Reference binding to nullptr in map operations
### Impact
An attacker can cause undefined behavior via binding a reference to null pointer in `tf.raw_ops.Map*` and `tf.raw_ops.OrderedMap*` operations:
```python
import tensorflow as tf
tf.raw_ops.MapPeek(
key=tf.constant([8],dtype=tf.int64),
indices=[],
dtypes=[tf.int32],
capacity=8,
memory_limit=128)
```
The implementation
https://github.com/tensorflow/tensorflow/blob/460e000de3a83278fb00b61a16d161b1964f15f4/tensorflow/core/kernels/map_stage_op.cc#L222-L248 has a check in place to ensure that `indices` is in ascending order, but does not check that `indices` is not empty.
### Patches
We have patched the issue in GitHub commit 532f5c5a547126c634fefd43bbad1dc6417678ac
https://github.com/tensorflow/tensorflow/commit/532f5c5a547126c634fefd43bbad1dc6417678ac.
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.