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

Jason Wang
2021-10-14T06:23:47Z

On Thu, Oct 14, 2021 at 1:45 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> 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@redhat.com> 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@redhat.com>
> > > > Cc: Stefan Hajnoczi <stefanha@redhat.com>
> > > > Cc: Stefano Garzarella <sgarzare@redhat.com>
> > > > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > >
> > > 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.

Right.

>
> > 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.

Ok.

Thanks

>
> > 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
> > >
>