Re: [PATCH 1/3] xhci: dbgtty: Fix unregister on tty_register_driver() failure

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 7/20/26 23:27, Lucas De Marchi wrote:
> 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
> 
> Fixes: 4521f1613940 ("xhci: dbctty: split dbc tty driver registration and unregistration functions.")
> Cc: stable@vger.kernel.org # v5.10
> Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Lucas De Marchi <ldemarchi@nvidia.com>
> ---

Thanks

Added series to queue

-Mathias