Merge pull request github#5726 from MathiasVP/fix-false-positive-in-return-stack-allocated-memory-2

C++: Fix false positive in return stack allocated memory (second attempt)

Author: jbj

cpp/ql/src/Likely Bugs/Memory Management/ReturnStackAllocatedMemory.ql

@@ -13,6 +13,7 @@
 
 import cpp
 import semmle.code.cpp.dataflow.EscapesTree
+import semmle.code.cpp.models.interfaces.PointerWrapper
 import semmle.code.cpp.dataflow.DataFlow
 
 /**
@@ -39,6 +40,10 @@ predicate hasNontrivialConversion(Expr e) {
     e instanceof ParenthesisExpr
   )
   or
+  // A smart pointer can be stack-allocated while the data it points to is heap-allocated.
+  // So we exclude such "conversions" from this predicate.
+  e = any(PointerWrapper wrapper).getAnUnwrapperFunction().getACallToThisFunction()
+  or
   hasNontrivialConversion(e.getConversion())
 }
 

cpp/ql/test/query-tests/Likely Bugs/Memory Management/ReturnStackAllocatedMemory/test.cpp

@@ -189,3 +189,30 @@ int *&conversionInFlow() {
   int *&pRef = p; // has conversion in the middle of data flow
   return pRef; // BAD [NOT DETECTED]
 }
+
+namespace std {
+	template<typename T>
+	class shared_ptr {
+	public:
+		shared_ptr() noexcept;
+		explicit shared_ptr(T*);
+		shared_ptr(const shared_ptr&) noexcept;
+		template<class U> shared_ptr(const shared_ptr<U>&) noexcept;
+		template<class U> shared_ptr(shared_ptr<U>&&) noexcept;
+
+		shared_ptr<T>& operator=(const shared_ptr<T>&) noexcept;
+		shared_ptr<T>& operator=(shared_ptr<T>&&) noexcept;
+
+		T& operator*() const noexcept;
+		T* operator->() const noexcept;
+
+		T* get() const noexcept;
+	};
+}
+
+auto make_read_port()
+{
+  auto port = std::shared_ptr<int>(new int);
+  auto ptr = port.get();
+  return ptr; // GOOD
+}