Preferred subj= with multiple LSMs

[Steve Grubb]

On Tuesday, July 16, 2019 1:43:18 PM EDT Paul Moore wrote:
> On Tue, Jul 16, 2019 at 1:30 PM Casey Schaufler <casey at schaufler-ca.com> 
wrote:
> > On 7/16/2019 10:12 AM, Paul Moore wrote:
> > > On Mon, Jul 15, 2019 at 6:56 PM Steve Grubb <sgrubb at redhat.com> wrote:
> > >> On Monday, July 15, 2019 5:28:56 PM EDT Paul Moore wrote:
> > >>> On Mon, Jul 15, 2019 at 3:37 PM Casey Schaufler
> > >>> <casey at schaufler-ca.com>
> > >> 
> > >> wrote:
> > >>>> On 7/15/2019 12:04 PM, Richard Guy Briggs wrote:
> > >>>>> On 2019-07-13 11:08, Steve Grubb wrote:
> > > ...
> > > 
> > >>>>> Steve's answer is the obvious one, ideally allocating a seperate
> > >>>>> range
> > >>>>> to each LSM with each message type having its own well defined
> > >>>>> format.
> > >>>> 
> > >>>> It doesn't address the issue of success records, or records
> > >>>> generated outside the security modules.
> > >>> 
> > >>> Yes, exactly.  The individual LSM will presumably will continue to
> > >>> generate their own audit records as they do today and I would imagine
> > >>> that the subject and object fields could remain as they do today for
> > >>> the LSM specific records.
> > >>> 
> > >>> The trick is the other records which are not LSM specific but still
> > >>> want to include subject and/or object information.  Unfortunately we
> > >>> are stuck with some tough limitations given the current audit record
> > >>> format and Steve's audit userspace tools;
> > >> 
> > >> Not really. We just need to approach the problem thinking about how to
> > >> make it work based on how things currently work.
> > > 
> > > I suppose it is all somewhat "subjective" - bad joke fully intended :)
> > > - with respect to what one considers good/bad/limiting.  My personal
> > > view is that an ideal solution would allow for multiple independent
> > > subj/obj labels without having to multiplex on a single subj/obj
> > > field.  My gut feeling is that this would confuse your tools, yes?
> > > 
> > >> For example Casey had a list of possible formats. Like this one:
> > >> 
> > >> Option 3:
> > >>         lsms=selinux,apparmor subj=x:y:z:s:c subj=a
> > >> 
> > >> I'd suggest something almost like that. The first field could be a map
> > >> to
> > >> decipher the labels. Then we could have a comma separated list of
> > >> labels.
> > >> 
> > >> lsms=selinux,apparmor subj=x:y:z:s:c,a
> > > 
> > > Some quick comments:
> > > 
> > > * My usual reminder that new fields for existing audit records must be
> > > added to the end of the record.
> > > 
> > > * If we are going to multiplex the labels on a single field (more on
> > > that below) I might suggest using "subj_lsms" instead of "lsms" so we
> > > leave ourself some wiggle room in the future.
> > > 
> > > * Multiplexing on a single "subj" field is going to be difficult
> > > because picking the label delimiter is going to be a pain.  For
> > > example, in the example above a comma is used, which at the very least
> > > is a valid part of a SELinux label and I suspect for Smack as well
> > > (I'm not sure about the other LSMs).  I suspect the only way to parse
> > > out the component labels would be to have knowledge of the LSMs in
> > > use, as well as the policies loaded at the time the audit record was
> > > generated.
> > > 
> > > This may be a faulty assumption, but assuming your tools will fall
> > > over if they see multiple "subj" fields, could we do something like
> > > 
> > > the following (something between option #2 and #3):
> > >   subj1_lsm=smack subj1=<smack_label> subj2_lsm=selinux
> > > 
> > > subj2=<selinux_label> ...
> > 
> > If it's not a subj= field why use the indirection?
> > 
> >         subj_smack=<smack_label> subj_selinux=<selinux_label>
> > 
> > would be easier.
> 
> Good point, that looks reasonable to me.

But doing something like this will totally break all parsers. To be honest, I 
don't know if I'll ever see more than one labeled security system running at 
the same time. And this would be a big penalty to pay for the flexibility that 
someone, somewhere just might possibly do this.

-Steve