Changing policies, using enforcing=0 the first time

[Stephen Smalley]

On Fri, 2008-02-08 at 08:20 -0700, Forrest Taylor wrote:
> On Fri, 2008-02-08 at 09:54 -0500, Stephen Smalley wrote:
> > On Fri, 2008-02-08 at 07:42 -0700, Forrest Taylor wrote:
> > > I am running into a strange occurrence running RHEL5.1 with an updated
> > > policy (2.4.6-106.el5_1.3).  By default, it runs the targeted policy.  I
> > > install the mls and the strict policy and touch /.autorelabel.  The
> > > first time that I boot to one of these other policies, I get a kernel
> > > panic, and I have to use enforcing=0.  The strange thing is that I can
> > > then go back and forth between any policy without setting permissive
> > > mode--that is, I only have to set enforcing=0 the first time that I make
> > > a policy change, but subsequent times it is not required.  Does fixfiles
> > > change something the first time that allows the relabel to work
> > > subsequent times in enforcing mode?  Any thoughts?
> > 
> > IIRC, RHEL5 still had separate shlib_t vs. lib_t types in the strict/mls
> > policies, which means that when you first switch from targeted, you
> > can't execute shared objects in enforcing mode until you've first
> > relabeled.  targeted policy aliases them into a single type, and
> > upstream policy has done away with the distinction now as well, I
> > believe.
> > 
> > So, on the first conversion, the xattrs get reset from lib_t to shlib_t,
> > then they stay that way because targeted views them as identical.
> 
> AH!  I knew it was something like that.  I couldn't find the difference
> because shlib_t is a typealias to lib_t, so it always shows lib_t.
> 
> Is there any way in the targeted policy to verify that it actually is
> shlib_t instead of lib_t?  It obviously must have some difference for
> strict/mls to work.

No, the kernel canonicalizes the context to the policy's native form
before returning it via getxattr.  That was introduced to accomodate the
transition from non-MCS/MLS to MCS/MLS, so that the kernel could
auto-magically add the MCS/MLS field for files on filesystems created
under the older policy (e.g. for going from RHEL4 -> RHEL5).  But it
also means that even if the on-disk xattr has shlib_t, the kernel will
return lib_t under targeted policy due to the canonicalization.


-- 
Stephen Smalley
National Security Agency