WPS ER: Add more details to wps_er_pbc failure returns

Indicate the reason for the failure when wps_er_pbc is rejected.

src/wps/wps_er.c

@@ -1455,7 +1455,7 @@ int wps_er_pbc(struct wps_er *er, const u8 *uuid)
 	if (wps_registrar_pbc_overlap(er->wps->registrar, NULL, NULL)) {
 		wpa_printf(MSG_DEBUG, "WPS ER: PBC overlap - do not start PBC "
 			   "mode");
-		return -1;
+		return -2;
 	}
 
 	ap = wps_er_ap_get(er, NULL, uuid);
@@ -1469,7 +1469,12 @@ int wps_er_pbc(struct wps_er *er, const u8 *uuid)
 			}
 		}
 		if (sta == NULL)
-			return -1; /* Unknown UUID */
+			return -3; /* Unknown UUID */
+	}
+
+	if (ap->ap_settings == NULL) {
+		wpa_printf(MSG_DEBUG, "WPS ER: AP settings not known");
+		return -4;
 	}
 
 	er->set_sel_reg_uuid_filter = uuid;

wpa_supplicant/ctrl_iface.c

@@ -2809,7 +2809,17 @@ char * wpa_supplicant_ctrl_iface_process(struct wpa_supplicant *wpa_s,
 		if (wpa_supplicant_ctrl_iface_wps_er_pin(wpa_s, buf + 11))
 			reply_len = -1;
 	} else if (os_strncmp(buf, "WPS_ER_PBC ", 11) == 0) {
-		if (wpas_wps_er_pbc(wpa_s, buf + 11))
+		int ret = wpas_wps_er_pbc(wpa_s, buf + 11);
+		if (ret == -2) {
+			os_memcpy(reply, "FAIL-PBC-OVERLAP\n", 17);
+			reply_len = 17;
+		} else if (ret == -3) {
+			os_memcpy(reply, "FAIL-UNKNOWN-UUID\n", 18);
+			reply_len = 18;
+		} else if (ret == -4) {
+			os_memcpy(reply, "FAIL-NO-AP-SETTINGS\n", 20);
+			reply_len = 20;
+		} else if (ret)
 			reply_len = -1;
 	} else if (os_strncmp(buf, "WPS_ER_LEARN ", 13) == 0) {
 		if (wpa_supplicant_ctrl_iface_wps_er_learn(wpa_s, buf + 13))