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RE: Detecting MLS mode



> From: Stephen Smalley [mailto:sds@xxxxxxxxxxxxx]
> Sent: 06 March 2012 15:21
> 
> On Tue, 2012-03-06 at 15:03 +0000, Moray Henderson wrote:
> > > From: Stephen Smalley [mailto:sds@xxxxxxxxxxxxx]
> > > Sent: 05 March 2012 20:16
> > >
> > > On Mon, 2012-03-05 at 17:26 +0000, Moray Henderson wrote:
> > > > Is there an easy way for a script to detect whether MLS mode is
> > > enabled?
> > > >
> > > > On CentOS 5 whether running normally or in Anaconda's rescue
> mode,
> > > > SELINUX=enforcing (or permissive), SELINUXTYPE=targeted, there is
> no
> > > > /etc/selinux/mls directory and cat /selinux/mls prints "1".
> > > >
> > > > However, with CentOS running normally a command to set a context
> > > works,
> > > > while from rescue mode the same command fails with "cannot setup
> > > default
> > > > context" unless I add and :s0 MLS piece.  That's fine when I'm
> doing
> > > things
> > > > manually, but  I'd like a script to detect whether it's being run
> in
> > > an
> > > > environment that needs the :s0 added.  I don't want to just add
> :s0
> > > all the
> > > > time, in case it's already there in the context string I'm trying
> to
> > > set.
> > >
> > > Technically you should always provide the MLS piece if /selinux/mls
> is
> > > 1
> > > (is_selinux_mls_enabled() in C or selinux.is_selinux_mls_enabled()
> in
> > > python).  The only reason you get away with not specifying it in
> > > multi-user mode is that mcstransd is running.
> >
> > Thanks Stephen.  So if /selinux/mls is 1 a suitable  way to fetch the
> full context of (say) everything in root whether we're in single or
> multi-user mode would be:
> >
> >   SUFFIX=`/bin/ps -C mcstransd > /dev/null && echo :s0`
> >   find / -maxdepth 1 -printf "%p:\t%Z${SUFFIX}\n"
> >
> > It won't be run on a system that actually uses MLS, so I can get away
> with hardwiring the :s0.
> 
> Maybe I'm misreading it, but the logic seems the opposite of what you
> want presently.> 
> Also, as a caveat, while CentOS 5 might be stripping the :s0 entirely
> when mcstrans is running, it appears that on modern Fedora (and thus
> likely CentOS 6), it is just translating it to :SystemLow.

This is CentOS 5-specific: looks like I'll have to rewrite all sorts of things when we go up to 6 :-)

What I'm aiming for is a script that can be run in both single- and multi- user modes to collect a full context string which will be valid for multi- or single- user mode.  So in multi-user mode, where the OS doesn't display the MLS context, I need to add it; while in single-user mode it's already there and I shouldn't add it again.  Once I've got the full string including MLS piece, I can use it anywhere to set a context as you said earlier.


Moray.
“To err is human; to purr, feline.”




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