[apparmor] wrong loggingtime in apparmorlog

[Hajo Locke]

Hello,


Am 05.02.2015 um 00:11 schrieb Seth Arnold:
> On Wed, Feb 04, 2015 at 10:47:58AM +0100, Hajo Locke wrote:
>> Feb  4 09:55:01 hostname CRON[3898]: (root)...
>> Feb  4 11:30:50 hostname kernel: type=1400
>> audit(1423040101.577:7785293): apparmor="DENIED"...
>> Feb  4 09:55:01 hostname CRON[3911]: (root)...
>>
>> a relation to audit seems possible.  i found more kernel loglines in
>> syslog with wrong date which are not in direct relation to apparmor.
>> i think complete kern.log is wrong.
>> may be more kernel related?  we upgrade regularly, current version
>> on this machine is 3.13.0-43-generic (Ubuntu 14.04 LTS)
>> Currently only rebooting solves this problem. after reboot
>> timestamps in loglines are identical. But by increasing uptime the
>> difference between realtime and kernel-log-time grows.
>> one server with uptime ~2 days has kernel-time 53 seconds in future
>> (3.13.0-45-generic).  server from loglines above has uptime 48 days
>> and difference is more than 1,5 hours.
> I've got a theory that's not very well thought through yet; to be honest,
> this is an interesting problem that I've never seen before.
>
> Here's some source code that's very similar to the rsyslog daemon used in
> Ubuntu 14.04 LTS:
>
> http://sources.debian.net/src/rsyslog/7.4.8-1%7Ebpo70%2B1/plugins/imklog/bsd.c/#L58
>
> Note this section:
>
> /* ... */
> 	clock_gettime(CLOCK_MONOTONIC, &monotonic);
> 	clock_gettime(CLOCK_REALTIME, &realtime);
> 	secOffs = realtime.tv_sec - monotonic.tv_sec;
> 	usecOffs = (realtime.tv_nsec - monotonic.tv_nsec) / 1000;
> 	if(usecOffs < 0) {
> 		secOffs--;
> 		usecOffs += 1000000l;
> 	}
> 	
> 	usecs += usecOffs;
> 	if(usecs > 999999l) {
> 		secs++;
> 		usecs -= 1000000l;
> 	}
> 	secs += secOffs;
> 	tv.tv_sec = secs;
> 	tv.tv_usec = usecs;
> 	tp = &tv;
>
> done:
> 	Syslog(pri, buf, tp);
> /* ... */
>
> rsyslog is changing the timestamp supplied to its internal Syslog()
> routine based on the time difference between the CLOCK_MONOTONIC and
> CLOCK_REALTIME clocks. The CLOCK_MONOTONIC clock will only ever move
> forward, while CLOCK_REALTIME can jump backwards if e.g. ntpdate(8) or
> date(1) sets an entirely new time.
>
> So, my theory -- this system is using ntpdate(8) in a cronjob to set the
> time rather than using ntpd(8), which would _skew_ the time in a fashion
> that's more amenable to keeping CLOCK_MONOTONIC and CLOCK_REALTIME closer
> to synchronized. (ntpd(8) can ask the system clock to speed up or slow
> down so that seconds take more or less time, but when skewing it won't
> jump the time forwards or backwards abruptly.)
>
> I've attached a little program that will output all the clocks documented
> in clock_gettime(3) as well as the difference between the MONOTONIC clock
> and REALTIME clock. If you've installed build-essential, you should be
> able to compile it and run with just "make clocks ; ./clocks".
>
> If I'm correct, the difference between the MONOTONIC and the REALTIME
> clock will get worse over the uptime of the system. And if I'm correct,
> you can fix the issue by switching to ntpd rather than using ntpdate
> periodically. You may also be able to use the klogParseKernelTimestamp
> configuration variable from rsyslog:
> http://www.rsyslog.com/doc/master/configuration/modules/imklog.html

Thanks for your effort. i ran your program on affected machine and this 
is output:


            CLOCK_REALTIME Thu Feb  5 10:36:40 2015
     CLOCK_REALTIME_COARSE Thu Feb  5 10:36:40 2015
           CLOCK_MONOTONIC Thu Feb 19 09:50:37 1970
    CLOCK_MONOTONIC_COARSE Thu Feb 19 09:50:37 1970
       CLOCK_MONOTONIC_RAW Thu Feb 19 09:51:01 1970
            CLOCK_BOOTTIME Thu Feb 19 09:50:37 1970
  CLOCK_PROCESS_CPUTIME_ID Thu Jan  1 01:00:00 1970
   CLOCK_THREAD_CPUTIME_ID Thu Jan  1 01:00:00 1970
CLOCK_REALTIME - CLOCK_MONOTONIC 1418863562.991217


Current real-time is: Do 5. Feb 10:36:42 CET 2015

we do not use rsyslog, for historical reasons we use syslog-ng. I dont 
know if this matters.
our systems run ntpd. In consultation with my fellows, nobody knows 
about using ntpdate. while running ntpd the use of ntpdate results in error.
The difference between CLOCK_REALTIME - CLOCK_MONOTONIC is 1:46:02

if i reload apparmor and use date-command to compare times, i see a 
difference of ~ 1:38
Feb  5 13:00:05 hostname kernel: type=1400 
audit(1423131731.158:8016925): apparmor...
Do 5. Feb 11:22:11 CET 2015

hmm, i cant handle these results. I can do some more tests if you want.

>
> I hope this helps solve this issue.
>
> Thanks

Thanks,
Hajo