1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * TTL modification target for IP tables
4 * (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
5 *
6 * Hop Limit modification target for ip6tables
7 * Maciej Soltysiak <solt@dns.toxicfilms.tv>
8 */
9#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10#include <linux/module.h>
11#include <linux/skbuff.h>
12#include <linux/ip.h>
13#include <linux/ipv6.h>
14#include <net/checksum.h>
15
16#include <linux/netfilter/x_tables.h>
17#include <linux/netfilter_ipv4/ipt_TTL.h>
18#include <linux/netfilter_ipv6/ip6t_HL.h>
19
20MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
21MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
22MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
23MODULE_LICENSE("GPL");
24
25static unsigned int
26ttl_tg(struct sk_buff *skb, const struct xt_action_param *par)
27{
28	struct iphdr *iph;
29	const struct ipt_TTL_info *info = par->targinfo;
30	int new_ttl;
31
32	if (skb_ensure_writable(skb, sizeof(*iph)))
33		return NF_DROP;
34
35	iph = ip_hdr(skb);
36
37	switch (info->mode) {
38	case IPT_TTL_SET:
39		new_ttl = info->ttl;
40		break;
41	case IPT_TTL_INC:
42		new_ttl = iph->ttl + info->ttl;
43		if (new_ttl > 255)
44			new_ttl = 255;
45		break;
46	case IPT_TTL_DEC:
47		new_ttl = iph->ttl - info->ttl;
48		if (new_ttl < 0)
49			new_ttl = 0;
50		break;
51	default:
52		new_ttl = iph->ttl;
53		break;
54	}
55
56	if (new_ttl != iph->ttl) {
57		csum_replace2(&iph->check, htons(iph->ttl << 8),
58					   htons(new_ttl << 8));
59		iph->ttl = new_ttl;
60	}
61
62	return XT_CONTINUE;
63}
64
65static unsigned int
66hl_tg6(struct sk_buff *skb, const struct xt_action_param *par)
67{
68	struct ipv6hdr *ip6h;
69	const struct ip6t_HL_info *info = par->targinfo;
70	int new_hl;
71
72	if (skb_ensure_writable(skb, sizeof(*ip6h)))
73		return NF_DROP;
74
75	ip6h = ipv6_hdr(skb);
76
77	switch (info->mode) {
78	case IP6T_HL_SET:
79		new_hl = info->hop_limit;
80		break;
81	case IP6T_HL_INC:
82		new_hl = ip6h->hop_limit + info->hop_limit;
83		if (new_hl > 255)
84			new_hl = 255;
85		break;
86	case IP6T_HL_DEC:
87		new_hl = ip6h->hop_limit - info->hop_limit;
88		if (new_hl < 0)
89			new_hl = 0;
90		break;
91	default:
92		new_hl = ip6h->hop_limit;
93		break;
94	}
95
96	ip6h->hop_limit = new_hl;
97
98	return XT_CONTINUE;
99}
100
101static int ttl_tg_check(const struct xt_tgchk_param *par)
102{
103	const struct ipt_TTL_info *info = par->targinfo;
104
105	if (info->mode > IPT_TTL_MAXMODE)
106		return -EINVAL;
107	if (info->mode != IPT_TTL_SET && info->ttl == 0)
108		return -EINVAL;
109	return 0;
110}
111
112static int hl_tg6_check(const struct xt_tgchk_param *par)
113{
114	const struct ip6t_HL_info *info = par->targinfo;
115
116	if (info->mode > IP6T_HL_MAXMODE)
117		return -EINVAL;
118	if (info->mode != IP6T_HL_SET && info->hop_limit == 0)
119		return -EINVAL;
120	return 0;
121}
122
123static struct xt_target hl_tg_reg[] __read_mostly = {
124	{
125		.name       = "TTL",
126		.revision   = 0,
127		.family     = NFPROTO_IPV4,
128		.target     = ttl_tg,
129		.targetsize = sizeof(struct ipt_TTL_info),
130		.table      = "mangle",
131		.checkentry = ttl_tg_check,
132		.me         = THIS_MODULE,
133	},
134	{
135		.name       = "HL",
136		.revision   = 0,
137		.family     = NFPROTO_IPV6,
138		.target     = hl_tg6,
139		.targetsize = sizeof(struct ip6t_HL_info),
140		.table      = "mangle",
141		.checkentry = hl_tg6_check,
142		.me         = THIS_MODULE,
143	},
144};
145
146static int __init hl_tg_init(void)
147{
148	return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
149}
150
151static void __exit hl_tg_exit(void)
152{
153	xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
154}
155
156module_init(hl_tg_init);
157module_exit(hl_tg_exit);
158MODULE_ALIAS("ipt_TTL");
159MODULE_ALIAS("ip6t_HL");
160