103 строки
2.3 KiB
C
103 строки
2.3 KiB
C
/* 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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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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*/
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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 <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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MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
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MODULE_DESCRIPTION("Xtables: IPv4 TTL 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 net_device *in,
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const struct net_device *out, unsigned int hooknum,
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const struct xt_target *target, const void *targinfo)
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{
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struct iphdr *iph;
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const struct ipt_TTL_info *info = targinfo;
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int new_ttl;
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if (!skb_make_writable(skb, skb->len))
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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 bool
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ttl_tg_check(const char *tablename, const void *e,
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const struct xt_target *target, void *targinfo,
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unsigned int hook_mask)
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{
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const struct ipt_TTL_info *info = targinfo;
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if (info->mode > IPT_TTL_MAXMODE) {
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printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
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info->mode);
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return false;
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}
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if (info->mode != IPT_TTL_SET && info->ttl == 0)
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return false;
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return true;
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}
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static struct xt_target ttl_tg_reg __read_mostly = {
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.name = "TTL",
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.family = AF_INET,
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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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static int __init ttl_tg_init(void)
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{
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return xt_register_target(&ttl_tg_reg);
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}
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static void __exit ttl_tg_exit(void)
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{
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xt_unregister_target(&ttl_tg_reg);
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}
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module_init(ttl_tg_init);
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module_exit(ttl_tg_exit);
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