On Fri, Jan 29, 2016 at 01:31:51AM -0600, Serge E. Hallyn wrote: > On Wed, Jan 27, 2016 at 04:36:02PM -0800, Andy Lutomirski wrote: > > On Wed, Jan 27, 2016 at 9:22 AM, Jann Horn <jann@xxxxxxxxx> wrote: > > > I think it sounds good from a security perspective. > > > > I'm a bit late to the game, but I have a question: why should this be > > keyed to the *root* uid of the namespace in particular? Certainly if > > user foo trusts the cap bits on some file, then user foo might trust > > those caps to be exerted over any namespace that user foo owns, since > > user foo owns the namespace. > > ... Tying it to a kuid which represents the userns->owner of any > namespace in which the capability will be honored might be fine > with me. Is that what you mean? So if uid 1000 creates a userns > mapping uids 100000-200000, and 100000 in that container puts X=pe > on /bin/foo, uid 101000 in that container runs /bin/foo with privilege > X. Uid 101000 in someone else's container does not. > > Although, if I create two containers and provide them different > uidmaps, it may well be because I want them segragated and want > to minimize the changes of one container breaking out into the > other. This risks breaking that. Thinking differently now... I really want it to "just work" to tar and untar these. So I'm thinking of simply using the file owner as the uid. So to write a security.ns_capability xattr, you must be uid 0 in the inode's namespace, the file must be owned by uid 0, and the capabilities in the xattr will be honored for any namespace where in that uid_t 0 is root. Does that sound overly restrictive? I expect file capabilities to be used on files owned by root but not setuid-root, so I think it is ok. -serge -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
