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/*
* Hop Limit modification target for ip6tables
* Maciej Soltysiak <solt@dns.toxicfilms.tv>
* Based on HW's TTL module
*
* This software is distributed under the terms of GNU GPL
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv6/ip6t_HL.h>
MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
MODULE_DESCRIPTION("Xtables: IPv6 Hop Limit field modification target");
MODULE_LICENSE("GPL");
static unsigned int
hl_tg6(struct sk_buff *skb, const struct xt_target_param *par)
{
struct ipv6hdr *ip6h;
const struct ip6t_HL_info *info = par->targinfo;
int new_hl;
if (!skb_make_writable(skb, skb->len))
return NF_DROP;
ip6h = ipv6_hdr(skb);
switch (info->mode) {
case IP6T_HL_SET:
new_hl = info->hop_limit;
break;
case IP6T_HL_INC:
new_hl = ip6h->hop_limit + info->hop_limit;
if (new_hl > 255)
new_hl = 255;
break;
case IP6T_HL_DEC:
new_hl = ip6h->hop_limit - info->hop_limit;
if (new_hl < 0)
new_hl = 0;
break;
default:
new_hl = ip6h->hop_limit;
break;
}
ip6h->hop_limit = new_hl;
return XT_CONTINUE;
}
static bool
hl_tg6_check(const char *tablename, const void *entry,
const struct xt_target *target, void *targinfo,
unsigned int hook_mask)
{
const struct ip6t_HL_info *info = targinfo;
if (info->mode > IP6T_HL_MAXMODE) {
printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
info->mode);
return false;
}
if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
"make sense with value 0\n");
return false;
}
return true;
}
static struct xt_target hl_tg6_reg __read_mostly = {
.name = "HL",
.family = NFPROTO_IPV6,
.target = hl_tg6,
.targetsize = sizeof(struct ip6t_HL_info),
.table = "mangle",
.checkentry = hl_tg6_check,
.me = THIS_MODULE
};
static int __init hl_tg6_init(void)
{
return xt_register_target(&hl_tg6_reg);
}
static void __exit hl_tg6_exit(void)
{
xt_unregister_target(&hl_tg6_reg);
}
module_init(hl_tg6_init);
module_exit(hl_tg6_exit);
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