`std::abort` raised from `TensorListReserve`

Impact

Providing a negative element to num_elements list argument of tf.raw_ops.TensorListReserve causes the runtime to abort the process due to reallocating a std::vector to have a negative number of elements:

```python

import tensorflow as tf

tf.raw_ops.TensorListReserve(

element_shape = tf.constant([1]),

num_elements=tf.constant([-1]),

element_dtype = tf.int32)

`

The [implementation](https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/list_kernels.cc#L312) calls std::vector.resize() with the new size controlled by input given by the user, without checking that this input is valid.

Patches

We have patched the issue in GitHub commit [8a6e874437670045e6c7dc6154c7412b4a2135e2](https://github.com/tensorflow/tensorflow/commit/8a6e874437670045e6c7dc6154c7412b4a2135e2).

The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1, TensorFlow 2.4.3, and TensorFlow 2.3.4, 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 members of the Aivul Team from Qihoo 360.