Occasional delayed output of events
Burn Alting
burn.alting at iinet.net.au
Sat Jan 16 02:42:23 UTC 2021
On Fri, 2021-01-15 at 19:35 -0500, Richard Guy Briggs wrote:
> On 2021-01-16 09:18, Burn Alting wrote:
> > On Sun, 2021-01-10 at 15:39 +1100, Burn Alting wrote:
> > > On Tue, 2021-01-05 at 07:12 +1100, Burn Alting wrote:
> > > > On Mon, 2021-01-04 at 09:46 -0500, Steve Grubb wrote:
> > > > > On Monday, January 4, 2021 2:55:25 AM EST Burn Alting wrote:
> > > > > > On Sun, 2021-01-03 at 10:41 -0500, Steve Grubb wrote:
> > > > > > > On Friday, January 1, 2021 4:22:33 PM EST Burn Alting wrote:
> > > > > > > > Sometimes, events recorded in /var/log/audit/audit.log
> > > > > > > > appearsomeseconds past co- located events which
> > > > > > > > resultsinauparse:au_check_events() marking these events complete
> > > > > > > > beforetheyare. An example of this can be seen below with the
> > > > > > > > offending eventid44609.This has been plaguing me for a year or two
> > > > > > > > and this morning wasthefirst time I still had access to the raw
> > > > > > > > audit.log files (I monitor alotof event types and the log files roll
> > > > > > > > over fairly quickly).Theexample below is from a fully patched Centos
> > > > > > > > 7 but I have also seenthison a patched Fedora 32.Has this been seen
> > > > > > > > before? Do we need to re-evaluate howauparse'completes' an event (ie
> > > > > > > > 2 seconds is too quick).
> > > > > > >
> > > > > > > I have never seen this. But on the way to disk, auditd only
> > > > > > > doeslightprocessing of the event. If the format is enriched, it looks
> > > > > > > thingsupon a record by record basis. It does not collect events until
> > > > > > > theyarecomplete - it dumps it to disk as soon as it can tack on
> > > > > > > theextrainformation.So, the question would be, does this delay happen
> > > > > > > on the way to disk? Oristhis an artifact of post processing the logs
> > > > > > > with an auparse basedutility?Can this be observed repeatedly on the
> > > > > > > same raw logs? If so,then maybeauparse does have some issue. But if
> > > > > > > this is a postprocessing issue, thenthe wall clock doesn't matter
> > > > > > > because this eventshould have collected uptogether.I'd say this merits
> > > > > > > some investigation.
> > > > > >
> > > > > > OK. I think this needs to be addressed on two fronts. There may
> > > > > > bemore.A. Within post processing ... a 2 second timeout is not
> > > > > > sufficient.Iwould suggest we modify auparse.c:au_check_events() to i)
> > > > > > perform theeventtype checks first, then ii) increase the timeout of 2
> > > > > > seconds to be alarger value based onempirical tests.
> > > > >
> > > > > In the post processing, there are 2 use cases. The first is events that
> > > > > are ondisk. In this usage, the 2 second timeout does not come into effect
> > > > > becausethe events are run through probably within nanoseconds or
> > > > > microseconds at theworst. The only time it would come into effect is if
> > > > > the terminating record ismissing.
> > > >
> > > > In this first case, the 2 second timeout is on the event's time, not
> > > > the'processing time'. See ausearch-lol.c:check_events()
> > > > andauparse.c:au_get_ready_event().And I use the checkpointing code to avoid
> > > > the incomplete event issue.
> > > > In my case, I have not lost records, it's just that an event has arrived on
> > > > diskwith an event time more than 2 seconds after the previously written
> > > > event.Basically,a. The event was delayed getting to auditd and we look to
> > > > the kernel for asolution.b. The event arrived at a reasonable point in time
> > > > at auditd and for some reasonauditd delayed it's printing (by the way I tend
> > > > to use RAW log format, notenriched.
> > > > In either case, I believe ausearch-lol.c:check_events()
> > > > andauparse.c:au_get_ready_event() do need to be changed as we have complete
> > > > eventswritten by auditdwhich these two routines fail to process properly.
> > > Changing the two second timeout in ausearch-lol.c:check_events() and, one
> > > assumesin auparse.c:au_get_ready_event() (but I have not tested the auparse
> > > code) fixesthe processing of the delayed event.Changing the value to say 10
> > > seconds fixes my example use case, but given thekernel or auditd could emit an
> > > event with a larger delay, should this be aconfiguration item in
> > > /etc/audit/auditd.conf?
> > > I have raised both a bugzilla report (
> > > https://bugzilla.redhat.com/show_bug.cgi?id=1914603) and Issue (
> > > https://github.com/linux-audit/audit-userspace/issues/148)
> > > How do you want me to proceed ... a simple change to 10 seconds or a
> > > moreversatile configuration item in auditd.conf?I can perform either and issue
> > > a PR if so required.
> >
> > What do people think ... I would point out this currently occurs in both audit-
> > 2.8.5-4.el7.x86_64 and audit-3.0-0.17.20191104git1c2f876.el8.x86_64 and a
> > justcompiled checkout of the audit-userspace code audit-3.0-1.fc33.x86_64.I have
> > found examples (under audit-3.0-0.17.20191104git1c2f876.el8.x86_64) that Ineed a
> > 15 second delay.I accept there may be an issue in the kernel but if it is not
> > simple (I only seethis occasionally), then we need a fix in the userspace. Since
> > I have found variedtimes required, do I go down the path of a big value OR a
> > configuration item in/etc/audit/auditd.conf?
