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

On Tue, Sep 8, 2020 at 8:21 PM John Johansen <john.johansen(a)canonical.com&gt; wrote: > On 9/8/20 4:37 PM, Casey Schaufler wrote: >> On 9/8/2020 6:35 AM, Stephen Smalley wrote: >>> On Mon, Sep 7, 2020 at 9:28 PM Stephen Smalley >>> <stephen.smalley.work(a)gmail.com&gt; wrote: >>>> On Sat, Sep 5, 2020 at 3:07 PM John Johansen >>>> <john.johansen(a)canonical.com&gt; 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(a)schaufler-ca.com&gt; wrote: >>>>>>>> On 9/4/2020 2:53 PM, Paul Moore wrote: >>>>>>>>> On Fri, Sep 4, 2020 at 5:35 PM Casey Schaufler <casey(a)schaufler-ca.com&gt; 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. >> Stephen is, as is so often the case, correct. AppArmor has a stub >> socket_getpeersec_dgram() that gets removed in patch 23. If I remove > right but as I said before this is coming, I have been playing with > it and have code. So the series doesn't need it today but sooner than > later it will be needed

I don't understand why. Is there a userspace component that relies on SCM_SECURITY today for anything real (more than just blindly passing it along and maybe writing to a log somewhere)? And this doesn't provide support for a composite SCM_SECURITY or SCM_CONTEXT, so it doesn't really solve the stacking problem for it anyway. What am I missing? Why do you care about this patch?