1 /*
2 * Hop Limit modification target for ip6tables
3 * Maciej Soltysiak <solt@dns.toxicfilms.tv>
4 * Based on HW's TTL module
5 *
6 * This software is distributed under the terms of GNU GPL
7 */
8
9 #include <linux/module.h>
10 #include <linux/skbuff.h>
11 #include <linux/ip.h>
12 #include <linux/ipv6.h>
13
14 #include <linux/netfilter/x_tables.h>
15 #include <linux/netfilter_ipv6/ip6t_HL.h>
16
17 MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
18 MODULE_DESCRIPTION("Xtables: IPv6 Hop Limit field modification target");
19 MODULE_LICENSE("GPL");
20
21 static unsigned int
hl_tg6(struct sk_buff * skb,const struct xt_target_param * par)22 hl_tg6(struct sk_buff *skb, const struct xt_target_param *par)
23 {
24 struct ipv6hdr *ip6h;
25 const struct ip6t_HL_info *info = par->targinfo;
26 int new_hl;
27
28 if (!skb_make_writable(skb, skb->len))
29 return NF_DROP;
30
31 ip6h = ipv6_hdr(skb);
32
33 switch (info->mode) {
34 case IP6T_HL_SET:
35 new_hl = info->hop_limit;
36 break;
37 case IP6T_HL_INC:
38 new_hl = ip6h->hop_limit + info->hop_limit;
39 if (new_hl > 255)
40 new_hl = 255;
41 break;
42 case IP6T_HL_DEC:
43 new_hl = ip6h->hop_limit - info->hop_limit;
44 if (new_hl < 0)
45 new_hl = 0;
46 break;
47 default:
48 new_hl = ip6h->hop_limit;
49 break;
50 }
51
52 ip6h->hop_limit = new_hl;
53
54 return XT_CONTINUE;
55 }
56
hl_tg6_check(const struct xt_tgchk_param * par)57 static bool hl_tg6_check(const struct xt_tgchk_param *par)
58 {
59 const struct ip6t_HL_info *info = par->targinfo;
60
61 if (info->mode > IP6T_HL_MAXMODE) {
62 printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
63 info->mode);
64 return false;
65 }
66 if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
67 printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
68 "make sense with value 0\n");
69 return false;
70 }
71 return true;
72 }
73
74 static struct xt_target hl_tg6_reg __read_mostly = {
75 .name = "HL",
76 .family = NFPROTO_IPV6,
77 .target = hl_tg6,
78 .targetsize = sizeof(struct ip6t_HL_info),
79 .table = "mangle",
80 .checkentry = hl_tg6_check,
81 .me = THIS_MODULE
82 };
83
hl_tg6_init(void)84 static int __init hl_tg6_init(void)
85 {
86 return xt_register_target(&hl_tg6_reg);
87 }
88
hl_tg6_exit(void)89 static void __exit hl_tg6_exit(void)
90 {
91 xt_unregister_target(&hl_tg6_reg);
92 }
93
94 module_init(hl_tg6_init);
95 module_exit(hl_tg6_exit);
96