Null pointer dereference in `SparseFillEmptyRows`

### Impact An attacker can trigger a null pointer dereference in the implementation of `tf.raw_ops.SparseFillEmptyRows`: ```python import tensorflow as tf indices = tf.constant([], shape=[0, 0], dtype=tf.int64) values = tf.constant([], shape=[0], dtype=tf.int64) dense_shape = tf.constant([], shape=[0], dtype=tf.int64) default_value = 0 tf.raw_ops.SparseFillEmptyRows( indices=indices, values=values, dense_shape=dense_shape, default_value=default_value) ``` This is because of missing [validation](https://github.com/tensorflow/tensorflow/blob/fdc82089d206e281c628a93771336bf87863d5e8/tensorflow/core/kernels/sparse_fill_empty_rows_op.cc#L230-L231) that was covered under a `TODO`. If the `dense_shape` tensor is empty, then `dense_shape_t.vec<>()` would cause a null pointer dereference in the implementation of the op: ```cc template <typename T, typename Tindex> struct SparseFillEmptyRows<CPUDevice, T, Tindex> { Status operator()(OpKernelContext* context, const Tensor& default_value_t, const Tensor& indices_t, const Tensor& values_t, const Tensor& dense_shape_t, typename AsyncOpKernel::DoneCallback done) { ... const auto dense_shape = dense_shape_t.vec<Tindex>(); ... } } ``` ### Patches We have patched the issue in GitHub commit [faa76f39014ed3b5e2c158593b1335522e573c7f](https://github.com/tensorflow/tensorflow/commit/faa76f39014ed3b5e2c158593b1335522e573c7f). 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-2021-29565, CVE-2021-29565, PYSEC-2021-202, PYSEC-2021-493, PYSEC-2021-691

• github.com/tensorflow/tensorflow/security/advisories/GHSA-r6pg-pjwc-j585
• nvd.nist.gov/vuln/detail/CVE-2021-29565
• github.com/tensorflow/tensorflow/commit/faa76f39014ed3b5e2c158593b1335522e573c7f
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-493.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-691.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-202.yaml
• github.com/tensorflow/tensorflow