Vulnerability: Division by zero in TFLite's implementation of `BatchToSpaceNd` ### Impact
The implementation of the `BatchToSpaceNd` TFLite operator is [vulnerable to a division by zero error](https://github.com/tensorflow/tensorflow/blob/b5ed552fe55895aee8bd8b191f744a069957d18d/tensorflow/lite/kernels/batch_to_space_nd.cc#L81-L82):

```cc
TF_LITE_ENSURE_EQ(context, output_batch_size % block_shape[dim], 0);
output_batch_size = output_batch_size / block_shape[dim];
```

An attacker can craft a model such that one dimension of the `block` input is 0. Hence, the corresponding value in `block_shape` is 0.

### Patches
We have patched the issue in GitHub commit [2c74674348a4708ced58ad6eb1b23354df8ee044](https://github.com/tensorflow/tensorflow/commit/2c74674348a4708ced58ad6eb1b23354df8ee044).

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 members of the Aivul Team from Qihoo 360.
Vulnerability ID: GHSA-cfx7-2xpc-8w4h
CWE: CWE-369
Severity score: 2.5
Project: https://github.com/tensorflow/tensorflow
Published: 2021-05-21
File: tensorflow/lite/kernels/batch_to_space_nd.cc
Commit message: Prevent division by 0

PiperOrigin-RevId: 370979352
Change-Id: Ic79191c316d986fc6072ecaebfec9d5f2b924d00
Commit author: Mihai Maruseac

Vulnerable version (before fix):
 TfLiteStatus ResizeOutputTensor(TfLiteContext* context,   int output_batch_size = input_size->data[0];   for (int dim = 0; dim < spatial_dims_num; ++dim) {     // Number of batch must be multiple of (block_shape[dim]).     TF_LITE_ENSURE_EQ(context, output_batch_size % block_shape[dim], 0);     output_batch_size = output_batch_size / block_shape[dim];     output_size->data[dim + 1] = input_size->data[dim + 1] * block_shape[dim] -

Fixed version (after fix):
 TfLiteStatus ResizeOutputTensor(TfLiteContext* context,   int output_batch_size = input_size->data[0];   for (int dim = 0; dim < spatial_dims_num; ++dim) {     // Number of batch must be multiple of (block_shape[dim]).     TF_LITE_ENSURE(context, block_shape[dim] != 0);     TF_LITE_ENSURE_EQ(context, output_batch_size % block_shape[dim], 0);     output_batch_size = output_batch_size / block_shape[dim];     output_size->data[dim + 1] = input_size->data[dim + 1] * block_shape[dim] -

Patch:
patch: @@ -78,6 +78,7 @@ TfLiteStatus ResizeOutputTensor(TfLiteContext* context,
   int output_batch_size = input_size->data[0];
   for (int dim = 0; dim < spatial_dims_num; ++dim) {
     // Number of batch must be multiple of (block_shape[dim]).
+    TF_LITE_ENSURE(context, block_shape[dim] != 0);
     TF_LITE_ENSURE_EQ(context, output_batch_size % block_shape[dim], 0);
     output_batch_size = output_batch_size / block_shape[dim];
     output_size->data[dim + 1] = input_size->data[dim + 1] * block_shape[dim] -
path: tensorflow/lite/kernels/batch_to_space_nd.cc