Re: [RFC][PATCH 0/3] vfs: Detach mounts on unlink.

[Linus Torvalds]

On Sat, Oct 5, 2013 at 5:18 PM, Rob Landley <rob@xxxxxxxxxxx> wrote:
>
> Which is why containers have all sorts of extra plumbing. But that extra
> plumbing is currently built on pivot_root(), not on chroot(). And I'd
> dismissed pivot_root() as residue from initramfs with all that kernel thread
> reparenting, so it seemed like the wrong tool for the job, but obviously
> I'll take your and Al's word it's not...

Yeah, chroot() really doesn't cut it if you allow root access - and
thus internal chroot() calls - as you noticed (I didn't realize that
your example was meant to be run _inside_ a chroot).

There are generally other ways to escape chroot too if you're root.
It's just too hard to plug. That doesn't make chroot() useless - it
just means that the uses are elsewhere (it's useful for various
non-security issues like development environments, but it can also be
useful as one small _part_ of some bigger model, like a VM etc).

pivot_root() does end up being a "better chroot than chroot" if you're
looking for containment. It may not be a pretty system call, but it
does avoid at least the most obvious gotchas with chroot()..

            Linus
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