This is a note to let you know that I've just added the patch titled
ALSA: timer: Set lower bound of start tick time
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
alsa-timer-set-lower-bound-of-start-tick-time.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7135223dedc8c3395286133970ddecae77b2a9d2
Author: Takashi Iwai <tiwai@xxxxxxx>
Date: Tue May 14 20:27:36 2024 +0200
ALSA: timer: Set lower bound of start tick time
[ Upstream commit 4a63bd179fa8d3fcc44a0d9d71d941ddd62f0c4e ]
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/r/000000000000fa00a1061740ab6d@xxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240514182745.4015-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/sound/core/timer.c b/sound/core/timer.c
index e6e551d4a29e0..42c4c2b029526 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -553,6 +553,14 @@ static int snd_timer_start1(struct snd_timer_instance *timeri,
goto unlock;
}
+ /* 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)
