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ALSA: timer: Set lower bound of start tick time

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commit 4a63bd179f upstream.

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: 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: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Takashi Iwai
2024-05-14 20:27:36 +02:00
committed by Greg Kroah-Hartman
parent 6b8374ee2c
commit abb1ad69d9
1 changed files with 8 additions and 0 deletions
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8
sound/core/timer.c
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@@ -544,6 +544,14 @@ static int snd_timer_start1(struct snd_timer_instance *timeri,
SNDRV_TIMER_IFLG_START)) SNDRV_TIMER_IFLG_START))
return -EBUSY; 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) if (start)
timeri->ticks = timeri->cticks = ticks; timeri->ticks = timeri->cticks = ticks;
else if (!timeri->cticks) else if (!timeri->cticks)