On Fri, Dec 16, 2011 at 1:21 AM, Greg Smith <g...@2ndquadrant.com> wrote:
> This is a problem with the existing code though, and the proposed changes
> don't materially alter that; there's just another quick check in one path
> through.  Right now we check if someone is superuser, then if it's a backend
> PID, then we send the signal.  If you assume someone can run through all the
> PIDs between those checks and the kill, the system is already broken that
> way.

From a theoretical point of view, I believe it to be slightly
different.  If a superuser sends a kill, they will certainly be
authorized to kill whatever they end up killing, because they are
authorized to kill anything.  On the other hand, the proposed patch
would potentially result - in the extremely unlikely event of a
super-fast PID wraparound - in someone cancelling a query they
otherwise wouldn't have been able to cancel.

In practice, the chances of this seem fairly remote.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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