WPS: Lock AP Setup on multiple AP PIN validation failures

If a Registrar tries to configure the AP, but fails to validate the
device password (AP PIN), lock the AP setup after four failures. This
protects the AP PIN against brute force guessing attacks.

hostapd/hostapd.conf

@@ -956,6 +956,11 @@ own_ip_addr=127.0.0.1
 #	to external program(s)
 # Note: With wps_cred_processing=1, skip_cred_build should be set to 1 and
 # extra_cred be used to provide the Credential data for Enrollees.
+#
+# wps_cred_processing=1 will disabled automatic updates of hostapd.conf file
+# both for Credential processing and for marking AP Setup Locked based on
+# validation failures of AP PIN. An external program is responsible on updating
+# the configuration appropriately in this case.
 #wps_cred_processing=0
 
 # AP Settings Attributes for M7

hostapd/hostapd.h

@@ -95,6 +95,7 @@ struct hostapd_data {
 	size_t wps_beacon_ie_len;
 	u8 *wps_probe_resp_ie;
 	size_t wps_probe_resp_ie_len;
+	unsigned int ap_pin_failures;
 #endif /* CONFIG_WPS */
 };
 

hostapd/wps_hostapd.c

@@ -376,6 +376,57 @@ static int hostapd_wps_cred_cb(void *ctx, const struct wps_credential *cred)
 }
 
 
+static void hostapd_pwd_auth_fail(struct hostapd_data *hapd,
+				  struct wps_event_pwd_auth_fail *data)
+{
+	FILE *f;
+
+	if (!data->enrollee)
+		return;
+
+	/*
+	 * Registrar failed to prove its knowledge of the AP PIN. Lock AP setup
+	 * if this happens multiple times.
+	 */
+	hapd->ap_pin_failures++;
+	if (hapd->ap_pin_failures < 4)
+		return;
+
+	wpa_msg(hapd, MSG_INFO, WPS_EVENT_AP_SETUP_LOCKED);
+	hapd->wps->ap_setup_locked = 1;
+
+	wps_registrar_update_ie(hapd->wps->registrar);
+
+	if (hapd->conf->wps_cred_processing == 1)
+		return;
+
+	f = fopen(hapd->iface->config_fname, "a");
+	if (f == NULL) {
+		wpa_printf(MSG_WARNING, "WPS: Could not append to the current "
+			   "configuration file");
+		return;
+	}
+
+	fprintf(f, "# WPS AP Setup Locked based on possible attack\n");
+	fprintf(f, "ap_setup_locked=1\n");
+	fclose(f);
+
+	/* TODO: dualband AP may need to update multiple configuration files */
+
+	wpa_printf(MSG_DEBUG, "WPS: AP configuration updated");
+}
+
+
+static void hostapd_wps_event_cb(void *ctx, enum wps_event event,
+				 union wps_event_data *data)
+{
+	struct hostapd_data *hapd = ctx;
+
+	if (event == WPS_EV_PWD_AUTH_FAIL)
+		hostapd_pwd_auth_fail(hapd, &data->pwd_auth_fail);
+}
+
+
 static void hostapd_wps_clear_ies(struct hostapd_data *hapd)
 {
 	os_free(hapd->wps_beacon_ie);
@@ -406,6 +457,7 @@ int hostapd_init_wps(struct hostapd_data *hapd,
 		return -1;
 
 	wps->cred_cb = hostapd_wps_cred_cb;
+	wps->event_cb = hostapd_wps_event_cb;
 	wps->cb_ctx = hapd;
 
 	os_memset(&cfg, 0, sizeof(cfg));

src/common/wpa_ctrl.h

@@ -73,6 +73,7 @@ extern "C" {
 #define WPS_EVENT_PIN_NEEDED "WPS-PIN-NEEDED "
 #define WPS_EVENT_NEW_AP_SETTINGS "WPS-NEW-AP-SETTINGS "
 #define WPS_EVENT_REG_SUCCESS "WPS-REG-SUCCESS "
+#define WPS_EVENT_AP_SETUP_LOCKED "WPS-AP-SETUP-LOCKED "
 
 
 /* wpa_supplicant/hostapd control interface access */

src/wps/wps.h

@@ -278,7 +278,12 @@ enum wps_event {
 	/**
 	 * WPS_EV_SUCCESS - Registration succeeded
 	 */
-	WPS_EV_SUCCESS
+	WPS_EV_SUCCESS,
+
+	/**
+	 * WPS_EV_PWD_AUTH_FAIL - Password authentication failed
+	 */
+	WPS_EV_PWD_AUTH_FAIL
 };
 
