`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.