ALSA: usb-audio: Add sanity checks to FE parser

When the usb-audio descriptor contains the malformed feature unit
description with a too short length, the driver may access
out-of-bounds.  Add a sanity check of the header size at the beginning
of parse_audio_feature_unit().

Fixes: 23caaf1 ("ALSA: usb-mixer: Add support for Audio Class v2.0")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -1469,6 +1469,12 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid,
 	__u8 *bmaControls;
 
 	if (state->mixer->protocol == UAC_VERSION_1) {
+		if (hdr->bLength < 7) {
+			usb_audio_err(state->chip,
+				      "unit %u: invalid UAC_FEATURE_UNIT descriptor\n",
+				      unitid);
+			return -EINVAL;
+		}
 		csize = hdr->bControlSize;
 		if (!csize) {
 			usb_audio_dbg(state->chip,
@@ -1486,6 +1492,12 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid,
 		}
 	} else {
 		struct uac2_feature_unit_descriptor *ftr = _ftr;
+		if (hdr->bLength < 6) {
+			usb_audio_err(state->chip,
+				      "unit %u: invalid UAC_FEATURE_UNIT descriptor\n",
+				      unitid);
+			return -EINVAL;
+		}
 		csize = 4;
 		channels = (hdr->bLength - 6) / 4 - 1;
 		bmaControls = ftr->bmaControls;