[PATCH] ALSA: usb-audio: Drop snd_BUG_ON() from snd_usbmidi_output_open()

[Takashi Iwai]

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 at syzkaller.appspotmail.com
Cc: <stable at vger.kernel.org>
Link: https://lore.kernel.org/r/syzbot+9abda841d636d86c41da@syzkaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/midi.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index bbff0923d264..2839f6b6f09b 100644
--- 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;
-- 
2.35.3