Re: [NSE] Draft - targets-sniffer.nse

[Nick Nikolaou <nikolasnikolaou1 () gmail com>]

> Not exactly, at least not if timeout stands for "total execution
> time". In case the timeout is set to 4sec for instance, and if the
> script receives a packet after 3.90 sec, it will start a loop for
> another 4 seconds. Maybe it is an intended behavior but I think that
> most users will expect the script to sniff for the exact duration they
> supplied. You could update the timeout at each iteration to have a
> finer control of the execution time.


You are right, I meant to set the socket timeout as a constant (example 1-2
seconds) and that way depending on the frequency of packets it would always
timeout within 1 or 2 seconds. Your way makes more sense since it would
allow the script to sniff for the exact time specified and there's no reason
for all the extra receive calls.

 Cool! Unless I am missing a reason not to do so, you could even move
> the last call into the prerule function


Done.


> Finally, I would also suggest to use stdnse.get_script_args() instead
> of reading arguments from the registry. This could be combined with
> the addition of a default value for the timeout.


Good idea, thanks.

I made all the changes.
Thanks again for your help.


Nick

On 28 March 2011 15:48, Henri Doreau <henri.doreau () greenbone net> wrote:

> Hi Nick,
>
> 2011/3/28 Nick Nikolaou <nikolasnikolaou1 () gmail com>:
> > Hello everyone once again,
> >
> > I made some further changes to the script:
> >
> > 1. Removed the simple *.*.*.255 broadcast check since it wouldn't do
> > anything on a VLSM network. The script now gets the broadcast address
> > using Djalal's patch and iface_info.broadcast.
> >
> > 2. Changed the way IP addresses are extracted from packets. That is now
> done
> > using the packet library.
> Nice work.
>
> > 3. Timeout works as it should.
> Not exactly, at least not if timeout stands for "total execution
> time". In case the timeout is set to 4sec for instance, and if the
> script receives a packet after 3.90 sec, it will start a loop for
> another 4 seconds. Maybe it is an intended behavior but I think that
> most users will expect the script to sniff for the exact duration they
> supplied. You could update the timeout at each iteration to have a
> finer control of the execution time.
> Here is an example:
>
> <...>
> sock:pcap_open(iface, 104, false , "ip")
> stdnse.print_debug(1, "Using interface %s", iface)
>
> repeat
>
>    local start_time = nmap.clock_ms() -- Used for script timeout
>
>    sock:set_timeout(timeout)
>    local status, _, _, layer3 = sock:pcap_receive()
>
>    if status then
>        local ip_src, ip_dst = get_ip_addresses(layer3)
>        <...check and store IP addresses...>
>    end
>
>    -- update timeout
>    timeout = timeout - (nmap.clock_ms() - start_time)
>
> until timeout <= 0
>
> sock:pcap_close()
> <...>
>
> This code uses a repeat...until form that avoid duplicate calls to
> pcap_receive(). The timeout is also set before the call to
> pcap_receive().
>
> > 4. As per Henri's suggestion most of the initializations are now inside
> > functions (with a couple of exceptions) and code should be easier to
> follow.
> >  I also checked that variables and functions have the correct scope.
>
> Cool! Unless I am missing a reason not to do so, you could even move
> the last call into the prerule function:
> <...>
> if nmap.is_privileged() then
>     iface = nmap.get_interface()
>     if iface then
>        return true
> <...>
>
> > 5. The script doesn't default to eth0 if no interface is specified but
> > prints an error message.
> >
> > As you know by now, the script relies heavily on Djalal's interface patch
> so
> > the patch needs to be added first in order to use the script.
>
> Finally, I would also suggest to use stdnse.get_script_args() instead
> of reading arguments from the registry. This could be combined with
> the addition of a default value for the timeout.
> <...>
> local timeoutstr = stdnse.get_script_args("targets-sniffer.timeout")
> or tostring(DEFAULT_TIMEOUT_SEC)
> local timeout = stdnse.parse_timespec(timeoutstr) * 1000
> <...>
>
> > I hope you find this useful.
> >
> >
> > Cheers,
> > Nick
> Regards.
>
> --
> Henri Doreau |  Greenbone Networks GmbH  |  http://www.greenbone.net
> Neuer Graben 17, 49074 Osnabrueck, Germany | AG Osnabrueck, HR B 202460
> Executive Directors: Lukas Grunwald, Dr. Jan-Oliver Wagner

Attachment: targets-sniffer.nse
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