linux-kernel - [PATCH 5.15 045/145] random: fix locking in crng_fast

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Date:   Fri, 27 May 2022 10:49:06 +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 5.15 045/145] random: fix locking in crng_fast_load()

From: Dominik Brodowski <linux@...inikbrodowski.net>

commit 7c2fe2b32bf76441ff5b7a425b384e5f75aa530a upstream.

crng_init is protected by primary_crng->lock, so keep holding that lock
when incrementing crng_init from 0 to 1 in crng_fast_load(). The call to
pr_notice() can wait until the lock is released; this code path cannot
be reached twice, as crng_fast_load() aborts early if crng_init > 0.

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 |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -647,12 +647,13 @@ static size_t crng_fast_load(const u8 *c
 		p[crng_init_cnt % CHACHA_KEY_SIZE] ^= *cp;
 		cp++; crng_init_cnt++; len--; ret++;
 	}
-	spin_unlock_irqrestore(&primary_crng.lock, flags);
 	if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
 		invalidate_batched_entropy();
 		crng_init = 1;
-		pr_notice("fast init done\n");
 	}
+	spin_unlock_irqrestore(&primary_crng.lock, flags);
+	if (crng_init == 1)
+		pr_notice("fast init done\n");
 	return ret;
 }