[PATCH 5.10 044/121] random: wake up /dev/random writers after zap

Greg Kroah-Hartman
2022-02-21T09:27:00Z

From: Jason A. Donenfeld <Jason@zx2c4.com>

[ Upstream commit 042e293e16e3aa9794ce60c29f5b7b0c8170f933 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/char/random.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5444206f35e22..5f541c9465598 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1987,7 +1987,10 @@ 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))
--
2.34.1