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/* Kernel module to match packet length. */
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/netfilter_ipv4/ipt_length.h>
#include <linux/netfilter_ipv4/ip_tables.h>
MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
MODULE_DESCRIPTION("IP tables packet length matching module");
MODULE_LICENSE("GPL");
static int
match(const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
const void *matchinfo,
int offset,
const void *hdr,
u_int16_t datalen,
int *hotdrop)
{
const struct ipt_length_info *info = matchinfo;
u_int16_t pktlen = ntohs(skb->nh.iph->tot_len);
return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
}
static int
checkentry(const char *tablename,
const struct ipt_ip *ip,
void *matchinfo,
unsigned int matchsize,
unsigned int hook_mask)
{
if (matchsize != IPT_ALIGN(sizeof(struct ipt_length_info)))
return 0;
return 1;
}
static struct ipt_match length_match
= { { NULL, NULL }, "length", &match, &checkentry, NULL, THIS_MODULE };
static int __init init(void)
{
return ipt_register_match(&length_match);
}
static void __exit fini(void)
{
ipt_unregister_match(&length_match);
}
module_init(init);
module_exit(fini);
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