WPS: Reduce wps_ap_priority_compar() stack use

There is no need to maintain two concurrent instances of struct
wps_parse_attr in this function. Share a single structure for parsing
both IEs.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/wps/wps.c

@@ -355,16 +355,16 @@ int wps_is_addr_authorized(const struct wpabuf *msg, const u8 *addr,
 int wps_ap_priority_compar(const struct wpabuf *wps_a,
 			   const struct wpabuf *wps_b)
 {
-	struct wps_parse_attr attr_a, attr_b;
+	struct wps_parse_attr attr;
 	int sel_a, sel_b;
 
-	if (wps_a == NULL || wps_parse_msg(wps_a, &attr_a) < 0)
+	if (wps_a == NULL || wps_parse_msg(wps_a, &attr) < 0)
 		return 1;
-	if (wps_b == NULL || wps_parse_msg(wps_b, &attr_b) < 0)
-		return -1;
+	sel_a = attr.selected_registrar && *attr.selected_registrar != 0;
 
-	sel_a = attr_a.selected_registrar && *attr_a.selected_registrar != 0;
-	sel_b = attr_b.selected_registrar && *attr_b.selected_registrar != 0;
+	if (wps_b == NULL || wps_parse_msg(wps_b, &attr) < 0)
+		return -1;
+	sel_b = attr.selected_registrar && *attr.selected_registrar != 0;
 
 	if (sel_a && !sel_b)
 		return -1;