USB: serial: ftdi_sio: only allow valid event_char values

The "event_char" device attribute value, when written, is interpreted as
an enable bit in bit 8, and an "event character" in bits 7 to 0.

Return an error -EINVAL for out-of-range values.  Use kstrtouint() to
parse the integer instead of the obsolete simple_strtoul().
Signed-off-by: NIan Abbott <abbotti@mev.co.uk>
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/ftdi_sio.c

@@ -1738,9 +1738,12 @@ static ssize_t store_event_char(struct device *dev,
 	struct usb_serial_port *port = to_usb_serial_port(dev);
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	struct usb_device *udev = port->serial->dev;
-	int v = simple_strtoul(valbuf, NULL, 10);
+	unsigned int v;
 	int rv;
 
+	if (kstrtouint(valbuf, 10, &v) || v >= 0x200)
+		return -EINVAL;
+
 	dev_dbg(&port->dev, "%s: setting event char = %i\n", __func__, v);
 
 	rv = usb_control_msg(udev,