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Commit a027f30d authored by Rusty Russell's avatar Rusty Russell Committed by Herbert Xu
Browse files

hwrng: fix unregister race. 



The previous patch added one potential problem: we can still be
reading from a hwrng when it's unregistered.  Add a wait for zero
in the hwrng_unregister path.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAmos Kong <akong@redhat.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 3a2c0ba5

drivers/char/hw_random/core.c

+12 −0
Original line number Diff line number Diff line
@@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex); 
static DEFINE_MUTEX(reading_mutex);

static int data_avail;

static u8 *rng_buffer, *rng_fillbuf;

static DECLARE_WAIT_QUEUE_HEAD(rng_done);

static unsigned short current_quality;

static unsigned short default_quality; /* = 0; default to "off" */
@@ -98,6 +99,11 @@ static inline void cleanup_rng(struct kref *kref) 


	if (rng->cleanup)

		rng->cleanup(rng);



	/* cleanup_done should be updated after cleanup finishes */

	smp_wmb();

	rng->cleanup_done = true;

	wake_up_all(&rng_done);

}



static void set_current_rng(struct hwrng *rng)
@@ -494,6 +500,8 @@ int hwrng_register(struct hwrng *rng) 
		add_early_randomness(rng);

	}



	rng->cleanup_done = false;



out_unlock:

	mutex_unlock(&rng_mutex);

out:
@@ -525,6 +533,10 @@ void hwrng_unregister(struct hwrng *rng) 
			kthread_stop(hwrng_fill);

	} else

		mutex_unlock(&rng_mutex);



	/* Just in case rng is reading right now, wait. */

	wait_event(rng_done, rng->cleanup_done &&

		   atomic_read(&rng->ref.refcount) == 0);

}

EXPORT_SYMBOL_GPL(hwrng_unregister);

include/linux/hw_random.h

+1 −0
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ struct hwrng { 
	/* internal. */

	struct list_head list;

	struct kref ref;

	bool cleanup_done;

};



/** Register a new Hardware Random Number Generator driver. */