`MEM53-CPP`: False positive due to flow through `realloc`

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评估

难度
4/5
预计耗时
3-5 天
新手友好度
30/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
停滞
技术栈
cpp
领域
devtools, testing-qa

调研方向

从 MEM53-CPP 测试用例和 taint-tracking 配置的 isSource 定义开始，然后审查与 realloc 流程变更相关的已链接 pull request。确定旧的基于 AST 的库如何处理 realloc，以及受影响的测试场景是否有效；完成的标准是在不接受关于重新分配新分配内存的不安全假设的情况下解决 false positive。

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描述

Difficulty-Medium false positive/false negative Impact-Low Stardard-CERT-C++
Affected rules
  • MEM53-CPP
Description

In https://github.com/github/codeql/pull/14637 we added taint-flow through the indirection of the pointer passed to realloc to the indirection of the result. That is, flow through the following example:

int* p = ...;
*p = tainted_value;
int* q = (int*)realloc(p, 1024);
sink(*p);

this relies on the new taint-tracking library to distinguish between the result of realloc(...), and the result of what realloc(...) points to. Since the old AST-based taint-tracking library cannot do this this results in a FP in the testcases for MEM53-CPP (that we accepted on the next branch here: https://github.com/github/codeql-coding-standards/pull/419)

The query already tries to rule out realloc cases by excluding them in the definition of the taint-tracking configuration's isSource, but to get this query back to not reporting a FP here a barrier on realloc would have to be inserted.

As @jketema points out the affected test is actually really sketchy since there’s no guarantee that memory allocated with new can safely be realloc'ed. So maybe this scenario should be thought about more carefully by someone on your team.

主要语言
CodeQL
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派生
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6 天 7 小时
30 天内合并 PR
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