The original patch to disallow non-passworded connections to non-superusers

failed to cover all the ways in which a connection can be initiated in dblink.
Plug the remaining holes.  Also, disallow transient connections in functions
for which that feature makes no sense (because they are only sensible as
part of a sequence of operations on the same connection).  Joe Conway

Security: CVE-2007-6601

contrib/dblink/dblink.c

@@ -84,6 +84,7 @@ static HeapTuple get_tuple_of_interest(Oid relid, int2vector *pkattnums, int16 p
 static Oid	get_relid_from_relname(text *relname_text);
 static char *generate_relation_name(Oid relid);
 static char *connstr_strip_password(const char *connstr);
+static void dblink_security_check(PGconn *conn, remoteConn *rconn, const char *connstr);
 
 /* Global */
 static remoteConn *pconn = NULL;
@@ -170,6 +171,7 @@ typedef struct remoteConnHashEnt
 			else \
 			{ \
 				connstr = conname_or_str; \
+				dblink_security_check(conn, rconn, connstr); \
 				conn = PQconnectdb(connstr); \
 				if (PQstatus(conn) == CONNECTION_BAD) \
 				{ \
@@ -224,27 +226,8 @@ dblink_connect(PG_FUNCTION_ARGS)
 	if (connname)
 		rconn = (remoteConn *) palloc(sizeof(remoteConn));
 
-	/* for non-superusers, check that server requires a password */
-	if (!superuser())
-	{
-		/* this attempt must fail */
-		conn = PQconnectdb(connstr_strip_password(connstr));
-
-		if (PQstatus(conn) == CONNECTION_OK)
-		{
-			PQfinish(conn);
-			if (rconn)
-				pfree(rconn);
-
-			ereport(ERROR,
-					(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
-					 errmsg("password is required"),
-					 errdetail("Non-superuser cannot connect if the server does not request a password."),
-					 errhint("Target server's authentication method must be changed.")));
-		}
-		else
-			PQfinish(conn);
-	}
+	/* check password used if not superuser */
+	dblink_security_check(conn, rconn, connstr);
 	conn = PQconnectdb(connstr);
 
 	MemoryContextSwitchTo(oldcontext);
@@ -2296,3 +2279,28 @@ connstr_strip_password(const char *connstr)
 
 	return result.data;
 }
+
+static void
+dblink_security_check(PGconn *conn, remoteConn *rconn, const char *connstr)
+{
+	if (!superuser())
+	{
+		/* this attempt must fail */
+		conn = PQconnectdb(connstr_strip_password(connstr));
+
+		if (PQstatus(conn) == CONNECTION_OK)
+		{
+			PQfinish(conn);
+			if (rconn)
+				pfree(rconn);
+
+			ereport(ERROR,
+					(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
+					 errmsg("password is required"),
+					 errdetail("Non-superuser cannot connect if the server does not request a password."),
+					 errhint("Target server's authentication method must be changed.")));
+		}
+		else
+			PQfinish(conn);
+	}
+}