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/* TTL modification target for IP tables
* (C) 2000 by Harald Welte <laforge@gnumonks.org>
*
* Version: 1.8
*
* This software is distributed under the terms of GNU GPL
*/
#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@gnumonks.org>");
MODULE_DESCRIPTION("IP tables TTL modification module");
MODULE_LICENSE("GPL");
static unsigned int ipt_ttl_target(struct sk_buff **pskb, unsigned int hooknum,
const struct net_device *in, const struct net_device *out,
const void *targinfo, void *userinfo)
{
struct iphdr *iph = (*pskb)->nh.iph;
const struct ipt_TTL_info *info = targinfo;
u_int16_t diffs[2];
int new_ttl;
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));
(*pskb)->nfcache |= NFC_ALTERED;
}
return IPT_CONTINUE;
}
static int ipt_ttl_checkentry(const char *tablename,
const struct ipt_entry *e,
void *targinfo,
unsigned int targinfosize,
unsigned int hook_mask)
{
struct ipt_TTL_info *info = targinfo;
if (targinfosize != IPT_ALIGN(sizeof(struct ipt_TTL_info))) {
printk(KERN_WARNING "TTL: targinfosize %u != %Zu\n",
targinfosize,
IPT_ALIGN(sizeof(struct ipt_TTL_info)));
return 0;
}
if (strcmp(tablename, "mangle")) {
printk(KERN_WARNING "TTL: can only be called from \"mangle\" table, not \"%s\"\n", tablename);
return 0;
}
if (info->mode > IPT_TTL_MAXMODE) {
printk(KERN_WARNING "TTL: invalid or unknown Mode %u\n",
info->mode);
return 0;
}
if ((info->mode != IPT_TTL_SET) && (info->ttl == 0)) {
printk(KERN_WARNING "TTL: increment/decrement doesn't make sense with value 0\n");
return 0;
}
return 1;
}
static struct ipt_target ipt_TTL = { { NULL, NULL }, "TTL",
ipt_ttl_target, ipt_ttl_checkentry, NULL, THIS_MODULE };
static int __init init(void)
{
return ipt_register_target(&ipt_TTL);
}
static void __exit fini(void)
{
ipt_unregister_target(&ipt_TTL);
}
module_init(init);
module_exit(fini);
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