[PATCH 4.19 072/234] random: continually use hwgenerator randomness

[Greg Kroah-Hartman]

From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>

commit c321e907aa4803d562d6e70ebed9444ad082f953 upstream.

The rngd kernel thread may sleep indefinitely if the entropy count is
kept above random_write_wakeup_bits by other entropy sources. To make
best use of multiple sources of randomness, mix entropy from hardware
RNGs into the pool at least once within CRNG_RESEED_INTERVAL.

Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/char/random.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2193,13 +2193,15 @@ void add_hwgenerator_randomness(const ch
 			return;
 	}
 
-	/* Suspend writing if we're above the trickle threshold.
+	/* Throttle writing if we're above the trickle threshold.
 	 * We'll be woken up again once below random_write_wakeup_thresh,
-	 * or when the calling thread is about to terminate.
+	 * when the calling thread is about to terminate, or once
+	 * CRNG_RESEED_INTERVAL has lapsed.
 	 */
-	wait_event_interruptible(random_write_wait,
+	wait_event_interruptible_timeout(random_write_wait,
 			!system_wq || kthread_should_stop() ||
-			POOL_ENTROPY_BITS() <= random_write_wakeup_bits);
+			POOL_ENTROPY_BITS() <= random_write_wakeup_bits,
+			CRNG_RESEED_INTERVAL);
 	mix_pool_bytes(buffer, count);
 	credit_entropy_bits(entropy);
 }