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Date: Sun, 28 Apr 2013 16:40:19 +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 04:32 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.
>> ---
>>  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