Is it possible to exit the chroot(2) environment?

[Kyle Evans]

On Sun, Sep 27, 2020 at 2:03 PM Warner Losh <imp at bsdimp.com> wrote:
>
> On Sun, Sep 27, 2020 at 12:30 PM Yuri <yuri at rawbw.com> wrote:
>
> > This line
> >
> > https://github.com/rpm-software-management/rpm/blob/master/lib/rpmchroot.c#L155
> > calls chroot(".") in order to exit from the chroot environment.
> >
>
> Interesting. FreeBSD doesn't allow that.
>
>
> > It apparently succeeds on Linux (this is rpm), but it fails on FreeBSD
> > with "Operation not permitted", while executed under sudo.
> >
> > The chroot(2) man page doesn't mention anything about exiting the chroot
> > environment.
> >
>
> True. Such behavior is undefined. There's no defined notion of exiting a
> chroot. It doesn't seem to be documented in the few examples of the
> chroot(2) call linux man pages I've found. Do you have documentation on
> what, exactly, it's supposed to do?
>

I'm almost certain they just aren't restricting you from chrooting to
a directory out of the chroot if you have a reference to it, so it
probably does something like:

chdir("/");
chroot("/some/root");
/* Do stuff, but never chdir */
chroot("."); /* Working directory is still the real root. */

Thanks,

Kyle Evans