chore: import upstream snapshot with attribution

tensorflow/security/advisory/tfsa-2021-033.md

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+## TFSA-2021-033: Heap buffer overflow in `SparseTensorToCSRSparseMatrix`
+
+### CVE Number
+CVE-2021-29545
+
+### Impact
+An attacker can trigger a denial of service via a `CHECK`-fail in
+converting sparse tensors to CSR Sparse matrices:
+
+```python
+import tensorflow as tf
+import numpy as np
+from tensorflow.python.ops.linalg.sparse import sparse_csr_matrix_ops
+
+indices_array = np.array([[0, 0]])
+value_array = np.array([0.0], dtype=np.float32)
+dense_shape = [0, 0]
+
+st = tf.SparseTensor(indices_array, value_array, dense_shape)
+
+values_tensor = sparse_csr_matrix_ops.sparse_tensor_to_csr_sparse_matrix(
+       st.indices, st.values, st.dense_shape)
+```
+
+This is because the
+[implementation](https://github.com/tensorflow/tensorflow/blob/800346f2c03a27e182dd4fba48295f65e7790739/tensorflow/core/kernels/sparse/kernels.cc#L66)
+does a double redirection to access an element of an array allocated on the
+heap:
+
+```cc
+csr_row_ptr(indices(i, 0) + 1) += 1;
+```
+
+If the value at `indices(i, 0)` is such that `indices(i, 0) + 1` is outside the
+bounds of `csr_row_ptr`, this results in writing outside of bounds of heap
+allocated data.
+
+### Patches
+We have patched the issue in GitHub commit
+[1e922ccdf6bf46a3a52641f99fd47d54c1decd13](https://github.com/tensorflow/tensorflow/commit/1e922ccdf6bf46a3a52641f99fd47d54c1decd13).
+
+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.