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Re: [libvirt] [PATCH] Fix a compilation problem with LXC drop capabilities



On Tue, Jun 02, 2009 at 11:15:58AM +0900, Ryota Ozaki wrote:
> On Mon, Jun 1, 2009 at 6:24 PM, Daniel P. Berrange <berrange redhat com> wrote:
> > On Fri, May 29, 2009 at 04:42:54PM -0500, Serge E. Hallyn wrote:
> >> Quoting Ryota Ozaki (ozaki ryota gmail com):
> >> > On Fri, May 29, 2009 at 9:20 PM, Daniel Veillard <veillard redhat com> wrote:
> >>
> >> Hmm, yeah but note that often userspace is out of date with respect to
> >> "recent" new kernel-related defines.  I do a lot of testing on a rhel
> >> 5.3 partition with spanking-new kernels, so rare is the time that I
> >> don't have to do
> >>
> >> #ifndef PR_CAPBSET_DROP
> >> #define PR_CAPBSET_DROP 24
> >> #endif
> >>
> >> and same for clone flags (CLONE_NEWIPC), securebits, capabilities,
> >> etc.
> >>
> >> So if the prctl(PR_CAPBSET_DROP) returns -ENOSYS then absolutely I
> >> agree,
> >
> > This makes sense as a way to deal with this problem, since it matches
> > what we already do with the various CLONE_XXX & MOUNT_XXX flags too.
> 
> That convinces me too.
> 
> > NB, in the not too distant future I'm going to submit code for making
> > the libvirtd daemon drop alot of its capabilities, including clearing
> > the bounding set to prevent inheritance by any child processes except
> > in required circumstances. For that I'll likely use libcap-ng so we
> > will be able to stop callin prctl() directly in the LXC driver.
> 
> Oh, good. Will the new facility allow us to specify which capabilities
> to be dropped in a XML file or somewhere? Or the set of caps will be
> hard-coded?

That's TBD.  My currently proof of concept code is to restrict the set
of capabilities to just those required by the libvirtd daemon itself.
LXC is an interesting problem, because inside the container, you could
argue that it should just get all capabilities. This would assume the 
container prevented use of the caapbilities impacting things outside
the container.

Daniel
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