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

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Date:   Fri, 18 Jun 2021 16:05:40 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...dia.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 6/18/21 2:23 PM, Jason Gunthorpe wrote:
> 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

After thinking about it, it's probably more than overkill as I
assume the container_of() function would fail if dev was
not contained in matrix_mdev:

Reviewed-by: Tony Krowiak <akrowiak@...ux.ibm.com>

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