ALSA: usb-audio: fix race condition to UAF in snd_usbmidi_free

commit 9f2c0ac1 upstream.

The previous commit 0718a78f ("ALSA: usb-audio: Kill timer properly at
removal") patched a UAF issue caused by the error timer.

However, because the error timer kill added in this patch occurs after the
endpoint delete, a race condition to UAF still occurs, albeit rarely.

Additionally, since kill-cleanup for urb is also missing, freed memory can
be accessed in interrupt context related to urb, which can cause UAF.

Therefore, to prevent this, error timer and urb must be killed before
freeing the heap memory.

Cc: <stable@vger.kernel.org>
Reported-by:  <syzbot+f02665daa2abeef4a947@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947


Fixes: 0718a78f ("ALSA: usb-audio: Kill timer properly at removal")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>