linux-kernel - Re: [PATCH net] virtio-net: fix race between ndo_open() and virtio_device

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Date:   Mon, 27 Jun 2022 03:44:20 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     davem@...emloft.net, kuba@...nel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] virtio-net: fix race between ndo_open() and
 virtio_device_ready()

On Mon, Jun 27, 2022 at 02:36:56PM +0800, Jason Wang wrote:
> We used to call virtio_device_ready() after netdev registration.

s/used to call/currently call/

> This
> cause

s/This cause/Since ndo_open can be called immediately
after register_netdev, this means there exists/

> a race between ndo_open() and virtio_device_ready(): if
> ndo_open() is called before virtio_device_ready(), the driver may
> start to use the device before DRIVER_OK which violates the spec.
> 
> Fixing

s/Fixing/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")

it's an unusual use of Fixes - the patch in question does not
introduce the problem, it just does not fix it completely.
But OK I guess.

> Signed-off-by: Jason Wang <jasowang@...hat.com>

With commit log changes:

Acked-by: Michael S. Tsirkin <mst@...hat.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