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

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Date:   Mon, 27 Jun 2022 16:17:54 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     davem <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <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 3:44 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> 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.

Yes, but I couldn't find a better commit.

> But OK I guess.
>
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
>
> With commit log changes:

Will post a new version with the above fixed.

Thanks

>
> 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
>