PYSEC-2021-831

TensorFlow is an open source platform for machine learning. In affected versions the implementation of SparseFillEmptyRows can be made to trigger a heap OOB access. This occurs whenever the size of indices does not match the size of values. The fix will be included in TensorFlow 2.7.0. We will also cherrypick this commit on TensorFlow 2.6.1, TensorFlow 2.5.2, and TensorFlow 2.4.4, as these are also affected and still in supported range.