Re: Crash on attempt to connect to nonstarted server

Tom Lane wrote:
> Magnus Hagander <magnus@hagander.net> writes:
> > I get a crash on win32 when connecting to a server that's not started.
> > In fe-connect.c, we have:
> 
> > 		display_host_addr = (conn->pghostaddr == NULL) &&
> > 			(strcmp(conn->pghost, host_addr) != 0);
> 
> > In my case, conn->pghost is NULL at this point, as is
> > conn->pghostaddr. Thus, it crashes in strcmp().
> 
> [ scratches head... ]  I seem to remember having decided that patch was
> OK because what was there before already assumed conn->pghost would be
> set.  Under exactly what conditions could we get this far with neither
> field being set?

OK, sure, I can explain.  What happens in libpq is that when no host
name is supplied, you get a default.  On Unix, that is unix-domain
sockets, but on Win32, that is localhost, meaning IP.

The problem is that the mapping of "" maps to localhost in
connectDBStart(), specificially here:

	#ifdef HAVE_UNIX_SOCKETS
	        /* pghostaddr and pghost are NULL, so use Unix domain socket */
	        node = NULL;
	        hint.ai_family = AF_UNIX;
	        UNIXSOCK_PATH(portstr, portnum, conn->pgunixsocket);
	#else
	        /* Without Unix sockets, default to localhost instead */
	        node = "localhost";
	        hint.ai_family = AF_UNSPEC;
	#endif   /* HAVE_UNIX_SOCKETS */

The problem is that this is setting up the pg_getaddrinfo_all() call,
and is _not_ setting any of the libpq variables that we actually test in
the error message section that had the bug.

The 9.0 code has a convoluted test in the appendPQExpBuffer statement:

        appendPQExpBuffer(&conn->errorMessage,
                          libpq_gettext("could not connect to server: %s\n"
                     "\tIs the server running on host \"%s\" and accepting\n"
                                        "\tTCP/IP connections on port %s?\n"),
                          SOCK_STRERROR(errorno, sebuf, sizeof(sebuf)),
                          conn->pghostaddr
                          ? conn->pghostaddr
                          : (conn->pghost
                             ? conn->pghost
                             : "???"),
                          conn->pgport);

but it clearly expects either or both could be NULL.  That code is
actually still in appendPQExpBuffer() in git master.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +