linux-kernel - Re: [PATCH] s390/vfio_ap: fix memory leak in vfio

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Date:   Wed, 15 Mar 2023 18:25:34 +0100
From:   Harald Freudenberger <freude@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, borntraeger@...ux.ibm.com
Subject: Re: [PATCH] s390/vfio_ap: fix memory leak in vfio_ap device driver

On 2023-03-15 16:39, Tony Krowiak wrote:
> The device release callback function invoked to release the matrix 
> device
> uses the dev_get_drvdata(device *dev) function to retrieve the
> pointer to the vfio_matrix_dev object in order to free its storage. The
> problem is, this object is not stored as drvdata with the device; since 
> the
> kfree function will accept a NULL pointer, the memory for the
> vfio_matrix_dev object is never freed.
> 
> Since the device being released is contained within the vfio_matrix_dev
> object, the container_of macro will be used to retrieve its pointer.
> 
> Fixes: 1fde573413b5 ("s390: vfio-ap: base implementation of VFIO AP
> device driver")
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_drv.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_drv.c
> b/drivers/s390/crypto/vfio_ap_drv.c
> index 997b524bdd2b..15e9de9f4574 100644
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> @@ -54,8 +54,9 @@ static struct ap_driver vfio_ap_drv = {
> 
>  static void vfio_ap_matrix_dev_release(struct device *dev)
>  {
> -	struct ap_matrix_dev *matrix_dev = dev_get_drvdata(dev);
> -
> +	struct ap_matrix_dev *matrix_dev = container_of(dev,
> +							struct ap_matrix_dev,
> +							device);
>  	kfree(matrix_dev);
>  }

I needed some indirections to follow what exactly happens here and how 
you
fix it, but finally I got it.
Reviewed-by: Harald Freudenberger <freude@...ux.ibm.com>