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 3e133d9583a08c35b1736407f98ce13bbd9ec148..c336c78820cdf8c0050035841073ecf74e739578 100644 (file)
--- 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))