>
> Or we go back to userspace code looking for the EOE record? Thisdoesn't help if
> they arrive out of order. Do we number the records inthe kernel? N of M...
I like the N of M concept but there would be a LOT of change - especially for all
the non-kernel event sources. The EOE would be the most seamless, but at a cost.My
preference is to allow the 2 second 'timer' to be configurable.
> > > > > The other use case is realtime processing as an audispd plugin. In this
> > > > > usecase the wall clock could matter because records could potentially get
> > > > > lostdue to overflows or another plugin taking too long. This is the use
> > > > > case wherethe wall clock matters. And again, it matters when records get
> > > > > lost or delayedin transit. As long as everything is flowing, it should not
> > > > > factor into eventprocessing.
> > > > > > B. I will build a temporary auditd daemon to perform some
> > > > > > empiricaltestingto see how long events can reside within the daemon. I
> > > > > > may needsomeadvice on this. I assume that the code that sets the
> > > > > > timestamp isinsrc/auditd.c:send_audit_event().
> > > > >
> > > > > This is only for audit daemon's internal events. For all "real" events,
> > > > > it'sset in the kernel.
> > > >
> > > > If that is the case and the kernel is establishing the timestamp, then
> > > > eitherthe kernel has delayed the eventsarrival at the daemon or the daemon
> > > > has delayedit's writing.
> > > > > > If so, I will see if I can put orchestration debug code in to
> > > > > > monitoranevent's 'time in daemon' until this point. I will then report
> > > > > > on this.I believe given that AUDIT_PROCTITLE and AUDIT_EOE is fairly
> > > > > > widespread,thenthe testing switch in A. will not be a big issue (time
> > > > > > cost wise). Itwillalso mean that if we over compensate the timeout that
> > > > > > would causeadditionalmemory cost in auparse() then this is mittigated.
> > > > >
> > > > > I'd suggest breaking up the event completion tests so that an exact
> > > > > collectiontermination reason code could be associated to the event.
> > > > > > With respect to 'There may be more' fronts. Are there other points
> > > > > > inthe'audit ecosystem' that makes use of the '2 second timeout'.
> > > > >
> > > > > Ausearch/report has its own special copy of the event collection logic.
> > > > > Itshould be nearly identical to what auparse does.
> > > >
> > > > They appear identical ... ausearch-lol.c:check_events()
> > > > andauparse.c:au_get_ready_event().
> > > > > > I will start work on this, this coming weekend if the above makes sense.
> > > > >
> > > > > One other thought, the current shipping code is audit-3.0, doing a
> > > > > diffbetween it and audit-2.8.5 for the auparse directory does show
> > > > > somedifferences in event collection/grouping/next_event. A lot of the
> > > > > differencesare cosmetic to fix extra whitespace or indentation. But if you
> > > > > skip all that,there are some real changes that probably were because of
> > > > > bug reports. Forexample,
> > > >
> > > > I will go through these, although this occurs on my Centos 7's (audit-2.8.5-
> > > > 4.el7.x86_64) as well as my 8's (audit-3.0-
> > > > 0.17.20191104git1c2f876.el8.x86_64).
> > > > > @@ -259,15 +260,6 @@ static event_list_t
> > > > > *au_get_ready_event( if(lowest && lowest->status == EBS_COMPLETE)
> > > > > { lowest->status =EBS_EMPTY; au->au_ready
> > > > > --;- // Try to consolidatethe array so that we
> > > > > iterate- // over a smaller portion
> > > > > nexttime- if (lowest == &lol->array[lol
> > > > > ->maxi]){- au_lolnode *ptr
> > > > > =lowest;- while (ptr->status == EBS_EMPTY && lol-
> > > > > >maxi >0) {- lol->maxi
> > > > > --;- ptr = &lol->array[lol
> > > > > ->maxi];- }- } returnlo
> > > > > west->l; }and@@ -1536,6 +1550,13 @@ static
> > > > > intau_auparse_next_event(auparse aup_list_create(l);
> > > > > aup_list_set_event(l, &e); aup_list_append(l, au-
> > > > > >cur_buf,au->list_idx, au-
> > > > > > line_number);
> > > > > + // Eat standalone EOE - main event was already
> > > > > markedcomplete+ if (l->head->type ==
> > > > > AUDIT_EOE){+ au->cur_buf
> > > > > =NULL;+ aup_list_clear(l);+ fr
> > > > > ee(l);+ continue;+ } if
> > > > > (au_lol_append(au->au_lo, l) == NULL)
> > > > > { free((char*)e.host); #ifdef LOL_EVENTS_DEBUG01I
> > > > > don't know if those have an effect on what you are seeing. But that is
> > > > > theonly substantial changes that I can see.-Steve
> > >
> > > Burn
>
> - RGB
> --Richard Guy Briggs <rgb at redhat.com>Sr. S/W Engineer, Kernel Security, Base
> Operating SystemsRemote, Ottawa, Red Hat CanadaIRC: rgb, SunRaycerVoice:
> +1.647.777.2635, Internal: (81) 32635
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