Re: ncat udp

[Marius Sturm <marius.sturm () web de>]

Hello David,
thanks for your comments. I followed your suggestions and the patch
looks much cleaner now.
Only two points, should the ncat client be terminated after receiving a
datagram like in tcp mode?
And, should --send-only/--recv-only effect the --exec option?

Best regards,

Marius

David Fifield schrieb:
> On Wed, Mar 25, 2009 at 02:49:17PM +0100, Marius Sturm wrote:
> > I could't find a good reason, why ncat must run in a while loop when
> > using udp protocol. I would expect, that it behaves almost the same as
> > in tcp mode. Attached is a patch to go into this direction. Any comments
> > are welcome!
>
> Thank you for your patch. It is indeed a goal that --exec in UDP mode
> should work mostly like it does in TCP mode. The patch has a few
> problems but I think with some work we can make it do what we want.
>
> netrun has to return immediately after starting the child process. You
> can't call waitpid on it because Ncat won't accept any new connections
> until the child process finishes (which may be never). For example, if
> you run
>
> ncat -l --exec "/bin/cat"
> ncat localhost
> ncat localhost
>
> both clients must be able to connect at the same time and see their
> messages echoed.
>
> Where you have moved the call to netrun, the first packet received is
> discarded. If I run
>
> ncat -l --udp --exec "/bin/cat"
> ncat --udp localhost
>
> and type "a\nb\nc\n", all I get back is "b\nc\n".
>
> Can you try making the following changes? Call netrun instead of netexec
> in ncat_listen_udp, as you are doing. netrun should not need any changes;
> I don't want it to have special behavior for SOCK_DGRAM sockets. Put the
> do_listen and connect logic in its own outer loop. The idea is that we
> should create a new socket for each connection and pass it to netrun.
>
> David Fifield
>
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diff -urNb nmap/ncat/ncat_listen.c nmap-udp/ncat/ncat_listen.c
--- nmap/ncat/ncat_listen.c     2009-03-25 14:23:09.000000000 +0100
+++ nmap-udp/ncat/ncat_listen.c 2009-03-26 10:43:30.000000000 +0100
@@ -307,6 +307,12 @@
     zmem(&remotess, sizeof(remotess));
     remotess.ss_family = o.af;
 
+#ifndef WIN32
+    /* Reap on SIGCHLD */
+    Signal(SIGCHLD, sig_chld);
+#endif
+
+    while (1) {
     /* create the UDP listen socket */
     sockfd = do_listen(SOCK_DGRAM);
 
@@ -342,8 +348,10 @@
     zmem(buf, sizeof(buf));
 
     /* are we executing a command? then do it */
-    if (o.cmdexec)
-        netexec(sockfd, o.cmdexec);
+      if (o.cmdexec) {
+          netrun(sockfd, o.cmdexec);
+          continue;
+      }
 
     FD_SET(sockfd, &master);
     FD_SET(STDIN_FILENO, &master);
@@ -377,6 +385,7 @@
         
         zmem(buf, sizeof(buf));
     }
+    }
 
     return 0;
 }



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