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    Subject[PATCH 5.17 008/146] ALSA: usb-audio: Clear MIDI port active flag after draining
    Date
    From: Takashi Iwai <tiwai@suse.de>

    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
    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    sound/usb/midi.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/sound/usb/midi.c
    +++ b/sound/usb/midi.c
    @@ -1194,6 +1194,7 @@ static void snd_usbmidi_output_drain(str
    } while (drain_urbs && timeout);
    finish_wait(&ep->drain_wait, &wait);
    }
    + port->active = 0;
    spin_unlock_irq(&ep->buffer_lock);
    }


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