// SPDX-License-Identifier: GPL-2.0-only
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/*
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* TTL modification target for IP tables
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* (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
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*
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* Hop Limit modification target for ip6tables
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* Maciej Soltysiak <solt@dns.toxicfilms.tv>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/ip.h>
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#include <linux/ipv6.h>
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#include <net/checksum.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter_ipv4/ipt_TTL.h>
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#include <linux/netfilter_ipv6/ip6t_HL.h>
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MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
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MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
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MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
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MODULE_LICENSE("GPL");
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static unsigned int
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ttl_tg(struct sk_buff *skb, const struct xt_action_param *par)
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{
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struct iphdr *iph;
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const struct ipt_TTL_info *info = par->targinfo;
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int new_ttl;
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if (skb_ensure_writable(skb, sizeof(*iph)))
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return NF_DROP;
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iph = ip_hdr(skb);
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switch (info->mode) {
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case IPT_TTL_SET:
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new_ttl = info->ttl;
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break;
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case IPT_TTL_INC:
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new_ttl = iph->ttl + info->ttl;
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if (new_ttl > 255)
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new_ttl = 255;
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break;
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case IPT_TTL_DEC:
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new_ttl = iph->ttl - info->ttl;
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if (new_ttl < 0)
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new_ttl = 0;
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break;
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default:
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new_ttl = iph->ttl;
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break;
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}
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if (new_ttl != iph->ttl) {
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csum_replace2(&iph->check, htons(iph->ttl << 8),
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htons(new_ttl << 8));
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iph->ttl = new_ttl;
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}
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return XT_CONTINUE;
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}
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static unsigned int
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hl_tg6(struct sk_buff *skb, const struct xt_action_param *par)
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{
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struct ipv6hdr *ip6h;
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const struct ip6t_HL_info *info = par->targinfo;
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int new_hl;
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if (skb_ensure_writable(skb, sizeof(*ip6h)))
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return NF_DROP;
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ip6h = ipv6_hdr(skb);
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switch (info->mode) {
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case IP6T_HL_SET:
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new_hl = info->hop_limit;
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break;
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case IP6T_HL_INC:
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new_hl = ip6h->hop_limit + info->hop_limit;
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if (new_hl > 255)
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new_hl = 255;
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break;
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case IP6T_HL_DEC:
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new_hl = ip6h->hop_limit - info->hop_limit;
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if (new_hl < 0)
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new_hl = 0;
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break;
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default:
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new_hl = ip6h->hop_limit;
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break;
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}
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ip6h->hop_limit = new_hl;
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return XT_CONTINUE;
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}
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static int ttl_tg_check(const struct xt_tgchk_param *par)
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{
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const struct ipt_TTL_info *info = par->targinfo;
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if (info->mode > IPT_TTL_MAXMODE)
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return -EINVAL;
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if (info->mode != IPT_TTL_SET && info->ttl == 0)
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return -EINVAL;
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return 0;
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}
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static int hl_tg6_check(const struct xt_tgchk_param *par)
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{
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const struct ip6t_HL_info *info = par->targinfo;
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if (info->mode > IP6T_HL_MAXMODE)
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return -EINVAL;
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if (info->mode != IP6T_HL_SET && info->hop_limit == 0)
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return -EINVAL;
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return 0;
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}
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static struct xt_target hl_tg_reg[] __read_mostly = {
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{
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.name = "TTL",
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.revision = 0,
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.family = NFPROTO_IPV4,
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.target = ttl_tg,
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.targetsize = sizeof(struct ipt_TTL_info),
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.table = "mangle",
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.checkentry = ttl_tg_check,
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.me = THIS_MODULE,
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},
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{
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.name = "HL",
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.revision = 0,
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.family = NFPROTO_IPV6,
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.target = hl_tg6,
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.targetsize = sizeof(struct ip6t_HL_info),
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.table = "mangle",
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.checkentry = hl_tg6_check,
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.me = THIS_MODULE,
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},
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};
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static int __init hl_tg_init(void)
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{
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return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
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}
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static void __exit hl_tg_exit(void)
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{
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xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
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}
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module_init(hl_tg_init);
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module_exit(hl_tg_exit);
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MODULE_ALIAS("ipt_TTL");
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MODULE_ALIAS("ip6t_HL");
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