Re: [PATCH V2 01/12] virtio-blk: validate num_queues during probe

[Michael S. Tsirkin]

On Thu, Oct 14, 2021 at 10:32:32AM +0800, Jason Wang wrote:
> On Wed, Oct 13, 2021 at 6:04 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >
> > On Tue, Oct 12, 2021 at 02:52:16PM +0800, Jason Wang wrote:
> > > If an untrusted device neogitates BLK_F_MQ but advertises a zero
> > > num_queues, the driver may end up trying to allocating zero size
> > > buffers where ZERO_SIZE_PTR is returned which may pass the checking
> > > against the NULL. This will lead unexpected results.
> > >
> > > Fixing this by using single queue if num_queues is zero.
> > >
> > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> > > Cc: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > > Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> >
> > I'd rather fail probe so we don't need to support that.
> 
> I think we should be consistent among all virtio drivers.

Well we started being permissive. We can't change that
since that might break on some hosts. But given focus on
security being restrictive sounds better now.

> E.g without this patch, we stick to 1 if virtio_create_feature() fail.
> Do we need to fix that?

We can't easily, some hosts might be broken.

> And we do something similar at least for the virtio-net and a lot of
> other places.
> 
>         /* We need at least 2 queue's */
>         if (err || max_queue_pairs < VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN ||
>             max_queue_pairs > VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX ||
>             !virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
>                 max_queue_pairs = 1;
> 
> Thanks
> 
> >
> > > ---
> > >  drivers/block/virtio_blk.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > index 9b3bd083b411..9deff01a38cb 100644
> > > --- a/drivers/block/virtio_blk.c
> > > +++ b/drivers/block/virtio_blk.c
> > > @@ -495,7 +495,8 @@ static int init_vq(struct virtio_blk *vblk)
> > >       err = virtio_cread_feature(vdev, VIRTIO_BLK_F_MQ,
> > >                                  struct virtio_blk_config, num_queues,
> > >                                  &num_vqs);
> > > -     if (err)
> > > +     /* We need at least one virtqueue */
> > > +     if (err || !num_vqs)
> > >               num_vqs = 1;
> > >
> > >       num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs);
> > > --
> > > 2.25.1
> >