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Commit 2eff25c1 authored by Patrick McHardy's avatar Patrick McHardy
Browse files

netfilter: xt_hashlimit: fix race condition and simplify locking 



As noticed by Shin Hong <hongshin@gmail.com>, there is a race between
htable_find_get() and htable_put():

htable_put():				htable_find_get():

					spin_lock_bh(&hashlimit_lock);
					<search entry>
atomic_dec_and_test(&hinfo->use)
					atomic_inc(&hinfo->use)
					spin_unlock_bh(&hashlimit_lock)
					return hinfo;
spin_lock_bh(&hashlimit_lock);
hlist_del(&hinfo->node);
spin_unlock_bh(&hashlimit_lock);
htable_destroy(hinfo);

The entire locking concept is overly complicated, tables are only
created/referenced and released in process context, so a single
mutex works just fine. Remove the hashinfo_spinlock and atomic
reference count and use the mutex to protect table lookups/creation
and reference count changes.

Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
parent 10a19939

net/netfilter/xt_hashlimit.c

+18 −34
Original line number Diff line number Diff line
@@ -90,7 +90,7 @@ struct dsthash_ent { 


struct xt_hashlimit_htable {

	struct hlist_node node;		/* global list of all htables */

	atomic_t use;

	int use;

	u_int8_t family;

	bool rnd_initialized;
@@ -109,8 +109,7 @@ struct xt_hashlimit_htable { 
	struct hlist_head hash[0];	/* hashtable itself */

};



static DEFINE_SPINLOCK(hashlimit_lock);	/* protects htables list */

static DEFINE_MUTEX(hlimit_mutex);	/* additional checkentry protection */

static DEFINE_MUTEX(hashlimit_mutex);	/* protects htables list */

static struct kmem_cache *hashlimit_cachep __read_mostly;



static inline bool dst_cmp(const struct dsthash_ent *ent,
@@ -244,7 +243,7 @@ static int htable_create_v0(struct net *net, struct xt_hashlimit_info *minfo, u_ 
	for (i = 0; i < hinfo->cfg.size; i++)

		INIT_HLIST_HEAD(&hinfo->hash[i]);



	atomic_set(&hinfo->use, 1);

	hinfo->use = 1;

	hinfo->count = 0;

	hinfo->family = family;

	hinfo->rnd_initialized = false;
@@ -263,9 +262,9 @@ static int htable_create_v0(struct net *net, struct xt_hashlimit_info *minfo, u_ 
	hinfo->timer.expires = jiffies + msecs_to_jiffies(hinfo->cfg.gc_interval);

	add_timer(&hinfo->timer);



	spin_lock_bh(&hashlimit_lock);

	mutex_lock(&hashlimit_mutex);

	hlist_add_head(&hinfo->node, &hashlimit_net->htables);

	spin_unlock_bh(&hashlimit_lock);

	mutex_unlock(&hashlimit_mutex);



	return 0;

}
@@ -308,7 +307,7 @@ static int htable_create(struct net *net, struct xt_hashlimit_mtinfo1 *minfo, 
	for (i = 0; i < hinfo->cfg.size; i++)

		INIT_HLIST_HEAD(&hinfo->hash[i]);



	atomic_set(&hinfo->use, 1);

	hinfo->use = 1;

	hinfo->count = 0;

	hinfo->family = family;

	hinfo->rnd_initialized = false;
@@ -328,9 +327,9 @@ static int htable_create(struct net *net, struct xt_hashlimit_mtinfo1 *minfo, 
	hinfo->timer.expires = jiffies + msecs_to_jiffies(hinfo->cfg.gc_interval);

	add_timer(&hinfo->timer);



	spin_lock_bh(&hashlimit_lock);

	mutex_lock(&hashlimit_mutex);

	hlist_add_head(&hinfo->node, &hashlimit_net->htables);

	spin_unlock_bh(&hashlimit_lock);

	mutex_unlock(&hashlimit_mutex);



	return 0;

}
@@ -402,27 +401,24 @@ static struct xt_hashlimit_htable *htable_find_get(struct net *net, 
	struct xt_hashlimit_htable *hinfo;

	struct hlist_node *pos;



	spin_lock_bh(&hashlimit_lock);

	hlist_for_each_entry(hinfo, pos, &hashlimit_net->htables, node) {

		if (!strcmp(name, hinfo->pde->name) &&

		    hinfo->family == family) {

			atomic_inc(&hinfo->use);

			spin_unlock_bh(&hashlimit_lock);

			hinfo->use++;

			return hinfo;

		}

	}

	spin_unlock_bh(&hashlimit_lock);

	return NULL;

}



static void htable_put(struct xt_hashlimit_htable *hinfo)

{

	if (atomic_dec_and_test(&hinfo->use)) {

		spin_lock_bh(&hashlimit_lock);

	mutex_lock(&hashlimit_mutex);

	if (--hinfo->use == 0) {

		hlist_del(&hinfo->node);

		spin_unlock_bh(&hashlimit_lock);

		htable_destroy(hinfo);

	}

	mutex_unlock(&hashlimit_mutex);

}



/* The algorithm used is the Simple Token Bucket Filter (TBF)
@@ -710,19 +706,13 @@ static bool hashlimit_mt_check_v0(const struct xt_mtchk_param *par) 
	if (r->name[sizeof(r->name) - 1] != '\0')

		return false;



	/* This is the best we've got: We cannot release and re-grab lock,

	 * since checkentry() is called before x_tables.c grabs xt_mutex.

	 * We also cannot grab the hashtable spinlock, since htable_create will

	 * call vmalloc, and that can sleep.  And we cannot just re-search

	 * the list of htable's in htable_create(), since then we would

	 * create duplicate proc files. -HW */

	mutex_lock(&hlimit_mutex);

	mutex_lock(&hashlimit_mutex);

	r->hinfo = htable_find_get(net, r->name, par->match->family);

	if (!r->hinfo && htable_create_v0(net, r, par->match->family) != 0) {

		mutex_unlock(&hlimit_mutex);

		mutex_unlock(&hashlimit_mutex);

		return false;

	}

	mutex_unlock(&hlimit_mutex);

	mutex_unlock(&hashlimit_mutex);



	return true;

}
@@ -752,19 +742,13 @@ static bool hashlimit_mt_check(const struct xt_mtchk_param *par) 
			return false;

	}



	/* This is the best we've got: We cannot release and re-grab lock,

	 * since checkentry() is called before x_tables.c grabs xt_mutex.

	 * We also cannot grab the hashtable spinlock, since htable_create will

	 * call vmalloc, and that can sleep.  And we cannot just re-search

	 * the list of htable's in htable_create(), since then we would

	 * create duplicate proc files. -HW */

	mutex_lock(&hlimit_mutex);

	mutex_lock(&hashlimit_mutex);

	info->hinfo = htable_find_get(net, info->name, par->match->family);

	if (!info->hinfo && htable_create(net, info, par->match->family) != 0) {

		mutex_unlock(&hlimit_mutex);

		mutex_unlock(&hashlimit_mutex);

		return false;

	}

	mutex_unlock(&hlimit_mutex);

	mutex_unlock(&hashlimit_mutex);

	return true;

}