code review request: 7077172: KerberosTime does not take into account system clock adjustement

[Weijun Wang]

Resent with an updated subject.

-------- Original Message --------
Subject: Fwd: CR 7077172 Updated, P3 jgss/krb5plugin KerberosTime does 
not take into account system clock adjustement
Date: Wed, 16 Nov 2011 17:54:49 +0800
From: Weijun Wang <weijun.wang at oracle.com>
To: Valerie (Yu-Ching) Peng <valerie.peng at oracle.com>
CC: OpenJDK <security-dev at openjdk.java.net>

Hi Valerie

In code changes for 6882687, in order to increase the precision of
KerberosTime, I use System.nanoTime() to calculate the current time. It
is precise, but it's only an elapse of nanaseconds after the VM starts.
What I did is, when the VM starts, I record a clock time, and after
that, I add the elapsed time to it and get a current clock time. This
would break if the user adjust the system time during the program
execution, which will change the clock time, but not the elapse time
since VM starts, and won't be noticed by me.

Lines are added to detect system clock change. Please review:

    http://cr.openjdk.java.net/~weijun/7077172/webrev.00/

No reg, hard to simulate system clock change.

Thanks
Max


-------- Original Message --------
*Change Request ID*: 7077172
*Synopsis*: KerberosTime does not take into account system clock adjustement

=== *Description*
============================================================
FULL PRODUCT VERSION :
7

A DESCRIPTION OF THE PROBLEM :
Context
-----------
In the Kerberos procotol, current client timestamp is encapsulated in
the Kerberos query sent to the KDC to obtain a TGT. The timestamp in the
query must be accurate (The KDC timestamp  accepts 5mn deviation in most
case); if not the KDC return a "Clock too skew" error.

Problem
------------
   To obtain the current Timestamp, previously in the JDK 6, the
'KerberosTime' 'setNow()' method  instanciates a 'new Date()' object . A
JDK 7 bug fix
(http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6882687) introduces
a major change in this class. The current timestamp is evaluated using
the time elapsed since the JVM startup (use of System.nanoTime()).
This implementation totally misses the fact that both client and server
generally use a time server (NTP) to synchronize their clocks. Clock
adjustement is not taking into account in the current implementation
while the previous implementation does.

REGRESSION.  Last worked in version 6u26

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Develop a small Java client application that queries a KDC to obtain
TGT each minutes. (Both client and KDC are hosted on the same machine)
2. Run the Java application.
3. Set the system clock and add 15 minutes to the current time

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The KDC continues to deliver client TGT using the new time
ACTUAL -
The KDC returns an error 'Clock skew too great'

ERROR MESSAGES/STACK TRACES THAT OCCUR :
The Java application thrown an Exception
javax.security.auth.login.LoginException: Clock skew too great (37) -
PREAUTH_FAILED

REPRODUCIBILITY :
This bug can be reproduced always.