mount-move-test.c

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sched.h>
#include <unistd.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/wait.h>

void error (const char *func) {
  perror (func);
  exit (1);
}

int child (void *arg) {
  if (mount (0, "/", 0, MS_REC | MS_PRIVATE, 0))
    error ("mount[1]");
  if (mount (".", ".", 0, MS_BIND, 0))
    error ("mount[2]");
  if (chdir ("/bin"))
    error ("chdir[2]");
  if (mount (".", "/", 0, MS_MOVE, 0))
    error ("mount[3]");
  system ("ls /");
  return 0;
}

#define CHILD_STACK_SIZE (1 << 13)

int main () {
  if (chdir ("/bin"))
    error ("chdir[1]");
  char *child_stack = malloc(CHILD_STACK_SIZE);
  if (child_stack == 0)
    error ("malloc");
  int child_pid = clone (child, child_stack + CHILD_STACK_SIZE, CLONE_NEWNS | CLONE_NEWUSER | SIGCHLD, 0);
  if (child_pid == -1)
    error ("clone");
  if (waitpid (child_pid, 0, 0) == -1)
    error ("waitpid");
  return 0;
}