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// SPDX-License-Identifier: GPL-2.0-only
/*
* TTL modification target for IP tables
* (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
*
* Hop Limit modification target for ip6tables
* Maciej Soltysiak <solt@dns.toxicfilms.tv>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <net/checksum.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ipt_TTL.h>
#include <linux/netfilter_ipv6/ip6t_HL.h>
MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
MODULE_LICENSE("GPL");
static unsigned int
ttl_tg(struct sk_buff *skb, const struct xt_action_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 unsigned int
hl_tg6(struct sk_buff *skb, const struct xt_action_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 int ttl_tg_check(const struct xt_tgchk_param *par)
{
const struct ipt_TTL_info *info = par->targinfo;
if (info->mode > IPT_TTL_MAXMODE)
return -EINVAL;
if (info->mode != IPT_TTL_SET && info->ttl == 0)
return -EINVAL;
return 0;
}
static int hl_tg6_check(const struct xt_tgchk_param *par)
{
const struct ip6t_HL_info *info = par->targinfo;
if (info->mode > IP6T_HL_MAXMODE)
return -EINVAL;
if (info->mode != IP6T_HL_SET && info->hop_limit == 0)
return -EINVAL;
return 0;
}
static struct xt_target hl_tg_reg[] __read_mostly = {
{
.name = "TTL",
.revision = 0,
.family = NFPROTO_IPV4,
.target = ttl_tg,
.targetsize = sizeof(struct ipt_TTL_info),
.table = "mangle",
.checkentry = ttl_tg_check,
.me = THIS_MODULE,
},
{
.name = "HL",
.revision = 0,
.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_tg_init(void)
{
return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
}
static void __exit hl_tg_exit(void)
{
xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
}
module_init(hl_tg_init);
module_exit(hl_tg_exit);
MODULE_ALIAS("ipt_TTL");
MODULE_ALIAS("ip6t_HL");
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