Virtualization - Jun 2022 - [PATCH net V2] virtio-net: fix race between ndo_open() and virtio_device_ready()

We currently call virtio_device_ready() after netdev
registration. Since ndo_open() can be called immediately
after register_netdev, this means there exists a race between
ndo_open() and virtio_device_ready(): the driver may start to use the
device before DRIVER_OK which violates the spec.

Fix this by switching to use register_netdevice() and protect the
virtio_device_ready() with rtnl_lock() to make sure ndo_open() can
only be called after virtio_device_ready().

Fixes: 4baf1e33d0842 ("virtio_net: enable VQs early")
Acked-by: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index db05b5e930be..8a5810bcb839 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3655,14 +3655,20 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (vi->has_rss || vi->has_rss_hash_report)
 		virtnet_init_default_rss(vi);
 
-	err = register_netdev(dev);
+	/* serialize netdev register + virtio_device_ready() with ndo_open() */
+	rtnl_lock();
+
+	err = register_netdevice(dev);
 	if (err) {
 		pr_debug("virtio_net: registering device failed\n");
+		rtnl_unlock();
 		goto free_failover;
 	}
 
 	virtio_device_ready(vdev);
 
+	rtnl_unlock();
+
 	err = virtnet_cpu_notif_add(vi);
 	if (err) {
 		pr_debug("virtio_net: registering cpu notifier failed\n");
-- 
2.25.1

On Mon, Jun 27, 2022 at 04:30:40PM +0800, Jason Wang
wrote:
> We currently call virtio_device_ready() after netdev
> registration. Since ndo_open() can be called immediately
> after register_netdev, this means there exists a race between
> ndo_open() and virtio_device_ready(): the driver may start to use the
> device before DRIVER_OK which violates the spec.
> 
> Fix this by switching to use register_netdevice() and protect the
> virtio_device_ready() with rtnl_lock() to make sure ndo_open() can
> only be called after virtio_device_ready().
> 
> Fixes: 4baf1e33d0842 ("virtio_net: enable VQs early")
> Acked-by: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
I reworded the caif commit log similarly and put both on my tree.
> ---
>  drivers/net/virtio_net.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index db05b5e930be..8a5810bcb839 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3655,14 +3655,20 @@ static int virtnet_probe(struct virtio_device
*vdev)
>  	if (vi->has_rss || vi->has_rss_hash_report)
>  		virtnet_init_default_rss(vi);
>  
> -	err = register_netdev(dev);
> +	/* serialize netdev register + virtio_device_ready() with ndo_open() */
> +	rtnl_lock();
> +
> +	err = register_netdevice(dev);
>  	if (err) {
>  		pr_debug("virtio_net: registering device failed\n");
> +		rtnl_unlock();
>  		goto free_failover;
>  	}
>  
>  	virtio_device_ready(vdev);
>  
> +	rtnl_unlock();
> +
>  	err = virtnet_cpu_notif_add(vi);
>  	if (err) {
>  		pr_debug("virtio_net: registering cpu notifier failed\n");
> -- 
> 2.25.1