[xenial,CVE-2016-4568,media] videobuf2-v4l2: Verify planes array in buffer dequeueing

From: Sakari Ailus <sakari.ailus@linux.intel.com>

When a buffer is being dequeued using VIDIOC_DQBUF IOCTL, the exact buffer
which will be dequeued is not known until the buffer has been removed from
the queue. The number of planes is specific to a buffer, not to the queue.

This does lead to the situation where multi-plane buffers may be requested
and queued with n planes, but VIDIOC_DQBUF IOCTL may be passed an argument
struct with fewer planes.

__fill_v4l2_buffer() however uses the number of planes from the dequeued
videobuf2 buffer, overwriting kernel memory (the m.planes array allocated
in video_usercopy() in v4l2-ioctl.c)  if the user provided fewer
planes than the dequeued buffer had. Oops!

Fixes: b0e0e1f83de3 ("[media] media: videobuf2: Prepare to divide videobuf2")

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: stable@vger.kernel.org # for v4.4 and later
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
CVE-2016-4568
(cherry picked from commit 83934b75c368f529d084815c463a7ef781dc9751)
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/media/v4l2-core/videobuf2-v4l2.c | 6 ++++++
 1 file changed, 6 insertions(+)

On 15/11/16 12:03, Luis Henriques wrote:
> From: Sakari Ailus <sakari.ailus@linux.intel.com>
> 
> When a buffer is being dequeued using VIDIOC_DQBUF IOCTL, the exact buffer
> which will be dequeued is not known until the buffer has been removed from
> the queue. The number of planes is specific to a buffer, not to the queue.
> 
> This does lead to the situation where multi-plane buffers may be requested
> and queued with n planes, but VIDIOC_DQBUF IOCTL may be passed an argument
> struct with fewer planes.
> 
> __fill_v4l2_buffer() however uses the number of planes from the dequeued
> videobuf2 buffer, overwriting kernel memory (the m.planes array allocated
> in video_usercopy() in v4l2-ioctl.c)  if the user provided fewer
> planes than the dequeued buffer had. Oops!
> 
> Fixes: b0e0e1f83de3 ("[media] media: videobuf2: Prepare to divide videobuf2")
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
> Cc: stable@vger.kernel.org # for v4.4 and later
> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> CVE-2016-4568
> (cherry picked from commit 83934b75c368f529d084815c463a7ef781dc9751)
> Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
> ---
>  drivers/media/v4l2-core/videobuf2-v4l2.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
> index 502984c724ff..6c441be8f893 100644
> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
> @@ -67,6 +67,11 @@ static int __verify_planes_array(struct vb2_buffer *vb, const struct v4l2_buffer
>  	return 0;
>  }
>  
> +static int __verify_planes_array_core(struct vb2_buffer *vb, const void *pb)
> +{
> +	return __verify_planes_array(vb, pb);
> +}
> +
>  /**
>   * __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.
> @@ -432,6 +437,7 @@ static int __fill_vb2_buffer(struct vb2_buffer *vb,
>  }
>  
>  static const struct vb2_buf_ops v4l2_buf_ops = {
> +	.verify_planes_array	= __verify_planes_array_core,
>  	.fill_user_buffer	= __fill_v4l2_buffer,
>  	.fill_vb2_buffer	= __fill_vb2_buffer,
>  	.set_timestamp		= __set_timestamp,
> 

Clean upstream cherry pick, seems to do what it says, so..

Acked-by: Colin Ian King <colin.king@canonical.com>

Though the change does not really make it obvious how this helps. I assume
having a verify operation defined will call it at the right stages...

Applied to xenial master-next branch.

Cheers,
--
Luís