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/* TTL modification target for IP tables
* (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <net/checksum.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_TTL.h>
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_DESCRIPTION("IP tables TTL modification module");
MODULE_LICENSE("GPL");
static unsigned int
ipt_ttl_target(struct sk_buff **pskb,
const struct net_device *in, const struct net_device *out,
unsigned int hooknum, const struct xt_target *target,
const void *targinfo, void *userinfo)
{
struct iphdr *iph;
const struct ipt_TTL_info *info = targinfo;
u_int16_t diffs[2];
int new_ttl;
if (!skb_make_writable(pskb, (*pskb)->len))
return NF_DROP;
iph = (*pskb)->nh.iph;
switch (info->mode) {
case IPT_TTL_SET:
new_ttl = info->ttl;
break;
case IPT_TTL_INC:
new_ttl = iph->ttl + info->ttl;
if (new_ttl > 255)
new_ttl = 255;
break;
case IPT_TTL_DEC:
new_ttl = iph->ttl - info->ttl;
if (new_ttl < 0)
new_ttl = 0;
break;
default:
new_ttl = iph->ttl;
break;
}
if (new_ttl != iph->ttl) {
diffs[0] = htons(((unsigned)iph->ttl) << 8) ^ 0xFFFF;
iph->ttl = new_ttl;
diffs[1] = htons(((unsigned)iph->ttl) << 8);
iph->check = csum_fold(csum_partial((char *)diffs,
sizeof(diffs),
iph->check^0xFFFF));
}
return IPT_CONTINUE;
}
static int ipt_ttl_checkentry(const char *tablename,
const void *e,
const struct xt_target *target,
void *targinfo,
unsigned int targinfosize,
unsigned int hook_mask)
{
struct ipt_TTL_info *info = targinfo;
if (info->mode > IPT_TTL_MAXMODE) {
printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
info->mode);
return 0;
}
if ((info->mode != IPT_TTL_SET) && (info->ttl == 0))
return 0;
return 1;
}
static struct ipt_target ipt_TTL = {
.name = "TTL",
.target = ipt_ttl_target,
.targetsize = sizeof(struct ipt_TTL_info),
.table = "mangle",
.checkentry = ipt_ttl_checkentry,
.me = THIS_MODULE,
};
static int __init ipt_ttl_init(void)
{
return ipt_register_target(&ipt_TTL);
}
static void __exit ipt_ttl_fini(void)
{
ipt_unregister_target(&ipt_TTL);
}
module_init(ipt_ttl_init);
module_exit(ipt_ttl_fini);
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