xt_quota.c

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/*
 * netfilter module to enforce network quotas
 *
 * Sam Johnston <[email protected]>
 */
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

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

struct xt_quota_priv {
    spinlock_t  lock;
    uint64_t    quota;
};

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Sam Johnston <[email protected]>");
MODULE_DESCRIPTION("Xtables: countdown quota match");
MODULE_ALIAS("ipt_quota");
MODULE_ALIAS("ip6t_quota");

static bool
quota_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct xt_quota_info *q = (void *)par->matchinfo;
    struct xt_quota_priv *priv = q->master;
    bool ret = q->flags & XT_QUOTA_INVERT;

    spin_lock_bh(&priv->lock);
    if (priv->quota >= skb->len) {
        priv->quota -= skb->len;
        ret = !ret;
    } else {
        /* we do not allow even small packets from now on */
        priv->quota = 0;
    }
    spin_unlock_bh(&priv->lock);

    return ret;
}

static int quota_mt_check(const struct xt_mtchk_param *par)
{
    struct xt_quota_info *q = par->matchinfo;

    if (q->flags & ~XT_QUOTA_MASK)
        return -EINVAL;

    q->master = kmalloc(sizeof(*q->master), GFP_KERNEL);
    if (q->master == NULL)
        return -ENOMEM;

    spin_lock_init(&q->master->lock);
    q->master->quota = q->quota;
    return 0;
}

static void quota_mt_destroy(const struct xt_mtdtor_param *par)
{
    const struct xt_quota_info *q = par->matchinfo;

    kfree(q->master);
}

static struct xt_match quota_mt_reg __read_mostly = {
    .name       = "quota",
    .revision   = 0,
    .family     = NFPROTO_UNSPEC,
    .match      = quota_mt,
    .checkentry = quota_mt_check,
    .destroy    = quota_mt_destroy,
    .matchsize  = sizeof(struct xt_quota_info),
    .me         = THIS_MODULE,
};

static int __init quota_mt_init(void)
{
    return xt_register_match(&quota_mt_reg);
}

static void __exit quota_mt_exit(void)
{
    xt_unregister_match(&quota_mt_reg);
}

module_init(quota_mt_init);
module_exit(quota_mt_exit);