hostapd: Add Multi-AP protocol support

The purpose of Multi-AP specification is to enable inter-operability
across Wi-Fi access points (APs) from different vendors.

This patch introduces one new configuration parameter 'multi_ap' to
enable Multi-AP functionality and to configure the BSS as a backhaul
and/or fronthaul BSS.

Advertise vendor specific Multi-AP capabilities in (Re)Association
Response frame, if Multi-AP functionality is enabled through the
configuration parameter.

A backhaul AP must support receiving both 3addr and 4addr frames from a
backhaul STA, so create a VLAN for it just like is done for WDS, i.e.,
by calling hostapd_set_wds_sta(). Since Multi-AP requires WPA2 (never
WEP), we can safely call hostapd_set_wds_encryption() as well and we can
reuse the entire WDS condition.

To parse the Multi-AP Extension subelement, we use get_ie(): even though
that function is meant for parsing IEs, it works for subelements.

Signed-off-by: Venkateswara Naralasetty <vnaralas@codeaurora.org>
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

hostapd/config_file.c

@@ -4130,6 +4130,16 @@ static int hostapd_config_fill(struct hostapd_config *conf,
 	} else if (os_strcmp(buf, "coloc_intf_reporting") == 0) {
 		bss->coloc_intf_reporting = atoi(pos);
 #endif /* CONFIG_OWE */
+	} else if (os_strcmp(buf, "multi_ap") == 0) {
+		int val = atoi(pos);
+
+		if (val < 0 || val > 3) {
+			wpa_printf(MSG_ERROR, "Line %d: Invalid multi_ap '%s'",
+				   line, buf);
+			return -1;
+		}
+
+		bss->multi_ap = val;
 	} else {
 		wpa_printf(MSG_ERROR,
 			   "Line %d: unknown configuration item '%s'",

hostapd/hostapd.conf

@@ -438,6 +438,13 @@ wmm_ac_vo_txop_limit=47
 wmm_ac_vo_acm=0
 # Note: for IEEE 802.11b mode: cWmin=3 cWmax=4 burst=102
 
+# Enable Multi-AP functionality
+# 0 = disabled (default)
+# 1 = AP support backhaul BSS
+# 2 = AP support fronthaul BSS
+# 3 = AP supports both backhaul BSS and fronthaul BSS
+#multi_ap=0
+
 # Static WEP key configuration
 #
 # The key number to use when transmitting.

src/ap/ap_config.h

@@ -694,6 +694,10 @@ struct hostapd_bss_config {
 	int coloc_intf_reporting;
 
 	u8 send_probe_response;
+
+#define BACKHAUL_BSS 1
+#define FRONTHAUL_BSS 2
+	int multi_ap; /* bitmap of BACKHAUL_BSS, FRONTHAUL_BSS */
 };
 
 /**

src/ap/ieee802_11.c

@@ -63,6 +63,22 @@ prepare_auth_resp_fils(struct hostapd_data *hapd,
 		       int *is_pub);
 #endif /* CONFIG_FILS */
 
+
+u8 * hostapd_eid_multi_ap(struct hostapd_data *hapd, u8 *eid)
+{
+	u8 multi_ap_val = 0;
+
+	if (!hapd->conf->multi_ap)
+		return eid;
+	if (hapd->conf->multi_ap & BACKHAUL_BSS)
+		multi_ap_val |= MULTI_AP_BACKHAUL_BSS;
+	if (hapd->conf->multi_ap & FRONTHAUL_BSS)
+		multi_ap_val |= MULTI_AP_FRONTHAUL_BSS;
+
+	return eid + add_multi_ap_ie(eid, 9, multi_ap_val);
+}
+
+
 u8 * hostapd_eid_supp_rates(struct hostapd_data *hapd, u8 *eid)
 {
 	u8 *pos = eid;
@@ -2211,6 +2227,57 @@ static u16 check_wmm(struct hostapd_data *hapd, struct sta_info *sta,
 	return WLAN_STATUS_SUCCESS;
 }
 
+static u16 check_multi_ap(struct hostapd_data *hapd, struct sta_info *sta,
+			  const u8 *multi_ap_ie, size_t multi_ap_len)
+{
+	u8 multi_ap_value = 0;
+
+	sta->flags &= ~WLAN_STA_MULTI_AP;
+
+	if (!hapd->conf->multi_ap)
+		return WLAN_STATUS_SUCCESS;
+
+	if (multi_ap_ie) {
+		const u8 *multi_ap_subelem;
+
+		multi_ap_subelem = get_ie(multi_ap_ie + 4,
+					  multi_ap_len - 4,
+					  MULTI_AP_SUB_ELEM_TYPE);
+		if (multi_ap_subelem && multi_ap_subelem[1] == 1) {
+			multi_ap_value = multi_ap_subelem[2];
+		} else {
+			hostapd_logger(hapd, sta->addr,
+				       HOSTAPD_MODULE_IEEE80211,
+				       HOSTAPD_LEVEL_INFO,
+				       "Multi-AP IE has missing or invalid Multi-AP subelement");
+			return WLAN_STATUS_INVALID_IE;
+		}
+	}
+
+	if (multi_ap_value == MULTI_AP_BACKHAUL_STA)
+		sta->flags |= WLAN_STA_MULTI_AP;
+
+	if ((hapd->conf->multi_ap & BACKHAUL_BSS) &&
+	    multi_ap_value == MULTI_AP_BACKHAUL_STA)
+		return WLAN_STATUS_SUCCESS;
+
+	if (hapd->conf->multi_ap & FRONTHAUL_BSS) {
+		if (multi_ap_value == MULTI_AP_BACKHAUL_STA) {
+			hostapd_logger(hapd, sta->addr,
+				       HOSTAPD_MODULE_IEEE80211,
+				       HOSTAPD_LEVEL_INFO,
+				       "Backhaul STA tries to associate with fronthaul-only BSS");
+			return WLAN_STATUS_ASSOC_DENIED_UNSPEC;
+		}
+		return WLAN_STATUS_SUCCESS;
+	}
+
+	hostapd_logger(hapd, sta->addr, HOSTAPD_MODULE_IEEE80211,
+		       HOSTAPD_LEVEL_INFO,
+		       "Non-Multi-AP STA tries to associate with backhaul-only BSS");
+	return WLAN_STATUS_ASSOC_DENIED_UNSPEC;
+}
+
 
