net/ipv6/netfilter/ip6t_HL.c

   1 /*
   2  * Hop Limit modification target for ip6tables
   3  * Maciej Soltysiak <solt@dns.toxicfilms.tv>
   4  * Based on HW's TTL module
   5  *
   6  * This software is distributed under the terms of GNU GPL
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <linux/ip.h>
  12
  13 #include <linux/netfilter_ipv6/ip6_tables.h>
  14 #include <linux/netfilter_ipv6/ip6t_HL.h>
  15
  16 MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
  17 MODULE_DESCRIPTION("IP tables Hop Limit modification module");
  18 MODULE_LICENSE("GPL");
  19
  20 static unsigned int ip6t_hl_target(struct sk_buff **pskb,
  21                                    const struct net_device *in,
  22                                    const struct net_device *out,
  23                                    unsigned int hooknum,
  24                                    const struct xt_target *target,
  25                                    const void *targinfo)
  26 {
  27         struct ipv6hdr *ip6h;
  28         const struct ip6t_HL_info *info = targinfo;
  29         int new_hl;
  30
  31         if (!skb_make_writable(pskb, (*pskb)->len))
  32                 return NF_DROP;
  33
  34         ip6h = (*pskb)->nh.ipv6h;
  35
  36         switch (info->mode) {
  37                 case IP6T_HL_SET:
  38                         new_hl = info->hop_limit;
  39                         break;
  40                 case IP6T_HL_INC:
  41                         new_hl = ip6h->hop_limit + info->hop_limit;
  42                         if (new_hl > 255)
  43                                 new_hl = 255;
  44                         break;
  45                 case IP6T_HL_DEC:
  46                         new_hl = ip6h->hop_limit - info->hop_limit;
  47                         if (new_hl < 0)
  48                                 new_hl = 0;
  49                         break;
  50                 default:
  51                         new_hl = ip6h->hop_limit;
  52                         break;
  53         }
  54
  55         if (new_hl != ip6h->hop_limit)
  56                 ip6h->hop_limit = new_hl;
  57
  58         return IP6T_CONTINUE;
  59 }
  60
  61 static int ip6t_hl_checkentry(const char *tablename,
  62                 const void *entry,
  63                 const struct xt_target *target,
  64                 void *targinfo,
  65                 unsigned int hook_mask)
  66 {
  67         struct ip6t_HL_info *info = targinfo;
  68
  69         if (info->mode > IP6T_HL_MAXMODE) {
  70                 printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
  71                         info->mode);
  72                 return 0;
  73         }
  74         if ((info->mode != IP6T_HL_SET) && (info->hop_limit == 0)) {
  75                 printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
  76                         "make sense with value 0\n");
  77                 return 0;
  78         }
  79         return 1;
  80 }
  81
  82 static struct ip6t_target ip6t_HL = {
  83         .name           = "HL",
  84         .target         = ip6t_hl_target,
  85         .targetsize     = sizeof(struct ip6t_HL_info),
  86         .table          = "mangle",
  87         .checkentry     = ip6t_hl_checkentry,
  88         .me             = THIS_MODULE
  89 };
  90
  91 static int __init ip6t_hl_init(void)
  92 {
  93         return ip6t_register_target(&ip6t_HL);
  94 }
  95
  96 static void __exit ip6t_hl_fini(void)
  97 {
  98         ip6t_unregister_target(&ip6t_HL);
  99 }
 100
 101 module_init(ip6t_hl_init);
 102 module_exit(ip6t_hl_fini);