Crash on attempt to connect to nonstarted server

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/

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(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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

Magnus Hagander <magnus(at)hagander(dot)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

Tom Lane wrote:
> Magnus Hagander <magnus(at)hagander(dot)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(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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