C++: Fix struct field conflation in IR data flow #3501
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This cleans up the test results, which were confusing because functions like `sink` had multiple locations. There are some additional results now involving casts to `const char *` because previously it varied whether `sink` used `const`, and now it always does.
This test demonstrates that IR data flow conflates unrelated fields of a global struct-typed variable and that this bug is not present in the old AST-based implementation of `semmle.code.cpp.security.TaintTracking`.
The virtual-dispatch code for globals was missing any relationship between the union field access and the global variable, which meant it propagated function-pointer flow between any two fields of a global struct. This resulted in false positives from `cpp/tainted-format-string` on projects using SDL, such as WohlSoft/PGE-Project. In addition to fixing that bug, this commit also brings the code up to date with the new style of modeling flow through global variables: `DataFlow::Node.asVariable()`.
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Performance looks unchanged. |
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LGTM as it fixes a regression without performance issues. |
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I recommend reading this PR one commit at a time.
From the main commit:
The false positives can be seen on https://lgtm.com/rules/2159571090/alerts/ if you're lucky enough that WohlSoft/PGE-Project shows up at the top.
Cc @alexet as release manager. I've targeted this at 1.24 because it's a regression since 1.23 that could affect a lot of projects.