From: Jason A. Donenfeld <Jason@zx2c4.com>
Date: Fri, 28 Jan 2022 22:44:03 +0000 (+0100)
Subject: random: wake up /dev/random writers after zap
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=042e293e16e3aa9794ce60c29f5b7b0c8170f933;p=linux.git

random: wake up /dev/random writers after zap

When account() is called, and the amount of entropy dips below
random_write_wakeup_bits, we wake up the random writers, so that they
can write some more in. However, the RNDZAPENTCNT/RNDCLEARPOOL ioctl
sets the entropy count to zero -- a potential reduction just like
account() -- but does not unblock writers. This commit adds the missing
logic to that ioctl to unblock waiting writers.

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 3e133d9583a08..c336c78820cdf 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1856,7 +1856,10 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 		 */
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;
-		input_pool.entropy_count = 0;
+		if (xchg(&input_pool.entropy_count, 0) && random_write_wakeup_bits) {
+			wake_up_interruptible(&random_write_wait);
+			kill_fasync(&fasync, SIGIO, POLL_OUT);
+		}
 		return 0;
 	case RNDRESEEDCRNG:
 		if (!capable(CAP_SYS_ADMIN))