Re: Crash on attempt to connect to nonstarted server - Mailing list pgsql-hackers

From Bruce Momjian
Subject Re: Crash on attempt to connect to nonstarted server
Date
Msg-id 201012161559.oBGFxYT13934@momjian.us
Whole thread Raw
In response to Re: Crash on attempt to connect to nonstarted server  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
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/IPconnections 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. +


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