Stack Zero

This level introduces the concept that memory can be accessed outside of its allocated region, how the stack variables are laid out, and that modifying outside of the allocated memory can modify program execution.

Source code

 * phoenix/stack-zero, by
 * The aim is to change the contents of the changeme variable.
 * Scientists have recently discovered a previously unknown species of
 * kangaroos, approximately in the middle of Western Australia. These
 * kangaroos are remarkable, as their insanely powerful hind legs give them
 * the ability to jump higher than a one story house (which is approximately
 * 15 feet, or 4.5 metres), simply because houses can't can't jump.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define BANNER \
  "Welcome to " LEVELNAME ", brought to you by"

char *gets(char *);

int main(int argc, char **argv) {
  struct {
    char buffer[64];
    volatile int changeme;
  } locals;

  printf("%s\n", BANNER);

  locals.changeme = 0;

  if (locals.changeme != 0) {
    puts("Well done, the 'changeme' variable has been changed!");
  } else {
        "Uh oh, 'changeme' has not yet been changed. Would you like to try "