Re: [HACKERS] flock patch breaks things here - Mailing list pgsql-hackers

>
> Bruce Momjian <maillist@candle.pha.pa.us> writes:
> > Can't we just have configure check for flock().  Another idea is to
> > create a 'pid' file in the pgsql/data/base directory, and do a kill -0
> > to see if it is stil running before removing the lock.
>
> The latter approach is what I was going to suggest.  Writing a pid file
> would be a fine idea anyway --- for one thing, it makes it a lot easier
> to write a "kill the postmaster" script.  Given that the postmaster
> should write a pid file, a new postmaster should look for an existing
> pid file, and try to do a kill(pid, 0) on the number contained therein.
> If this doesn't return an error, then you figure there is already a
> postmaster running, complain, and exit.  Otherwise you figure you is it,
> (re)write the pid file and away you go.  Then pqcomm.c can just
> unconditionally delete any old file that's in the way of making the
> pipe.
>
> The pidfile checking and creation probably ought to go in postmaster.c,
> not down inside pqcomm.c.  I never liked the fact that a critical
> interlock function was being done by a low-level library that one might
> not even want to invoke (if all your clients are using TCP, opening up
> the Unix-domain socket is a waste of time, no?).
>
> BTW, there is another problem with relying on flock on the socket file
> for this purpose: it opens up a hole for a denial-of-service attack.
> Anyone who can write the file can flock it.  (We already had a problem
> with DOS via creating a dummy file at /tmp/.s.PGSQL.5432, but it would
> be harder to spot the culprit with an flock-based interference.)

This came to my mind, but I didn't think this would have happened so
quickly. In my opinion the socket and the pidfile should be created in a
directory owned by postgres, for example /tmp/.Pgsql-unix, like does X.

--
Massimo Dal Zotto

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