ALSA: usb-audio: Clear MIDI port active flag after draining

When a rawmidi output stream is closed, it calls the drain at first,
then does trigger-off only when the drain returns -ERESTARTSYS as a
fallback.  It implies that each driver should turn off the stream
properly after the drain.  Meanwhile, USB-audio MIDI interface didn't
change the port->active flag after the drain.  This may leave the
output work picking up the port that is closed right now, which
eventually leads to a use-after-free for the already released rawmidi
object.

This patch fixes the bug by properly clearing the port->active flag
after the output drain.

Reported-by: syzbot+70e777a39907d6d5fd0a@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/00000000000011555605dceaff03@google.com
Link: https://lore.kernel.org/r/20220420130247.22062-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 2c01649c70f619d6e9994e81bdc16c171bb6e471..7c6ca2b433a53ee718b093b768e2e442ac9f6c3a 100644 (file)
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1194,6 +1194,7 @@ static void snd_usbmidi_output_drain(struct snd_rawmidi_substream *substream)
                } while (drain_urbs && timeout);
                finish_wait(&ep->drain_wait, &wait);
        }
+       port->active = 0;
        spin_unlock_irq(&ep->buffer_lock);
 }