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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14 #include <linux/module.h>
  15 #include <linux/netdevice.h>
  16 #include <linux/spinlock.h>
  17 #include <linux/netfilter/x_tables.h>
  18 #include <linux/netfilter_bridge/ebtables.h>
  19 #include <linux/netfilter_bridge/ebt_limit.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 bool
  35 ebt_limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
  36 {
  37         struct ebt_limit_info *info = (void *)par->matchinfo;
  38         unsigned long now = jiffies;
  39
  40         spin_lock_bh(&limit_lock);
  41         info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
  42         if (info->credit > info->credit_cap)
  43                 info->credit = info->credit_cap;
  44
  45         if (info->credit >= info->cost) {
  46                 /* We're not limited. */
  47                 info->credit -= info->cost;
  48                 spin_unlock_bh(&limit_lock);
  49                 return true;
  50         }
  51
  52         spin_unlock_bh(&limit_lock);
  53         return false;
  54 }
  55
  56 /* Precision saver. */
  57 static u_int32_t
  58 user2credits(u_int32_t user)
  59 {
  60         /* If multiplying would overflow... */
  61         if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
  62                 /* Divide first. */
  63                 return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
  64
  65         return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
  66 }
  67
  68 static int ebt_limit_mt_check(const struct xt_mtchk_param *par)
  69 {
  70         struct ebt_limit_info *info = par->matchinfo;
  71
  72         /* Check for overflow. */
  73         if (info->burst == 0 ||
  74             user2credits(info->avg * info->burst) < user2credits(info->avg)) {
  75                 pr_info("overflow, try lower: %u/%u\n",
  76                         info->avg, info->burst);
  77                 return -EINVAL;
  78         }
  79
  80         /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
  81         info->prev = jiffies;
  82         info->credit = user2credits(info->avg * info->burst);
  83         info->credit_cap = user2credits(info->avg * info->burst);
  84         info->cost = user2credits(info->avg);
  85         return 0;
  86 }
  87
  88
  89 #ifdef CONFIG_COMPAT
  90 /*
  91  * no conversion function needed --
  92  * only avg/burst have meaningful values in userspace.
  93  */
  94 struct ebt_compat_limit_info {
  95         compat_uint_t avg, burst;
  96         compat_ulong_t prev;
  97         compat_uint_t credit, credit_cap, cost;
  98 };
  99 #endif
 100
 101 static struct xt_match ebt_limit_mt_reg __read_mostly = {
 102         .name           = "limit",
 103         .revision       = 0,
 104         .family         = NFPROTO_BRIDGE,
 105         .match          = ebt_limit_mt,
 106         .checkentry     = ebt_limit_mt_check,
 107         .matchsize      = sizeof(struct ebt_limit_info),
 108 #ifdef CONFIG_COMPAT
 109         .compatsize     = sizeof(struct ebt_compat_limit_info),
 110 #endif
 111         .me             = THIS_MODULE,
 112 };
 113
 114 static int __init ebt_limit_init(void)
 115 {
 116         return xt_register_match(&ebt_limit_mt_reg);
 117 }
 118
 119 static void __exit ebt_limit_fini(void)
 120 {
 121         xt_unregister_match(&ebt_limit_mt_reg);
 122 }
 123
 124 module_init(ebt_limit_init);
 125 module_exit(ebt_limit_fini);
 126 MODULE_DESCRIPTION("Ebtables: Rate-limit match");
 127 MODULE_LICENSE("GPL");