Integer division by 0 in sparse reshaping
### Impact
The implementation of `tf.raw_ops.SparseReshape` can be made to trigger an integral division by 0 exception:
```python
import tensorflow as tf
tf.raw_ops.SparseReshape(
input_indices = np.ones((1,3)),
input_shape = np.array([1,1,0]),
new_shape = np.array([1,0]))
```
The implementation
https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/reshape_util.cc#L176-L181 calls the reshaping functor whenever there is at least an index in the input but does not check that shape of the input or the target shape have both a non-zero number of elements.
The reshape functor
https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/reshape_util.cc#L40-L78 blindly divides by the dimensions of the target shape. Hence, if this is not checked, code will result in a division by 0.
### Patches
We have patched the issue in GitHub commit 4923de56ec94fff7770df259ab7f2288a74feb41
https://github.com/tensorflow/tensorflow/commit/4923de56ec94fff7770df259ab7f2288a74feb41.
The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1 as this is the other affected version.
### 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.