Re: [PATCH v2] vsock/virtio: initialize the_virtio_vsock before using VQs

[Stefano Garzarella]

On Mon, Oct 23, 2023 at 05:59:45PM +0300, Alexandru Matei wrote:
> On 10/23/2023 5:52 PM, Alexandru Matei wrote:
> > On 10/23/2023 5:29 PM, Stefano Garzarella wrote:
> > > On Mon, Oct 23, 2023 at 05:08:33PM +0300, Alexandru Matei wrote:
> > > > Once VQs are filled with empty buffers and we kick the host,
> > > > it can send connection requests.  If 'the_virtio_vsock' is not
> > > > initialized before, replies are silently dropped and do not reach the host.
> > > >
> > > > Fixes: 0deab087b16a ("vsock/virtio: use RCU to avoid use-after-free on the_virtio_vsock")
> > > > Signed-off-by: Alexandru Matei <alexandru.matei@xxxxxxxxxx>
> > > > ---
> > > > v2:
> > > > - split virtio_vsock_vqs_init in vqs_init and vqs_fill and moved
> > > >  the_virtio_vsock initialization after vqs_init
> > > >
> > > > net/vmw_vsock/virtio_transport.c | 9 +++++++--
> > > > 1 file changed, 7 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> > > > index e95df847176b..92738d1697c1 100644
> > > > --- a/net/vmw_vsock/virtio_transport.c
> > > > +++ b/net/vmw_vsock/virtio_transport.c
> > > > @@ -559,6 +559,11 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
> > > >     vsock->tx_run = true;
> > > >     mutex_unlock(&vsock->tx_lock);
> > > >
> > > > +    return 0;
> > > > +}
> > > > +
> > > > +static void virtio_vsock_vqs_fill(struct virtio_vsock *vsock)
> > >
> > > What about renaming this function in virtio_vsock_vqs_start() and move also the setting of `tx_run` here?
> >
> > It works but in this case we also need to move rcu_assign_pointer in virtio_vsock_vqs_start(),
> > the assignment needs to be right after setting tx_run to true and before filling the VQs.

Why?

If `rx_run` is false, we shouldn't need to send replies to the host 
IIUC.

If we need this instead, please add a comment in the code, but also in 
the commit, because it's not clear why.

> >
>
> And if we move rcu_assign_pointer then there is no need to split the function in two,
> We can move rcu_assign_pointer() directly inside virtio_vsock_vqs_init() after setting tx_run.

Yep, this could be another option, but we need to change the name of 
that function in this case.

Stefano

> > > Thanks,
> > > Stefano
> > >
> > > > +{
> > > >     mutex_lock(&vsock->rx_lock);
> > > >     virtio_vsock_rx_fill(vsock);
> > > >     vsock->rx_run = true;
> > > > @@ -568,8 +573,6 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
> > > >     virtio_vsock_event_fill(vsock);
> > > >     vsock->event_run = true;
> > > >     mutex_unlock(&vsock->event_lock);
> > > > -
> > > > -    return 0;
> > > > }
> > > >
> > > > static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
> > > > @@ -664,6 +667,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
> > > >         goto out;
> > > >
> > > >     rcu_assign_pointer(the_virtio_vsock, vsock);
> > > > +    virtio_vsock_vqs_fill(vsock);
> > > >
> > > >     mutex_unlock(&the_virtio_vsock_mutex);
> > > >
> > > > @@ -736,6 +740,7 @@ static int virtio_vsock_restore(struct virtio_device *vdev)
> > > >         goto out;
> > > >
> > > >     rcu_assign_pointer(the_virtio_vsock, vsock);
> > > > +    virtio_vsock_vqs_fill(vsock);
> > > >
> > > > out:
> > > >     mutex_unlock(&the_virtio_vsock_mutex);
> > > > -- 
> > > > 2.34.1