ALSA: usb-audio: Fix UAC2 get_ctl request with a RANGE attribute

The layout of the UAC2 Control request and response varies depending on
the request type. With the current implementation, only the Layout 2
Parameter Block (with the 2-byte sized RANGE attribute) is handled
properly. For the Control requests with the 1-byte sized RANGE attribute
(Bass Control, Mid Control, Tremble Control), the response is parsed
incorrectly.

This commit:
* fixes the wLength field value in the request
* fixes parsing the range values from the response

Fixes: 23caaf1 ("ALSA: usb-mixer: Add support for Audio Class v2.0")
Signed-off-by: Kirill Marinushkin <k.marinushkin@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -347,17 +347,20 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 			    int validx, int *value_ret)
 {
 	struct snd_usb_audio *chip = cval->head.mixer->chip;
-	unsigned char buf[4 + 3 * sizeof(__u32)]; /* enough space for one range */
+	/* enough space for one range */
+	unsigned char buf[sizeof(__u16) + 3 * sizeof(__u32)];
 	unsigned char *val;
-	int idx = 0, ret, size;
+	int idx = 0, ret, val_size, size;
 	__u8 bRequest;
 
+	val_size = uac2_ctl_value_size(cval->val_type);
+
 	if (request == UAC_GET_CUR) {
 		bRequest = UAC2_CS_CUR;
-		size = uac2_ctl_value_size(cval->val_type);
+		size = val_size;
 	} else {
 		bRequest = UAC2_CS_RANGE;
-		size = sizeof(buf);
+		size = sizeof(__u16) + 3 * val_size;
 	}
 
 	memset(buf, 0, sizeof(buf));
@@ -390,16 +393,17 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 		val = buf + sizeof(__u16);
 		break;
 	case UAC_GET_MAX:
-		val = buf + sizeof(__u16) * 2;
+		val = buf + sizeof(__u16) + val_size;
 		break;
 	case UAC_GET_RES:
-		val = buf + sizeof(__u16) * 3;
+		val = buf + sizeof(__u16) + val_size * 2;
 		break;
 	default:
 		return -EINVAL;
 	}
 
-	*value_ret = convert_signed_value(cval, snd_usb_combine_bytes(val, sizeof(__u16)));
+	*value_ret = convert_signed_value(cval,
+					  snd_usb_combine_bytes(val, val_size));
 
 	return 0;
 }