Incorrect validation of `SaveV2` inputs

### Impact The code for `tf.raw_ops.SaveV2` does not properly validate the inputs and an attacker can trigger a null pointer dereference: ```python import tensorflow as tf tf.raw_ops.SaveV2( prefix=['tensorflow'], tensor_name=['v'], shape_and_slices=[], tensors=[1,2,3]) ``` The [implementation](https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/save_restore_v2_ops.cc) uses `ValidateInputs` to check that the input arguments are valid. This validation would have caught the illegal state represented by the reproducer above. However, the validation uses `OP_REQUIRES` which translates to setting the `Status` object of the current `OpKernelContext` to an error status, followed by an empty `return` statement which just terminates the execution of the function it is present in. However, this does not mean that the kernel execution is finalized: instead, execution continues from the next line in `Compute` that follows the call to `ValidateInputs`. This is equivalent to lacking the validation. ### Patches We have patched the issue in GitHub commit [9728c60e136912a12d99ca56e106b7cce7af5986](https://github.com/tensorflow/tensorflow/commit/9728c60e136912a12d99ca56e106b7cce7af5986). The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1, TensorFlow 2.4.3, and TensorFlow 2.3.4, 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 members of the Aivul Team from Qihoo 360.

CVSS 3.1

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

Severity from

GitHub (reviewed advisory)

Weakness

CWE-476

Also known as

BIT-tensorflow-2021-37648, CVE-2021-37648, PYSEC-2021-270, PYSEC-2021-561, PYSEC-2021-759

• github.com/tensorflow/tensorflow/security/advisories/GHSA-wp77-4gmm-7cq8
• nvd.nist.gov/vuln/detail/CVE-2021-37648
• github.com/tensorflow/tensorflow/commit/9728c60e136912a12d99ca56e106b7cce7af5986
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-561.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-759.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-270.yaml
• github.com/tensorflow/tensorflow