[PATCH v20 05/23] net: Prepare UDS for security module stacking

[Stephen Smalley]

On Mon, Sep 7, 2020 at 9:28 PM Stephen Smalley
<stephen.smalley.work at gmail.com> wrote:
>
> On Sat, Sep 5, 2020 at 3:07 PM John Johansen
> <john.johansen at canonical.com> wrote:
> >
> > On 9/5/20 11:13 AM, Casey Schaufler wrote:
> > > On 9/5/2020 6:25 AM, Paul Moore wrote:
> > >> On Fri, Sep 4, 2020 at 7:58 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
> > >>> On 9/4/2020 2:53 PM, Paul Moore wrote:
> > >>>> On Fri, Sep 4, 2020 at 5:35 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
> > >>>>> On 9/4/2020 1:08 PM, Paul Moore wrote:
> > >> ...
> > >>
> > >>>> I understand the concerns you mention, they are all valid as far as
> > >>>> I'm concerned, but I think we are going to get burned by this code as
> > >>>> it currently stands.
> > >>> Yes, I can see that. We're getting burned by the non-extensibility
> > >>> of secids. It will take someone smarter than me to figure out how to
> > >>> fit N secids into 32bits without danger of either failure or memory
> > >>> allocation.
> > >> Sooo what are the next steps here?  It sounds like there is some
> > >> agreement that the currently proposed unix_skb_params approach is a
> > >> problem, but it also sounds like you just want to merge it anyway?
> > >
> > > There are real problems with all the approaches. This is by far the
> > > least invasive of the lot. If this is acceptable for now I will commit
> > > to including the dynamic allocation version in the full stacking
> > > (e.g. Smack + SELinux) stage. If it isn't, well, this stage is going
> > > to take even longer than it already has. Sigh.
> > >
> > >
> > >> I was sorta hoping for something a bit better.
> > >
> > > I will be looking at alternatives. I am very much open to suggestions.
> > > I'm not even 100% convinced that Stephen's objections to my separate
> > > allocation strategy outweigh its advantages. If you have an opinion on
> > > that, I'd love to hear it.
> > >
> >
> > fwiw I prefer the separate allocation strategy, but as you have already
> > said it trading off one set of problems for another. I would rather see
> > this move forward and one set of trade offs isn't significantly worse
> > than the other to me so, either wfm.
>
> I remain unclear that AppArmor needs this patch at all even when
> support for SO_PEERSEC lands.
> Contrary to the patch description, it is about supporting SCM_SECURITY
> for datagram not SO_PEERSEC.  And I don't know of any actual users of
> SCM_SECURITY even for SELinux, just SO_PEERSEC.

I remembered that systemd once tried using SCM_SECURITY but that was a
bug since systemd was using it with stream sockets and that wasn't
supported by the kernel at the time,
https://bugzilla.redhat.com/show_bug.cgi?id=1224211, so systemd
switched over to using SO_PEERSEC.  Subsequently I did fix
SCM_SECURITY to work with stream sockets via kernel commit
37a9a8df8ce9de6ea73349c9ac8bdf6ba4ec4f70 but SO_PEERSEC is still
preferred.  Looking around, I see that there is still one usage of
SCM_SECURITY in systemd-journald but it doesn't seem to be required
(if provided, journald will pass the label along but nothing seems to
depend on it AFAICT).  In any event, I don't believe this patch is
needed to support stacking AppArmor.