Option to reduce Probe Response frame responses during max STA

The new hostapd configuration parameter no_probe_resp_if_max_sta=1 can
be used to request hostapd not to reply to broadcast Probe Request
frames from unassociated STA if there is no room for additional stations
(max_num_sta). This can be used to discourage a STA from trying to
associate with this AP if the association would be rejected due to
maximum STA limit.

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

hostapd/config_file.c

@@ -2734,6 +2734,8 @@ static int hostapd_config_fill(struct hostapd_config *conf,
 			conf->preamble = LONG_PREAMBLE;
 	} else if (os_strcmp(buf, "ignore_broadcast_ssid") == 0) {
 		bss->ignore_broadcast_ssid = atoi(pos);
+	} else if (os_strcmp(buf, "no_probe_resp_if_max_sta") == 0) {
+		bss->no_probe_resp_if_max_sta = atoi(pos);
 	} else if (os_strcmp(buf, "wep_default_key") == 0) {
 		bss->ssid.wep.idx = atoi(pos);
 		if (bss->ssid.wep.idx > 3) {

hostapd/hostapd.conf

@@ -267,6 +267,13 @@ auth_algs=3
 #     requests for broadcast SSID
 ignore_broadcast_ssid=0
 
+# Do not reply to broadcast Probe Request frames from unassociated STA if there
+# is no room for additional stations (max_num_sta). This can be used to
+# discourage a STA from trying to associate with this AP if the association
+# would be rejected due to maximum STA limit.
+# Default: 0 (disabled)
+#no_probe_resp_if_max_sta=0
+
 # Additional vendor specific elements for Beacon and Probe Response frames
 # This parameter can be used to add additional vendor specific element(s) into
 # the end of the Beacon and Probe Response frames. The format for these

src/ap/ap_config.h

@@ -366,6 +366,7 @@ struct hostapd_bss_config {
 
 	int ap_max_inactivity;
 	int ignore_broadcast_ssid;
+	int no_probe_resp_if_max_sta;
 
 	int wmm_enabled;
 	int wmm_uapsd;

src/ap/beacon.c

@@ -844,6 +844,17 @@ void handle_probe_req(struct hostapd_data *hapd,
 		return;
 	}
 
+	if (hapd->conf->no_probe_resp_if_max_sta &&
+	    is_multicast_ether_addr(mgmt->da) &&
+	    is_multicast_ether_addr(mgmt->bssid) &&
+	    hapd->num_sta >= hapd->conf->max_num_sta &&
+	    !ap_get_sta(hapd, mgmt->sa)) {
+		wpa_printf(MSG_MSGDUMP, "%s: Ignore Probe Request from " MACSTR
+			   " since no room for additional STA",
+			   hapd->conf->iface, MAC2STR(mgmt->sa));
+		return;
+	}
+
 #ifdef CONFIG_TESTING_OPTIONS
 	if (hapd->iconf->ignore_probe_probability > 0.0 &&
 	    drand48() < hapd->iconf->ignore_probe_probability) {