 /**
@@ -312,6 +317,11 @@ union wps_event_data {
 	struct wps_event_fail {
 		int msg;
 	} fail;
+
+	struct wps_event_pwd_auth_fail {
+		int enrollee;
+		int part;
+	} pwd_auth_fail;
 };
 
 /**
@@ -444,6 +454,7 @@ int wps_registrar_unlock_pin(struct wps_registrar *reg, const u8 *uuid);
 int wps_registrar_button_pushed(struct wps_registrar *reg);
 void wps_registrar_probe_req_rx(struct wps_registrar *reg, const u8 *addr,
 				const struct wpabuf *wps_data);
+int wps_registrar_update_ie(struct wps_registrar *reg);
 
 unsigned int wps_pin_checksum(unsigned int pin);
 unsigned int wps_pin_valid(unsigned int pin);

src/wps/wps_common.c

@@ -321,3 +321,17 @@ void wps_success_event(struct wps_context *wps)
 
 	wps->event_cb(wps->cb_ctx, WPS_EV_SUCCESS, NULL);
 }
+
+
+void wps_pwd_auth_fail_event(struct wps_context *wps, int enrollee, int part)
+{
+	union wps_event_data data;
+
+	if (wps->event_cb == NULL)
+		return;
+
+	os_memset(&data, 0, sizeof(data));
+	data.pwd_auth_fail.enrollee = enrollee;
+	data.pwd_auth_fail.part = part;
+	wps->event_cb(wps->cb_ctx, WPS_EV_PWD_AUTH_FAIL, &data);
+}

src/wps/wps_enrollee.c

@@ -580,6 +580,7 @@ static int wps_process_r_snonce1(struct wps_data *wps, const u8 *r_snonce1)
 		wpa_printf(MSG_DEBUG, "WPS: R-Hash1 derived from R-S1 does "
 			   "not match with the pre-committed value");
 		wps->config_error = WPS_CFG_DEV_PASSWORD_AUTH_FAILURE;
+		wps_pwd_auth_fail_event(wps->wps, 1, 1);
 		return -1;
 	}
 
@@ -619,6 +620,7 @@ static int wps_process_r_snonce2(struct wps_data *wps, const u8 *r_snonce2)
 		wpa_printf(MSG_DEBUG, "WPS: R-Hash2 derived from R-S2 does "
 			   "not match with the pre-committed value");
 		wps->config_error = WPS_CFG_DEV_PASSWORD_AUTH_FAILURE;
+		wps_pwd_auth_fail_event(wps->wps, 1, 2);
 		return -1;
 	}
 

src/wps/wps_i.h

@@ -187,6 +187,7 @@ struct wpabuf * wps_decrypt_encr_settings(struct wps_data *wps, const u8 *encr,
 					  size_t encr_len);
 void wps_fail_event(struct wps_context *wps, enum wps_msg_type msg);
 void wps_success_event(struct wps_context *wps);
+void wps_pwd_auth_fail_event(struct wps_context *wps, int enrollee, int part);
 
 /* wps_attr_parse.c */
 int wps_parse_msg(const struct wpabuf *msg, struct wps_parse_attr *attr);

src/wps/wps_registrar.c

@@ -1477,6 +1477,7 @@ static int wps_process_e_snonce1(struct wps_data *wps, const u8 *e_snonce1)
 		wpa_printf(MSG_DEBUG, "WPS: E-Hash1 derived from E-S1 does "
 			   "not match with the pre-committed value");
 		wps->config_error = WPS_CFG_DEV_PASSWORD_AUTH_FAILURE;
+		wps_pwd_auth_fail_event(wps->wps, 0, 1);
 		return -1;
 	}
 
@@ -1517,6 +1518,7 @@ static int wps_process_e_snonce2(struct wps_data *wps, const u8 *e_snonce2)
 			   "not match with the pre-committed value");
 		wps_registrar_invalidate_pin(wps->wps->registrar, wps->uuid_e);
 		wps->config_error = WPS_CFG_DEV_PASSWORD_AUTH_FAILURE;
+		wps_pwd_auth_fail_event(wps->wps, 0, 2);
 		return -1;
 	}
 
@@ -2219,3 +2221,9 @@ enum wps_process_res wps_registrar_process_msg(struct wps_data *wps,
 		return WPS_FAILURE;
 	}
 }
+
+
+int wps_registrar_update_ie(struct wps_registrar *reg)
+{
+	return wps_set_ie(reg);
+}

wpa_supplicant/wps_supplicant.c

@@ -275,6 +275,8 @@ static void wpa_supplicant_wps_event(void *ctx, enum wps_event event,
 	case WPS_EV_SUCCESS:
 		wpa_supplicant_wps_event_success(wpa_s);
 		break;
+	case WPS_EV_PWD_AUTH_FAIL:
+		break;
 	}
 }