Preferred subj= with multiple LSMs

[Paul Moore]

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.

-- 
paul moore
www.paul-moore.com