Commit e9837e55 authored by Chenbo Feng's avatar Chenbo Feng Committed by Pablo Neira Ayuso
Browse files

netfilter: xt_quota: fix the behavior of xt_quota module 



A major flaw of the current xt_quota module is that quota in a specific
rule gets reset every time there is a rule change in the same table. It
makes the xt_quota module not very useful in a table in which iptables
rules are changed at run time. This fix introduces a new counter that is
visible to userspace as the remaining quota of the current rule. When
userspace restores the rules in a table, it can restore the counter to
the remaining quota instead of resetting it to the full quota.

Signed-off-by: default avatarChenbo Feng <fengc@google.com>
Suggested-by: default avatarMaciej Żenczykowski <maze@google.com>
Reviewed-by: default avatarMaciej Żenczykowski <maze@google.com>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent a2d88182

include/uapi/linux/netfilter/xt_quota.h

+5 −3
Original line number Diff line number Diff line
@@ -15,9 +15,11 @@ struct xt_quota_info { 
	__u32 flags;

	__u32 pad;

	__aligned_u64 quota;



	/* Used internally by the kernel */

	struct xt_quota_priv	*master;

#ifdef __KERNEL__

	atomic64_t counter;

#else

	__aligned_u64 remain;

#endif

};



#endif /* _XT_QUOTA_H */

net/netfilter/xt_quota.c

+22 −33
Original line number Diff line number Diff line
@@ -11,11 +11,6 @@ 
#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 <samj@samj.net>");

MODULE_DESCRIPTION("Xtables: countdown quota match");
@@ -26,54 +21,48 @@ 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;

	u64 current_count = atomic64_read(&q->counter);

	bool ret = q->flags & XT_QUOTA_INVERT;

	u64 old_count, new_count;



	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);



	do {

		if (current_count == 1)

			return ret;

		if (current_count <= skb->len) {

			atomic64_set(&q->counter, 1);

			return ret;

		}

		old_count = current_count;

		new_count = current_count - skb->len;

		current_count = atomic64_cmpxchg(&q->counter, old_count,

						 new_count);

	} while (current_count != old_count);

	return !ret;

}



static int quota_mt_check(const struct xt_mtchk_param *par)

{

	struct xt_quota_info *q = par->matchinfo;



	BUILD_BUG_ON(sizeof(atomic64_t) != sizeof(__aligned_u64));



	if (q->flags & ~XT_QUOTA_MASK)

		return -EINVAL;

	if (atomic64_read(&q->counter) > q->quota + 1)

		return -ERANGE;



	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;

	if (atomic64_read(&q->counter) == 0)

		atomic64_set(&q->counter, q->quota + 1);

	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),

	.usersize   = offsetof(struct xt_quota_info, master),

	.me         = THIS_MODULE,

};

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