Commit 4a63bd17 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: timer: Set lower bound of start tick time 



Currently ALSA timer doesn't have the lower limit of the start tick
time, and it allows a very small size, e.g. 1 tick with 1ns resolution
for hrtimer.  Such a situation may lead to an unexpected RCU stall,
where  the callback repeatedly queuing the expire update, as reported
by fuzzer.

This patch introduces a sanity check of the timer start tick time, so
that the system returns an error when a too small start size is set.
As of this patch, the lower limit is hard-coded to 100us, which is
small enough but can still work somehow.

Reported-by: default avatar <syzbot+43120c2af6ca2938cc38@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/r/000000000000fa00a1061740ab6d@google.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20240514182745.4015-1-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent d731b1ed

sound/core/timer.c

+8 −0
Original line number Diff line number Diff line
@@ -544,6 +544,14 @@ static int snd_timer_start1(struct snd_timer_instance *timeri, 
			     SNDRV_TIMER_IFLG_START))

		return -EBUSY;



	/* check the actual time for the start tick;

	 * bail out as error if it's way too low (< 100us)

	 */

	if (start) {

		if ((u64)snd_timer_hw_resolution(timer) * ticks < 100000)

			return -EINVAL;

	}



	if (start)

		timeri->ticks = timeri->cticks = ticks;

	else if (!timeri->cticks)