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

>
> System daemons that do chroot for a modicum of security already start
> privileged, so this doesn't help them either.

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

It would be really nice to have unprivileged filesystem namespace
features, but that would be more complicated to do safely.

--Andy

>
>
>



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Andy Lutomirski
AMA Capital Management, LLC
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