Bluetooth: btmtk: Fix short read errors in btmtk_usb_reg_read()

If btmtk_usb_reg_read() gets a "short" read from a device, it will
accidentally treat that as a "real" read and populate the returned value
with some unknown and probably totally invalid data.

Fix this logic error up by calling usb_control_msg_recv() which
guarantees a "full" read happens, and then simplify the error checking
for when btmtk_usb_reg_read() is called (it's really just
btmtk_usb_id_get() that calls btmtk_usb_reg_read(), so fix up those
return sites.

Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: gregkh

drivers/bluetooth/btmtk.c

@@ -827,27 +827,21 @@ static int btmtk_usb_uhw_reg_read(struct hci_dev *hdev, u32 reg, u32 *val)
 static int btmtk_usb_reg_read(struct hci_dev *hdev, u32 reg, u32 *val)
 {
 	struct btmtk_data *data = hci_get_priv(hdev);
-	int pipe, err, size = sizeof(u32);
-	void *buf;
-
-	buf = kzalloc(size, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
+	u8 buf[sizeof(u32)];
+	int err;
 
-	pipe = usb_rcvctrlpipe(data->udev, 0);
-	err = usb_control_msg(data->udev, pipe, 0x63,
-			      USB_TYPE_VENDOR | USB_DIR_IN,
-			      reg >> 16, reg & 0xffff,
-			      buf, size, USB_CTRL_GET_TIMEOUT);
+	*val = 0;
+	err = usb_control_msg_recv(data->udev, 0, 0x63,
+				   USB_TYPE_VENDOR | USB_DIR_IN,
+				   reg >> 16, reg & 0xffff,
+				   buf, sizeof(buf), USB_CTRL_GET_TIMEOUT,
+				   GFP_KERNEL);
 	if (err < 0)
-		goto err_free_buf;
+		return err;
 
 	*val = get_unaligned_le32(buf);
 
-err_free_buf:
-	kfree(buf);
-
-	return err;
+	return 0;
 }
 
 static int btmtk_usb_id_get(struct hci_dev *hdev, u32 reg, u32 *id)
@@ -974,7 +968,7 @@ int btmtk_usb_subsys_reset(struct hci_dev *hdev, u32 dev_id)
 	}
 
 	err = btmtk_usb_id_get(hdev, 0x70010200, &val);
-	if (err < 0 || (!val && dev_id != 0x6639))
+	if (err || (!val && dev_id != 0x6639))
 		bt_dev_err(hdev, "Can't get device id, subsys reset fail.");
 
 	return err;
@@ -1318,24 +1312,24 @@ int btmtk_usb_setup(struct hci_dev *hdev)
 	calltime = ktime_get();
 
 	err = btmtk_usb_id_get(hdev, 0x80000008, &dev_id);
-	if (err < 0) {
+	if (err) {
 		bt_dev_err(hdev, "Failed to get device id (%d)", err);
 		return err;
 	}
 
 	if (!dev_id || dev_id != 0x7663) {
 		err = btmtk_usb_id_get(hdev, 0x70010200, &dev_id);
-		if (err < 0) {
+		if (err) {
 			bt_dev_err(hdev, "Failed to get device id (%d)", err);
 			return err;
 		}
 		err = btmtk_usb_id_get(hdev, 0x80021004, &fw_version);
-		if (err < 0) {
+		if (err) {
 			bt_dev_err(hdev, "Failed to get fw version (%d)", err);
 			return err;
 		}
 		err = btmtk_usb_id_get(hdev, 0x70010020, &fw_flavor);
-		if (err < 0) {
+		if (err) {
 			bt_dev_err(hdev, "Failed to get fw flavor (%d)", err);
 			return err;
 		}