[ntp:bugs] [Bug 1503] New: enabling of monitor for "restrict ... limited" subtly wrong

[Dave Hart via the NTP Bugzilla]

http://bugs.ntp.org/1503

           Summary: enabling of monitor for "restrict ... limited" subtly
                    wrong
           Product: ntp
           Version: 4.2.6
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P3
         Component: ntpd
        AssignedTo: hart at ntp.org
        ReportedBy: hart at ntp.org
                CC: bugs at lists.ntp.org


When IPv6 support was added to ntpd, the approach taken for the ntp_restrict.c 
file was basically to duplicate every global variable and function into IPv4 and 
IPv6 variants.  In the process, a reference count used to light up the MRU list 
via mon_start() and shut it down via mon_stop() when any "restrict ... limited" 
are in effect was erroneously duplicated as well.

There should be a single reference count for "restrict ... limited" entries on 
either v4 or v6 restrict lists.  There is no reason to count them separately, 
and in fact it's wrong.  Imagine you have:

restrict default limited

That ends up as an entry on each of the v4 and v6 lists, for addresses 0.0.0.0 
and ::, and bumps both v4 and v6 reference counts.  Now suppose you at runtime 
used:

ntpq -c ":config restrict ::"

That modifies the v6 default restriction to no longer have RES_LIMITED.  In the 
process, the v6 reference count goes to zero and mon_stop() is called, yet there 
are still RES_LIMITED restrictions active that can not be enforced unless the 
MRU list is enabled.

The fix is trivial, consolidating the two reference counts into one.  I'm 
tempted after a bit more testing to simply backport the latest ntp_restrict.c 
and ntp_monitor.c to -stable, because there are a raft of improvements and I'd 
rather not try to maintain the old code.

-- 
Dave Hart <hart at ntp.org>



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