Re: [PATCH v5 8/9] s390/vfio-ap: Fix NULL deref in status_show() during queue probe

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 8/12/26 4:02 PM, Anthony Krowiak wrote:
> When vfio_ap_mdev_probe_queue() creates the sysfs attribute group,
> the queue's driver data has not yet been set. A concurrent read of
> the 'status' attribute can therefore call dev_get_drvdata() and
> get NULL, which is then passed directly to
> vfio_ap_mdev_for_queue() where q->apqn is unconditionally
> dereferenced, causing a NULL pointer dereference.
> 
> Fix this by acquiring the update locks before calling
> sysfs_create_group(). The status_show() function acquires
> guests_lock before reading the driver data, so any concurrent
> read will block until after dev_set_drvdata() has been called
> and the update locks are released.
> 
> As a bonus, the APQN no longer needs to be read from the queue
> struct after allocation — it can be read directly from apdev
> before allocation and stored in a local variable, which is then
> assigned to q->apqn once the allocation succeeds.
> 
> Fixes: 260f3ea141382 ("s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c")
> Cc: stable@vger.kernel.org
> Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>