linux-kernel - Re: [PATCH] audit: set TIF_AUDIT_SYSCALL only if audit filter has been populated

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Date:   Wed, 14 Mar 2018 00:35:44 +0000
From:   Andy Lutomirski <luto@...nel.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Steve Grubb <sgrubb@...hat.com>,
        Paul Moore <paul@...l-moore.com>, linux-audit@...hat.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Oleg Nesterov <oleg@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] audit: set TIF_AUDIT_SYSCALL only if audit filter has
 been populated

On Wed, Mar 14, 2018 at 12:28 AM, Jiri Kosina <jikos@...nel.org> wrote:
> On Wed, 14 Mar 2018, Andy Lutomirski wrote:
>
>> > Yes...I wished I was in on the beginning of this discussion. Here's the
>> > problem. We need all tasks auditable unless specifically dismissed as
>> > uninteresting. This would be a task,never rule.
>> >
>> > The way we look at it, is if it boots with audit=1, then we know auditd
>> > is expected to run at some point. So, we need all tasks to stay
>> > auditable. If they weren't and auditd enabled auditing, then we'd need
>> > to walk the whole proctable and stab TIF_AUDIT_SYSCALL into every
>> > process in the system. It was decided that this is too ugly.
>>
>> When was that decided?  That's what this patch does.
>
> I'd like to see some more justification as well.
>
> Namely, if I compare "setting TIF_AUDIT_SYSCALL for every process on a
> need-to-be-so basis" to "we always go through the slow path and
> pessimistically assume that audit is enabled and has reasonable ruleset
> loaded", I have my own (different) opinion of what is too ugly.

Me too.

That being said, on re-review of my old code, I think that
audit_dec_n_rules() may be the wrong approach.  It may be better to
leave TIF_AUDIT_SYSCALL set but to make the audit code itself clear
the flag the next time through.  That way we don't end up with a
partially filled in syscall audit record that never gets consumed if
we clear TIF_AUDIT_SYSCALL in the middle of a syscall.