[NETFILTER]: ipt_REJECT: fix memory corruption
[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_ipv4/ip_tables.h>
16 #include <linux/netfilter_ipv4/ipt_TTL.h>
17
18 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
19 MODULE_DESCRIPTION("IP tables TTL modification module");
20 MODULE_LICENSE("GPL");
21
22 static unsigned int 
23 ipt_ttl_target(struct sk_buff **pskb,
24                const struct net_device *in, const struct net_device *out,
25                unsigned int hooknum, const struct xt_target *target,
26                const void *targinfo)
27 {
28         struct iphdr *iph;
29         const struct ipt_TTL_info *info = targinfo;
30         int new_ttl;
31
32         if (!skb_make_writable(pskb, (*pskb)->len))
33                 return NF_DROP;
34
35         iph = (*pskb)->nh.iph;
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                 iph->check = nf_csum_update(htons((iph->ttl << 8)) ^ htons(0xFFFF),
58                                             htons(new_ttl << 8),
59                                             iph->check);
60                 iph->ttl = new_ttl;
61         }
62
63         return IPT_CONTINUE;
64 }
65
66 static int ipt_ttl_checkentry(const char *tablename,
67                 const void *e,
68                 const struct xt_target *target,
69                 void *targinfo,
70                 unsigned int hook_mask)
71 {
72         struct ipt_TTL_info *info = targinfo;
73
74         if (info->mode > IPT_TTL_MAXMODE) {
75                 printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n", 
76                         info->mode);
77                 return 0;
78         }
79         if ((info->mode != IPT_TTL_SET) && (info->ttl == 0))
80                 return 0;
81         return 1;
82 }
83
84 static struct ipt_target ipt_TTL = { 
85         .name           = "TTL",
86         .target         = ipt_ttl_target, 
87         .targetsize     = sizeof(struct ipt_TTL_info),
88         .table          = "mangle",
89         .checkentry     = ipt_ttl_checkentry, 
90         .me             = THIS_MODULE,
91 };
92
93 static int __init ipt_ttl_init(void)
94 {
95         return ipt_register_target(&ipt_TTL);
96 }
97
98 static void __exit ipt_ttl_fini(void)
99 {
100         ipt_unregister_target(&ipt_TTL);
101 }
102
103 module_init(ipt_ttl_init);
104 module_exit(ipt_ttl_fini);