Format Four

/*
 * phoenix/format-four, by https://exploit.education
 *
 * Can you affect code execution? Once you've got congratulations() to
 * execute, can you then execute your own shell code?
 *
 * Did you get a hair cut?
 * No, I got all of them cut.
 *
 */

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

#define BANNER \
  "Welcome to " LEVELNAME ", brought to you by https://exploit.education"

void bounce(char *str) {
  printf(str);
  exit(0);
}

void congratulations() {
  printf("Well done, you're redirected code execution!\n");
  exit(0);
}

int main(int argc, char **argv) {
  char buf[4096];

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

  if (read(0, buf, sizeof(buf) - 1) <= 0) {
    exit(EXIT_FAILURE);
  }

  bounce(buf);
}