Fedora buildsys and SELinux

[Stephen Smalley]

On Tue, 2008-04-22 at 16:58 +0200, Tomas Mraz wrote:
> > Bill Nottingham wrote:
> > > James Morris (jmorris at namei.org) said: 
> > >>> * All the parties are here now needed to figure this out
> > >>> * Someone better than me is going to reply with specifics about what is
> > >>> not working in the buildsys
> > >>> * We all agree it's pretty important to get this figured out in a good
> > >>> way
> > >> Can you please explain specifically what the problem is?
> > > 
> > > You cannot create files in a chroot of a context not known by the
> > > host policy. This means that if your host is running RHEL 5, you are
> > > unable to compose any trees/images/livecds with SELinux enabled for
> > > later releases.
> > > 
> > > Bill
> > > 
> > > --
> > > fedora-selinux-list mailing list
> > > fedora-selinux-list at redhat.com
> > > https://www.redhat.com/mailman/listinfo/fedora-selinux-list
> > Just catching up on this email chain.
> > 
> > The far more insidious problem is the act of loading policy in the
> > chroot effects the kernel of the host.  So processes that are running in
> > the host become invalidated when the client loads a policy.  This
> > happens even in the case where you are building a chroot environment on
> > the SAME os.  Since the spec file is running semanage commands to modify
> > and add unconfined_t users, the unconfined processes of the parent and
> > potential labels become unknown to the kernel for a period of time,
> > which ends up labeling the files and processes as unlabeled_t.  When
> > this happens files labeled unlabeled_t can not be accesses by confined
> > process and if a process becomes unlabeled_t it will not be allowed any
> > access on the box, which can cause the process to crash or go into in
> > infinite loop.  If I build a livedvd, I end
> > 
> > setenforce 0
> > livedvd ...
> > load_policy
> > setenforce 1
> > And sometimes I still need to
> > fixfiles restore
> 
> Could it be solved by kernel preventing loading the policy when the
> process which tries that is in the chroot? It seems to me that it
> doesn't make any sense to allow that. Then with enabling creating files
> with a context unknown to the policy the machine could run in enforcing
> mode although the process which does the compose would of course have to
> be unconfined.

Why mount selinuxfs within the chroot at all?  Policy load isn't
possible without selinuxfs.

I had thought though that they wanted/needed to load the policy with
scope limited to children of rpm so that package scriptlets will run in
the correct domain and files created by them will be labeled as expected
for the image being built rather than based on the host policy.   Which
is rather complicated - it requires a per-process policy pointer and
some way to deal with files that may be visible both to scriptlets
within the chroot and to rpm and other processes outside of it.

-- 
Stephen Smalley
National Security Agency