linux-kernel - Re: [PATCH v2] s390/vfio-ap: Fix module unload memory leak of matrix

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Date:   Fri, 18 Jun 2021 15:23:36 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     "Jason J. Herne" <jjherne@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        pasic@...ux.ibm.com
Subject: Re: [PATCH v2] s390/vfio-ap: Fix module unload memory leak of
 matrix_dev

On Fri, Jun 18, 2021 at 02:11:23PM -0400, Tony Krowiak wrote:
> 
> 
> On 6/18/21 1:12 PM, Jason J. Herne wrote:
> > vfio_ap_matrix_dev_release is shadowing the global matrix_dev with a NULL
> > pointer. Driver data for the matrix device is never set and so
> > dev_get_drvdata() always returns NULL. When release is called we end up
> > not freeing matrix_dev. The fix is to remove the shadow variable and get
> > the correct pointer from the device using container_of. We'll also NULL
> > the global to prevent any future use.
> > 
> > Signed-off-by: Jason J. Herne <jjherne@...ux.ibm.com>
> >   drivers/s390/crypto/vfio_ap_drv.c | 5 ++---
> >   1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> > index 7dc72cb718b0..40e66cb363d1 100644
> > +++ b/drivers/s390/crypto/vfio_ap_drv.c
> > @@ -82,9 +82,8 @@ static void vfio_ap_queue_dev_remove(struct ap_device *apdev)
> >   static void vfio_ap_matrix_dev_release(struct device *dev)
> >   {
> > -	struct ap_matrix_dev *matrix_dev = dev_get_drvdata(dev);
> > -
> > -	kfree(matrix_dev);
> > +	kfree(container_of(dev, struct ap_matrix_dev, device));
> 
> I suppose if we're not going to assume that the release is being
> called to free the global matrix_dev, then if you are going to
> retrieve it using container_of(), then maybe we should verify
> the retrieved pointer is the same as the global matrix_dev?

That seems like overkill to me

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason