linux-kernel - Re: [PATCH RFC] allow some kernel filesystems to be mounted in a user namespace

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Date:	Tue, 16 Jul 2013 21:39:00 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Al Viro <viro@...IV.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] allow some kernel filesystems to be mounted in a
 user namespace

Quoting Serge E. Hallyn (serge@...lyn.com):
> Quoting Andy Lutomirski (luto@...capital.net):
> > On 07/16/2013 12:50 PM, Serge E. Hallyn wrote:
> > > Quoting Al Viro (viro@...IV.linux.org.uk):
> > >> On Tue, Jul 16, 2013 at 02:29:20PM -0500, Serge Hallyn wrote:
> > >>> All the files will be owned by host root, so there's no security
> > >>> concern in allowing this.
> > >>
> > >> Files owned by root != very bad things can't be done by non-root.
> > >> Especially for debugfs, which is very much a "don't even think about
> > >> mounting that on a production box" thing...
> > > 
> > > I would prefer it not be mounted.  But near as I can tell there
> > > should be no regression security-wise whether an unprivileged
> > > user on the host has access to it, or whether a user in a
> > > non-init user ns is allowed to mount it.  (Obviously I could very
> > > well be wrong)
> > 
> > I would argue that either (a) debugfs denies everything to non-root, so
> > mounting it in a (rootless) userns is useless or (b) it doesn't, in
> > which case it's dangerous.
> > 
> > In neither case does it make sense to me to allow the mount.
> 
> It makes sense from the POV of having sane user-space.  I can obviously
> work around this by tweaking a stock container rootfs to be different
> from a stock host rootfs.  It is undesirable.

(s/It/But that/)
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