[PATCH 5.4 084/240] random: fix locking for crng_init in crng_reseed()

Greg Kroah-Hartman
2022-06-20T13:41:15Z

From: Dominik Brodowski <linux@dominikbrodowski.net>

commit 7191c628fe07b70d3f37de736d173d1b115396ed upstream.

crng_init is protected by primary_crng->lock. Therefore, we need
to hold this lock when increasing crng_init to 2. As we shouldn't
hold this lock for too long, only hold it for those parts which
require protection.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -500,6 +500,7 @@ static void crng_reseed(void)
int entropy_count;
unsigned long next_gen;
u8 key[CHACHA_KEY_SIZE];
+ bool finalize_init = false;

/*
* First we make sure we have POOL_MIN_BITS of entropy in the pool,
@@ -527,12 +528,14 @@ static void crng_reseed(void)
++next_gen;
WRITE_ONCE(base_crng.generation, next_gen);
WRITE_ONCE(base_crng.birth, jiffies);
- spin_unlock_irqrestore(&base_crng.lock, flags);
- memzero_explicit(key, sizeof(key));
-
if (crng_init < 2) {
invalidate_batched_entropy();
crng_init = 2;
+ finalize_init = true;
+ }
+ spin_unlock_irqrestore(&base_crng.lock, flags);
+ memzero_explicit(key, sizeof(key));
+ if (finalize_init) {
process_random_ready_list();
wake_up_interruptible(&crng_init_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);