Re: Re: Re: [PATCH v7 04/12] virtio-blk: Add validation for block size in config space

Yongji Xie
2021-05-20T07:08:45Z

On Thu, May 20, 2021 at 1:43 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Thu, May 20, 2021 at 01:25:16PM +0800, Yongji Xie wrote:
> > On Wed, May 19, 2021 at 10:42 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > >
> > > On Wed, May 19, 2021 at 09:39:20PM +0800, Yongji Xie wrote:
> > > > On Mon, May 17, 2021 at 5:56 PM Xie Yongji <xieyongji@bytedance.com> wrote:
> > > > >
> > > > > This ensures that we will not use an invalid block size
> > > > > in config space (might come from an untrusted device).
> > >
> > > I looked at if I should add this as an untrusted function so that Smatch
> > > could find these sorts of bugs but this is reading data from the host so
> > > there has to be some level of trust...
> > >
> >
> > It would be great if Smatch could detect this case if possible. The
> > data might be trusted in traditional VM cases. But now the data can be
> > read from a userspace daemon when VDUSE is enabled.
> >
> > > I should add some more untrusted data kvm functions to Smatch. Right
> > > now I only have kvm_register_read() and I've added kvm_read_guest_virt()
> > > just now.
> > >
> > > > >
> > > > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> > > > > ---
> > > > > drivers/block/virtio_blk.c | 2 +-
> > > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > index ebb4d3fe803f..c848aa36d49b 100644
> > > > > --- a/drivers/block/virtio_blk.c
> > > > > +++ b/drivers/block/virtio_blk.c
> > > > > @@ -826,7 +826,7 @@ static int virtblk_probe(struct virtio_device *vdev)
> > > > > err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
> > > > > struct virtio_blk_config, blk_size,
> > > > > &blk_size);
> > > > > - if (!err)
> > > > > + if (!err && blk_size > 0 && blk_size <= max_size)
> > > >
> > > > The check here is incorrect. I will use PAGE_SIZE as the maximum
> > > > boundary in the new version.
> > >
> > > What does this bug look like to the user?
> >
> > The kernel will panic if the block size is larger than PAGE_SIZE.
>
> Kernel panic at this point is par for the course IMHO.

But it seems better if we can avoid this kind of panic. Because this
might also be triggered by a buggy VDUSE daemon.

> Let's focus on eliminating data corruption for starters.

OK, now the incorrect used length might cause data corruption in
virtio-net and virtio-console drivers as I mentioned in another mail.
I will send a fix ASAP.

Thanks,
Yongji