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Date: Tue, 07 May 2013 13:42:47 +0800
From: Jason Wang <jasowang@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: "Michael S. Tsirkin" <mst@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 04/28/2013 04:40 PM, Jason Wang wrote:
> On 04/28/2013 04:32 PM, Michael S. Tsirkin wrote:
>> 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?
> Ok, this looks more clear. Will do it in V2.

Recheck the code, looks like {get|set}_config() has been validated in
virtio_bus_get_vdev_config(). So the codes were ok here, will drop this
patch also.
 
>>> ---
>>>  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
>