UninitializedPtrField (Windows Driver CodeQL Query)

Overview

A pointer field which was not initialized during or since class construction will cause a null pointer dereference.

Recommendation

Make sure to initialize all pointer fields before usage.

Example

The following example shows a scenario where the field ptr_ is not initialized and later dereferenced:

template <typename T>
class ComPtr
{
public:
	T* ptr_;
	ComPtr() throw() : ptr_(nullptr)
	{
	}
	ComPtr(T* ptr) throw() : ptr_(ptr)
	{
	}
	T* operator->() const throw()
	{
		return ptr_;
	}
	void set(T* ptr) {
		ptr_ = ptr;
	}
	T** addr() {
		return &ptr_;
	}
};

class Test
{
public:
	int it_;
	int it() {
		return it_;
	}
};
void test() {
	Test t;
	int val;
	ComPtr<Test> ptr;
	// BAD: pointer is not initialized here
	val = ptr->it();
}

To correct the problem, we set the field before usage:

template <typename T>
class ComPtr
{
public:
	T* ptr_;
	ComPtr() throw() : ptr_(nullptr)
	{
	}
	ComPtr(T* ptr) throw() : ptr_(ptr)
	{
	}
	T* operator->() const throw()
	{
		return ptr_;
	}
	void set(T* ptr) {
		ptr_ = ptr;
	}
	T** addr() {
		return &ptr_;
	}
};
class Test
{
public:
	int it_;
	int it() {
		return it_;
	}
};
void test() {
	Test t;
	int val;
	ComPtr<Test> ptr2(&t);
	// GOOD: pointer was initialized
	val = ptr2->it();
	ComPtr<Test> ptr3;
	ptr3.set(&t);
	// GOOD: pointer was set in between
	val = ptr3->it();
}

Additional Details

This query can be found in the Microsoft GitHub CodeQL repository. See the CodeQL and the Static Tools Logo Test page for details on how Windows Driver developers can download and run CodeQL.