On Tue, Feb 09, 2021 at 07:02:08PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Fill in definitions for map, unmap and sync commands.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> with fix by misono.tomohiro@fujitsu.com
> ---
>  hw/virtio/vhost-user-fs.c | 115 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 111 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
> index 78401d2ff1..5f2fca4d82 100644
> --- a/hw/virtio/vhost-user-fs.c
> +++ b/hw/virtio/vhost-user-fs.c
> @@ -37,15 +37,122 @@
>  uint64_t vhost_user_fs_slave_map(struct vhost_dev *dev, VhostUserFSSlaveMsg *sm,
>                                   int fd)
>  {
> -    /* TODO */
> -    return (uint64_t)-1;
> +    VHostUserFS *fs = VHOST_USER_FS(dev->vdev);
> +    if (!fs) {
> +        /* Shouldn't happen - but seen on error path */
> +        error_report("Bad fs ptr");
> +        return (uint64_t)-1;
> +    }

If a non-vhost-user-fs vhost-user device backend sends this message
VHOST_USER_FS() -> object_dynamic_cast_assert() there will either be an
assertion failure (CONFIG_QOM_CAST_DEBUG) or the pointer will be
silently cast to the wrong type (!CONFIG_QOM_CAST_DEBUG).

Both of these outcomes are not suitable for input validation. We need to
fail cleanly here:

  VhostUserFS *fs = (VHostUserFS *)object_dynamic_cast(OBJECT(dev->vdev),
                                                       TYPE_VHOST_USER_FS);
  if (!fs) {
      ...handle failure...
  }

>  uint64_t vhost_user_fs_slave_unmap(struct vhost_dev *dev,
>                                     VhostUserFSSlaveMsg *sm)
>  {
> -    /* TODO */
> -    return (uint64_t)-1;
> +    VHostUserFS *fs = VHOST_USER_FS(dev->vdev);
> +    if (!fs) {
> +        /* Shouldn't happen - but seen on error path */
> +        error_report("Bad fs ptr");
> +        return (uint64_t)-1;
> +    }

Same here.