USB: mos7720: fix DMA to stack

commit 72ea18a5 upstream.

The read_mos_reg function is called with stack-allocated buffers, which
must not be used for control messages.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/serial/mos7720.c

@@ -234,11 +234,22 @@ static int read_mos_reg(struct usb_serial *serial, unsigned int serial_portnum,
 	__u8 requesttype = (__u8)0xc0;
 	__u16 index = get_reg_index(reg);
 	__u16 value = get_reg_value(reg, serial_portnum);
-	int status = usb_control_msg(usbdev, pipe, request, requesttype, value,
-				     index, data, 1, MOS_WDR_TIMEOUT);
-	if (status < 0)
+	u8 *buf;
+	int status;
+
+	buf = kmalloc(1, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	status = usb_control_msg(usbdev, pipe, request, requesttype, value,
+				     index, buf, 1, MOS_WDR_TIMEOUT);
+	if (status == 1)
+		*data = *buf;
+	else if (status < 0)
 		dev_err(&usbdev->dev,
 			"mos7720: usb_control_msg() failed: %d", status);
+	kfree(buf);
+
 	return status;
 }