netdev - Re: [Bug #11500] /proc/net bug related to selinux

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Date:	Fri, 19 Sep 2008 13:07:45 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	david@...g.hm
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Moore <paul.moore@...com>, jmorris@...ei.org, rjw@...k.pl,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	netdev@...r.kernel.org, Eric Paris <eparis@...isplace.org>
Subject: Re: [Bug #11500] /proc/net bug related to selinux


On Fri, 2008-09-19 at 09:58 -0700, david@...g.hm wrote:
> On Thu, 18 Sep 2008, Stephen Smalley wrote:
> 
> > On Thu, 2008-09-18 at 11:09 -0700, Eric W. Biederman wrote:
> >> Stephen Smalley <sds@...ho.nsa.gov> writes:
> >>
> >>> On Thu, 2008-09-18 at 08:38 -0400, Stephen Smalley wrote:
> >>>> I do however think that the mantra that we can't require users to update
> >>>> policy for kernel changes is unsupportable in general.  The precise set
> >>>> of permission checks on a given operation is not set in stone and it is
> >>>> not part of the kernel/userland interface/contract.  Policy isn't
> >>>> "userspace"; it governs what userspace can do, and it has to adapt to
> >>>> kernel changes.
> >>>
> >>> I should note here that for changes to SELinux, we have gone out of our
> >>> way to avoid such breakage to date through the introduction of
> >>> compatibility switches, policy flags to enable any new checks, etc
> >>> (albeit at a cost in complexity and ever creeping compatibility code).
> >>> But changes to the rest of the kernel can just as easily alter the set
> >>> of permission checks that get applied on a given operation, and I don't
> >>> think we are always going to be able to guarantee that new kernel + old
> >>> policy will Just Work.
> >>
> >> I know of at least 2 more directories that I intend to turn into
> >> symlinks into somewhere under /proc/self.  How do we keep from
> >> breaking selinux policies when I do that?
> >
> > I suspect we could tweak the logic in selinux_proc_get_sid() to always
> > label all symlinks under /proc with the base proc_t type already used
> > for e.g. /proc/self, at which point existing policies would be ok.
> 
> so if proc is mounted anywhere other then /proc the selinux policy would 
> do odd things?

No, the logic doesn't care where proc is mounted.  Only the name
relative to the root of proc is used.

-- 
Stephen Smalley
National Security Agency

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