CVE-2021-29614

一、漏洞信息
 漏洞编号：[CVE-2021-29614](https://nvd.nist.gov/vuln/detail/CVE-2021-29614)
 漏洞归属组件：tensorflow
 漏洞归属的版本：2.3.1
 CVSS V3.0分值：
  BaseScore：7.8 High
  Vector：CVSS：3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
 漏洞简述：
  TensorFlow is an end-to-end open source platform for machine learning. The implementation of `tf.io.decode_raw` produces incorrect results and crashes the Python interpreter when combining `fixed_length` and wider datatypes. The implementation of the padded version(https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc) is buggy due to a confusion about pointer arithmetic rules. First, the code computes(https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc#L61) the width of each output element by dividing the `fixed_length` value to the size of the type argument. The `fixed_length` argument is also used to determine the size needed for the output tensor(https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc#L63-L79). This is followed by reencoding code(https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc#L85-L94). The erroneous code is the last line above: it is moving the `out_data` pointer by `fixed_length * sizeof(T)` bytes whereas it only copied at most `fixed_length` bytes from the input. This results in parts of the input not being decoded into the output. Furthermore, because the pointer advance is far wider than desired, this quickly leads to writing to outside the bounds of the backing data. This OOB write leads to interpreter crash in the reproducer mentioned here, but more severe attacks can be mounted too, given that this gadget allows writing to periodically placed locations in memory. 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.
 漏洞公开时间：2021-05-14
 漏洞创建时间：2021-05-21 11:31:29
 漏洞详情参考链接：
  https://nvd.nist.gov/vuln/detail/CVE-2021-29614
 漏洞分析指导链接：
  https://gitee.com/openeuler/cve-manager/blob/master/doc/md/manual.md
二、漏洞分析结构反馈
 影响性分析说明：
  TensorFlow 是一个端到端的机器学习开源平台。当结合“fixed_length”和更宽的数据类型时，“tf.io.decode_raw”的实现会产生错误的结果并导致 Python 解释器崩溃。由于对指针运算规则的混淆，填充版本（https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc）的实现存在问题。首先，代码计算（https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc#L61）每个输出元素的宽度除以`fixed size_length`值类型参数的。`fixed_length` 参数也用于确定输出张量所需的大小（https://github. com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc#L63-L79）。接下来是重新编码代码（https://github.com/tensorflow/tensorflow/blob/1d8903e5b167ed0432077a3db6e462daf781d1fe/tensorflow/core/kernels/decode_padded_raw_op.cc#L85-L94）。错误的代码是上面的最后一行:它正在将 `out_data` 指针移动 `fixed_length * sizeof(T)` 字节，而它最多只从输入中复制 `fixed_length` 字节。这导致部分输入未被解码为输出。此外，由于指针前进比预期的要宽得多，这会很快导致写入到支持数据的边界之外。这个OOB写导致这里提到的复制器中的解释器崩溃，但也可以安装更严重的攻击，鉴于此小工具允许写入定期放置在内存中的位置。该修复将包含在 TensorFlow 2.5.0 中。我们还将在 TensorFlow 2.4.2、TensorFlow 2.3.3、TensorFlow 2.2.3 和 TensorFlow 2.1.4 上挑选此提交，因为它们也受到影响并且仍在支持范围内。
 openEuler评分：
  7.8
 Vector：CVSS：3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
 受影响版本排查(受影响/不受影响)：
  1.master(2.3.1):受影响
2.openEuler-21.03(2.3.1):受影响
3.openEuler-21.09(2.3.1):受影响

修复是否涉及abi变化(是/否)：
  1.master(2.3.1):否
2.openEuler-21.03(2.3.1):否
3.openEuler-21.09(2.3.1):否

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