xt_statistic.c

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/*
 * Copyright (c) 2006 Patrick McHardy <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Based on ipt_random and ipt_nth by Fabrice MARIE <[email protected]>.
 */

#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/skbuff.h>
#include <linux/net.h>
#include <linux/slab.h>

#include <linux/netfilter/xt_statistic.h>
#include <linux/netfilter/x_tables.h>
#include <linux/module.h>

struct xt_statistic_priv {
    atomic_t count;
} ____cacheline_aligned_in_smp;

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Patrick McHardy <[email protected]>");
MODULE_DESCRIPTION("Xtables: statistics-based matching (\"Nth\", random)");
MODULE_ALIAS("ipt_statistic");
MODULE_ALIAS("ip6t_statistic");

static bool
statistic_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct xt_statistic_info *info = par->matchinfo;
    bool ret = info->flags & XT_STATISTIC_INVERT;
    int nval, oval;

    switch (info->mode) {
    case XT_STATISTIC_MODE_RANDOM:
        if ((net_random() & 0x7FFFFFFF) < info->u.random.probability)
            ret = !ret;
        break;
    case XT_STATISTIC_MODE_NTH:
        do {
            oval = atomic_read(&info->master->count);
            nval = (oval == info->u.nth.every) ? 0 : oval + 1;
        } while (atomic_cmpxchg(&info->master->count, oval, nval) != oval);
        if (nval == 0)
            ret = !ret;
        break;
    }

    return ret;
}

static int statistic_mt_check(const struct xt_mtchk_param *par)
{
    struct xt_statistic_info *info = par->matchinfo;

    if (info->mode > XT_STATISTIC_MODE_MAX ||
        info->flags & ~XT_STATISTIC_MASK)
        return -EINVAL;

    info->master = kzalloc(sizeof(*info->master), GFP_KERNEL);
    if (info->master == NULL)
        return -ENOMEM;
    atomic_set(&info->master->count, info->u.nth.count);

    return 0;
}

static void statistic_mt_destroy(const struct xt_mtdtor_param *par)
{
    const struct xt_statistic_info *info = par->matchinfo;

    kfree(info->master);
}

static struct xt_match xt_statistic_mt_reg __read_mostly = {
    .name       = "statistic",
    .revision   = 0,
    .family     = NFPROTO_UNSPEC,
    .match      = statistic_mt,
    .checkentry = statistic_mt_check,
    .destroy    = statistic_mt_destroy,
    .matchsize  = sizeof(struct xt_statistic_info),
    .me         = THIS_MODULE,
};

static int __init statistic_mt_init(void)
{
    return xt_register_match(&xt_statistic_mt_reg);
}

static void __exit statistic_mt_exit(void)
{
    xt_unregister_match(&xt_statistic_mt_reg);
}

module_init(statistic_mt_init);
module_exit(statistic_mt_exit);