Thread

1. Crash on attempt to connect to nonstarted server

   Magnus Hagander <magnus@hagander.net> — 2010-12-16T13:27:18Z

   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().
   
   -- 
    Magnus Hagander
    Me: http://www.hagander.net/
    Work: http://www.redpill-linpro.com/
   
   

2. Re: Crash on attempt to connect to nonstarted server

   Bruce Momjian <bruce@momjian.us> — 2010-12-16T15:20:44Z

   Magnus Hagander wrote:
   > 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().
   
   I have researched this with Magnus, and was able to reproduce the
   failure.  It happens only on Win32 because that is missing unix-domain
   sockets so "" maps to localhost, which is an IP address.  I have applied
   the attached patch.  The new output is:
   
   	$ psql test
   	psql: could not connect to server: Connection refused
           Is the server running on host "???" and accepting
           TCP/IP connections on port 5432?
   
   Note the "???".  This happens because the mapping of "" to localhost
   happens below the libpq library variable level.
   
   -- 
     Bruce Momjian  <bruce@momjian.us>        http://momjian.us
     EnterpriseDB                             http://enterprisedb.com
   
     + It's impossible for everything to be true. +
   

3. Re: Crash on attempt to connect to nonstarted server

   Tom Lane <tgl@sss.pgh.pa.us> — 2010-12-16T15:39:04Z

   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?
   
   			regards, tom lane
   
   

4. Re: Crash on attempt to connect to nonstarted server

   Bruce Momjian <bruce@momjian.us> — 2010-12-16T15:59:34Z

   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. +