[clang] [StaticAnalyzer][MallocChecker] Detect use-after-free for field address (e.g., &ptr->field) (PR #152462)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (LoboQ1ng)

<details>
<summary>Changes</summary>

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
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;

``````````

</details>


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