Re: [PATCH v2] videobuf2-core: Verify planes lengths for output buffers

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

Hi All,

On 08/08/2013 02:35 PM, Laurent Pinchart wrote:
> Hi Marek,
> 
> On Thursday 08 August 2013 14:14:30 Marek Szyprowski wrote:
>> On 8/7/2013 12:44 PM, Laurent Pinchart wrote:
>>> On Monday 12 November 2012 12:35:35 Laurent Pinchart wrote:
>>>> On Friday 09 November 2012 15:33:22 Pawel Osciak wrote:
>>>>> On Tue, Oct 16, 2012 at 8:37 AM, Laurent Pinchart wrote:
>>>>>> For output buffers application provide to the kernel the number of
>>>>>> bytes they stored in each plane of the buffer. Verify that the value
>>>>>> is smaller than or equal to the plane length.
>>>>>>
>>>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>>>>> Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
>>>>>> ---
>>>>>
>>>>> Acked-by: Pawel Osciak <pawel@osciak.com>
>>>>
>>>> You're listed, as well as Marek and Kyungmin, as videobuf2 maintainers.
>>>> When you ack a videobuf2 patch, should we assume that you will take it
>>>> in your git tree ?
>>>
>>> Ping ? I'd like to get this patch in v3.12, should I send a pull request ?
>>
>> Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>
>> Feel free to include it in your pull-request. I'm sorry for so huge
>> delay in my response.
> 
> No worries. I'll send a pull request to Mauro.
> 
>>>>>>  drivers/media/v4l2-core/videobuf2-core.c |   39 +++++++++++++++++++
>>>>>>  1 files changed, 39 insertions(+), 0 deletions(-)
>>>>>>
>>>>>> Changes compared to v1:
>>>>>>
>>>>>> - Sanity check the data_offset value for each plane.
>>>>>>
>>>>>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>>>>>> b/drivers/media/v4l2-core/videobuf2-core.c index 432df11..479337d
>>>>>> 100644
>>>>>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>>>>>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>>>>>> @@ -296,6 +296,41 @@ static int __verify_planes_array(struct
>>>>>> vb2_buffer
>>>>>> *vb, const struct v4l2_buffer>
>>>>>>
>>>>>>  }
>>>>>>  
>>>>>>  /**
>>>>>>
>>>>>> + * __verify_length() - Verify that the bytesused value for each
>>>>>> plane
>>>>>> fits in
>>>>>> + * the plane length and that the data offset doesn't exceed the
>>>>>> bytesused value.
>>>>>> + */
>>>>>> +static int __verify_length(struct vb2_buffer *vb, const struct
>>>>>> v4l2_buffer *b)
>>>>>> +{
>>>>>> +       unsigned int length;
>>>>>> +       unsigned int plane;
>>>>>> +
>>>>>> +       if (!V4L2_TYPE_IS_OUTPUT(b->type))
>>>>>> +               return 0;
>>>>>> +
>>>>>> +       if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
>>>>>> +               for (plane = 0; plane < vb->num_planes; ++plane) {
>>>>>> +                       length = (b->memory == V4L2_MEMORY_USERPTR)
>>>>>> +                              ? b->m.planes[plane].length
>>>>>> +                              : vb->v4l2_planes[plane].length;
>>>>>> +
>>>>>> +                       if (b->m.planes[plane].bytesused > length)
>>>>>> +                               return -EINVAL;
>>>>>> +                       if (b->m.planes[plane].data_offset >=
>>>>>> +                           b->m.planes[plane].bytesused)
>>>>>> +                               return -EINVAL;


This patch causes regressions. After kernel upgrade applications that
zero the planes array and don't set bytesused will stop working.
We could say that these are buggy applications, but if it has been 
allowed for several kernel releases failing VIDIOC_QBUF on this check
now is plainly a regression IMO. I guess Linus wouldn't be happy about
a change like this.

With this patch it is no longer possible to queue a buffer with bytesused 
set to 0. I think it shouldn't be disallowed to queue a buffer with no 
data to be used. So the check should likely be instead:

 if (b->m.planes[plane].bytesused > 0 &&
     b->m.planes[plane].data_offset >=
     b->m.planes[plane].bytesused)
	return -EINVAL;

Sorry for the late review of this.

>>>>>> +               }
>>>>>> +       } else {
>>>>>> +               length = (b->memory == V4L2_MEMORY_USERPTR)
>>>>>> +                      ? b->length : vb->v4l2_planes[0].length;
>>>>>> +
>>>>>> +               if (b->bytesused > length)
>>>>>> +                       return -EINVAL;
>>>>>> +       }
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>>
>>>>>>   * __buffer_in_use() - return true if the buffer is in use and
>>>>>>   * the queue cannot be freed (by the means of REQBUFS(0)) call
>>>>>>   */
>>>>>>
>>>>>> @@ -975,6 +1010,10 @@ static int __buf_prepare(struct vb2_buffer
>>>>>> *vb,
>>>>>> const struct v4l2_buffer *b)>
>>>>>>
>>>>>>         struct vb2_queue *q = vb->vb2_queue;
>>>>>>         int ret;
>>>>>>
>>>>>> +       ret = __verify_length(vb, b);
>>>>>> +       if (ret < 0)
>>>>>> +               return ret;
>>>>>> +
>>>>>>
>>>>>>         switch (q->memory) {
>>>>>>         
>>>>>>         case V4L2_MEMORY_MMAP:
>>>>>>                 ret = __qbuf_mmap(vb, b);
> 

Regards,
-- 
Sylwester Nawrocki
Samsung R&D Institute Poland