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 | |
20 | MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>" ); |
21 | MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>" ); |
22 | MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target" ); |
23 | MODULE_LICENSE("GPL" ); |
24 | |
25 | static unsigned int |
26 | ttl_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, write_len: 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(sum: &iph->check, htons(iph->ttl << 8), |
58 | htons(new_ttl << 8)); |
59 | iph->ttl = new_ttl; |
60 | } |
61 | |
62 | return XT_CONTINUE; |
63 | } |
64 | |
65 | static unsigned int |
66 | hl_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, write_len: 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 | |
101 | static 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 | |
112 | static 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 | |
123 | static 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 | |
146 | static int __init hl_tg_init(void) |
147 | { |
148 | return xt_register_targets(target: hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); |
149 | } |
150 | |
151 | static void __exit hl_tg_exit(void) |
152 | { |
153 | xt_unregister_targets(target: hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); |
154 | } |
155 | |
156 | module_init(hl_tg_init); |
157 | module_exit(hl_tg_exit); |
158 | MODULE_ALIAS("ipt_TTL" ); |
159 | MODULE_ALIAS("ip6t_HL" ); |
160 | |