Re: [PATCH 6/6] hw/vfio/iommufd: Fix missing ERRP_GUARD() in iommufd_cdev_getfd()

[Markus Armbruster <armbru@redhat.com>]

Zhao Liu <zhao1.liu@linux.intel.com> writes:

> From: Zhao Liu <zhao1.liu@intel.com>
>
> As the comment in qapi/error, dereferencing @errp requires
> ERRP_GUARD():
>
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> * - It must not be dereferenced, because it may be null.
> * - It should not be passed to error_prepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * ERRP_GUARD() lifts these restrictions.
> *
> * To use ERRP_GUARD(), add it right at the beginning of the function.
> * @errp can then be used without worrying about the argument being
> * NULL or &error_fatal.
> *
> * Using it when it's not needed is safe, but please avoid cluttering
> * the source with useless code.
>
> Currently, since vfio_attach_device() - the caller of
> iommufd_cdev_getfd() - is always called in DeviceClass.realize() context
> and won't get the NULL errp parameter, iommufd_cdev_getfd()
> doesn't trigger the dereference issue.
>
> To follow the requirement of errp, add missing ERRP_GUARD() in
> iommufd_cdev_getfd().
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Suggested by credit:
>  Markus: Referred his explanation about ERRP_GUARD().
> ---
>  hw/vfio/iommufd.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index 9bfddc136089..7baf49e6ee9e 100644
> --- a/hw/vfio/iommufd.c
> +++ b/hw/vfio/iommufd.c
> @@ -116,6 +116,7 @@ static void iommufd_cdev_unbind_and_disconnect(VFIODevice *vbasedev)
>  
>  static int iommufd_cdev_getfd(const char *sysfs_path, Error **errp)
>  {
> +    ERRP_GUARD();
>      long int ret = -ENOTTY;
>      char *path, *vfio_dev_path = NULL, *vfio_path = NULL;
>      DIR *dir = NULL;

The problematic use is

       if (*errp) {
           error_prepend(errp, VFIO_MSG_PREFIX, path);
       }

Reviewed-by: Markus Armbruster <armbru@redhat.com>