
119	const struct ip6t_HL_info *info = par->targinfo;
120
121	if (info->mode > IP6T_HL_MAXMODE) {
122		pr_info("invalid or unknown mode %u\n", info->mode);
123		return -EINVAL;
124	}
125	if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
126		pr_info("increment/decrement does not "
127			"make sense with value 0\n");
128		return -EINVAL;
129	}
130	return 0;
131}
132
133static struct xt_target hl_tg_reg[] __read_mostly = {
134	{
135		.name       = "TTL",
136		.revision   = 0,
137		.family     = NFPROTO_IPV4,
138		.target     = ttl_tg,
139		.targetsize = sizeof(struct ipt_TTL_info),
140		.table      = "mangle",
141		.checkentry = ttl_tg_check,
142		.me         = THIS_MODULE,
143	},
144	{
145		.name       = "HL",
146		.revision   = 0,
147		.family     = NFPROTO_IPV6,
148		.target     = hl_tg6,
149		.targetsize = sizeof(struct ip6t_HL_info),
150		.table      = "mangle",
151		.checkentry = hl_tg6_check,
152		.me         = THIS_MODULE,
153	},
154};
155
156static int __init hl_tg_init(void)
157{
158	return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
159}
160
161static void __exit hl_tg_exit(void)
162{
163	xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
164}
165
166module_init(hl_tg_init);
167module_exit(hl_tg_exit);
168MODULE_ALIAS("ipt_TTL");
169MODULE_ALIAS("ip6t_HL");
170