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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/x_tables.h>
#include <linux/netfilter_ipv4/ipt_TTL.h>
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_DESCRIPTION("Xtables: IPv4 TTL field modification target");
MODULE_LICENSE("GPL");
static unsigned int
ttl_tg(struct sk_buff *skb, const struct xt_target_param *par)
{
struct iphdr *iph;
const struct ipt_TTL_info *info = par->targinfo;
int new_ttl;
if (!skb_make_writable(skb, skb->len))
return NF_DROP;
iph = ip_hdr(skb);
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) {
csum_replace2(&iph->check, htons(iph->ttl << 8),
htons(new_ttl << 8));
iph->ttl = new_ttl;
}
return XT_CONTINUE;
}
static bool ttl_tg_check(const struct xt_tgchk_param *par)
{
const struct ipt_TTL_info *info = par->targinfo;
if (info->mode > IPT_TTL_MAXMODE) {
printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
info->mode);
return false;
}
if (info->mode != IPT_TTL_SET && info->ttl == 0)
return false;
return true;
}
static struct xt_target ttl_tg_reg __read_mostly = {
.name = "TTL",
.family = NFPROTO_IPV4,
.target = ttl_tg,
.targetsize = sizeof(struct ipt_TTL_info),
.table = "mangle",
.checkentry = ttl_tg_check,
.me = THIS_MODULE,
};
static int __init ttl_tg_init(void)
{
return xt_register_target(&ttl_tg_reg);
}
static void __exit ttl_tg_exit(void)
{
xt_unregister_target(&ttl_tg_reg);
}
module_init(ttl_tg_init);
module_exit(ttl_tg_exit);
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