Audit rules for PCI : time change

[Maupertuis Philippe]

Hi,
Being subject to the PCI DSS standard, I implemented the proposed audit rules for PCI, albeit slightly changed because we are still using NTP instead of Chrony.
On a handful of vmware servers I have noticed that the clock_settime is  used every fifteen minutes.
These servers seem to have higher values than other for offset and jitter due to a heavy load on a firewall.
These regular messages prevent us to have an automatic analysis of the event generated by the key 10.4.2b-time-change which we are required to do.
If I add a rule to monitor /etc/ntp.conf, would it be safe to ignore them if the auid is unset and the uid ntp ?

Below are the event I am seeing.

node=xxxxxxxx type=PROCTITLE msg=audit(08/06/18 01:58:58.525:175718) : proctitle=/usr/sbin/ntpd -u ntp:ntp -g
node=xxxxxxxx type=SYSCALL msg=audit(08/06/18 01:58:58.525:175718) : arch=x86_64 syscall=clock_settime success=yes exit=0 a0=CLOCK_REALTIME a1=0x7ffcba67b950 a2=0xb62c3 a3=0x4000 items=0 ppid=1 pid=819 auid=unset uid=ntp gid=ntp euid=ntp suid=ntp fsuid=ntp egid=ntp sgid=ntp fsgid=ntp tty=(none) ses=unset comm=ntpd exe=/usr/sbin/ntpd key=10.4.2b-time-change
----
node=xxxxxxxx type=PROCTITLE msg=audit(08/06/18 02:14:01.746:175775) : proctitle=/usr/sbin/ntpd -u ntp:ntp -g
node=xxxxxxxx type=SYSCALL msg=audit(08/06/18 02:14:01.746:175775) : arch=x86_64 syscall=clock_settime success=yes exit=0 a0=CLOCK_REALTIME a1=0x7ffcba67b950 a2=0xec457 a3=0x4000 items=0 ppid=1 pid=819 auid=unset uid=ntp gid=ntp euid=ntp suid=ntp fsuid=ntp egid=ntp sgid=ntp fsgid=ntp tty=(none) ses=unset comm=ntpd exe=/usr/sbin/ntpd key=10.4.2b-time-change
----
node=xxxxxxxx type=PROCTITLE msg=audit(08/06/18 02:30:29.973:175847) : proctitle=/usr/sbin/ntpd -u ntp:ntp -g
node=xxxxxxxx type=SYSCALL msg=audit(08/06/18 02:30:29.973:175847) : arch=x86_64 syscall=clock_settime success=yes exit=0 a0=CLOCK_REALTIME a1=0x7ffcba67b950 a2=0x2fab6 a3=0x4000 items=0 ppid=1 pid=819 auid=unset uid=ntp gid=ntp euid=ntp suid=ntp fsuid=ntp egid=ntp sgid=ntp fsgid=ntp tty=(none) ses=unset comm=ntpd exe=/usr/sbin/ntpd key=10.4.2b-time-change


Thank you for advising on this.

Philippe

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