[analyzer] Detect use-after-free for field address (e.g., &ptr->field)

[LoboQ1ng]

This patch improves MallocChecker to detect use-after-free bugs when
a freed structure's field is passed by address (e.g., &ptr->field).

Previously, MallocChecker would miss such cases, as it only checked the top-level symbol of argument values.
This patch analyzes the base region of arguments and extracts the symbolic region (if any), allowing UAF detection even for field address expressions.

Fixes #152446

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[llvmbot]

@llvm/pr-subscribers-clang-static-analyzer-1

@llvm/pr-subscribers-clang

Author: None (LoboQ1ng)

Changes

This patch improves MallocChecker to detect use-after-free bugs when
a freed structure's field is passed by address (e.g., &ptr->field).

Previously, MallocChecker would miss such cases, as it only checked the top-level symbol of argument values.
This patch analyzes the base region of arguments and extracts the symbolic region (if any), allowing UAF detection even for field address expressions.

---

Full diff: https://github.com/llvm/llvm-project/pull/152462.diff

1 Files Affected:

• (modified) clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp (+8-2)

diff --git a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
index 369d6194dbb65..ad1d20779f384 100644
--- a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
@@ -3156,8 +3156,14 @@ void MallocChecker::checkPreCall(const CallEvent &Call,
   for (unsigned I = 0, E = Call.getNumArgs(); I != E; ++I) {
     SVal ArgSVal = Call.getArgSVal(I);
     if (isa<Loc>(ArgSVal)) {
-      SymbolRef Sym = ArgSVal.getAsSymbol();
-      if (!Sym)
+      const MemRegion *MR = ArgSVal.getAsRegion();
+      if (!MR)
+        continue;
+      const MemRegion *BaseRegion = MR->getBaseRegion();
+      SymbolRef Sym = nullptr;
+      if (const auto *SR = dyn_cast<SymbolicRegion>(BaseRegion))
+        Sym = SR->getSymbol();
+      if (!Sym) 
         continue;
       if (checkUseAfterFree(Sym, C, Call.getArgExpr(I)))
         return;

[steakhal]

Hey, thanks for contributing!

I usually look at the tests before looking at the actual change. Could you demonstrate the improvement?
You can grep for files containing similar diagnostics under the clang/test/Analysis folder if you look for the report messages. Pick one file which seems relevant to add your tests to.

[LoboQ1ng]

Hey, thanks for contributing!

I usually look at the tests before looking at the actual change. Could you demonstrate the improvement? You can grep for files containing similar diagnostics under the clang/test/Analysis folder if you look for the report messages. Pick one file which seems relevant to add your tests to.

Okay, I’ve now submitted a new test at clang/test/Analysis/malloc-checker-arg-uaf.c. It should help illustrate the improvement I made.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[steakhal]

Thank you for your finding. It will be automatically merged once the CI bots are happy.
It seems like I'll need to come back to this and check if the bots are green, and merge the PR.

[github-actions]

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