linux-kernel - [PATCH 5.4 084/240] random: fix locking for crng_init in crng

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Date:   Mon, 20 Jun 2022 14:49:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Eric Biggers <ebiggers@...gle.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.4 084/240] random: fix locking for crng_init in crng_reseed()

From: Dominik Brodowski <linux@...inikbrodowski.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@...inikbrodowski.net>
Reviewed-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);