Heap buffer overflow in `MaxPoolGrad`

### Impact The implementation of `tf.raw_ops.MaxPoolGrad` is vulnerable to a heap buffer overflow: ```python import tensorflow as tf orig_input = tf.constant([0.0], shape=[1, 1, 1, 1], dtype=tf.float32) orig_output = tf.constant([0.0], shape=[1, 1, 1, 1], dtype=tf.float32) grad = tf.constant([], shape=[0, 0, 0, 0], dtype=tf.float32) ksize = [1, 1, 1, 1] strides = [1, 1, 1, 1] padding = "SAME" tf.raw_ops.MaxPoolGrad( orig_input=orig_input, orig_output=orig_output, grad=grad, ksize=ksize, strides=strides, padding=padding, explicit_paddings=[]) ``` The [implementation](https://github.com/tensorflow/tensorflow/blob/ab1e644b48c82cb71493f4362b4dd38f4577a1cf/tensorflow/core/kernels/maxpooling_op.cc#L194-L203) fails to validate that indices used to access elements of input/output arrays are valid: ```cc for (int index = out_start; index < out_end; ++index) { int input_backprop_index = out_arg_max_flat(index); FastBoundsCheck(input_backprop_index - in_start, in_end - in_start); input_backprop_flat(input_backprop_index) += out_backprop_flat(index); } ``` Whereas accesses to `input_backprop_flat` are guarded by `FastBoundsCheck`, the indexing in `out_backprop_flat` can result in OOB access. ### Patches We have patched the issue in GitHub commit [a74768f8e4efbda4def9f16ee7e13cf3922ac5f7](https://github.com/tensorflow/tensorflow/commit/a74768f8e4efbda4def9f16ee7e13cf3922ac5f7). 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. ### For more information Please consult [our security guide](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) for more information regarding the security model and how to contact us with issues and questions. ### Attribution This vulnerability has been reported by Ying Wang and Yakun Zhang of Baidu X-Team.

CVSS 3.1

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L

Severity from

GitHub (reviewed advisory)

Weakness

CWE-119, CWE-787

Also known as

BIT-tensorflow-2021-29579, CVE-2021-29579, PYSEC-2021-216, PYSEC-2021-507, PYSEC-2021-705

• github.com/tensorflow/tensorflow/security/advisories/GHSA-79fv-9865-4qcv
• nvd.nist.gov/vuln/detail/CVE-2021-29579
• github.com/tensorflow/tensorflow/commit/a74768f8e4efbda4def9f16ee7e13cf3922ac5f7
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-507.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-705.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-216.yaml
• github.com/tensorflow/tensorflow