net/bridge/netfilter/ebt_limit.c

   1 /*
   2  *  ebt_limit
   3  *
   4  *      Authors:
   5  *      Tom Marshall <tommy@home.tig-grr.com>
   6  *
   7  *      Mostly copied from netfilter's ipt_limit.c, see that file for
   8  *      more explanation
   9  *
  10  *  September, 2003
  11  *
  12  */
  13 #include <linux/module.h>
  14 #include <linux/netdevice.h>
  15 #include <linux/spinlock.h>
  16 #include <linux/netfilter/x_tables.h>
  17 #include <linux/netfilter_bridge/ebtables.h>
  18 #include <linux/netfilter_bridge/ebt_limit.h>
  19
  20 static DEFINE_SPINLOCK(limit_lock);
  21
  22 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
  23
  24 #define _POW2_BELOW2(x) ((x)|((x)>>1))
  25 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
  26 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
  27 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
  28 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
  29 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
  30
  31 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
  32
  33 static bool
  34 ebt_limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
  35 {
  36         struct ebt_limit_info *info = (void *)par->matchinfo;
  37         unsigned long now = jiffies;
  38
  39         spin_lock_bh(&limit_lock);
  40         info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
  41         if (info->credit > info->credit_cap)
  42                 info->credit = info->credit_cap;
  43
  44         if (info->credit >= info->cost) {
  45                 /* We're not limited. */
  46                 info->credit -= info->cost;
  47                 spin_unlock_bh(&limit_lock);
  48                 return true;
  49         }
  50
  51         spin_unlock_bh(&limit_lock);
  52         return false;
  53 }
  54
  55 /* Precision saver. */
  56 static u_int32_t
  57 user2credits(u_int32_t user)
  58 {
  59         /* If multiplying would overflow... */
  60         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  61                 /* Divide first. */
  62                 return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  63
  64         return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
  65 }
  66
  67 static bool ebt_limit_mt_check(const struct xt_mtchk_param *par)
  68 {
  69         struct ebt_limit_info *info = par->matchinfo;
  70
  71         /* Check for overflow. */
  72         if (info->burst == 0 ||
  73             user2credits(info->avg * info->burst) < user2credits(info->avg)) {
  74                 printk("Overflow in ebt_limit, try lower: %u/%u\n",
  75                         info->avg, info->burst);
  76                 return false;
  77         }
  78
  79         /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
  80         info->prev = jiffies;
  81         info->credit = user2credits(info->avg * info->burst);
  82         info->credit_cap = user2credits(info->avg * info->burst);
  83         info->cost = user2credits(info->avg);
  84         return true;
  85 }
  86
  87 static struct xt_match ebt_limit_mt_reg __read_mostly = {
  88         .name           = "limit",
  89         .revision       = 0,
  90         .family         = NFPROTO_BRIDGE,
  91         .match          = ebt_limit_mt,
  92         .checkentry     = ebt_limit_mt_check,
  93         .matchsize      = XT_ALIGN(sizeof(struct ebt_limit_info)),
  94         .me             = THIS_MODULE,
  95 };
  96
  97 static int __init ebt_limit_init(void)
  98 {
  99         return xt_register_match(&ebt_limit_mt_reg);
 100 }
 101
 102 static void __exit ebt_limit_fini(void)
 103 {
 104         xt_unregister_match(&ebt_limit_mt_reg);
 105 }
 106
 107 module_init(ebt_limit_init);
 108 module_exit(ebt_limit_fini);
 109 MODULE_DESCRIPTION("Ebtables: Rate-limit match");
 110 MODULE_LICENSE("GPL");