linux-kernel - Re: [PATCH 0/2] file capabilities: two bugfixes

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Date:	Fri, 8 Dec 2006 14:08:57 -0800 (PST)
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>,
	Casey Schaufler <casey@...aufler-ca.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH 0/2] file capabilities: two bugfixes


--- "Serge E. Hallyn" <serue@...ibm.com> wrote:

> Quoting Casey Schaufler (casey@...aufler-ca.com):
> > 
> > --- "Serge E. Hallyn" <serue@...ibm.com> wrote:
> > 
> > > ...
> > > The other is that root can lose capabilities by
> > > executing files with
> > > only some capabilities set.  The next two
> patches
> > > change these
> > > behaviors.
> > 
> > It was the intention of the POSIX group that
> > capabilities be independent of uid. I would
> > argue that the old bevavior was correct, that
> > a program marked to lose a capability ought
> > to even if the uid is 0.
> 
> Agreed, and if SECURE_NOROOT is set, that is what
> happens.
> But by default SECURE_NOROOT is not set, in which
> case linux's
> implementation of capabilities behaves differently
> for root.
> 
> Without this latest patch, with SECURE_NOROOT not
> set, what was
> actually happening was that the kernel behaved as
> though
> SECURE_NOROOT was not set so long as there was no
> security.capability xattr, and always behaved as
> though
> SECURE_NOROOT was set if there was an xattr.  That's
> inconsistent
> and confusing behavior.
> 
> The worst part is that root can get around running
> the code
> with limited caps by just copying the file and
> running the
> copy.  So it adds no security benefit, and adds an
> inconsistency/complication which could cause
> security risks.

OK, no worries then.


Casey Schaufler
casey@...aufler-ca.com
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