RE: [squid-users] NTLM - invalid callback data error

2003/01/10 10:33:35| AuthenticateNTLMHandleReply: invalid callback data.
Releasing helper '0x8243160'.

Hi All,

I have been following this up further recently and have been able to find a
way to replicate this error consistently.

It appears that this error occurs when you access very small files in quick
succession, like those found on java-script roll-overs when you have your
browser configured to not cache pages but to check for newer versions of
stored pages every time.

If you go to http://www.traxxas.com/ via your NTLM enabled squid you will
see on the left hand side a main menu bar. You can see if you roll over this
bar a pop-up nav bar is displayed. If you roll over this new popped-up bar
you can see that the pop-up highlights the selection you are currently
hovering over.

I have found that if I repeatedly swap between one menu option and another
on this menu (Products > Nitro & Electric for example) that cache.log will
begin to log invalid callback data errors.

One thought we had here as to what is happening is that [in
AuthenticateNTLMHandleReply()] the callback data check [cbdataValid()] is
looking at the callback memory area and seeing that it is not valid and
exiting gracefully citing the invalid callback data error. This as Henrik
said is correct and the way such an error should be handled.

I guess my question is why is the callback data not valid? Is it due to the
fact that we are requesting small objects at such a fast rate and then not
allowing them to complete downloading (the equivalent of aborting the
request?) that the memory area is released by squid, however the NTLM helper
does not know this and still continues to attempt to access it only to find
that the memory area has been freed already?

I was able to load test this a little and have the error occur a number of
times in a row (roughly 30) within a minute, fortunately this didn't crash
this server that I have been testing on. The previous crashes I reported may
have been due to the fact that my test bed was a low spec'd Celeron 500 with
256Mb RAM as opposed to this PIII 700 with 768Mb RAM.

I am now confident that NTLM should be fine in a production environment
considering that this error seems to only occur when the browser is not
caching (not the default setting) and a number of small objects are being
requested. Even if this does happen, the server should not crash which
ultimately is the main thing.

Any thoughts are welcome

Regards
Jay

-----Original Message-----
From: hno@marasystems.com [mailto:hno@marasystems.com]On Behalf Of
Henrik Nordstrom
Sent: Tuesday, 7 January 2003 11:24 AM
To: jturner@bsis.com.au
Cc: squid-users@squid-cache.org
Subject: Re: [squid-users] NTLM - invalid callback data error

Jay Turner wrote:
>
> Should I be concerned about this?
> Is there something I can do to prevent this?
>
> I still receive the error frequently, but it has not actually crashed
squid
> for sometime.
>
> Do you have the contact details for the NTLM helper author, I would like
to
> resolve this if possible as we would like to use it in production.
>
> Thanks
> Jay

I see no reason to worry. Users aborting requests are a quite frequent
operation, and if it happens while Squid and the browser is negotiating
the NTLM authentication you will see such error..

Regards
Henrik
Received on Tue Jan 14 2003 - 01:37:00 MST