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Date: Sun, 28 Apr 2013 11:32:39 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] virtio-ccw: check config length before
	accessing it
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To: Jason Wang <jasowang@redhat.com>
Cc: aliguori@us.ibm.com, pmatouse@redhat.com, Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, Cornelia Huck <cornelia.huck@de.ibm.com>, Richard Henderson <rth@twiddle.net>

On Fri, Apr 26, 2013 at 04:34:03PM +0800, Jason Wang wrote:
> virtio-rng-ccw has zero config length, so we need validate the config length
> before trying to access it. Otherwise we may crash since vdev->config is NULL.
> 
> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Alexander Graf <agraf@suse.de>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

The real problem is dev->vdev->get_config being NULL,
isn't it? So why not validate it and be done with it?

> ---
>  hw/s390x/virtio-ccw.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
> index 56539d3..8d0dff5 100644
> --- a/hw/s390x/virtio-ccw.c
> +++ b/hw/s390x/virtio-ccw.c
> @@ -260,7 +260,7 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
>              }
>          }
>          len = MIN(ccw.count, dev->vdev->config_len);
> -        if (!ccw.cda) {
> +        if (!ccw.cda || !len) {
>              ret = -EFAULT;
>          } else {
>              dev->vdev->get_config(dev->vdev, dev->vdev->config);
> @@ -279,7 +279,7 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
>          }
>          len = MIN(ccw.count, dev->vdev->config_len);
>          hw_len = len;
> -        if (!ccw.cda) {
> +        if (!ccw.cda || !len) {
>              ret = -EFAULT;
>          } else {
>              config = cpu_physical_memory_map(ccw.cda, &hw_len, 0);
> -- 
> 1.7.1