LXR linux/net/bridge/netfilter/ebt

   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
  20static 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
  33static bool
  34ebt_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. */
  56static u_int32_t
  57user2credits(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
  67static 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
  87static 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
  97static int __init ebt_limit_init(void)
  98{
  99        return xt_register_match(&ebt_limit_mt_reg);
 100}
 101
 102static void __exit ebt_limit_fini(void)
 103{
 104        xt_unregister_match(&ebt_limit_mt_reg);
 105}
 106
 107module_init(ebt_limit_init);
 108module_exit(ebt_limit_fini);
 109MODULE_DESCRIPTION("Ebtables: Rate-limit match");
 110MODULE_LICENSE("GPL");
 111