release/src/linux/linux/net/ipv4/netfilter/ipt_length.c

   1 /* Kernel module to match packet length. */
   2 #include <linux/module.h>
   3 #include <linux/skbuff.h>
   4
   5 #include <linux/netfilter_ipv4/ipt_length.h>
   6 #include <linux/netfilter_ipv4/ip_tables.h>
   7
   8 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
   9 MODULE_DESCRIPTION("IP tables packet length matching module");
  10 MODULE_LICENSE("GPL");
  11
  12 static int
  13 match(const struct sk_buff *skb,
  14       const struct net_device *in,
  15       const struct net_device *out,
  16       const void *matchinfo,
  17       int offset,
  18       const void *hdr,
  19       u_int16_t datalen,
  20       int *hotdrop)
  21 {
  22         const struct ipt_length_info *info = matchinfo;
  23         u_int16_t pktlen = ntohs(skb->nh.iph->tot_len);
  24
  25         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  26 }
  27
  28 static int
  29 checkentry(const char *tablename,
  30            const struct ipt_ip *ip,
  31            void *matchinfo,
  32            unsigned int matchsize,
  33            unsigned int hook_mask)
  34 {
  35         if (matchsize != IPT_ALIGN(sizeof(struct ipt_length_info)))
  36                 return 0;
  37
  38         return 1;
  39 }
  40
  41 static struct ipt_match length_match
  42 = { { NULL, NULL }, "length", &match, &checkentry, NULL, THIS_MODULE };
  43
  44 static int __init init(void)
  45 {
  46         return ipt_register_match(&length_match);
  47 }
  48
  49 static void __exit fini(void)
  50 {
  51         ipt_unregister_match(&length_match);
  52 }
  53
  54 module_init(init);
  55 module_exit(fini);