Code: void MojoVideoEncodeAccelerator::Encode(const scoped_refptr<VideoFrame>& frame,
                                        bool force_keyframe) {
  DVLOG(2) << __func__ << " tstamp=" << frame->timestamp();
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK_EQ(PIXEL_FORMAT_I420, frame->format());
  DCHECK_EQ(VideoFrame::STORAGE_SHMEM, frame->storage_type());
  DCHECK(frame->shared_memory_handle().IsValid());

  const size_t allocation_size = frame->shared_memory_handle().GetSize();
 
  mojo::ScopedSharedBufferHandle handle =
      mojo::WrapSharedMemoryHandle(frame->shared_memory_handle().Duplicate(),
                                   allocation_size, true /* read_only */);
 
   const size_t y_offset = frame->shared_memory_offset();
   const size_t u_offset = y_offset + frame->data(VideoFrame::kUPlane) -
                          frame->data(VideoFrame::kYPlane);
  const size_t v_offset = y_offset + frame->data(VideoFrame::kVPlane) -
                          frame->data(VideoFrame::kYPlane);
  scoped_refptr<MojoSharedBufferVideoFrame> mojo_frame =
      MojoSharedBufferVideoFrame::Create(
          frame->format(), frame->coded_size(), frame->visible_rect(),
          frame->natural_size(), std::move(handle), allocation_size, y_offset,
          u_offset, v_offset, frame->stride(VideoFrame::kYPlane),
          frame->stride(VideoFrame::kUPlane),
          frame->stride(VideoFrame::kVPlane), frame->timestamp());

  DCHECK(vea_.is_bound());
  vea_->Encode(mojo_frame, force_keyframe,
               base::Bind(&KeepVideoFrameAlive, frame));
}

Vulnerability Type: 
CWE ID: CWE-787
Summary: Incorrect use of mojo::WrapSharedMemoryHandle in Mojo in Google Chrome prior to 65.0.3325.146 allowed a remote attacker who had compromised the renderer process to perform an out of bounds memory write via a crafted HTML page.
Commit Message: Correct mojo::WrapSharedMemoryHandle usage

Fixes some incorrect uses of mojo::WrapSharedMemoryHandle which
were assuming that the call actually has any control over the memory
protection applied to a handle when mapped.

Where fixing usage is infeasible for this CL, TODOs are added to
annotate follow-up work.

Also updates the API and documentation to (hopefully) improve clarity
and avoid similar mistakes from being made in the future.

BUG=792900

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I0578aaa9ca3bfcb01aaf2451315d1ede95458477
Reviewed-on: https://chromium-review.googlesource.com/818282
Reviewed-by: Wei Li <weili@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Yuzhu Shen <yzshen@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530268}