Re: [Qemu-devel] [PATCH] virtio-blk: refuse SG_IO requests with scsi=off

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/23/2011 03:39 PM, Paolo Bonzini wrote:
> QEMU does have a "scsi" option (to be used like -device
> virtio-blk-pci,drive=foo,scsi=off).  However, it only
> masks the feature bit, and does not reject the command
> if a malicious guest disregards the feature bits and
> issues a request.
>
> Without this patch, using scsi=off does not protect you
> from CVE-2011-4127.
>
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
> ---
>   hw/virtio-blk.c |    6 ++++++
>   1 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
> index b70d116..6cd3164 100644
> --- a/hw/virtio-blk.c
> +++ b/hw/virtio-blk.c
> @@ -153,6 +153,12 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
>       int status;
>       int i;
>
> +    if ((req->dev->vdev.guest_features&  (1<<  VIRTIO_BLK_F_SCSI)) == 0) {
> +        virtio_blk_req_complete(req, VIRTIO_BLK_S_UNSUPP);
> +        g_free(req);
> +        return;
> +    }
> +
>       /*
>        * We require at least one output segment each for the virtio_blk_outhdr
>        * and the SCSI command block.

Ping.

Paolo