linux-kernel - RE: [char-misc-next v2] mei: bus: fix device leak

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Message-ID: <CY5PR11MB63664DE1B93F480CCC199D8FED46A@CY5PR11MB6366.namprd11.prod.outlook.com>
Date: Mon, 30 Jun 2025 10:52:08 +0000
From: "Usyskin, Alexander" <alexander.usyskin@...el.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: "Abliyev, Reuven" <reuven.abliyev@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [char-misc-next v2] mei: bus: fix device leak

> Subject: Re: [char-misc-next v2] mei: bus: fix device leak
> 
> On Tue, Jun 24, 2025 at 02:05:20PM +0300, Alexander Usyskin wrote:
> > The bus rescan function creates bus devices for all clients.
> > The fixup routine is executed on all devices, unneeded
> > devices are removed and fully initialized once set
> > is_added flag to 1.
> 
> I don't understand why the mei bus is so special that it has to have
> this type of flag, when no other bus has that for its devices.  The bus
> code should know if the device has been properly added or not, if not,
> then no release function can be called and the structure isn't even
> viable to be used or touched at all.
> 
> So why is this needed?

It seems that is_added can be replaced by device_is_registered().
Am I right?
I'll send separate patch for this.

> 
> >
> > If link to firmware is reset right after all devices are
> > initialized, but before fixup is executed, the rescan tries
> > to remove devices.
> > The is_added flag is not set and the mei_cl_bus_dev_destroy
> > returns prematurely.
> > Allow to clean up device when is_added flag is unset to
> > account for above scenario.
> >
> > Fixes: 6009595a66e4 ("mei: bus: link client devices instead of host clients")
> > Signed-off-by: Alexander Usyskin <alexander.usyskin@...el.com>
> > ---
> >  drivers/misc/mei/bus.c | 11 ++++-------
> >  1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/misc/mei/bus.c b/drivers/misc/mei/bus.c
> > index 67176caf5416..f2e5d550c6b4 100644
> > --- a/drivers/misc/mei/bus.c
> > +++ b/drivers/misc/mei/bus.c
> > @@ -1430,17 +1430,14 @@ static void mei_cl_bus_dev_stop(struct
> mei_cl_device *cldev)
> >   */
> >  static void mei_cl_bus_dev_destroy(struct mei_cl_device *cldev)
> >  {
> > -
> >  	WARN_ON(!mutex_is_locked(&cldev->bus->cl_bus_lock));
> >
> > -	if (!cldev->is_added)
> > -		return;
> > -
> > -	device_del(&cldev->dev);
> > +	if (cldev->is_added) {
> > +		device_del(&cldev->dev);
> > +		cldev->is_added = 0;
> > +	}
> 
> How can destroy be called here if the device has not been added before?
> How can it be hanging around in memory at all if the device_add() call
> was not successful when it was originally called?
> 

Mei bus uses device_initialize() and device_add() pair, and in this corner case
only device_initialize() was called, so we should call put_device() without device_del().

> confused,
> 
> greg k-h

- - 
Thanks,
Sasha