Preferred subj= with multiple LSMs

[Casey Schaufler]

On 7/16/2019 11:06 AM, Steve Grubb wrote:
> On Tuesday, July 16, 2019 1:43:18 PM EDT 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.
> But doing something like this will totally break all parsers. To be honest, I 
> don't know if I'll ever see more than one labeled security system running at 
> the same time. And this would be a big penalty to pay for the flexibility that 
> someone, somewhere just might possibly do this.

While I have never seen multiple-LSM plans from RedHat/IBM I
have seen them from Ubuntu. This isn't hypothetical. I know that
it's a hard problem, which is why we need to get it as right as
possible.