[PATCH 5.4 09/62] ALSA: usb-audio: Clear MIDI port active flag after draining

From: Greg Kroah-Hartman
Date: Tue Apr 26 2022 - 04:43:25 EST

From: Takashi Iwai <tiwai@xxxxxxx>

commit 0665886ad1392e6b5bae85d7a6ccbed48dca1522 upstream.

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

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

Reported-by: syzbot+70e777a39907d6d5fd0a@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/00000000000011555605dceaff03@xxxxxxxxxx
Link: https://lore.kernel.org/r/20220420130247.22062-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
sound/usb/midi.c | 1 +
1 file changed, 1 insertion(+)

--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1210,6 +1210,7 @@ static void snd_usbmidi_output_drain(str
} while (drain_urbs && timeout);
finish_wait(&ep->drain_wait, &wait);
+ port->active = 0;