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 void *targinfo, void *userinfo)
  25 {
  26         struct ipv6hdr *ip6h;
  27         const struct ip6t_HL_info *info = targinfo;
  28         u_int16_t diffs[2];
  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                 diffs[0] = htons(((unsigned)ip6h->hop_limit) << 8) ^ 0xFFFF;
  57                 ip6h->hop_limit = new_hl;
  58                 diffs[1] = htons(((unsigned)ip6h->hop_limit) << 8);
  59         }
  60
  61         return IP6T_CONTINUE;
  62 }
  63
  64 static int ip6t_hl_checkentry(const char *tablename,
  65                 const void *entry,
  66                 void *targinfo,
  67                 unsigned int targinfosize,
  68                 unsigned int hook_mask)
  69 {
  70         struct ip6t_HL_info *info = targinfo;
  71
  72         if (targinfosize != IP6T_ALIGN(sizeof(struct ip6t_HL_info))) {
  73                 printk(KERN_WARNING "ip6t_HL: targinfosize %u != %Zu\n",
  74                                 targinfosize,
  75                                 IP6T_ALIGN(sizeof(struct ip6t_HL_info)));
  76                 return 0;
  77         }
  78
  79         if (strcmp(tablename, "mangle")) {
  80                 printk(KERN_WARNING "ip6t_HL: can only be called from "
  81                         "\"mangle\" table, not \"%s\"\n", tablename);
  82                 return 0;
  83         }
  84
  85         if (info->mode > IP6T_HL_MAXMODE) {
  86                 printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
  87                         info->mode);
  88                 return 0;
  89         }
  90
  91         if ((info->mode != IP6T_HL_SET) && (info->hop_limit == 0)) {
  92                 printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
  93                         "make sense with value 0\n");
  94                 return 0;
  95         }
  96
  97         return 1;
  98 }
  99
 100 static struct ip6t_target ip6t_HL = {
 101         .name           = "HL",
 102         .target         = ip6t_hl_target,
 103         .checkentry     = ip6t_hl_checkentry,
 104         .me             = THIS_MODULE
 105 };
 106
 107 static int __init init(void)
 108 {
 109         return ip6t_register_target(&ip6t_HL);
 110 }
 111
 112 static void __exit fini(void)
 113 {
 114         ip6t_unregister_target(&ip6t_HL);
 115 }
 116
 117 module_init(init);
 118 module_exit(fini);