USB: serial: fix port attribute-creation race

Fix attribute-creation race with userspace by using the port device
groups field to create the port attributes.

Also use %u when printing the port number, which is unsigned, even
though we do not currently support more than 128 ports per device.

Reported-by: Takashi Iwai <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/serial/bus.c

···
 	return 0;
 }
 
-static ssize_t port_number_show(struct device *dev,
-				struct device_attribute *attr, char *buf)
-{
-	struct usb_serial_port *port = to_usb_serial_port(dev);
-
-	return sprintf(buf, "%d\n", port->port_number);
-}
-static DEVICE_ATTR_RO(port_number);
-
 static int usb_serial_device_probe(struct device *dev)
 {
 	struct usb_serial_driver *driver;
···
 			goto exit_with_autopm;
 	}
 
-	retval = device_create_file(dev, &dev_attr_port_number);
-	if (retval) {
-		if (driver->port_remove)
-			driver->port_remove(port);
-		goto exit_with_autopm;
-	}
-
 	minor = port->minor;
 	tty_dev = tty_register_device(usb_serial_tty_driver, minor, dev);
 	if (IS_ERR(tty_dev)) {
 		retval = PTR_ERR(tty_dev);
-		device_remove_file(dev, &dev_attr_port_number);
 		if (driver->port_remove)
 			driver->port_remove(port);
 		goto exit_with_autopm;
···
 
 	minor = port->minor;
 	tty_unregister_device(usb_serial_tty_driver, minor);
-
-	device_remove_file(&port->dev, &dev_attr_port_number);
 
 	driver = port->serial->type;
 	if (driver->port_remove)

drivers/usb/serial/usb-serial.c

···
 		drv->dtr_rts(p, on);
 }
 
+static ssize_t port_number_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct usb_serial_port *port = to_usb_serial_port(dev);
+
+	return sprintf(buf, "%u\n", port->port_number);
+}
+static DEVICE_ATTR_RO(port_number);
+
+static struct attribute *usb_serial_port_attrs[] = {
+	&dev_attr_port_number.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(usb_serial_port);
+
 static const struct tty_port_operations serial_port_ops = {
 	.carrier_raised		= serial_port_carrier_raised,
 	.dtr_rts		= serial_port_dtr_rts,
···
 		port->dev.driver = NULL;
 		port->dev.bus = &usb_serial_bus_type;
 		port->dev.release = &usb_serial_port_release;
+		port->dev.groups = usb_serial_port_groups;
 		device_initialize(&port->dev);
 	}