current_in_userns
allow = current_in_userns(fc->user_ns);
current_in_userns(mnt->mnt_sb->s_user_ns);
if (!current_in_userns(fc->user_ns)) {
extern bool current_in_userns(const struct user_namespace *target_ns);
EXPORT_SYMBOL(current_in_userns);
if (!current_in_userns(file->f_path.mnt->mnt_sb->s_user_ns))