ALSA: usb-audio: Fix NULL dereference at parsing BADD

snd_usb_mixer_controls_badd() that parses UAC3 BADD profiles misses a
NULL check for the given interfaces.  When a malformed USB descriptor
is passed, this may lead to an Oops, as spotted by syzkaller.
Skip the iteration if the interface doesn't exist for avoiding the
crash.

Fixes: 17156f23e93c ("ALSA: usb: add UAC3 BADD profiles support")
Reported-by: syzbot+a36ab65c6653d7ccdd62@syzkaller.appspotmail.com
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191122112840.24797-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 45eee5cc312e61e202e3016b0bf1f45e96a7d93d..6cd4ff09c5ee60566aae77191fbd73960aa2a79a 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2930,6 +2930,9 @@ static int snd_usb_mixer_controls_badd(struct usb_mixer_interface *mixer,
                        continue;
 
                iface = usb_ifnum_to_if(dev, intf);
+               if (!iface)
+                       continue;
+
                num = iface->num_altsetting;
 
                if (num < 2)