linux-kernel - Re: [PATCH 1/3] vt: fix check for system/busy console drivers when unregistering them

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Date:	Fri, 12 Dec 2014 12:30:38 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Imre Deak <imre.deak@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] vt: fix check for system/busy console drivers when
 unregistering them

Hi Imre,

On 12/12/2014 11:38 AM, Imre Deak wrote:
> System console drivers (without the CON_DRIVER_FLAG_MODULE flag) and
> busy drivers bound to a console (as reported by con_is_bound())
> shouldn't be unregistered. The current code checks for the
> CON_DRIVER_FLAG_INIT flag but this doesn't really correspond to either
> of the above two conditions. CON_DRIVER_FLAG_INIT is set whenever its
> associated console's con_startup() function is called, which first
> happens when the console driver is registered (so before the console
> gets bound) and gets cleared when the console gets unbound. The
> purpose of this flag is to show if we need to call con_startup() on a
> console before we use it.
> 
> Based on the above, do_unregister_con_driver() in its current form will
> incorrectly allow unregistering a console driver only if it was never
> bound, but will refuse to unregister one that was bound and later
> unbound. It will also allow unregistering a system console driver.
> 
> Fix this by checking for CON_DRIVER_FLAG_MODULE to refuse unregistering
> a system console driver and relying on the existing con_is_bound() check
> earlier in the function to refuse unregistering a busy console driver.

Maybe reword these two paragraphs?

"Allow non-system console drivers to unregister, and prevent system
console drivers from unregistering."

Regards,
Peter Hurley

> Signed-off-by: Imre Deak <imre.deak@...el.com>
> ---
>  drivers/tty/vt/vt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index b33b00b..1862e89 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3660,7 +3660,7 @@ int do_unregister_con_driver(const struct consw *csw)
>  		struct con_driver *con_driver = &registered_con_driver[i];
>  
>  		if (con_driver->con == csw &&
> -		    con_driver->flag & CON_DRIVER_FLAG_INIT) {
> +		    con_driver->flag & CON_DRIVER_FLAG_MODULE) {
>  			vtconsole_deinit_device(con_driver);
>  			device_destroy(vtconsole_class,
>  				       MKDEV(0, con_driver->node));
> 

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