Occasional delayed output of events
Burn Alting
burn.alting at iinet.net.au
Fri Jan 15 22:18:35 UTC 2021
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 appear
> > > > > > someseconds past co- located events which results
> > > > > > inauparse:au_check_events() marking these events complete before
> > > > > > theyare. An example of this can be seen below with the offending event
> > > > > > id44609.
> > > > > > This has been plaguing me for a year or two and this morning was
> > > > > > thefirst time I still had access to the raw audit.log files (I monitor a
> > > > > > lotof event types and the log files roll over fairly quickly).The
> > > > > > example below is from a fully patched Centos 7 but I have also seenthis
> > > > > > on a patched Fedora 32.
> > > > > > Has this been seen before? Do we need to re-evaluate how
> > > > > > auparse'completes' an event (ie 2 seconds is too quick).
> > > > >
> > > > > I have never seen this. But on the way to disk, auditd only does
> > > > > lightprocessing of the event. If the format is enriched, it looks things
> > > > > upon a record by record basis. It does not collect events until they
> > > > > arecomplete - it dumps it to disk as soon as it can tack on the
> > > > > extrainformation.
> > > > > So, the question would be, does this delay happen on the way to disk? Oris
> > > > > this an artifact of post processing the logs with an auparse basedutility?
> > > > > Can this be observed repeatedly on the same raw logs? If so,then maybe
> > > > > auparse does have some issue. But if this is a postprocessing issue, then
> > > > > the wall clock doesn't matter because this eventshould have collected up
> > > > > together.
> > > > > I'd say this merits some investigation.
> > > >
> > > > OK. I think this needs to be addressed on two fronts. There may be
> > > > more.A. Within post processing ... a 2 second timeout is not sufficient.
> > > > Iwould suggest we modify auparse.c:au_check_events() to i) perform theevent
> > > > type checks first, then ii) increase the timeout of 2 seconds to be a
> > > > larger value based onempirical tests.
> > >
> > > In the post processing, there are 2 use cases. The first is events that are on
> > > disk. In this usage, the 2 second timeout does not come into effect because
> > > the events are run through probably within nanoseconds or microseconds at the
> > > worst. The only time it would come into effect is if the terminating record is
> > > missing.
> >
> > In this first case, the 2 second timeout is on the event's time, not the
> > 'processing time'. See ausearch-lol.c:check_events() and
> > auparse.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 disk
> > with 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 a
> > solution.
> > b. The event arrived at a reasonable point in time at auditd and for some reason
> > auditd delayed it's printing (by the way I tend to use RAW log format, not
> > enriched.
> >
> > In either case, I believe ausearch-lol.c:check_events() and
> > auparse.c:au_get_ready_event() do need to be changed as we have complete events
> > written by auditd
> > which these two routines fail to process properly.
> >
> Changing the two second timeout in ausearch-lol.c:check_events() and, one assumes
> in auparse.c:au_get_ready_event() (but I have not tested the auparse code) fixes
> the processing of the delayed event.
> Changing the value to say 10 seconds fixes my example use case, but given the
> kernel or auditd could emit an event with a larger delay, should this be a
> configuration 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 more
> versatile 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 just
compiled 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 I
need a 15 second delay.
I accept there may be an issue in the kernel but if it is not simple (I only see
this occasionally), then we need a fix in the userspace. Since I have found varied
times required, do I go down the path of a big value OR a configuration item in
/etc/audit/auditd.conf?
>
> > > The other use case is realtime processing as an audispd plugin. In this use
> > > case the wall clock could matter because records could potentially get lost
> > > due to overflows or another plugin taking too long. This is the use case where
> > > the wall clock matters. And again, it matters when records get lost or delayed
> > > in transit. As long as everything is flowing, it should not factor into event
> > > processing.
> > > > B. I will build a temporary auditd daemon to perform some empirical
> > > > testingto see how long events can reside within the daemon. I may need
> > > > someadvice on this. I assume that the code that sets the timestamp is
> > > > insrc/auditd.c:send_audit_event().
> > >
> > > This is only for audit daemon's internal events. For all "real" events, it's
> > > set in the kernel.
> >
> > If that is the case and the kernel is establishing the timestamp, then either
> > the kernel has delayed the eventsarrival at the daemon or the daemon has delayed
> > it's writing.
> > > > If so, I will see if I can put orchestration debug code in to monitor
> > > > anevent'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,then
> > > > the testing switch in A. will not be a big issue (time cost wise). Itwill
> > > > also mean that if we over compensate the timeout that would causeadditional
> > > > memory cost in auparse() then this is mittigated.
> > >
> > > I'd suggest breaking up the event completion tests so that an exact collection
> > > termination reason code could be associated to the event.
> > > > With respect to 'There may be more' fronts. Are there other points in
> > > > the'audit ecosystem' that makes use of the '2 second timeout'.
> > >
> > > Ausearch/report has its own special copy of the event collection logic. It
> > > should be nearly identical to what auparse does.
> >
> > They appear identical ... ausearch-lol.c:check_events() and
> > auparse.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 diff
> > > between it and audit-2.8.5 for the auparse directory does show some
> > > differences in event collection/grouping/next_event. A lot of the differences
> > > are 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. For
> > > example,
> >
> > 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 consolidate
> > > the array so that we iterate- // over a smaller portion next
> > > time- 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];- }- } return
> > > lowest->l; }
> > > and
> > > @@ -1536,6 +1550,13 @@ static int
> > > au_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 marked
> > > complete+ if (l->head->type == AUDIT_EOE)
> > > {+ au->cur_buf =
> > > NULL;+ aup_list_clear(l);+ free(l)
> > > ;+ continue;+ } if
> > > (au_lol_append(au->au_lo, l) == NULL) { free((char
> > > *)e.host); #ifdef LOL_EVENTS_DEBUG01
> > > I don't know if those have an effect on what you are seeing. But that is the
> > > only substantial changes that I can see.
> > > -Steve
>
> Burn
>
> --Linux-audit mailing listLinux-audit at redhat.com
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