hostapd: Add Key MIC in group EAPOL-Key frames corruption test option

For some testing it can be useful to force the Key MIC in group
EAPOL-Key frames to be corrupt. Add an option to allow setting a
probability for corrupting the Key MIC and use it in the WPA code,
increasing the first byte of the MIC by one to corrupt it if desired.

Signed-hostap: Johannes Berg <johannes.berg@intel.com>

hostapd/config_file.c

@@ -2893,6 +2893,7 @@ static int hostapd_config_fill(struct hostapd_config *conf,
 		PARSE_TEST_PROBABILITY(ignore_auth_probability)
 		PARSE_TEST_PROBABILITY(ignore_assoc_probability)
 		PARSE_TEST_PROBABILITY(ignore_reassoc_probability)
+		PARSE_TEST_PROBABILITY(corrupt_gtk_rekey_mic_probability)
 #endif /* CONFIG_TESTING_OPTIONS */
 		} else if (os_strcmp(buf, "vendor_elements") == 0) {
 			struct wpabuf *elems;

hostapd/hostapd.conf

@@ -1540,6 +1540,9 @@ own_ip_addr=127.0.0.1
 #
 # Ignore reassociation requests with the given probability
 #ignore_reassoc_probability=0.0
+#
+# Corrupt Key MIC in GTK rekey EAPOL-Key frames with the given probability
+#corrupt_gtk_rekey_mic_probability=0.0
 
 ##### Multiple BSSID support ##################################################
 #

src/ap/ap_config.c

@@ -168,6 +168,7 @@ struct hostapd_config * hostapd_config_defaults(void)
 	conf->ignore_auth_probability = 0.0d;
 	conf->ignore_assoc_probability = 0.0d;
 	conf->ignore_reassoc_probability = 0.0d;
+	conf->corrupt_gtk_rekey_mic_probability = 0.0d;
 #endif /* CONFIG_TESTING_OPTIONS */
 
 	return conf;

src/ap/ap_config.h

@@ -526,6 +526,7 @@ struct hostapd_config {
 	double ignore_auth_probability;
 	double ignore_assoc_probability;
 	double ignore_reassoc_probability;
+	double corrupt_gtk_rekey_mic_probability;
 #endif /* CONFIG_TESTING_OPTIONS */
 };
 

src/ap/wpa_auth.c

@@ -1347,6 +1347,16 @@ void __wpa_send_eapol(struct wpa_authenticator *wpa_auth,
 		}
 		wpa_eapol_key_mic(sm->PTK.kck, version, (u8 *) hdr, len,
 				  key->key_mic);
+#ifdef CONFIG_TESTING_OPTIONS
+		if (!pairwise &&
+		    wpa_auth->conf.corrupt_gtk_rekey_mic_probability > 0.0d &&
+		    drand48() <
+		    wpa_auth->conf.corrupt_gtk_rekey_mic_probability) {
+			wpa_auth_logger(wpa_auth, sm->addr, LOGGER_INFO,
+					"Corrupting group EAPOL-Key Key MIC");
+			key->key_mic[0]++;
+		}
+#endif /* CONFIG_TESTING_OPTIONS */
 	}
 
 	wpa_auth_set_eapol(sm->wpa_auth, sm->addr, WPA_EAPOL_inc_EapolFramesTx,

src/ap/wpa_auth.h

@@ -160,6 +160,9 @@ struct wpa_auth_config {
 #endif /* CONFIG_IEEE80211R */
 	int disable_gtk;
 	int ap_mlme;
+#ifdef CONFIG_TESTING_OPTIONS
+	double corrupt_gtk_rekey_mic_probability;
+#endif /* CONFIG_TESTING_OPTIONS */
 };
 
 typedef enum {

src/ap/wpa_auth_glue.c

@@ -28,6 +28,7 @@
 
 
 static void hostapd_wpa_auth_conf(struct hostapd_bss_config *conf,
+				  struct hostapd_config *iconf,
 				  struct wpa_auth_config *wconf)
 {
 	os_memset(wconf, 0, sizeof(*wconf));
@@ -74,6 +75,10 @@ static void hostapd_wpa_auth_conf(struct hostapd_bss_config *conf,
 #ifdef CONFIG_HS20
 	wconf->disable_gtk = conf->disable_dgaf;
 #endif /* CONFIG_HS20 */
+#ifdef CONFIG_TESTING_OPTIONS
+	wconf->corrupt_gtk_rekey_mic_probability =
+		iconf->corrupt_gtk_rekey_mic_probability;
+#endif /* CONFIG_TESTING_OPTIONS */
 }
 
 
@@ -509,7 +514,7 @@ int hostapd_setup_wpa(struct hostapd_data *hapd)
 	const u8 *wpa_ie;
 	size_t wpa_ie_len;
 
-	hostapd_wpa_auth_conf(hapd->conf, &_conf);
+	hostapd_wpa_auth_conf(hapd->conf, hapd->iconf, &_conf);
 	if (hapd->iface->drv_flags & WPA_DRIVER_FLAGS_EAPOL_TX_STATUS)
 		_conf.tx_status = 1;
 	if (hapd->iface->drv_flags & WPA_DRIVER_FLAGS_AP_MLME)
@@ -583,7 +588,7 @@ int hostapd_setup_wpa(struct hostapd_data *hapd)
 void hostapd_reconfig_wpa(struct hostapd_data *hapd)
 {
 	struct wpa_auth_config wpa_auth_conf;
-	hostapd_wpa_auth_conf(hapd->conf, &wpa_auth_conf);
+	hostapd_wpa_auth_conf(hapd->conf, hapd->iconf, &wpa_auth_conf);
 	wpa_reconfig(hapd->wpa_auth, &wpa_auth_conf);
 }