Error: heap-use-after-free

Address Sanitizer Error: Use of deallocated memory

We show three examples where storage in the heap can be allocated via malloc, realloc (C), and new (C++), along with a mistaken use of volatile.

Example - malloc

// example1.cpp
// heap-use-after-free error
#include <stdlib.h>

int main() {
  char *x = (char*)malloc(10 * sizeof(char));
  free(x);

  // ...

  return x[5];   // Boom!
}

To build and test this example, run these commands in a Visual Studio 2019 version 16.9 or later developer command prompt:

cl example1.cpp /fsanitize=address /Zi
devenv /debugexe example1.exe

Resulting error

Example - operator new

// example2.cpp
// heap-use-after-free error
#include <windows.h>

int main() {
  char *buffer = new char[42];
  delete [] buffer;

  // ...

  buffer[0] = 42;  // Boom!
  return 0;
}

To build and test this example, run these commands in a Visual Studio 2019 version 16.9 or later developer command prompt:

cl example2.cpp /fsanitize=address /Zi
devenv /debugexe example2.exe

Resulting error - operator new

Example - realloc

// example3.cpp
// heap-use-after-free error
#include <malloc.h>

int main() {
  char *buffer = (char*)realloc(0, 42);
  free(buffer);

  // ...

  buffer[0] = 42;  // Boom!
  return 0;
}

To build and test this example, run these commands in a Visual Studio 2019 version 16.9 or later developer command prompt:

cl example3.cpp /fsanitize=address /Zi
devenv /debugexe example3.exe

Resulting error - realloc

Example - volatile

// example4.cpp
// heap-use-after-free error
#include <stdlib.h>

int main() {

  volatile char *x = (char*)malloc(sizeof(char));
  free((void*)x);

      //...

  *x = 42;        // Boom!
}

To build and test this example, run these commands in a Visual Studio 2019 version 16.9 or later developer command prompt:

cl example4.cpp /fsanitize=address /Zi
devenv /debugexe example4.exe

Resulting error - volatile

See also

AddressSanitizer overview
AddressSanitizer known issues
AddressSanitizer build and language reference
AddressSanitizer runtime reference
AddressSanitizer shadow bytes
AddressSanitizer cloud or distributed testing
AddressSanitizer debugger integration
AddressSanitizer error examples