Re: [PATCH 0/3] Enable namespaced file capabilities

From: Serge E. Hallyn
Date: Fri Jun 23 2017 - 14:35:24 EST

Quoting Stefan Berger (stefanb@xxxxxxxxxxxxxxxxxx):
> On 06/23/2017 12:16 PM, Casey Schaufler wrote:
> >On 6/23/2017 9:00 AM, Serge E. Hallyn wrote:
> >>Quoting Amir Goldstein (amir73il@xxxxxxxxx):
> >>>On Thu, Jun 22, 2017 at 9:59 PM, Stefan Berger
> >>><stefanb@xxxxxxxxxxxxxxxxxx> wrote:
> >>>>This series of patches primary goal is to enable file capabilities
> >>>>in user namespaces without affecting the file capabilities that are
> >>>>effective on the host. This is to prevent that any unprivileged user
> >>>>on the host maps his own uid to root in a private namespace, writes
> >>>>the xattr, and executes the file with privilege on the host.
> >>>>
> >>>>We achieve this goal by writing extended attributes with a different
> >>>>name when a user namespace is used. If for example the root user
> >>>>in a user namespace writes the security.capability xattr, the name
> >>>>of the xattr that is actually written is encoded as
> >>>>security.capability@uid=1000 for root mapped to uid 1000 on the host.
> >>>>When listing the xattrs on the host, the existing security.capability
> >>>>as well as the security.capability@uid=1000 will be shown. Inside the
> >>>>namespace only 'security.capability', with the value of
> >>>>security.capability@uid=1000, is visible.
> >>>>
> >>>Am I the only one who thinks that suffix is perhaps not the best grammar
> >>>to use for this namespace?
> >>You're the only one to have mentioned it so far.
> >>
> >>>xattrs are clearly namespaced by prefix, so it seems right to me to keep
> >>>it that way - define a new special xattr namespace "ns" and only if that
> >>>prefix exists, the @uid suffix will be parsed.
> >>>This could be either or
> >>> The latter seems more correct to me,
> >>>because then we will be able to namespace any xattr without having to
> >>>protect from "unprivileged xattr injection", i.e.:
> >>>setfattr -n ""
> >>I like it for simplifying the parser code. One concern I have is that,
> >>since ns.* is currently not gated, one could write ns.* on an older
> >>kernel and then exploit it on a newer one.
> >security.ns.capability@uid=1000, then?
> Imo, '.ns' is redundant and 'encoded' in the '@'.

So how about
security.@uid=1000@@capability ?

Maybe it's not worth it.