[ntp:security] [Bug 1331] DoS with mode 7 packets (CVE-2009-3563)

Dave Hart davehart at gmail.com
Thu Oct 8 05:19:33 UTC 2009

On Thu, Oct 8, 2009 at 3:16 AM, Danny Mayer <mayer at ntp.org> wrote:
> After review of the rate-limited logging that was suggested I have
> concluded that it would be a potential problem dealing with the
> "current_time" variable which has not been declared volatile and has no
> locks around it for potential problems with multiple access and changes.
> This kind of logging should be left to a regular release of the code
> when there is time to ensure that the time used to check for
> rate-limiting is atomically retrieved.

This concern of atomic access to current_time is misplaced.  ntpd has
a single thread which modifies current_time, and it's the same thread
which executes process_private().  There is no need for "volatile" or
locking when the fact that process_private() is running guarantees
that the code that modifies current_time will not run.

Dave Hart

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