Re: [PATCH 3/3] caif_virtio: fix the race between reset and netdev unregister

From: Michael S. Tsirkin
Date: Mon Jun 20 2022 - 05:09:31 EST


On Mon, Jun 20, 2022 at 01:11:15PM +0800, Jason Wang wrote:
> We use to do the following steps during .remove():

We currently do


> static void cfv_remove(struct virtio_device *vdev)
> {
> struct cfv_info *cfv = vdev->priv;
>
> rtnl_lock();
> dev_close(cfv->ndev);
> rtnl_unlock();
>
> tasklet_kill(&cfv->tx_release_tasklet);
> debugfs_remove_recursive(cfv->debugfs);
>
> vringh_kiov_cleanup(&cfv->ctx.riov);
> virtio_reset_device(vdev);
> vdev->vringh_config->del_vrhs(cfv->vdev);
> cfv->vr_rx = NULL;
> vdev->config->del_vqs(cfv->vdev);
> unregister_netdev(cfv->ndev);
> }
> This is racy since device could be re-opened after dev_close() but
> before unregister_netdevice():
>
> 1) RX vringh is cleaned before resetting the device, rx callbacks that
> is called after the vringh_kiov_cleanup() will result a UAF
> 2) Network stack can still try to use TX virtqueue even if it has been
> deleted after dev_vqs()
>
> Fixing this by unregistering the network device first to make sure not
> device access from both TX and RX side.
>
> Fixes: 0d2e1a2926b18 ("caif_virtio: Introduce caif over virtio")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> drivers/net/caif/caif_virtio.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/caif/caif_virtio.c b/drivers/net/caif/caif_virtio.c
> index 66375bea2fcd..a29f9b2df5b1 100644
> --- a/drivers/net/caif/caif_virtio.c
> +++ b/drivers/net/caif/caif_virtio.c
> @@ -752,9 +752,8 @@ static void cfv_remove(struct virtio_device *vdev)
> {
> struct cfv_info *cfv = vdev->priv;
>
> - rtnl_lock();
> - dev_close(cfv->ndev);
> - rtnl_unlock();
> + /* Make sure NAPI/TX won't try to access the device */
> + unregister_netdev(cfv->ndev);
>
> tasklet_kill(&cfv->tx_release_tasklet);
> debugfs_remove_recursive(cfv->debugfs);
> @@ -764,7 +763,6 @@ static void cfv_remove(struct virtio_device *vdev)
> vdev->vringh_config->del_vrhs(cfv->vdev);
> cfv->vr_rx = NULL;
> vdev->config->del_vqs(cfv->vdev);
> - unregister_netdev(cfv->ndev);
> }


This gives me pause, callbacks can now trigger after device
has been unregistered. Are we sure this is safe?
Won't it be safer to just keep the rtnl_lock around
the whole process?

> static struct virtio_device_id id_table[] = {
> --
> 2.25.1