chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2021-005.md

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+## TFSA-2021-005: Null pointer dereference via invalid Ragged Tensors
+
+### CVE Number
+CVE-2021-29516
+
+### Impact
+Calling `tf.raw_ops.RaggedTensorToVariant` with arguments specifying an invalid ragged tensor results in a null pointer dereference:
+
+```python
+import tensorflow as tf
+
+input_tensor = tf.constant([], shape=[0, 0, 0, 0, 0], dtype=tf.float32)
+filter_tensor = tf.constant([], shape=[0, 0, 0, 0, 0], dtype=tf.float32)
+
+tf.raw_ops.Conv3D(input=input_tensor, filter=filter_tensor, strides=[1, 56, 56, 56, 1], padding='VALID', data_format='NDHWC', dilations=[1, 1, 1, 23, 1])
+```
+
+```python
+import tensorflow as tf
+
+input_tensor = tf.constant([], shape=[2, 2, 2, 2, 0], dtype=tf.float32)
+filter_tensor = tf.constant([], shape=[0, 0, 2, 6, 2], dtype=tf.float32)
+
+tf.raw_ops.Conv3D(input=input_tensor, filter=filter_tensor, strides=[1, 56, 39, 34, 1], padding='VALID', data_format='NDHWC', dilations=[1, 1, 1, 1, 1])
+```
+
+The implementation of [`RaggedTensorToVariant`
+operations](https://github.com/tensorflow/tensorflow/blob/904b3926ed1c6c70380d5313d282d248a776baa1/tensorflow/core/kernels/ragged_tensor_to_variant_op.cc#L39-L40)
+does not validate that the ragged tensor argument is non-empty:
+
+```cc
+  int ragged_rank = batched_ragged.ragged_rank();
+  auto batched_splits_top_vec = batched_ragged.splits(0).vec<SPLIT_TYPE>();
+```
+
+Since `batched_ragged` contains no elements, `batched_ragged.splits` is a null vector, thus `batched_ragged.splits(0)` will result in dereferencing `nullptr`.
+
+### Patches
+We have patched the issue in GitHub commit
+[b055b9c474cd376259dde8779908f9eeaf097d93](https://github.com/tensorflow/tensorflow/commit/b055b9c474cd376259dde8779908f9eeaf097d93).
+
+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.