From: Casey Schaufler <casey@schaufler-ca.com>
To: Steve Grubb <sgrubb@redhat.com>
Cc: "linux-audit@redhat.com" <linux-audit@redhat.com>
Subject: Re: Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.
Date: Tue, 15 Jun 2021 10:01:18 -0700 [thread overview]
Message-ID: <30449857-fb74-4203-d464-7ff09c909663@schaufler-ca.com> (raw)
In-Reply-To: <7967755.NyiUUSuA9g@x2>
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 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
Linux-audit@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-audit
next prev parent reply other threads:[~2021-06-15 17:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <e252b332-1a32-2103-f299-d0376b8a4615.ref@schaufler-ca.com>
2021-06-14 19:34 ` Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace Casey Schaufler
2021-06-14 21:13 ` Steve Grubb
2021-06-15 17:01 ` Casey Schaufler [this message]
2021-06-15 21:15 ` Steve Grubb
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=30449857-fb74-4203-d464-7ff09c909663@schaufler-ca.com \
--to=casey@schaufler-ca.com \
--cc=linux-audit@redhat.com \
--cc=sgrubb@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).