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

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Date:   Mon, 21 Jun 2021 12:04:32 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     "Jason J. Herne" <jjherne@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        akrowiak@...ux.ibm.com, jgg@...dia.com
Subject: Re: [PATCH v2] s390/vfio-ap: Fix module unload memory leak of
 matrix_dev

On Fri, 18 Jun 2021 13:12:55 -0400
"Jason J. Herne" <jjherne@...ux.ibm.com> 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
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ 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));
> +	matrix_dev = NULL;

Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>

I'm not sure nulling the global here buys us anything (especially after
the kfree()). But it does not hurt either, so I'm fine with it. Style
wise I think vfio_ap_matrix_dev_destroy() is a better place for the
nulling IMHO, as it is dealing with module global state.

Regards,
Halil


>  }
>  
>  static int matrix_bus_match(struct device *dev, struct device_driver *drv)