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

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Message-ID: <20180308160324.xhjp22ieqq4a5fs3@madcap2.tricolour.ca>
Date:   Thu, 8 Mar 2018 11:03:24 -0500
From:   Richard Guy Briggs <rgb@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Paul Moore <paul@...l-moore.com>, Jiri Kosina <jikos@...nel.org>,
        Andy Lutomirski <luto@...nel.org>, 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 2018-03-08 06:30, Andy Lutomirski wrote:
> 
> 
> > On Mar 8, 2018, at 1:12 AM, Richard Guy Briggs <rgb@...hat.com> wrote:
> > 
> >> On 2018-03-07 18:43, Paul Moore wrote:
> >>> On Wed, Mar 7, 2018 at 6:41 PM, Paul Moore <paul@...l-moore.com> wrote:
> >>>> On Wed, Mar 7, 2018 at 11:48 AM, Jiri Kosina <jikos@...nel.org> wrote:
> >>>>> On Wed, 7 Mar 2018, Andy Lutomirski wrote:
> >>>>> Wow, this was a long time ago.
> >>>> 
> >>>> Oh yeah; but it now resurfaced on our side, as we are of course receiving
> >>>> a lot of requests with respect to making syscall performance great again
> >>>> :)
> >>> 
> >>> Ooof.  I'm not sure I can handle making more things "great again" ;)
> >>> 
> >>>>> From memory and a bit of email diving, there are two reasons.
> >>>>> 
> >>>>> 1. The probably was partially solved (by Oleg, IIRC) by making auditctl
> >>>>>   -a task,never cause newly spawned tasks to not suck.  Yes, it's a
> >>>>>   very partial solution.  After considerable nagging, I got Fedora to
> >>>>>   default to -a task,never.
> >>>> 
> >>>> Hm, right; that's a bit inconvenient, because it takes each and every
> >>>> vendor having to realize this option, and put it in. Making kernel do the
> >>>> right thing automatically sounds like a better option to me.
> >>> 
> >>> This predates audit falling into my lap, but speaking generally I
> >>> think it would be good if the kernel did The Right Thing, so long as
> >>> it isn't too painful.
> >>> 
> >>>>> 2. This patch, as is, may be a bit problematic.  In particular, if one
> >>>>>   task changes the audit rules while another task is in the middle of
> >>>>>   the syscall, then it's too late to audit that syscall correctly.
> >>>>>   This could be seen as a bug or it could be seen as being just fine.
> >>>> 
> >>>> I don't think this should be a problem, given the fact that the whole
> >>>> timing/ordering is not predictable anyway due to scheduling.
> >>>> 
> >>>> Paul, what do you think?
> >>> 
> >>> I'm not overly concerned about the race condition between configuring
> >>> the audit filters and syscalls that are currently in-flight; after all
> >>> we have that now and "fixing" it would be pretty much impractical
> >>> (impossible maybe?).  Most serious audit users configure it during
> >>> boot and let it run, frequent runtime changes are not common as far as
> >>> I can tell.
> > 
> > I'd agree the race condition here can't easily be fixed and isn't worth
> > fixing for the reasons already stated (rules don't change often and may
> > even be locked once in place relatively early, scheduling uncertainties).
> > 
> >>> I just looked quickly at the patch and decided it isn't something I'm
> >>> going to be able to carefully review in the time I've got left today,
> >>> so it's going to have to wait until tomorrow and Friday ... however,
> >>> speaking on general principle I don't have an objection to the ideas
> >>> put forth here.
> > 
> > The approach seems a bit draconian since it touches all tasks but only
> > when adding the first rule or deleting the last.
> > 
> > What we lose is the ability to set or clear individual task auditing and
> > have it stick to speed up non-audited tasks when there are rules
> > present, though this isn't currently used, in favour of audit_context
> > presence.
> > 
> >>> Andy, if you've got any Reviewed-by/Tested-by/NACK/etc. you want to
> >>> add, that would be good to have.
> >> 
> >> ... and I just realized that linux-audit isn't on the To/CC line,
> >> adding them now.
> > 
> > (and Andy's non-NACK missed too...)  The mailing list *is* in MAINTAINERS.
> > 
> 
> The mailing list bounces my emails. 

They'll get approved.

> >> Link to the patch is below.
> >> 
> >> * https://marc.info/?t=152041887600003&r=1&w=2
> >> 
> >> paul moore
> > 
> > - RGB

- RGB

--
Richard Guy Briggs <rgb@...hat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635