On Thu, 30 May 2024 21:02:36 +0200, Sasha Levin wrote:

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 6.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: alsa-timer-set-lower-bound-of-start-tick-time.patch and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

Please drop this one for 6.8 and older (you posted for 6.6 too). As already explained in another mail, this commit needs a prerequisite use of guard().

An alternative patch has been already submitted. Take it instead: https://lore.kernel.org/all/20240527062431.18709-1-tiwai@suse.de/

thanks,

Takashi

commit d717dbdb94145bee1e9cf9eca387d973564203c4 Author: Takashi Iwai tiwai@suse.de 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@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: Sasha Levin sashal@kernel.org

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)