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

[Casey Schaufler <casey@schaufler-ca.com>]

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

> Quoting Casey Schaufler (casey@schaufler-ca.com):
> > 
> > --- "Serge E. Hallyn" <serue@us.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@schaufler-ca.com