Vulnerability: Missing validation causes `TensorSummaryV2` to crash ### Impact
The implementation of [`tf.raw_ops.TensorSummaryV2`](https://github.com/tensorflow/tensorflow/blob/f3b9bf4c3c0597563b289c0512e98d4ce81f886e/tensorflow/core/kernels/summary_tensor_op.cc#L33-L58) does not fully validate the input arguments. This results in a `CHECK`-failure which can be used to trigger a denial of service attack:

```python
import numpy as np
import tensorflow as tf

tf.raw_ops.TensorSummaryV2(
  tag=np.array('test'),
  tensor=np.array(3),
  serialized_summary_metadata=tf.io.encode_base64(np.empty((0))))
```

The code assumes `axis` is a scalar but there is no validation for this.

```cc
    const Tensor& serialized_summary_metadata_tensor = c->input(2);
    // ...
    ParseFromTString(serialized_summary_metadata_tensor.scalar<tstring>()(),
                     v->mutable_metadata());
``` 

### Patches
We have patched the issue in GitHub commit [290bb05c80c327ed74fae1d089f1001b1e2a4ef7](https://github.com/tensorflow/tensorflow/commit/290bb05c80c327ed74fae1d089f1001b1e2a4ef7).
    
The fix will be included in TensorFlow 2.9.0. We will also cherrypick this commit on TensorFlow 2.8.1, TensorFlow 2.7.2, and TensorFlow 2.6.4, 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 Neophytos Christou from Secure Systems Lab at Brown University and Hong Jin from Singapore Management University.
Vulnerability ID: GHSA-2p9q-h29j-3f5v
CWE: CWE-20
Severity score: 5.5
Project: https://github.com/tensorflow/tensorflow
Published: 2022-05-24
File: tensorflow/core/kernels/summary_tensor_op.cc
Commit message: Fix tf.raw_ops.TensorSummaryV2 vulnerability with invalid serialized_summary_metadata.

Check that input is actually a scalar before treating it as such.

PiperOrigin-RevId: 445197183
Commit author: Alan Liu

Vulnerable version (before fix):
 class SummaryTensorOpV2 : public OpKernel {                 errors::InvalidArgument("tag must be scalar"));     const Tensor& tensor = c->input(1);     const Tensor& serialized_summary_metadata_tensor = c->input(2);      Summary s;     Summary::Value* v = s.add_value();

Fixed version (after fix):
 class SummaryTensorOpV2 : public OpKernel {                 errors::InvalidArgument("tag must be scalar"));     const Tensor& tensor = c->input(1);     const Tensor& serialized_summary_metadata_tensor = c->input(2);     OP_REQUIRES(         c,         TensorShapeUtils::IsScalar(serialized_summary_metadata_tensor.shape()),         errors::InvalidArgument("serialized_summary_metadata must be scalar"));      Summary s;     Summary::Value* v = s.add_value();

Patch:
patch: @@ -36,6 +36,10 @@ class SummaryTensorOpV2 : public OpKernel {
                 errors::InvalidArgument("tag must be scalar"));
     const Tensor& tensor = c->input(1);
     const Tensor& serialized_summary_metadata_tensor = c->input(2);
+    OP_REQUIRES(
+        c,
+        TensorShapeUtils::IsScalar(serialized_summary_metadata_tensor.shape()),
+        errors::InvalidArgument("serialized_summary_metadata must be scalar"));
 
     Summary s;
     Summary::Value* v = s.add_value();
path: tensorflow/core/kernels/summary_tensor_op.cc