hostapd: Add mechanism to track unconnected stations

hostapd can now be configured to track unconnected stations based on
Probe Request frames seen from them. This can be used, e.g., to detect
dualband capable station before they have associated. Such information
could then be used to provide guidance on which colocated BSS to use in
case of a dualband AP that operates concurrently on multiple bands under
the control of a single hostapd process.

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

hostapd/config_file.c

@@ -3399,6 +3399,10 @@ static int hostapd_config_fill(struct hostapd_config *conf,
 		}
 		conf->fst_cfg.llt = (u32) val;
 #endif /* CONFIG_FST */
+	} else if (os_strcmp(buf, "track_sta_max_num") == 0) {
+		conf->track_sta_max_num = atoi(pos);
+	} else if (os_strcmp(buf, "track_sta_max_age") == 0) {
+		conf->track_sta_max_age = atoi(pos);
 	} else {
 		wpa_printf(MSG_ERROR,
 			   "Line %d: unknown configuration item '%s'",

hostapd/ctrl_iface.c

@@ -2007,6 +2007,39 @@ static int hostapd_ctrl_iface_log_level(struct hostapd_data *hapd, char *cmd,
 }
 
 
+#ifdef NEED_AP_MLME
+static int hostapd_ctrl_iface_track_sta_list(struct hostapd_data *hapd,
+					     char *buf, size_t buflen)
+{
+	struct hostapd_iface *iface = hapd->iface;
+	char *pos, *end;
+	struct hostapd_sta_info *info;
+	struct os_reltime now;
+
+	sta_track_expire(iface, 0);
+
+	pos = buf;
+	end = buf + buflen;
+
+	os_get_reltime(&now);
+	dl_list_for_each_reverse(info, &iface->sta_seen,
+				 struct hostapd_sta_info, list) {
+		struct os_reltime age;
+		int ret;
+
+		os_reltime_sub(&now, &info->last_seen, &age);
+		ret = os_snprintf(pos, end - pos, MACSTR " %u\n",
+				  MAC2STR(info->addr), (unsigned int) age.sec);
+		if (os_snprintf_error(end - pos, ret))
+			break;
+		pos += ret;
+	}
+
+	return pos - buf;
+}
+#endif /* NEED_AP_MLME */
+
+
 static int hostapd_ctrl_iface_receive_process(struct hostapd_data *hapd,
 					      char *buf, char *reply,
 					      int reply_size,
@@ -2238,6 +2271,11 @@ static int hostapd_ctrl_iface_receive_process(struct hostapd_data *hapd,
 	} else if (os_strncmp(buf, "LOG_LEVEL", 9) == 0) {
 		reply_len = hostapd_ctrl_iface_log_level(
 			hapd, buf + 9, reply, reply_size);
+#ifdef NEED_AP_MLME
+	} else if (os_strcmp(buf, "TRACK_STA_LIST") == 0) {
+		reply_len = hostapd_ctrl_iface_track_sta_list(
+			hapd, reply, reply_size);
+#endif /* NEED_AP_MLME */
 	} else {
 		os_memcpy(reply, "UNKNOWN COMMAND\n", 16);
 		reply_len = 16;

hostapd/hostapd.conf

@@ -1279,6 +1279,15 @@ own_ip_addr=127.0.0.1
 # default: 60
 #ap_table_expiration_time=3600
 
+# Maximum number of stations to track on the operating channel
+# This can be used to detect dualband capable stations before they have
+# associated, e.g., to provide guidance on which colocated BSS to use.
+# Default: 0 (disabled)
+#track_sta_max_num=100
+
+# Maximum age of a station tracking entry in seconds
+# Default: 180
+#track_sta_max_age=180
 
 ##### Wi-Fi Protected Setup (WPS) #############################################
 

src/ap/ap_config.c

@@ -172,6 +172,7 @@ struct hostapd_config * hostapd_config_defaults(void)
 
 	conf->ap_table_max_size = 255;
 	conf->ap_table_expiration_time = 60;
+	conf->track_sta_max_age = 180;
 
 #ifdef CONFIG_TESTING_OPTIONS
 	conf->ignore_probe_probability = 0.0;

src/ap/ap_config.h

@@ -586,6 +586,9 @@ struct hostapd_config {
 	int ap_table_max_size;
 	int ap_table_expiration_time;
 
+	unsigned int track_sta_max_num;
+	unsigned int track_sta_max_age;
+
 	char country[3]; /* first two octets: country code as described in
 			  * ISO/IEC 3166-1. Third octet:
 			  * ' ' (ascii 32): all environments

src/ap/beacon.c

@@ -552,6 +552,76 @@ static enum ssid_match_result ssid_match(struct hostapd_data *hapd,
 }
 
