Virtualization - Oct 2021 - [PATCH V2 01/12] virtio-blk: validate num_queues during probe

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 at redhat.com>
Cc: Stefan Hajnoczi <stefanha at redhat.com>
Cc: Stefano Garzarella <sgarzare at redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 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

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 at redhat.com>
> Cc: Stefan Hajnoczi <stefanha at redhat.com>
> Cc: Stefano Garzarella <sgarzare at redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
I'd rather fail probe so we don't need to support that.
> ---
>  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