Nmap Development: RE: Possible error message bug in nmap-4.11 on Gentoo

["Thomas Buchanan" <TBuchanan () thecompassgrp net>]

> -----Original Message-----
> From: nmap-dev-bounces () insecure org 
> [mailto:nmap-dev-bounces () insecure org] On Behalf Of Andreas Ericsson
> Sent: Thursday, October 12, 2006 8:29 AM
> To: Diman Todorov
> Cc: nmap-dev () insecure org
> Subject: Re: Possible error message bug in nmap-4.11 on Gentoo
>
> Diman Todorov wrote:
> > > Well, you *are* telling nmap to do a ping-scan (-sP) which 
> doesn't use
> > > ports, but then you specify ports as well.
> > This is not correct.
> > from the nmap man page:
> > <snip>
> >                The -sP option sends an ICMP echo request and a TCP  
> > packet to
> >                port 80 by default. When executed by an 
> unprivileged  
> > user, a SYN
> >                packet is sent (using a connect() call) to 
> port 80 on the
> > </snip>
> >
> > IMHO -sP should respect -p
> Touché. I should rtfm more carefully or, as in this case, at all :-)
>
> I'm still not sure it makes sense though, unless you use the 
> scan option 
> to control output (i.e. make hosts responding to any of the tcp-ports 
> given in the range show as "up", but nothing else). Oh well. I'm sure 
> it'll all turn out for the best.
>
> -- 
> Andreas Ericsson                   andreas.ericsson () op5 se
> OP5 AB                             www.op5.se
> Tel: +46 8-230225                  Fax: +46 8-230231

I think if you want to scan specific ports using ping style probes, you should use -PS [portlist].  From the man page: 

<snip>
-PS [portlist] (TCP SYN Ping)
     This option sends an empty TCP packet with the SYN flag set. The default destination port is
     80 (configurable at compile time by changing DEFAULT_TCP_PROBE_PORT in nmap.h), but an
     alternate port can be specified as a parameter. A comma separated list of ports can even be
     specified (e.g.  -PS22,23,25,80,113,1050,35000), in which case probes will be attempted
     against each port in parallel.
</snip>

In the source code for nmap.cc, it states that -F and -p[portlist] are NOT allowed with -sP (or -sL for that matter)

nmap.cc:
<snip>
   1166   if ((o.pingscan || o.listscan) && ports) {
   1167     fatal("You cannot use -F (fast scan) or -p (explicit port selection) with PING scan or LIST scan");
   1168   }
</snip

However, this check was being performed after a list of ports was generated by the following call:

   1151     ports = getpts(portlist);

The function getpts(portlist) is what actually prints the error message that was originally posted.

The attached proposed patch just moves the check for -F and -p up above the call to getpts().  This actually saves us 
the trouble of generating the portslist (which we end up not using).  The patched nmap produces the following output:

sudo ./nmap -sP -p1-1024 -v -v -v 192.168....

Starting Nmap 4.20ALPHA8 ( http://Insecure.Org ) at 2006-10-12 14:31 CDT
You cannot use -F (fast scan) or -p (explicit port selection) with PING scan or LIST scan
QUITTING!


Patch (against nmap-4.20ALPHA8) works for me on Linux (have not tested under Windows).  Patch also cleanly applies to 
nmap-4.11

Thomas

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