In the Linux kernel, the following vulnerability has been resolved:

xhci: dbgtty: Fix unregister on tty_register_driver() failure

If tty_register_driver() fails, it drops the reference, but fails to set
the global dbc_tty_driver to NULL, causing the unregister to be called
again when module exits.

On module unload dbc_tty_exit() only gates its cleanup on the driver
pointer being non-NULL, so it operates on the already-freed driver:

    module_init(xhci_hcd_init)
      xhci_hcd_init()
        xhci_dbc_init()                       [return value ignored]
          dbc_tty_init()
            tty_register_driver() fails
              tty_driver_kref_put()           -> driver freed
              (dbc_tty_driver left dangling)
    ...
    module_exit(xhci_hcd_fini)
      xhci_hcd_fini()
        xhci_dbc_exit()
          dbc_tty_exit()
            if (dbc_tty_driver)               -> true (dangling)
              tty_unregister_driver()         -> use-after-free