ALSA: usb-audio: Drop snd_BUG_ON() from snd_usbmidi_output_open()

snd_usbmidi_output_open() has a check of the NULL port with
snd_BUG_ON().  snd_BUG_ON() was used as this shouldn't have happened,
but in reality, the NULL port may be seen when the device gives an
invalid endpoint setup at the descriptor, hence the driver skips the
allocation.  That is, the check itself is valid and snd_BUG_ON()
should be dropped from there.  Otherwise it's confusing as if it were
a real bug, as recently syzbot stumbled on it.

Reported-by: syzbot+9abda841d636d86c41da@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/syzbot+9abda841d636d86c41da@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/20221112141223.6144-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index bbff0923d26460f6a086d26fdf3c631c3f4d8c05..2839f6b6f09b496a455ed5a4da04ff5c92bcb547 100644 (file)
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1133,10 +1133,8 @@ static int snd_usbmidi_output_open(struct snd_rawmidi_substream *substream)
                                        port = &umidi->endpoints[i].out->ports[j];
                                        break;
                                }
-       if (!port) {
-               snd_BUG();
+       if (!port)
                return -ENXIO;
-       }
 
        substream->runtime->private_data = port;
        port->state = STATE_UNKNOWN;