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Re: Timing race cars with a sundial (-sV match performance)
From: Fyodor <fyodor () insecure org>
Date: Fri, 8 May 2009 17:27:58 -0700

On Fri, May 08, 2009 at 10:07:03PM +0000, Brandon Enright wrote:
A few weeks ago I embarked on a (mostly) futile attempt to measure the
performance of applying a PCRE match expression in our

Thanks for sending the results, even if they weren't all you hoped.

As for optimizing these matches, for the LPD match we really need to
add an anchor.  I did some checking and all UCSD hosts that match the
service can safely add '^' and still match.

Sounds like a good idea.

The '^.*' usage in the ser2net match is counter-productive.  I don't
have any matching services so I don't know what can be done to
improve on '^.*' besides just removing it.

Removing the "^.*" sounds like the way to go, as it seems completely
pointless to me.

The Xylan PizzaSwitch telnetd match is pretty zealous in its use
of .* early in the match.  Telnet services often match the start and
then print a large amount of data (banners, abuse warnings, etc).  '.*'
is consuming all of that data on all telnet services and then
backtracking a byte at a time.  We should make the '.*' lazy by changing
it to ".*?". Even better would be to add a few more matching bytes to
match the telnet control bytes before using '.*' but we may not have
enough data to do this.

I'll forward you some Xylan PizzaSwitch signatures in a few minutes in
case it helps to have the extra data.

The Cyrus Murder matches look like a '^' can be added.  The protocol
looks like IMAP and it is safe to anchor the \* in IMAP with '^'.  UCSD
doesn't have any Cyrus Murder installs for me to test.  I'd suggest we
add the anchor and then wait for new submissions if it doesn't match.

Sounds reasonable.

I'm happy to submit a patch that does all of the above if it sounds
reasonable.

Yeah, please do create such a patch and check it in.

We might also think about adding Nmap internal performance statistics
logging to Nmap proper similar to my addition of
log_write(LOG_STATS, ...) in this branch.  I feel like sometimes using
- -d3 or more is too much data when all you want to do is measure
performance stats.

Have written up anywhere how this feature works?  We do try to avoid
filling Nmap with too much debugging code, but sometimes it is
definitely worthwhile.

Cheers,
-F


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