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 net_device *in,
  35              const struct net_device *out, const struct xt_match *match,
  36              const void *data, int offset, unsigned int protoff, bool *hotdrop)
  37 {
  38         struct ebt_limit_info *info = (void *)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 true;
  51         }
  52
  53         spin_unlock_bh(&limit_lock);
  54         return false;
  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 bool
  70 ebt_limit_mt_check(const char *table, const void *e,
  71                    const struct xt_match *match, void *data,
  72                    unsigned int hook_mask)
  73 {
  74         struct ebt_limit_info *info = data;
  75
  76         /* Check for overflow. */
  77         if (info->burst == 0 ||
  78             user2credits(info->avg * info->burst) < user2credits(info->avg)) {
  79                 printk("Overflow in ebt_limit, try lower: %u/%u\n",
  80                         info->avg, info->burst);
  81                 return false;
  82         }
  83
  84         /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
  85         info->prev = jiffies;
  86         info->credit = user2credits(info->avg * info->burst);
  87         info->credit_cap = user2credits(info->avg * info->burst);
  88         info->cost = user2credits(info->avg);
  89         return true;
  90 }
  91
  92 static struct xt_match ebt_limit_mt_reg __read_mostly = {
  93         .name           = "limit",
  94         .revision       = 0,
  95         .family         = NFPROTO_BRIDGE,
  96         .match          = ebt_limit_mt,
  97         .checkentry     = ebt_limit_mt_check,
  98         .matchsize      = XT_ALIGN(sizeof(struct ebt_limit_info)),
  99         .me             = THIS_MODULE,
 100 };
 101
 102 static int __init ebt_limit_init(void)
 103 {
 104         return xt_register_match(&ebt_limit_mt_reg);
 105 }
 106
 107 static void __exit ebt_limit_fini(void)
 108 {
 109         xt_unregister_match(&ebt_limit_mt_reg);
 110 }
 111
 112 module_init(ebt_limit_init);
 113 module_exit(ebt_limit_fini);
 114 MODULE_DESCRIPTION("Ebtables: Rate-limit match");
 115 MODULE_LICENSE("GPL");