Preferred subj= with multiple LSMs

[Casey Schaufler]

On 7/16/2019 10:43 AM, Paul Moore wrote:
> On Tue, Jul 16, 2019 at 1:30 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
>> 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.
> Good point, that looks reasonable to me.

Which raises the question of what to do with the subj= :

	- omit it
	- subj=?
	- subj=some-special-message
	- subj=label-of-first-lsm