MailScanner/Postfix message duplication - possible fix

[Drew Marshall]

Thanks, I'll give it a go. Am I right in assuming this is a Postfix patch
not a MailScanner patch?

Drew

Kash, Howard (Civ,ARL/CISD) said:
> Here is a solution Julian proposed to the postfix/still being
> delivered/duplicate message problem back in September.  Based on my
> analysis of the Postfix code and logs from actual occurrences of the
> bug, I think this is along the right track.  However, postfix postdates
> messages that it moves into the deferred queue by 1000 seconds
> (minimal_backoff_time default value).  My version of this patch is:
>
>     next if ($ModDate{$file} + 10) > (time + 1000);
>
> or more efficiently:
>
>     next if $ModDate{$file} > (time + 990);
>
> This accounts for the 1000 second postdate period and adds 10 seconds to
> get around the apparent race condition.  In every occurrence that I've
> seen of the bug, MailScanner starts it's scan just as a message is being
> processed (moved into the deferred queue) by postfix.  I think there is
> a brief instance when postfix does not have a lock on the file and
> MailScanner picks it up (and locks it).  Then postfix tries to lock the
> file.  Seeing that it is already locked, it generates the "skipped,
> still being delivered" message and backs off for 60 seconds (see
> nqmgr/qmgr_active.c:qmgr_active_feed()) and then re-queues the message
> again.
>
> You will need to adjust the 1000 second value if you have changed the
> default postfix setting for minimal_backoff_time.  You may also want to
> play around with the 10 second delay if it's too long or short.  Since
> the bug is very difficult to reproduce and occurs so infrequently, it's
> hard to say yet if this is actually working.  If others could try it out
> and let the list know if it seems to be working for them, maybe Julian
> can add it to the next release.  The only side affect of adding this
> line will be a 10 second delay in mail delivery.
>
>
>
> Howard
>
>
> -----Original Message-----
> From: Julian Field [mailto:mailscanner at ECS.SOTON.AC.UK]
> Sent: Thursday, September 04, 2003 6:45 AM
> To: MAILSCANNER at JISCMAIL.AC.UK
> Subject: Re: MailScanner+PostFix ---- try this
>
>
> Here's a patch to Postfix.pm. I know it's not exactly a neat solution to
> the problem, but if it fixes it I will know I have found the problem.
>
> --- Postfix.pm.old      2003-09-01 12:28:21.000000000 +0100
> +++ Postfix.pm  2003-09-04 11:49:17.000000000 +0100
> @@ -1132,6 +1132,9 @@
>         #print STDERR "Files are " . join(', ', @SortedFiles) . "\n";
>         while(defined($file = shift @SortedFiles) &&
>               $HitLimit1+$HitLimit2+$HitLimit3+$HitLimit4<1) {
> +        # Yes I know this is a hack but it will help isolate the
> problem
> +        next if $ModDate{$file} > time-3;
> +
>           # must separate next two lines or $1 gets re-tainted by being
> part of
>           # same expression as $file [mumble mumble grrr mumble mumble]
>           #print STDERR "Reading file $file from list\n";
>