On Thu, 27 Oct 2022 05:12:36 +0200,
Steven Rostedt wrote:
>
> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
>
> 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.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Applied now with the fix of unused variable warning.
Thanks!
Takashi
> ---
> sound/synth/emux/emux.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/sound/synth/emux/emux.c b/sound/synth/emux/emux.c
> index 5ed8e36d2e04..a2ee78809cfb 100644
> --- a/sound/synth/emux/emux.c
> +++ b/sound/synth/emux/emux.c
> @@ -131,10 +131,7 @@ int snd_emux_free(struct snd_emux *emu)
> 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);
> --
> 2.35.1
>
