#include <mutex>

class some_data {
  int a;
  std::string b;

public:
  void do_something() {}
};

class data_wrapper {
private:
  some_data data;
  std::mutex m;

public:
  template <typename Function>
  void process_data(Function func)
  {
    std::lock_guard<std::mutex> l(m);
    func(data);
  }
};

some_data* unprotected;

void
malicious_function(some_data& protected_data)
{
  unprotected = &protected_data;
}

data_wrapper x;

void
foo()
{
  x.process_data(malicious_function);
  unprotected->do_something();
}

int
main()
{
  foo();
}