Re: [PATCH v3 4/4] Allow unprivileged chroot when safe

[Colin Walters <walters@verbum.org>]

On Mon, 2012-01-30 at 14:10 -0800, Andy Lutomirski wrote:
> On Mon, Jan 30, 2012 at 1:58 PM, Colin Walters <walters@verbum.org> wrote:
> > On Mon, 2012-01-30 at 08:17 -0800, Andy Lutomirski wrote:
> >> Chroot can easily be used to subvert setuid programs.  If no_new_privs,
> >> then setuid programs don't gain any privilege, so allow chroot.
> >
> > Is this needed/desired by anyone now, or are you just using it to "demo"
> > NO_NEW_PRIVS?  I don't see it as very useful on its own, since in any
> > "container"-type chroot you really want /proc and /dev, and your patch
> > doesn't help with that.
> 
> It's a demo, but it could still be useful for container-ish things.
> If something privileged sets up /proc, /sys, and /dev, then
> unprivileged code can chroot into the container.  This would allow
> much simpler implementations of tools like schroot.

What's the win if you still need a setuid binary?  schroot (and my
linux-user chroot binary) can just as easily call chroot as they can
create bind mounts; I'm not buying a code complexity argument.

> With this change, they wouldn't need to start privileged.
> (Admittedly, this isn't a great argument for this patch.)

Right...I'm not aware of anyone who would find that useful.