On Tuesday, June 15, 2021 1:01:18 PM EDT Casey Schaufler wrote: > On 6/14/2021 2:13 PM, Steve Grubb wrote: > > 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. > > Understood. Part of what I'm looking at is ensuring that as multiple > concurrent LSMs come in that the audit user-space isn't mucked up. > ausearch has these options: > > -o,--object <SE Linux Object context> > -se,--context <SE Linux context> > -su,--subject <SE Linux context> > > Without multiple LSMs we can easily ignore "SE Linux" in these > options and use whatever kind of "context" is available. If I > have SELinux and AppArmor, the implication is that you can't > search on AppArmor information. Should we be adding > > -aa,--apparmorcontext <AppArmor context> > -as,--apparmorsubject <AppArmor subject context> > > or should we change -se to look at all "contexts", and change > the description to reflect that? Basicaly, I'm asking whether you'd > rather add options for other LSMs or remove descriptions that > specify SELinux.
I'd say any/all contexts available by default. Then we can maybe make a restriction to specific LSM's later. -Steve > > 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 -- Linux-audit mailing list [email protected] https://listman.redhat.com/mailman/listinfo/linux-audit
