Changing policies, using enforcing=0 the first time

[Forrest Taylor]

On Fri, 2008-02-08 at 10:39 -0500, Stephen Smalley wrote:
> 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.

Ah, that makes sense.  Just for future reference, I can change policies
without setting permissive mode by changing the context to shlib_t on
the following:

/lib/libblkid.so*
/lib/libc.so*
/lib/libdevmapper.so*
/lib/libdl.so*
/lib/libselinux.so*
/lib/libsepol.so
/lib/libtermcap.so*
/lib/libuuid.so*

These came from the shared libraries needed for init, mount and sh.
Once those are changed, the system can get far enough through rc.sysinit
to run fixfiles.

Thanks for the help,

Forrest
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