root/net/bridge/netfilter/ebt_limit.c

DEFINITIONS

1. ebt_limit_mt
2. user2credits
3. ebt_limit_mt_check
4. ebt_limit_init
5. ebt_limit_fini

/*
 *  ebt_limit
 *
 *      Authors:
 *      Tom Marshall <tommy@home.tig-grr.com>
 *
 *      Mostly copied from netfilter's ipt_limit.c, see that file for
 *      more explanation
 *
 *  September, 2003
 *
 */
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/spinlock.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_limit.h>

static DEFINE_SPINLOCK(limit_lock);

#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))

#define _POW2_BELOW2(x) ((x)|((x)>>1))
#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)

#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)

static bool
ebt_limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
{
        struct ebt_limit_info *info = (void *)par->matchinfo;
        unsigned long now = jiffies;

        spin_lock_bh(&limit_lock);
        info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
        if (info->credit > info->credit_cap)
                info->credit = info->credit_cap;

        if (info->credit >= info->cost) {
                /* We're not limited. */
                info->credit -= info->cost;
                spin_unlock_bh(&limit_lock);
                return true;
        }

        spin_unlock_bh(&limit_lock);
        return false;
}

/* Precision saver. */
static u_int32_t
user2credits(u_int32_t user)
{
        /* If multiplying would overflow... */
        if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
                /* Divide first. */
                return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;

        return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
}

static bool ebt_limit_mt_check(const struct xt_mtchk_param *par)
{
        struct ebt_limit_info *info = par->matchinfo;

        /* Check for overflow. */
        if (info->burst == 0 ||
            user2credits(info->avg * info->burst) < user2credits(info->avg)) {
                printk("Overflow in ebt_limit, try lower: %u/%u\n",
                        info->avg, info->burst);
                return false;
        }

        /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
        info->prev = jiffies;
        info->credit = user2credits(info->avg * info->burst);
        info->credit_cap = user2credits(info->avg * info->burst);
        info->cost = user2credits(info->avg);
        return true;
}

static struct xt_match ebt_limit_mt_reg __read_mostly = {
        .name           = "limit",
        .revision       = 0,
        .family         = NFPROTO_BRIDGE,
        .match          = ebt_limit_mt,
        .checkentry     = ebt_limit_mt_check,
        .matchsize      = XT_ALIGN(sizeof(struct ebt_limit_info)),
        .me             = THIS_MODULE,
};

static int __init ebt_limit_init(void)
{
        return xt_register_match(&ebt_limit_mt_reg);
}

static void __exit ebt_limit_fini(void)
{
        xt_unregister_match(&ebt_limit_mt_reg);
}

module_init(ebt_limit_init);
module_exit(ebt_limit_fini);
MODULE_DESCRIPTION("Ebtables: Rate-limit match");
MODULE_LICENSE("GPL");