chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2021-042.md

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+## TFSA-2021-042: Division by 0 in `DenseCountSparseOutput`
+
+### CVE Number
+CVE-2021-29554
+
+### Impact
+An attacker can cause a denial of service via a FPE runtime error in
+`tf.raw_ops.DenseCountSparseOutput`:
+
+```python
+import tensorflow as tf
+
+values = tf.constant([], shape=[0, 0], dtype=tf.int64)
+weights = tf.constant([])
+
+tf.raw_ops.DenseCountSparseOutput(
+  values=values, weights=weights,
+  minlength=-1, maxlength=58, binary_output=True)
+```
+
+This is because the
+[implementation](https://github.com/tensorflow/tensorflow/blob/efff014f3b2d8ef6141da30c806faf141297eca1/tensorflow/core/kernels/count_ops.cc#L123-L127)
+computes a divisor value from user data but does not check that the result is 0
+before doing the division:
+
+```cc
+int num_batch_elements = 1;
+for (int i = 0; i < num_batch_dimensions; ++i) {
+  num_batch_elements *= data.shape().dim_size(i);
+}
+int num_value_elements = data.shape().num_elements() / num_batch_elements;
+```
+
+Since `data` is given by the `values` argument, `num_batch_elements` is 0.
+
+### Patches
+We have patched the issue in GitHub commit
+[da5ff2daf618591f64b2b62d9d9803951b945e9f](https://github.com/tensorflow/tensorflow/commit/da5ff2daf618591f64b2b62d9d9803951b945e9f).
+
+The fix will be included in TensorFlow 2.5.0. We will also cherrypick this
+commit on TensorFlow 2.4.2, and TensorFlow 2.3.3, as these are also affected.
+
+### 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.