Allow dynamic choice of source port

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As it is openvpn has no way to allow the kernel to dynamically choose a source port for it's connections. If you have two openvpn client processes on the same machine both you have to configure lport to different ports manually. This patch allows you to specify '--lport 0' and get the behaviour of normal programs, where the source port is dynamically chosen.

Not sure if this is an issue for others, but here's the patch in case anyone has run into the same issue.

Cheers,
Nate Nielsen

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diff -rU 3 ../openvpn-2.0/options.c ./options.c
@@ -3189,7 +3189,7 @@
       ++i;
       VERIFY_PERMISSION (OPT_P_GENERAL);
       port = atoi (p[1]);
-      if (!legal_ipv4_port (port))
+      if (port != 0 && !legal_ipv4_port (port))
 	{
 	  msg (msglevel, "Bad local port number: %s", p[1]);
 	  goto err;

diff -rU 3 ../openvpn-2.0/socket.c ./socket.c
@@ -737,7 +737,20 @@
 	       print_sockaddr (&sock->info.lsa->local, &gc),
 	       strerror_ts (errnum, &gc));
 	}
+
+      /* If the local port was '0' look it up again */
+      if (sock->local_port == 0)
+	{
+	  socklen_t l = sizeof(sock->info.lsa->local);
+	  if (getsockname (sock->sd, (struct sockaddr *)&sock->info.lsa->local, &l) < 0)
+	    {
+	      const int errnum = openvpn_errno_socket ();
+	      msg (M_FATAL, "TCP/UDP: Socket lookup failed: %s",
+		   strerror_ts (errnum, &gc));
+	    }
+	}
     }
+
   gc_free (&gc);
 }
 

How is this different from simply using --nobind to allocate a dynamic port #?

James

The issue I ran into was that I did want to bind to an address (in order to make the packets come from a specific interface) but not to a specific port (as in some cases I needed to run multiple openvpn processes on a single interface).

Cheers,
Nate