Re: [PULL 38/68] hw/vfio/iommufd: Fix missing ERRP_GUARD() in iommufd_cdev_getfd()

[Zhao Liu]

This one is needed that it doesn't merge. Thanks!

On Tue, Mar 12, 2024 at 06:27:29PM -0400, Michael S. Tsirkin wrote:
> Date: Tue, 12 Mar 2024 18:27:29 -0400
> From: "Michael S. Tsirkin" <mst@redhat.com>
> Subject: [PULL 38/68] hw/vfio/iommufd: Fix missing ERRP_GUARD() in
>  iommufd_cdev_getfd()
> X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1
> 
> 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.
> ...
> * 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.
> 
> But in iommufd_cdev_getfd(), @errp is dereferenced without ERRP_GUARD():
> 
> if (*errp) {
>     error_prepend(errp, VFIO_MSG_PREFIX, path);
> }
> 
> Currently, since vfio_attach_device() - the caller of
> iommufd_cdev_getfd() - is always called in DeviceClass.realize() context
> and doesn't get the NULL @errp parameter, iommufd_cdev_getfd()
> hasn't triggered the bug that dereferencing the NULL @errp.
> 
> 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>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Message-Id: <20240223085653.1255438-7-zhao1.liu@linux.intel.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/vfio/iommufd.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index 9bfddc1360..7baf49e6ee 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;
> -- 
> MST
>