malloc() and free()

#include <stdlib.h>

int * b;

int main(void)
{
    int * a = NULL;
    a = (int *) malloc(sizeof(int));
    b = &a;
    free(b);
    return 0;
}

Would this result in a memory leak? If yes, why?

there is no memory leak OP. a and b points to the same memory. once you free one of them that memory location is unallocated and both pointers are invalid.