linux-kernel - [PATCH] random: only wake up writers after zap if threshold was passed

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Date:   Tue, 22 Feb 2022 14:05:03 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Theodore Ts'o <tytso@....edu>
Subject: [PATCH] random: only wake up writers after zap if threshold was passed

The only time that we need to wake up /dev/random writers on
RNDCLEARPOOL/RNDZAPPOOL is when we're changing from a value that is
greater than or equal to POOL_MIN_BITS to zero, because if we're
changing from below POOL_MIN_BITS to zero, the writers are already
unblocked.

Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Cc: Theodore Ts'o <tytso@....edu>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/char/random.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index a4dedeea35e9..536237a0f073 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1582,7 +1582,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 		 */
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;
-		if (xchg(&input_pool.entropy_count, 0)) {
+		if (xchg(&input_pool.entropy_count, 0) >= POOL_MIN_BITS) {
 			wake_up_interruptible(&random_write_wait);
 			kill_fasync(&fasync, SIGIO, POLL_OUT);
 		}
-- 
2.35.1