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Commit 15b66cd5 authored by Herbert Xu's avatar Herbert Xu
Browse files

hwrng: core - Fix current_rng init/cleanup race yet again 



The kref solution is still buggy because we were only focusing
on the register/unregister race.  The same race affects the
setting of current_rng through sysfs.

This patch fixes it by using kref_get_unless_zero.

Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 77584ee5

drivers/char/hw_random/core.c

+11 −3
Original line number Diff line number Diff line
@@ -105,7 +105,6 @@ static inline void cleanup_rng(struct kref *kref) 
static void set_current_rng(struct hwrng *rng)

{

	BUG_ON(!mutex_is_locked(&rng_mutex));

	kref_get(&rng->ref);

	current_rng = rng;

}
@@ -150,6 +149,9 @@ static void put_rng(struct hwrng *rng) 


static inline int hwrng_init(struct hwrng *rng)

{

	if (kref_get_unless_zero(&rng->ref))

		goto skip_init;



	if (rng->init) {

		int ret;
@@ -157,6 +159,11 @@ static inline int hwrng_init(struct hwrng *rng) 
		if (ret)

			return ret;

	}



	kref_init(&rng->ref);

	reinit_completion(&rng->cleanup_done);



skip_init:

	add_early_randomness(rng);



	current_quality = rng->quality ? : default_quality;
@@ -467,6 +474,9 @@ int hwrng_register(struct hwrng *rng) 
			goto out_unlock;

	}



	init_completion(&rng->cleanup_done);

	complete(&rng->cleanup_done);



	old_rng = current_rng;

	err = 0;

	if (!old_rng) {
@@ -494,8 +504,6 @@ int hwrng_register(struct hwrng *rng) 
		add_early_randomness(rng);

	}



	init_completion(&rng->cleanup_done);



out_unlock:

	mutex_unlock(&rng_mutex);

out: