selinux + livecd-creator, May 20, 2008

[Stephen Smalley]

On Tue, 2008-05-27 at 16:25 -0400, Eric Paris wrote:
> On Tue, 2008-05-20 at 16:10 -0400, Eric Paris wrote:
> > On Tue, 2008-05-20 at 15:33 -0400, Stephen Smalley wrote:
> > > On Tue, 2008-05-20 at 15:12 -0400, Eric Paris wrote:
> > > > ***passwd:
> > > > running a system with selinux enforcing/permissive (doesn't matter) and
> > > > attempting to run livecd-creator with selinux --disabled results in
> > > > passwd espoloding.  passwd called is_selinux_enabled() which says yes
> > > > since /proc/mounts has an selinuxfs and the passwd calls
> > > > selinux_enforcing() which explodes when it can't find
> > > > a /selinux/enforce.  First discussion was to change /proc/mounts to hide
> > > > the selinuxfs, sounds like a good plan until I realize /proc/mounts is
> > > > actually link to /proc/self/mounts and that its getting way to complex
> > > > tying to set up FS namespaces or whatever this is going to take.  Right
> > > > now I'm thinking of creating a /selinux with enforce=0 in all cases
> > > > inside the chroot, anyone see a problem with that?  (I could also work
> > > > on fixing passwd, but i'm trying to be as 'backwards compatible' as
> > > > possible....
> > > 
> > > Wait - you are confusing /proc/mounts and /proc/filesystems.
> > 
> > You are (once again) correct.  Should be a lot easier to lie to  :)
> 
> I feel vindicated, I knew I saw that /proc/mounts was part of it....
> 
> init_selinuxmnt() is going to go through /proc/mounts inside the chroot
> and find an selinuxfs mounted back out on the host system.  I think this
> in turn is going to cause is_selinux_enabled() to return that selinux is
> in fact enabled.  No proof but what i know for sure is that
> 
> cat /proc/filesystems | grep -v selinux > /tmp.filesystems
> mount -o bind /tmp.filesystems /chroot/proc/filesystems
> 
> still caused passwd to fail because it thought selinux was enabled....

Ah, yes - the optimization by Steve G changed is_selinux_enabled() to
first check for a selinux_mnt previously set upon library init and uses
that as indication of being enabled if present; otherwise, it falls back
to checking /proc/filesystems.

Regardless, as long as you create /selinux/enforce == 0, you're ok with
passwd, right?

-- 
Stephen Smalley
National Security Agency