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
  14 #include <linux/netfilter_bridge/ebtables.h>
  15 #include <linux/netfilter_bridge/ebt_limit.h>
  16 #include <linux/module.h>
  17
  18 #include <linux/netdevice.h>
  19 #include <linux/spinlock.h>
  20
  21 static DEFINE_SPINLOCK(limit_lock);
  22
  23 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
  24
  25 #define _POW2_BELOW2(x) ((x)|((x)>>1))
  26 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
  27 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
  28 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
  29 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
  30 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
  31
  32 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
  33
  34 static int ebt_limit_match(const struct sk_buff *skb,
  35    const struct net_device *in, const struct net_device *out,
  36    const void *data, unsigned int datalen)
  37 {
  38         struct ebt_limit_info *info = (struct ebt_limit_info *)data;
  39         unsigned long now = jiffies;
  40
  41         spin_lock_bh(&limit_lock);
  42         info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
  43         if (info->credit > info->credit_cap)
  44                 info->credit = info->credit_cap;
  45
  46         if (info->credit >= info->cost) {
  47                 /* We're not limited. */
  48                 info->credit -= info->cost;
  49                 spin_unlock_bh(&limit_lock);
  50                 return EBT_MATCH;
  51         }
  52
  53         spin_unlock_bh(&limit_lock);
  54         return EBT_NOMATCH;
  55 }
  56
  57 /* Precision saver. */
  58 static u_int32_t
  59 user2credits(u_int32_t user)
  60 {
  61         /* If multiplying would overflow... */
  62         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  63                 /* Divide first. */
  64                 return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  65
  66         return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
  67 }
  68
  69 static int ebt_limit_check(const char *tablename, unsigned int hookmask,
  70    const struct ebt_entry *e, void *data, unsigned int datalen)
  71 {
  72         struct ebt_limit_info *info = (struct ebt_limit_info *)data;
  73
  74         if (datalen != EBT_ALIGN(sizeof(struct ebt_limit_info)))
  75                 return -EINVAL;
  76
  77         /* Check for overflow. */
  78         if (info->burst == 0 ||
  79             user2credits(info->avg * info->burst) < user2credits(info->avg)) {
  80                 printk("Overflow in ebt_limit, try lower: %u/%u\n",
  81                         info->avg, info->burst);
  82                 return -EINVAL;
  83         }
  84
  85         /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
  86         info->prev = jiffies;
  87         info->credit = user2credits(info->avg * info->burst);
  88         info->credit_cap = user2credits(info->avg * info->burst);
  89         info->cost = user2credits(info->avg);
  90         return 0;
  91 }
  92
  93 static struct ebt_match ebt_limit_reg =
  94 {
  95         .name           = EBT_LIMIT_MATCH,
  96         .match          = ebt_limit_match,
  97         .check          = ebt_limit_check,
  98         .me             = THIS_MODULE,
  99 };
 100
 101 static int __init init(void)
 102 {
 103         return ebt_register_match(&ebt_limit_reg);
 104 }
 105
 106 static void __exit fini(void)
 107 {
 108         ebt_unregister_match(&ebt_limit_reg);
 109 }
 110
 111 module_init(init);
 112 module_exit(fini);
 113 MODULE_LICENSE("GPL");