linux: attempt to make rootfs private too

commit 6682432 introduced the
regression.  After that change, crun does not attempt anymore to make
the rootfs directory private but starts from its parent directory,
causing pivot_root to fail when the rootfs itself is a mountpoint.

Closes: containers#1514

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

src/libcrun/linux.c

@@ -2565,20 +2565,21 @@ make_parent_mount_private (const char *rootfs, libcrun_error_t *err)
     {
       int ret;
       errno = 0;
-      cleanup_close int parentfd = openat (rootfsfd, "..", O_PATH | O_CLOEXEC);
+      cleanup_close int parentfd = -1;
 
+      get_proc_self_fd_path (proc_path, rootfsfd);
+      ret = mount (NULL, proc_path, NULL, MS_PRIVATE, NULL);
+      if (ret == 0)
+        return 0;
+
+      parentfd = openat (rootfsfd, "..", O_PATH | O_CLOEXEC);
       if (parentfd < 0)
         {
           ret = faccessat (rootfsfd, "..", X_OK, AT_EACCESS);
           if (ret != 0)
             return crun_make_error (err, EACCES, "make `%s` private: a component is not accessible", rootfs);
         }
 
-      get_proc_self_fd_path (proc_path, parentfd);
-      ret = mount (NULL, proc_path, NULL, MS_PRIVATE, NULL);
-      if (ret == 0)
-        return 0;
-
       close_and_reset (&rootfsfd);
       rootfsfd = get_and_reset (&parentfd);
     }