This is a note to let you know that I've just added the patch titled
ALSA: Use del_timer_sync() before freeing timer
to the 5.10-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-use-del_timer_sync-before-freeing-timer.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f0a868788fcbf63cdab51f5adcf73b271ede8164 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
Date: Wed, 26 Oct 2022 23:12:36 -0400
Subject: ALSA: Use del_timer_sync() before freeing timer
From: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
commit f0a868788fcbf63cdab51f5adcf73b271ede8164 upstream.
The current code for freeing the emux timer is extremely dangerous:
CPU0 CPU1
---- ----
snd_emux_timer_callback()
snd_emux_free()
spin_lock(&emu->voice_lock)
del_timer(&emu->tlist); <-- returns immediately
spin_unlock(&emu->voice_lock);
[..]
kfree(emu);
spin_lock(&emu->voice_lock);
[BOOM!]
Instead just use del_timer_sync() which will wait for the timer to finish
before continuing. No need to check if the timer is active or not when
doing so.
This doesn't fix the race of a possible re-arming of the timer, but at
least it won't use the data that has just been freed.
[ Fixed unused variable warning by tiwai ]
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221026231236.6834b551@xxxxxxxxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
sound/synth/emux/emux.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
--- a/sound/synth/emux/emux.c
+++ b/sound/synth/emux/emux.c
@@ -125,15 +125,10 @@ EXPORT_SYMBOL(snd_emux_register);
*/
int snd_emux_free(struct snd_emux *emu)
{
- unsigned long flags;
-
if (! emu)
return -EINVAL;
- spin_lock_irqsave(&emu->voice_lock, flags);
- if (emu->timer_active)
- del_timer(&emu->tlist);
- spin_unlock_irqrestore(&emu->voice_lock, flags);
+ del_timer_sync(&emu->tlist);
snd_emux_proc_free(emu);
snd_emux_delete_virmidi(emu);
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-5.10/alsa-use-del_timer_sync-before-freeing-timer.patch
