Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
[linux-2.6] / net / ipv4 / netfilter / ipt_TTL.c
1 /* TTL modification target for IP tables
2  * (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License version 2 as
6  * published by the Free Software Foundation.
7  *
8  */
9
10 #include <linux/module.h>
11 #include <linux/skbuff.h>
12 #include <linux/ip.h>
13 #include <net/checksum.h>
14
15 #include <linux/netfilter/x_tables.h>
16 #include <linux/netfilter_ipv4/ipt_TTL.h>
17
18 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
19 MODULE_DESCRIPTION("Xtables: IPv4 TTL field modification target");
20 MODULE_LICENSE("GPL");
21
22 static unsigned int
23 ttl_tg(struct sk_buff *skb, const struct net_device *in,
24        const struct net_device *out, unsigned int hooknum,
25        const struct xt_target *target, const void *targinfo)
26 {
27         struct iphdr *iph;
28         const struct ipt_TTL_info *info = targinfo;
29         int new_ttl;
30
31         if (!skb_make_writable(skb, skb->len))
32                 return NF_DROP;
33
34         iph = ip_hdr(skb);
35
36         switch (info->mode) {
37                 case IPT_TTL_SET:
38                         new_ttl = info->ttl;
39                         break;
40                 case IPT_TTL_INC:
41                         new_ttl = iph->ttl + info->ttl;
42                         if (new_ttl > 255)
43                                 new_ttl = 255;
44                         break;
45                 case IPT_TTL_DEC:
46                         new_ttl = iph->ttl - info->ttl;
47                         if (new_ttl < 0)
48                                 new_ttl = 0;
49                         break;
50                 default:
51                         new_ttl = iph->ttl;
52                         break;
53         }
54
55         if (new_ttl != iph->ttl) {
56                 csum_replace2(&iph->check, htons(iph->ttl << 8),
57                                            htons(new_ttl << 8));
58                 iph->ttl = new_ttl;
59         }
60
61         return XT_CONTINUE;
62 }
63
64 static bool
65 ttl_tg_check(const char *tablename, const void *e,
66              const struct xt_target *target, void *targinfo,
67              unsigned int hook_mask)
68 {
69         const struct ipt_TTL_info *info = targinfo;
70
71         if (info->mode > IPT_TTL_MAXMODE) {
72                 printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
73                         info->mode);
74                 return false;
75         }
76         if (info->mode != IPT_TTL_SET && info->ttl == 0)
77                 return false;
78         return true;
79 }
80
81 static struct xt_target ttl_tg_reg __read_mostly = {
82         .name           = "TTL",
83         .family         = AF_INET,
84         .target         = ttl_tg,
85         .targetsize     = sizeof(struct ipt_TTL_info),
86         .table          = "mangle",
87         .checkentry     = ttl_tg_check,
88         .me             = THIS_MODULE,
89 };
90
91 static int __init ttl_tg_init(void)
92 {
93         return xt_register_target(&ttl_tg_reg);
94 }
95
96 static void __exit ttl_tg_exit(void)
97 {
98         xt_unregister_target(&ttl_tg_reg);
99 }
100
101 module_init(ttl_tg_init);
102 module_exit(ttl_tg_exit);