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Date:   Wed, 13 Oct 2021 06:04:39 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Jason Wang <jasowang@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, f.hetzelt@tu-berlin.de,
        david.kaplan@amd.com, konrad.wilk@oracle.com,
        Paolo Bonzini <pbonzini@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>
Subject: Re: [PATCH V2 01/12] virtio-blk: validate num_queues during probe
Message-ID: <20211013060341-mutt-send-email-mst@kernel.org>
References: <20211012065227.9953-1-jasowang@redhat.com>
 <20211012065227.9953-2-jasowang@redhat.com>
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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.

> ---
>  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