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

[Jason Wang <jasowang@redhat.com>]

We use to do the following steps during .remove():

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@redhat.com>
---
 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);
 }
 
 static struct virtio_device_id id_table[] = {
-- 
2.25.1