 
+void sta_track_expire(struct hostapd_iface *iface, int force)
+{
+	struct os_reltime now;
+	struct hostapd_sta_info *info;
+
+	if (!iface->num_sta_seen)
+		return;
+
+	os_get_reltime(&now);
+	while ((info = dl_list_first(&iface->sta_seen, struct hostapd_sta_info,
+				     list))) {
+		if (!force &&
+		    !os_reltime_expired(&now, &info->last_seen,
+					iface->conf->track_sta_max_age))
+			break;
+		force = 0;
+
+		wpa_printf(MSG_MSGDUMP, "%s: Expire STA tracking entry for "
+			   MACSTR, iface->bss[0]->conf->iface,
+			   MAC2STR(info->addr));
+		dl_list_del(&info->list);
+		iface->num_sta_seen--;
+		os_free(info);
+	}
+}
+
+
+static struct hostapd_sta_info * sta_track_get(struct hostapd_iface *iface,
+					       const u8 *addr)
+{
+	struct hostapd_sta_info *info;
+
+	dl_list_for_each(info, &iface->sta_seen, struct hostapd_sta_info, list)
+		if (os_memcmp(addr, info->addr, ETH_ALEN) == 0)
+			return info;
+
+	return NULL;
+}
+
+
+static void sta_track_add(struct hostapd_iface *iface, const u8 *addr)
+{
+	struct hostapd_sta_info *info;
+
+	info = sta_track_get(iface, addr);
+	if (info) {
+		/* Move the most recent entry to the end of the list */
+		dl_list_del(&info->list);
+		dl_list_add_tail(&iface->sta_seen, &info->list);
+		os_get_reltime(&info->last_seen);
+		return;
+	}
+
+	/* Add a new entry */
+	info = os_zalloc(sizeof(*info));
+	os_memcpy(info->addr, addr, ETH_ALEN);
+	os_get_reltime(&info->last_seen);
+
+	if (iface->num_sta_seen >= iface->conf->track_sta_max_num) {
+		/* Expire oldest entry to make room for a new one */
+		sta_track_expire(iface, 1);
+	}
+
+	wpa_printf(MSG_MSGDUMP, "%s: Add STA tracking entry for "
+		   MACSTR, iface->bss[0]->conf->iface, MAC2STR(addr));
+	dl_list_add_tail(&iface->sta_seen, &info->list);
+	iface->num_sta_seen++;
+}
+
+
 void handle_probe_req(struct hostapd_data *hapd,
 		      const struct ieee80211_mgmt *mgmt, size_t len,
 		      int ssi_signal)
@@ -567,6 +637,8 @@ void handle_probe_req(struct hostapd_data *hapd,
 	ie = mgmt->u.probe_req.variable;
 	if (len < IEEE80211_HDRLEN + sizeof(mgmt->u.probe_req))
 		return;
+	if (hapd->iconf->track_sta_max_num)
+		sta_track_add(hapd->iface, mgmt->sa);
 	ie_len = len - (IEEE80211_HDRLEN + sizeof(mgmt->u.probe_req));
 
 	for (i = 0; hapd->probereq_cb && i < hapd->num_probereq_cb; i++)

src/ap/beacon.h

@@ -21,5 +21,6 @@ int ieee802_11_update_beacons(struct hostapd_iface *iface);
 int ieee802_11_build_ap_params(struct hostapd_data *hapd,
 			       struct wpa_driver_ap_params *params);
 void ieee802_11_free_ap_params(struct wpa_driver_ap_params *params);
+void sta_track_expire(struct hostapd_iface *iface, int force);
 
 #endif /* BEACON_H */

src/ap/hostapd.c

@@ -355,6 +355,22 @@ static void hostapd_cleanup(struct hostapd_data *hapd)
 }
 
 
+static void sta_track_deinit(struct hostapd_iface *iface)
+{
+	struct hostapd_sta_info *info;
+
+	if (!iface->num_sta_seen)
+		return;
+
+	while ((info = dl_list_first(&iface->sta_seen, struct hostapd_sta_info,
+				     list))) {
+		dl_list_del(&info->list);
+		iface->num_sta_seen--;
+		os_free(info);
+	}
+}
+
+
 static void hostapd_cleanup_iface_partial(struct hostapd_iface *iface)
 {
 	wpa_printf(MSG_DEBUG, "%s(%p)", __func__, iface);
@@ -370,6 +386,7 @@ static void hostapd_cleanup_iface_partial(struct hostapd_iface *iface)
 	os_free(iface->basic_rates);
 	iface->basic_rates = NULL;
 	ap_list_deinit(iface);
+	sta_track_deinit(iface);
 }
 
 
@@ -1623,6 +1640,7 @@ int hostapd_setup_interface_complete(struct hostapd_iface *iface, int err)
 	hostapd_tx_queue_params(iface);
 
 	ap_list_init(iface);
+	dl_list_init(&iface->sta_seen);
 
 	hostapd_set_acl(hapd);
 

src/ap/hostapd.h

@@ -281,6 +281,12 @@ struct hostapd_data {
 };
 
 
+struct hostapd_sta_info {
+	struct dl_list list;
+	u8 addr[ETH_ALEN];
+	struct os_reltime last_seen;
+};
+
 /**
  * struct hostapd_iface - hostapd per-interface data structure
  */
@@ -409,6 +415,9 @@ struct hostapd_iface {
 
 	void (*scan_cb)(struct hostapd_iface *iface);
 	int num_ht40_scan_tries;
+
+	struct dl_list sta_seen; /* struct hostapd_sta_info */
+	unsigned int num_sta_seen;
 };
 
 /* hostapd.c */