On Tue, Jul 21, 2020 at 06:28:10PM +0200, Christoph Hellwig wrote:

+int __init init_chroot(const char *filename)
+{
+	struct path path;
+	int error;
+
+	error = kern_path(filename, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
+	if (error)
+		return error;
+	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);

Matter of taste, but if we do that, I wonder if we would be better off with
	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
	if (!error && !ns_capable(current_user_ns(), CAP_SYS_CHROOT))
		error = -EPERM;
	if (!error)
		error = security_path_chroot(&path);
	if (!error)
		set_fs_root(current->fs, &path);
	path_put(&path);
	return error;