Heap out of bounds write in `RaggedBinCount`

### Impact If the `splits` argument of `RaggedBincount` does not specify a valid [`SparseTensor`](https://www.tensorflow.org/api_docs/python/tf/sparse/SparseTensor), then an attacker can trigger a heap buffer overflow: ```python import tensorflow as tf tf.raw_ops.RaggedBincount(splits=[7,8], values= [5, 16, 51, 76, 29, 27, 54, 95],\ size= 59, weights= [0, 0, 0, 0, 0, 0, 0, 0],\ binary_output=False) ``` This will cause a read from outside the bounds of the `splits` tensor buffer in the [implementation of the `RaggedBincount` op](https://github.com/tensorflow/tensorflow/blob/8b677d79167799f71c42fd3fa074476e0295413a/tensorflow/core/kernels/bincount_op.cc#L430-L446): ```cc for (int idx = 0; idx < num_values; ++idx) { while (idx >= splits(batch_idx)) { batch_idx++; } ... if (bin < size) { if (binary_output_) { out(batch_idx - 1, bin) = T(1); } else { T value = (weights_size > 0) ? weights(idx) : T(1); out(batch_idx - 1, bin) += value; } } } ``` Before the `for` loop, `batch_idx` is set to 0. The attacker sets `splits(0)` to be 7, hence the `while` loop does not execute and `batch_idx` remains 0. This then results in writing to `out(-1, bin)`, which is before the heap allocated buffer for the output tensor. ### Patches We have patched the issue in GitHub commit [eebb96c2830d48597d055d247c0e9aebaea94cd5](https://github.com/tensorflow/tensorflow/commit/eebb96c2830d48597d055d247c0e9aebaea94cd5). The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2 and TensorFlow 2.3.3, as these are also affected. ### 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:H/PR:L/UI:N/S:U/C:N/I:N/A:L

Severity from

GitHub (reviewed advisory)

Weakness

CWE-787

Also known as

BIT-tensorflow-2021-29514, CVE-2021-29514, PYSEC-2021-151, PYSEC-2021-442, PYSEC-2021-640

• github.com/tensorflow/tensorflow/security/advisories/GHSA-8h46-5m9h-7553
• nvd.nist.gov/vuln/detail/CVE-2021-29514
• github.com/tensorflow/tensorflow/commit/eebb96c2830d48597d055d247c0e9aebaea94cd5
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-442.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-640.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-151.yaml
• github.com/tensorflow/tensorflow