Re: [gentoo-dev] [PATCH] user.eclass: die if hard coded UID or GID is already in use

[Mike Gilbert]

On Tue, May 28, 2019 at 10:43 AM William Hubbs <williamh@g.o> wrote:
>
> On Tue, May 28, 2019 at 02:21:23AM -0400, Mike Gilbert wrote:
> > On Tue, May 28, 2019 at 1:41 AM Robin H. Johnson <robbat2@g.o> wrote:
> > >
> > > On Mon, May 27, 2019 at 08:44:09PM -0400, Mike Gilbert wrote:
> > > > On Mon, May 27, 2019 at 11:45 AM William Hubbs <williamh@g.o> wrote:
> > > > >
> > > > > If a package hard codes the UID or GID when adding a user or group to
> > > > > the system and that UID/GID already exists, we should abort rather than
> > > > > changing the UID/GID.
> > > > These functions have behaved this way for a long time.
> > > Yes, I recall this breakage being raised even prior to GLEP27.
> > >
> > > Some coverage of prior work firstly.
> > > 2003/May: eid_database [1]
> > > 2004/May: GLEP27 [2]
> > > 2006/Summer: GSOC Project for GLEP27 implementation [3]
> > > Later: Creandus [4][5]
> > >
> > > [1] https://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-src/eid_database/
> > > [2] https://www.gentoo.org/glep/glep-0027.html
> > > [3] https://github.com/creandus/creandus.github.com/blob/master/glep27-proposal.txt
> > > [4] https://github.com/creandus/
> > > [5] http://creandus.github.io/
> > >
> > > > What problem are you trying to solve here?
> > > Specifically:
> > > 1. Package A is emerged, and the ebuild specifies enewuser/enewgroup
> > > with -1 as the numeric input, and some user or group is created with
> > > value X.
> > > 2.  Package B is emerged, and the ebuild specifies enewuser/enewgroup
> > > with a fixed UID/GID value Y && explicitly depends on having that
> > > specific value.
> >
> > Could you provide some examples of packages that require a specific
> > numeric UID/GID to function properly? That seems like a significant
> > design flaw.
>
> The example I specifically found was kubernetes security contexts -- to
> set one of these up, you need numeric uids/gids [1].
>
> [1] https://kubernetes.io/docs/tasks/configure-pod-container/security-context/
>
> I agree this could be possibly seen as a flaw, but I don't know enough
> about kubernetes to know if symbolic uids/gids could be used.
>
> I am speculating here, but I'm guessing that if the pod spans
> multiple hosts, the uids/gids might need to be the same, which would
> require fixed UIDs/GIDs.

Your kubernetes example is not a very compelling one. Firstly, none of
the kubernetes-related ebuilds in the gentoo repo actually call
enewuser or enewgroup with a static id. Secondly, I would expect the
sysadmin of a kubernetes cluster to allocate a UID/GID range outside
the "system range" defined in /etc/login.defs.

> > As mgorny suggests, I suspect the static UID/GID that is sometimes
> > passed to enewuser/enewgroup is more of a preference/suggestion than a
> > requirement.
> >
> > I do not believe William's patch should be merged without some very
> > good reason for the change in behavior.
>
> Consider this situation:
>
> in package-a.ebuild:
> enewuser usera 300 ...
> enewgroup groupa 300 ...
>
> in package-b.ebuild:
> enewuser userb 300 ...
> enewgroup groupb 300 ...
>
> Ok, cool, if I need a security context for package b, the uid/gid is 300
> correct? Yes, unless package a gets installed on some host where package
> b is without me knowing about it.
>
> I see no way around this other than to make uids/gids fixed when
> packages request specific ones.

If you are running a cluster system that requires static ids, you
should really create these ids yourself as part of the cluster node
setup process.