Re: [RFC] [NSE] DNS library

[Sven Klemm <sven () c3d2 de>]

Hi Philip,

> I've been working on a DNS library for NSE.

very nice library.

> The most interesting function for you probably is
>
> dns.query(dname, dtype, host, port, tries)
>
> where all but the first arguments are optional:
> * dname is the domain name to query
> * dtype is the number of the DNS record type you want.
>   Usually you use dns.types.* (e.g. dns.types.MX).
>   It also accepts strings (e.g. "A", "PTR", ...) which it looks
>   up in the dns.types table.
> * host and port are the nameserver you want to ask
> * tries is the number of tries, so it won't get into an
>    infinite loop on circular references
>
> It then tries to find a nice answer depending on the answer it
> received and the DNS record type.

Can you explain this a bit more?

> If no nameserver is given it tries to use the nameservers known
> to Nmap. This works only if you apply the patch I attached,
> which is against the current svn version (rev 9443).
>
> For a reverse lookup you need dns.reverse(ip) to
> prepare the IP address for a PTR query:
>
> dns.query(dns.reverse(ip), dns.types.PTR))

I am getting the following error with the version you posted:
SCRIPT ENGINE: ./nselib/dns.lua:422: bad argument #2 to 'unpack' 
(string expected, got nil)

The reason for this is L is 64 bit on my architecture and it will be 
for all architectures once my patch for binlib gets applied. The 
attached patch fixes dns.lua to use I instead.

Is querying for SRV implemented? I tried it but it returned false and 
a table with an empty questions table and an empty answers table. 
Maybe it could give an error message for types not supported.

> One detail I'd like to change is instead of passing four optional
> arguments to pass only one option table (maybe with some
> more options, e.g. set "no recurse" option or omit trying to
> format the answer).

I think passing the options in a table is a great idea as it allows to 
add further options later without changing the function signature.

Cheers,
Sven

--
Sven Klemm
http://cthulhu.c3d2.de/~sven/

--- nselib/dns.lua.orig 2008-08-14 16:08:05.000000000 +0200
+++ nselib/dns.lua      2008-08-14 16:02:48.000000000 +0200
@@ -473,7 +473,7 @@
         entry.SOA.retry, 
         entry.SOA.expire, 
         entry.SOA.minimum 
-        = bin.unpack(">L5", data, np)
+        = bin.unpack(">I5", data, np)
    end
 
 ---
@@ -526,7 +526,7 @@
    for i = 1, count do
       local currRR = {}
       pos, currRR.dname = decStr(data, pos)
-      pos, currRR.dtype, currRR.class, currRR.ttl = bin.unpack(">SSL", data, pos)
+      pos, currRR.dtype, currRR.class, currRR.ttl = bin.unpack(">SSI", data, pos)
 
       local reslen
       pos, reslen = bin.unpack(">S", data, pos)


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