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

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.