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 #include <linux/ipv6.h>
  13
  14 #include <linux/netfilter/x_tables.h>
  15 #include <linux/netfilter_ipv6/ip6t_HL.h>
  16
  17 MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
  18 MODULE_DESCRIPTION("IP6 tables Hop Limit modification module");
  19 MODULE_LICENSE("GPL");
  20
  21 static unsigned int ip6t_hl_target(struct sk_buff *skb,
  22                                    const struct net_device *in,
  23                                    const struct net_device *out,
  24                                    unsigned int hooknum,
  25                                    const struct xt_target *target,
  26                                    const void *targinfo)
  27 {
  28         struct ipv6hdr *ip6h;
  29         const struct ip6t_HL_info *info = targinfo;
  30         int new_hl;
  31
  32         if (!skb_make_writable(skb, skb->len))
  33                 return NF_DROP;
  34
  35         ip6h = ipv6_hdr(skb);
  36
  37         switch (info->mode) {
  38                 case IP6T_HL_SET:
  39                         new_hl = info->hop_limit;
  40                         break;
  41                 case IP6T_HL_INC:
  42                         new_hl = ip6h->hop_limit + info->hop_limit;
  43                         if (new_hl > 255)
  44                                 new_hl = 255;
  45                         break;
  46                 case IP6T_HL_DEC:
  47                         new_hl = ip6h->hop_limit - info->hop_limit;
  48                         if (new_hl < 0)
  49                                 new_hl = 0;
  50                         break;
  51                 default:
  52                         new_hl = ip6h->hop_limit;
  53                         break;
  54         }
  55
  56         ip6h->hop_limit = new_hl;
  57
  58         return XT_CONTINUE;
  59 }
  60
  61 static bool 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         const 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 false;
  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 false;
  78         }
  79         return true;
  80 }
  81
  82 static struct xt_target ip6t_HL __read_mostly = {
  83         .name           = "HL",
  84         .family         = AF_INET6,
  85         .target         = ip6t_hl_target,
  86         .targetsize     = sizeof(struct ip6t_HL_info),
  87         .table          = "mangle",
  88         .checkentry     = ip6t_hl_checkentry,
  89         .me             = THIS_MODULE
  90 };
  91
  92 static int __init ip6t_hl_init(void)
  93 {
  94         return xt_register_target(&ip6t_HL);
  95 }
  96
  97 static void __exit ip6t_hl_fini(void)
  98 {
  99         xt_unregister_target(&ip6t_HL);
 100 }
 101
 102 module_init(ip6t_hl_init);
 103 module_exit(ip6t_hl_fini);