Disclaimer: I have no idea how to build and run this code, so my analysis could be completely wrong.

In AddHuffmanTable() in v4l2_jpeg_decode_accelerator.cc (https://cs.chromium.org/chromium/src/media/gpu/v4l2_jpeg_decode_accelerator.cc):

|input_ptr| is the mapped shared memory whose handle is provided by a renderer. |output_ptr| in this function is the buffer used as input for the V4L2 device, whose size is checked is to be at least the input shared memory size + |sizeof(kDefaultDhtSeg)| (sizeof(kDefaultDhtSeg) should be 420). 

However:

  while (!has_marker_sos && !has_marker_dht) {

    ...

    switch (marker2) {
      case JPEG_DHT: {
        has_marker_dht = true;
        break;
      }
      case JPEG_SOS: {
        if (!has_marker_dht) {
          memcpy(static_cast<uint8_t*>(output_ptr) + current_offset,
                 kDefaultDhtSeg, sizeof(kDefaultDhtSeg));
          current_offset += sizeof(kDefaultDhtSeg);
        }
        has_marker_sos = true;
        break;
      }
      default:
        break;
    }


There is no limit on how many times kDefaultDhtSeg could be written to the output, meaning the |current_offset| (which isn't checked against |output_size|), could be incremented by 421 an arbitrary number of times for each 5ish bytes in an input provided by a malicious renderer, leading to an eventual OOB write.