[PATCH] D31650: [Analyzer] Detect when function pointer is freed

[Anders Rönnholm via Phabricator via cfe-commits]

AndersRonnholm created this revision.

The MallocChecker does not currently detect freeing of function pointers.

Example code.

  void (*fnptr)(int);
  void freeIndirectFunctionPtr() {
    void *p = (void*)fnptr;
    free(p); // expected-warning {{Argument to free() points to a function pointer}}
  }


Repository:
  rL LLVM

https://reviews.llvm.org/D31650

Files:
  lib/StaticAnalyzer/Checkers/MallocChecker.cpp
  test/Analysis/malloc.c


Index: test/Analysis/malloc.c
===================================================================
--- test/Analysis/malloc.c
+++ test/Analysis/malloc.c
@@ -1774,6 +1774,16 @@
    return ok; // no warning
 }
 
+void (*fnptr)(int);
+void freeIndirectFunctionPtr() {
+  void *p = (void*)fnptr;
+  free(p); // expected-warning {{Argument to free() points to a function pointer}}
+}
+
+void freeFunctionPtr() {
+  free((void*)fnptr); // expected-warning {{Argument to free() is a function pointer}}
+}
+
 // ----------------------------------------------------------------------------
 // False negatives.
 
Index: lib/StaticAnalyzer/Checkers/MallocChecker.cpp
===================================================================
--- lib/StaticAnalyzer/Checkers/MallocChecker.cpp
+++ lib/StaticAnalyzer/Checkers/MallocChecker.cpp
@@ -392,6 +392,10 @@
   void ReportUseZeroAllocated(CheckerContext &C, SourceRange Range,
                               SymbolRef Sym) const;
 
+  void ReportFunctionPointerFree(CheckerContext &C, SVal ArgVal,
+                                 SourceRange Range, const Expr *DeallocExpr,
+                                 const Expr *ArgExpr) const;
+
   /// Find the location of the allocation for Sym on the path leading to the
   /// exploded node N.
   LeakInfo getAllocationSite(const ExplodedNode *N, SymbolRef Sym,
@@ -1516,6 +1520,12 @@
     }
   }
 
+  if (SymBase->getType()->isFunctionPointerType()) {
+    ReportFunctionPointerFree(C, ArgVal, ArgExpr->getSourceRange(), ParentExpr,
+                              ArgExpr);
+    return nullptr;
+  }
+
   ReleasedAllocated = (RsBase != nullptr) && (RsBase->isAllocated() ||
                                               RsBase->isAllocatedOfSizeZero());
 
@@ -1976,6 +1986,47 @@
   }
 }
 
+void MallocChecker::ReportFunctionPointerFree(CheckerContext &C, SVal ArgVal,
+                                              SourceRange Range,
+                                              const Expr *DeallocExpr,
+                                              const Expr *ArgExpr) const {
+
+  if (!ChecksEnabled[CK_MallocChecker])
+    return;
+
+  Optional<MallocChecker::CheckKind> CheckKind =
+      getCheckIfTracked(C, DeallocExpr);
+  if (!CheckKind.hasValue())
+    return;
+
+  if (ExplodedNode *N = C.generateErrorNode()) {
+    if (!BT_BadFree[*CheckKind])
+      BT_BadFree[*CheckKind].reset(
+          new BugType(CheckNames[*CheckKind], "Bad free", "Memory Error"));
+
+    SmallString<100> Buf;
+    llvm::raw_svector_ostream Os(Buf);
+
+    const MemRegion *MR = ArgVal.getAsRegion();
+    while (const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(MR))
+      MR = ER->getSuperRegion();
+
+    Os << "Argument to ";
+    if (!printAllocDeallocName(Os, C, DeallocExpr))
+      Os << "deallocator";
+
+    if (ArgExpr->IgnoreParenCasts()->getType()->isFunctionPointerType())
+      Os << " is a function pointer";
+    else
+      Os << " points to a function pointer";
+
+    auto R = llvm::make_unique<BugReport>(*BT_BadFree[*CheckKind], Os.str(), N);
+    R->markInteresting(MR);
+    R->addRange(Range);
+    C.emitReport(std::move(R));
+  }
+}
+
 ProgramStateRef MallocChecker::ReallocMem(CheckerContext &C,
                                           const CallExpr *CE,
                                           bool FreesOnFail,


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