// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2006 Patrick McHardy <kaber@trash.net>
 *
 * Based on ipt_random and ipt_nth by Fabrice MARIE <fabrice@netfilter.org>.
 */

#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 <kaber@trash.net>");
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 ((get_random_u32() & 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_obj(*info->master);
        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),
        .usersize   = offsetof(struct xt_statistic_info, master),
        .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);