Re: [PATCH 6.12.y 6.6.y 6.1.y 5.15.y 5.10.y 5.4.y] ALSA: usb-audio: Kill timer properly at removal

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Oct 08, 2025 at 12:58:08AM +0900, Jeongjun Park wrote:
> From: Takashi Iwai <tiwai@suse.de>
> 
> [ Upstream commit 0718a78f6a9f04b88d0dc9616cc216b31c5f3cf1 ]
> 
> The USB-audio MIDI code initializes the timer, but in a rare case, the
> driver might be freed without the disconnect call.  This leaves the
> timer in an active state while the assigned object is released via
> snd_usbmidi_free(), which ends up with a kernel warning when the debug
> configuration is enabled, as spotted by fuzzer.
> 
> For avoiding the problem, put timer_shutdown_sync() at
> snd_usbmidi_free(), so that the timer can be killed properly.
> While we're at it, replace the existing timer_delete_sync() at the
> disconnect callback with timer_shutdown_sync(), too.
> 
> Reported-by: syzbot+d8f72178ab6783a7daea@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/681c70d7.050a0220.a19a9.00c6.GAE@google.com
> Cc: <stable@vger.kernel.org>
> Link: https://patch.msgid.link/20250519212031.14436-1-tiwai@suse.de
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> [ del_timer vs timer_delete differences ]
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> ---
>  sound/usb/midi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/usb/midi.c b/sound/usb/midi.c
> index a792ada18863..c3de2b137435 100644
> --- a/sound/usb/midi.c
> +++ b/sound/usb/midi.c
> @@ -1530,6 +1530,7 @@ static void snd_usbmidi_free(struct snd_usb_midi *umidi)
>  			snd_usbmidi_in_endpoint_delete(ep->in);
>  	}
>  	mutex_destroy(&umidi->mutex);
> +	timer_shutdown_sync(&umidi->error_timer);

This function is not in older kernel versions, you did not test this
build :(

I've applied this to 6.6.y and newer, but for 6.1.y and older, please
use the proper function.

thanks,

greg k-h