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.

References:

http://seclists.org/oss-sec/2016/q2/272

Upstream fix:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2c1f6951a8a82e6de0d82b1158b5e493fc6c54ab

Introduced by:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=b0e0e1f83de31aa0428c38b692c590cc0ecd3f03