Preferred subj= with multiple LSMs

[Casey Schaufler]

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.