Re: ncat - UNIX-domain sockets support

[David Fifield <david () bamsoftware com>]

On Tue, Nov 13, 2012 at 04:13:48AM -0500, Tomas Hozza wrote:
> > I'm not sure that automatic generation of a source socket filename is
> > ready, so I removed it. Is this an essential feature that other
> > netcats have?
>
> It is an essential feature for DATAGRAM UNIX domain sockets. When client
> connects to the server and doesn't create its own socket (source socket)
> it won't be able to receive any messages from the server. So if user
> connecting to a DATAGRAM UNIX domain socket didn't specified a source
> socket, then it has to be generated in order for client to receive
> messages from the server.
>
> Also older netcats had this feature. 

Okay, I see this now in netcat-openbsd:
        /* Get name of temporary socket for unix datagram client */
        if ((family == AF_UNIX) && uflag && !lflag) {
                if (sflag) {
                        unix_dg_tmp_socket = sflag;
                } else {
                        strlcpy(unix_dg_tmp_socket_buf, "/tmp/nc.XXXXXXXXXX",
                                UNIX_DG_TMP_SOCKET_SIZE);
                        if (mkstemp(unix_dg_tmp_socket_buf) == -1)
                                err(1, "mkstemp");
                        unix_dg_tmp_socket = unix_dg_tmp_socket_buf;
                }
        }

I agree now that Ncat should do something compatible. Would you produce
a new patch (you can base it on your old patch) adding support for this
automatic creation? The only thing is that we shouldn't use a hardcoded
"/tmp". This page has a code example that reads the TMPDIR and TMP
environment variables in addition to using mkstemp:

http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/avoid-race.html#TEMPORARY-FILES

> > There is code in ncat_connect to delete the source socket, but
> > 1) it deletes the file even if not automatically generated; i.e., if the
> > user used --source, and 
>
> Actually it doesn't matter if it was generated or specified by user. It had
> to be created by Ncat when it was connecting and should be removed, because
> it is just temporary and only for the client to be able receive messages.

This seems weird to me. If I make my own socket in the filesystem and
tell Ncat to use it, I don't expect it to be deleted. But that's what
netcat-openbsd does, and I think we should be compatible in this case.

David Fifield
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