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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 | |
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 | |
23 | MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); |
24 | MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>"); |
25 | MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target"); |
26 | MODULE_LICENSE("GPL"); |
27 | |
28 | static unsigned int |
29 | ttl_tg(struct sk_buff *skb, const struct xt_target_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 | |
68 | static unsigned int |
69 | hl_tg6(struct sk_buff *skb, const struct xt_target_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 | |
104 | static bool 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 | printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n", |
110 | info->mode); |
111 | return false; |
112 | } |
113 | if (info->mode != IPT_TTL_SET && info->ttl == 0) |
114 | return false; |
115 | return true; |
116 | } |
117 | |
118 | static bool hl_tg6_check(const struct xt_tgchk_param *par) |
119 | { |
120 | const struct ip6t_HL_info *info = par->targinfo; |
121 | |
122 | if (info->mode > IP6T_HL_MAXMODE) { |
123 | printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n", |
124 | info->mode); |
125 | return false; |
126 | } |
127 | if (info->mode != IP6T_HL_SET && info->hop_limit == 0) { |
128 | printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't " |
129 | "make sense with value 0\n"); |
130 | return false; |
131 | } |
132 | return true; |
133 | } |
134 | |
135 | static struct xt_target hl_tg_reg[] __read_mostly = { |
136 | { |
137 | .name = "TTL", |
138 | .revision = 0, |
139 | .family = NFPROTO_IPV4, |
140 | .target = ttl_tg, |
141 | .targetsize = sizeof(struct ipt_TTL_info), |
142 | .table = "mangle", |
143 | .checkentry = ttl_tg_check, |
144 | .me = THIS_MODULE, |
145 | }, |
146 | { |
147 | .name = "HL", |
148 | .revision = 0, |
149 | .family = NFPROTO_IPV6, |
150 | .target = hl_tg6, |
151 | .targetsize = sizeof(struct ip6t_HL_info), |
152 | .table = "mangle", |
153 | .checkentry = hl_tg6_check, |
154 | .me = THIS_MODULE, |
155 | }, |
156 | }; |
157 | |
158 | static int __init hl_tg_init(void) |
159 | { |
160 | return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); |
161 | } |
162 | |
163 | static void __exit hl_tg_exit(void) |
164 | { |
165 | xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); |
166 | } |
167 | |
168 | module_init(hl_tg_init); |
169 | module_exit(hl_tg_exit); |
170 | MODULE_ALIAS("ipt_TTL"); |
171 | MODULE_ALIAS("ip6t_HL"); |
172 |
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