Bad alloc in `StringNGrams` caused by integer conversion

Impact

The implementation of tf.raw_ops.StringNGrams is vulnerable to an integer overflow issue caused by converting a signed integer value to an unsigned one and then allocating memory based on this value.

import tensorflow as tf

tf.raw_ops.StringNGrams(
  data=['',''],
  data_splits=[0,2],
  separator=' '*100,
  ngram_widths=[-80,0,0,-60],
  left_pad=' ',
  right_pad=' ',
  pad_width=100,
  preserve_short_sequences=False)

The implementation calls reserve on a tstring with a value that sometimes can be negative if user supplies negative ngram_widths. The reserve method calls TF_TString_Reserve which has an unsigned long argument for the size of the buffer. Hence, the implicit conversion transforms the negative value to a large integer.

Patches

We have patched the issue in GitHub commit c283e542a3f422420cfdb332414543b62fc4e4a5.

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 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.