[PATCH 4.9 46/63] ALSA: usb-audio: Avoid access before bLength check in build_audio_procunit()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit f4351a199cc120ff9d59e06d02e8657d08e6cc46 upstream.

The parser for the processing unit reads bNrInPins field before the
bLength sanity check, which may lead to an out-of-bound access when a
malformed descriptor is given.  Fix it by assignment after the bLength
check.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/usb/mixer.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1882,7 +1882,7 @@ static int build_audio_procunit(struct m
 				char *name)
 {
 	struct uac_processing_unit_descriptor *desc = raw_desc;
-	int num_ins = desc->bNrInPins;
+	int num_ins;
 	struct usb_mixer_elem_info *cval;
 	struct snd_kcontrol *kctl;
 	int i, err, nameid, type, len;
@@ -1897,7 +1897,13 @@ static int build_audio_procunit(struct m
 		0, NULL, default_value_info
 	};
 
-	if (desc->bLength < 13 || desc->bLength < 13 + num_ins ||
+	if (desc->bLength < 13) {
+		usb_audio_err(state->chip, "invalid %s descriptor (id %d)\n", name, unitid);
+		return -EINVAL;
+	}
+
+	num_ins = desc->bNrInPins;
+	if (desc->bLength < 13 + num_ins ||
 	    desc->bLength < num_ins + uac_processing_unit_bControlSize(desc, state->mixer->protocol)) {
 		usb_audio_err(state->chip, "invalid %s descriptor (id %d)\n", name, unitid);
 		return -EINVAL;