CVE-2021-29545: Incorrect Calculation of Buffer Size

TensorFlow is an end-to-end open source platform for machine learning. An attacker can trigger a denial of service via a CHECK-fail in converting sparse tensors to CSR Sparse matrices. This is because the implementation does a double redirection to access an element of an array allocated on the heap. If the value at indices + 1 is outside the bounds of csr_row_ptr, this results in writing outside of bounds of heap allocated data. 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.