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Date: Fri, 13 Mar 2015 11:03:02 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20150313030302.GA23717@ad.nay.redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-stable] [PATCH V2] virtio: validate the
 existence of handle_output before calling it
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To: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, dkoch@verizon.com, qemu-stable@nongnu.org

On Thu, 03/12 17:50, Jason Wang wrote:
> We don't validate the existence of handle_output which may let a buggy
> guest to trigger a SIGSEV easily. E.g:
> 
> 1) write 10 to queue_sel to a virtio net device with only 1 queue
> 2) setup an arbitrary pfn
> 3) then notify queue 10
> 
> Fixing this by validating the existence of handle_output before.
> 
> Cc: qemu-stable@nongnu.org
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Reviewed-by: Fam Zheng <famz@redhat.com>

> ---
> Changes from V1:
> - check the existence of both vring.desc and handle_output in the same
>   line
> - describe the reproducer in the commit log
> ---
>  hw/virtio/virtio.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 3c6e430..17c1260 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -759,8 +759,9 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, int align)
>  
>  void virtio_queue_notify_vq(VirtQueue *vq)
>  {
> -    if (vq->vring.desc) {
> +    if (vq->vring.desc && vq->handle_output) {
>          VirtIODevice *vdev = vq->vdev;
> +
>          trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
>          vq->handle_output(vdev, vq);
>      }
> -- 
> 2.1.0
> 
>