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

[John Johansen]

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 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.
> 
> 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

> it earlier and throw in a touch of scaffolding for secid_to_secctx()
> we can leave the secid as is for now. This can't be the final solution
> as AppArmor will be using the hook someday and we still have the all
> modules case to worry about for the next phase. It also assumes that
> The BPF module isn't going to suddenly sprout a security context.
> 

Yep this is something that needs to be dealt with, whether it is now
or kicked down the road a little further ...