108 lines
2.4 KiB
C
108 lines
2.4 KiB
C
/*
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* Hop Limit modification target for ip6tables
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* Maciej Soltysiak <solt@dns.toxicfilms.tv>
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* Based on HW's TTL module
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*
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* This software is distributed under the terms of GNU GPL
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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 <linux/netfilter_ipv6/ip6_tables.h>
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#include <linux/netfilter_ipv6/ip6t_HL.h>
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MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
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MODULE_DESCRIPTION("IP tables Hop Limit modification module");
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MODULE_LICENSE("GPL");
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static unsigned int ip6t_hl_target(struct sk_buff **pskb,
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const struct net_device *in,
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const struct net_device *out,
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unsigned int hooknum,
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const struct xt_target *target,
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const void *targinfo, void *userinfo)
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{
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struct ipv6hdr *ip6h;
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const struct ip6t_HL_info *info = targinfo;
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u_int16_t diffs[2];
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int new_hl;
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if (!skb_make_writable(pskb, (*pskb)->len))
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return NF_DROP;
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ip6h = (*pskb)->nh.ipv6h;
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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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if (new_hl != ip6h->hop_limit) {
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diffs[0] = htons(((unsigned)ip6h->hop_limit) << 8) ^ 0xFFFF;
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ip6h->hop_limit = new_hl;
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diffs[1] = htons(((unsigned)ip6h->hop_limit) << 8);
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}
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return IP6T_CONTINUE;
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}
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static int ip6t_hl_checkentry(const char *tablename,
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const void *entry,
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const struct xt_target *target,
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void *targinfo,
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unsigned int targinfosize,
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unsigned int hook_mask)
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{
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struct ip6t_HL_info *info = targinfo;
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if (info->mode > IP6T_HL_MAXMODE) {
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printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
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info->mode);
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return 0;
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}
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if ((info->mode != IP6T_HL_SET) && (info->hop_limit == 0)) {
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printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
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"make sense with value 0\n");
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return 0;
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}
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return 1;
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}
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static struct ip6t_target ip6t_HL = {
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.name = "HL",
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.target = ip6t_hl_target,
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.targetsize = sizeof(struct ip6t_HL_info),
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.table = "mangle",
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.checkentry = ip6t_hl_checkentry,
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.me = THIS_MODULE
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};
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static int __init ip6t_hl_init(void)
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{
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return ip6t_register_target(&ip6t_HL);
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}
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static void __exit ip6t_hl_fini(void)
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{
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ip6t_unregister_target(&ip6t_HL);
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}
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module_init(ip6t_hl_init);
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module_exit(ip6t_hl_fini);
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