Fix timeout in LDAP lookup of libpq connection parameters

Bind attempts to an LDAP server should time out after two seconds,
allowing additional lines in the service control file to be parsed
(which provide a fall back to a secondary LDAP server or default options).
The existing code failed to enforce that timeout during TCP connect,
resulting in a hang far longer than two seconds if the LDAP server
does not respond.

Laurenz Albe

src/interfaces/libpq/fe-connect.c

@@ -2758,12 +2758,37 @@ ldapServiceLookup(const char *purl, PQconninfoOption *options,
 	}
 
 	/*
-	 * Initialize connection to the server.  We do an explicit bind because we
-	 * want to return 2 if the bind fails.
+	 * Perform an explicit anonymous bind.
+	 * LDAP does not require that an anonymous bind is preformed explicitly,
+	 * but we want to distinguish between the case where LDAP bind does not
+	 * succeed within PGLDAP_TIMEOUT seconds (return 2 to continue parsing
+	 * the service control file) and the case where querying the LDAP server
+	 * fails (return 1 to end parsing).
+	 * Unfortunately there is no way of setting a timeout that works for
+	 * both Windows and OpenLDAP.
 	 */
+#ifdef WIN32
+	/* the nonstandard ldap_connect function performs an anonymous bind */
+	if (ldap_connect(ld, &time) != LDAP_SUCCESS)
+	{
+		/* error or timeout in ldap_connect */
+		free(url);
+		ldap_unbind(ld);
+		return 2;
+	}
+#else /* WIN32 */
+	/* in OpenLDAP, use the LDAP_OPT_NETWORK_TIMEOUT option */
+	if (ldap_set_option(ld, LDAP_OPT_NETWORK_TIMEOUT, &time) != LDAP_SUCCESS)
+	{
+		free(url);
+		ldap_unbind(ld);
+		return 3;
+	}
+
+	/* anonymous bind */
 	if ((msgid = ldap_simple_bind(ld, NULL, NULL)) == -1)
 	{
-		/* error in ldap_simple_bind() */
+		/* error or network timeout */
 		free(url);
 		ldap_unbind(ld);
 		return 2;
@@ -2774,18 +2799,25 @@ ldapServiceLookup(const char *purl, PQconninfoOption *options,
 	if ((rc = ldap_result(ld, msgid, LDAP_MSG_ALL, &time, &res)) == -1 ||
 		res == NULL)
 	{
+		/* error or timeout */
 		if (res != NULL)
-		{
-			/* timeout */
 			ldap_msgfree(res);
-		}
-		/* error in ldap_result() */
 		free(url);
 		ldap_unbind(ld);
 		return 2;
 	}
 	ldap_msgfree(res);
 
+	/* reset timeout */
+	time.tv_sec = -1;
+	if (ldap_set_option(ld, LDAP_OPT_NETWORK_TIMEOUT, &time) != LDAP_SUCCESS)
+	{
+		free(url);
+		ldap_unbind(ld);
+		return 3;
+	}
+#endif /* WIN32 */
+
 	/* search */
 	res = NULL;
 	if ((rc = ldap_search_st(ld, dn, scope, filter, attrs, 0, &time, &res))