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

[Jason Wang <jasowang@redhat.com>]

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.

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

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
>