USB: serial: console: fix use-after-free after failed setup

BugLink: http://bugs.launchpad.net/bugs/1724836

commit 299d7572 upstream.

Make sure to reset the USB-console port pointer when console setup fails
in order to avoid having the struct usb_serial be prematurely freed by
the console code when the device is later disconnected.

Fixes: 73e487fd ("[PATCH] USB console: fix disconnection issues")
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/usb/serial/console.c

@@ -189,6 +189,7 @@ static int usb_console_setup(struct console *co, char *options)
 	tty_kref_put(tty);
  reset_open_count:
 	port->port.count = 0;
+	info->port = NULL;
 	usb_autopm_put_interface(serial->interface);
  error_get_interface:
 	usb_serial_put(serial);