Re: Preferred subj= with multiple LSMs

On 7/17/2019 9:23 AM, Paul Moore wrote: > On Wed, Jul 17, 2019 at 11:49 AM Casey Schaufler <casey(a)schaufler-ca.com&gt; wrote: >> On 7/17/2019 5:14 AM, Paul Moore wrote: >>> On Tue, Jul 16, 2019 at 7:47 PM Casey Schaufler <casey(a)schaufler-ca.com&gt; wrote: >>>> On 7/16/2019 4:13 PM, Paul Moore wrote: >>>>> On Tue, Jul 16, 2019 at 6:18 PM Casey Schaufler <casey(a)schaufler-ca.com&gt; wrote: >>>>>> It sounds as if some variant of the Hideous format: >>>>>> >>>>>> subj=selinux='a:b:c:d',apparmor='z' >>>>>> subj=selinux/a:b:c:d/apparmor/z >>>>>> subj=(selinux)a:b:c:d/(apparmor)z >>>>>> >>>>>> would meet Steve's searchability requirements, but with significant >>>>>> parsing performance penalties. >>>>> I think "hideous format" sums it up nicely. Whatever we choose here >>>>> we are likely going to be stuck with for some time and I'm near to >>>>> 100% that multiplexing the labels onto a single field is going to be a >>>>> disaster. >>>> If the requirement is that subj= be searchable I don't see much of >>>> an alternative to a Hideous format. If we can get past that, and say >>>> that all subj_* have to be searchable we can avoid that set of issues. >>>> Instead of: >>>> >>>> s = strstr(source, "subj=") >>>> search_after_subj(s, ...); >>> This example does a lot of hand waving in search_after_subj(...) >>> regarding parsing the multiplexed LSM label. Unless we restrict the >>> LSM label formats (which seems both wrong, and too late IMHO) >> I don't think it's too late, and I think it would be healthy >> to restrict LSM "contexts" to character sets that make command >> line specification possible. Embedded newlines? Ewwww. > That would imply that the delimiter you would choose for the > multiplexed approach would be something odd (I think you suggested > 0x02, or similar, earlier) which would likely require the multiplexed > subj field to become a hex encoded field which would be very > unfortunate in my opinion and would technically break with the current > subj/obj field format spec. Picking a normal-ish delimiter, and > restricting its use by LSMs seems wrong to me. Just say "no" to hex encoding!

BTW, keys are not hex encoded.

We've never had to think about having general rules on what security modules do before, because with only one active each could do whatever it wanted without fear of conflict. If there is already a character that none of the existing modules use, how would it be wrong to reserve it?

> It's important to remember that Steve's strstr() comment only reflects > his set of userspace tools. When you start talking about log > aggregation and analytics, it seems very likely that there are other > tools in use, likely with their own parsers that do much more > complicated searches than a simple strstr() call. Point. But long term, they'll have to be updated to accommodate whatever we decide on. Which makes the "simple" case, where one security module is in use all the more important.

>>>> we have >>>> >>>> s = source >>>> for (i = 0; i < lsm_slots ; i++) { >>>> s = strstr(s, "subj_") >>>> if (!s) >>>> break; >>>> s = search_after_subj_(s, lsm_slot_name[i], ...) >>> The hand waving here in search_after_subj_(...) is much less; >>> essentially you just match "subj_X" and then you can take the field >>> value as the LSM's label without having to know the format, the policy >>> loaded, etc. It is both safer and doesn't require knowledge of the >>> LSMs (the LSM "name" can be specified as a parameter to the search >>> tool). >> You can do that with the Hideous format as well. I wouldn't >> say which would be easier without delving into the audit user >> space. > No, you can't. You still need to parse the multiplexed mess, that's > the problem. You move the parsing problem to the record, where you have to look for subj_selinux= instead of having the parsing problem in the subj= field, where you look for something like selinux= within the field. Neither looks like the work of an afternoon to get right.

It probably looks like I'm arguing for the Hideous format option. That would require less work and code disruption, so it is tempting to push for it. But I would have to know the user space side a whole lot better than I do to feel good about pushing anything that isn't obviously a good choice. I kind of prefer Paul's "subj=?" approach, but as it's harder, I don't want to spend too much time on it if it gets me a big, juicy, well deserved NAK.