Patch "ALSA: timer: Set lower bound of start tick time" has been added to the 6.8-stable tree

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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;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-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d717dbdb94145bee1e9cf9eca387d973564203c4
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)




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