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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * TTL modification target for IP tables
4 * (C) 2000,2005 by Harald Welte <[email protected]>
5 *
6 * Hop Limit modification target for ip6tables
7 * Maciej Soltysiak <[email protected]>
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 <[email protected]>");
21MODULE_AUTHOR("Maciej Soltysiak <[email protected]>");
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");