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

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Date:   Mon, 27 Jun 2022 14:33:08 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mst <mst@...hat.com>, jasowang <jasowang@...hat.com>,
        davem <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] virtio-net: fix race between ndo_open() and virtio_device_ready()

On Fri, Jun 17, 2022 at 3:29 PM Jason Wang <jasowang@...hat.com> wrote:
>
> We used to call virtio_device_ready() after netdev registration. This
> cause 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 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")
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Ok, I think we're fine with this. So I will repost against -net.

If we spot issues with unregistering, we can use a separate patch for that.

Thanks

> ---
>  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
>