Re: Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.

Hello, On Monday, June 14, 2021 3:34:33 PM EDT Casey Schaufler wrote: > I'm looking at the audit userspace implications of adding two > new kernel audit records. AUDIT_MAC_TASK_CONTEXTS and > AUDIT_MAC_OBJ_CONTEXTS are used when there are multiple security > modules with a "security context" active on the system. This > design has been discussed here at length. The records will look > like: > > AUDIT_MAC_TASK_CONTEXTS > subj_<lsmname>=value > subj_<lsmname>=value > ... > > Looking at the audit user-space code I see several things > that have me concerned. The first is the use of WITH_APPARMOR. > Going forward what behavior would we want if subj_apparmor=something > shows up on a system that has not got WITH_APPARMOR defined? I think it should be ignored. > The code is inconsistent in that it does not use WITH_SELINUX, > but that's hardly a surprise given its origins. There is also no > WITH_SMACK, but that's unlikely to be an issue since Smack's use > of audit is very much like SELinux's. We can add those WITH_* if you like. > The question is what to > do about filtering when subj=foo is specified. I suggest that if > any of subj_selinux, subj_smack or subj_something is "foo", it is > a match. I think that's how we already treat things. There is a linked list for AVC's and we match on any of. > But the SELinux components of a label (level, user, ...) > are also available for filtering. If someone wrote a simple Bell & > LaPadula LSM filtering by some of those fields could be useful > there, too. > > I would like guidance on whether I ought to go the route of > more extensive use of WITH_APPARMOR (and WITH_SMACK, WITH_MUMBLE) > or take the path of greater generalization. Or, whether I should > treat each case individually and give it my best whack. To be honest, I have no idea how well the audit system works with any MAC system except SE Linux.

I don't really know if its doing the right thing. Ausearch and report share a parser. It is time sensitive. I usually test it on 4 or 5 Gb of logs. We also have the ausearch-test program which can be used to test any changes to the parser. http://people.redhat.com/sgrubb/audit/ausearch-test-0.6.tar.gz Once that is squared away, there is the auparse library. It has a table that classifies a field name into what it is for interpretation purposes. You will find a #ifdef WITH_APPARMOR. I don't know if that table is complete or if it needs to be extended for any other MAC system. That then leads to the auparse normalizer. I don't know if we need to make any changes there. You can trigger its code with ausearch --format csv or -- format text. Also, we have some size limits in user space. How big can an event record be if the file is MAX_PATH name length and it has a space in its name or directory and each context is it's maximum size? We may need to think about how this might change the whole userspace ecosystem's size definition, MAX_AUDIT_MESSAGE_LENGTH, since this is part of the ABI. And the kernel also has AUDIT_MESSAGE_TEXT_MAX. What would you get with: # /usr/sbin/auditctl -m `perl -e 'print "A"x8880'` And last...what about auditctl? Is the syscall filter going to allow filtering on these other subject/object components? -Steve