FPE in `tf.raw_ops.UnravelIndex`
### Impact
An attacker can cause denial of service in applications serving models using `tf.raw_ops.UnravelIndex` by triggering a division by 0:
```python
import tensorflow as tf
tf.raw_ops.UnravelIndex(indices=-1, dims=[1,0,2])
```
The implementation
https://github.com/tensorflow/tensorflow/blob/460e000de3a83278fb00b61a16d161b1964f15f4/tensorflow/core/kernels/unravel_index_op.cc#L36 does not check that the tensor subsumed by `dims` is not empty. Hence, if one element of `dims` is 0, the implementation does a division by 0.
### Patches
We have patched the issue in GitHub commit a776040a5e7ebf76eeb7eb923bf1ae417dd4d233
https://github.com/tensorflow/tensorflow/commit/a776040a5e7ebf76eeb7eb923bf1ae417dd4d233.
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.