Hi. Unprivileged users already can do chroot. He should simply create userns and then call "chroot" inside. As an LWN commenter noted, you can simply run "unshare -r /usr/sbin/chroot some-dir". (I recommend reading all comments: https://lwn.net/Articles/849125/ .)
Also: if you need chroot for path resolving only, consider openat2 with RESOLVE_IN_ROOT ( https://lwn.net/Articles/796868/ ). == Askar Safin https://github.com/safinaskar