 static u16 copy_supp_rates(struct hostapd_data *hapd, struct sta_info *sta,
 			   struct ieee802_11_elems *elems)
@@ -2467,6 +2534,11 @@ static u16 check_assoc_ies(struct hostapd_data *hapd, struct sta_info *sta,
 	resp = copy_supp_rates(hapd, sta, &elems);
 	if (resp != WLAN_STATUS_SUCCESS)
 		return resp;
+
+	resp = check_multi_ap(hapd, sta, elems.multi_ap, elems.multi_ap_len);
+	if (resp != WLAN_STATUS_SUCCESS)
+		return resp;
+
 #ifdef CONFIG_IEEE80211N
 	resp = copy_sta_ht_capab(hapd, sta, elems.ht_capabilities);
 	if (resp != WLAN_STATUS_SUCCESS)
@@ -3040,6 +3112,9 @@ static u16 send_assoc_resp(struct hostapd_data *hapd, struct sta_info *sta,
 	}
 #endif /* CONFIG_WPS */
 
+	if (sta && (sta->flags & WLAN_STA_MULTI_AP))
+		p = hostapd_eid_multi_ap(hapd, p);
+
 #ifdef CONFIG_P2P
 	if (sta && sta->p2p_ie && hapd->p2p_group) {
 		struct wpabuf *p2p_resp_ie;
@@ -4291,7 +4366,7 @@ static void handle_assoc_cb(struct hostapd_data *hapd,
 		sta->flags |= WLAN_STA_WDS;
 	}
 
-	if (sta->flags & WLAN_STA_WDS) {
+	if (sta->flags & (WLAN_STA_WDS | WLAN_STA_MULTI_AP)) {
 		int ret;
 		char ifname_wds[IFNAMSIZ + 1];
 

src/ap/sta_info.c

@@ -166,7 +166,7 @@ void ap_free_sta(struct hostapd_data *hapd, struct sta_info *sta)
 	/* just in case */
 	ap_sta_set_authorized(hapd, sta, 0);
 
-	if (sta->flags & WLAN_STA_WDS)
+	if (sta->flags & (WLAN_STA_WDS | WLAN_STA_MULTI_AP))
 		hostapd_set_wds_sta(hapd, NULL, sta->addr, sta->aid, 0);
 
 	if (sta->ipaddr)

src/ap/sta_info.h

@@ -36,6 +36,7 @@
 #define WLAN_STA_VHT_OPMODE_ENABLED BIT(20)
 #define WLAN_STA_VENDOR_VHT BIT(21)
 #define WLAN_STA_PENDING_FILS_ERP BIT(22)
+#define WLAN_STA_MULTI_AP BIT(23)
 #define WLAN_STA_PENDING_DISASSOC_CB BIT(29)
 #define WLAN_STA_PENDING_DEAUTH_CB BIT(30)
 #define WLAN_STA_NONERP BIT(31)

src/common/ieee802_11_common.c

@@ -126,6 +126,10 @@ static int ieee802_11_parse_vendor_specific(const u8 *pos, size_t elen,
 			elems->roaming_cons_sel = pos;
 			elems->roaming_cons_sel_len = elen;
 			break;
+		case MULTI_AP_OUI_TYPE:
+			elems->multi_ap = pos;
+			elems->multi_ap_len = elen;
+			break;
 		default:
 			wpa_printf(MSG_MSGDUMP, "Unknown WFA "
 				   "information element ignored "
@@ -1558,6 +1562,26 @@ size_t mbo_add_ie(u8 *buf, size_t len, const u8 *attr, size_t attr_len)
 }
 
 
+size_t add_multi_ap_ie(u8 *buf, size_t len, u8 value)
+{
+	u8 *pos = buf;
+
+	if (len < 9)
+		return 0;
+
+	*pos++ = WLAN_EID_VENDOR_SPECIFIC;
+	*pos++ = 7; /* len */
+	WPA_PUT_BE24(pos, OUI_WFA);
+	pos += 3;
+	*pos++ = MULTI_AP_OUI_TYPE;
+	*pos++ = MULTI_AP_SUB_ELEM_TYPE;
+	*pos++ = 1; /* len */
+	*pos++ = value;
+
+	return pos - buf;
+}
+
+
 static const struct country_op_class us_op_class[] = {
 	{ 1, 115 },
 	{ 2, 118 },

src/common/ieee802_11_common.h

@@ -86,6 +86,7 @@ struct ieee802_11_elems {
 	const u8 *roaming_cons_sel;
 	const u8 *password_id;
 	const u8 *oci;
+	const u8 *multi_ap;
 
 	u8 ssid_len;
 	u8 supp_rates_len;
@@ -133,6 +134,7 @@ struct ieee802_11_elems {
 	u8 roaming_cons_sel_len;
 	u8 password_id_len;
 	u8 oci_len;
+	u8 multi_ap_len;
 
 	struct mb_ies_info mb_ies;
 };
@@ -194,6 +196,8 @@ const u8 * get_ie_ext(const u8 *ies, size_t len, u8 ext);
 
 size_t mbo_add_ie(u8 *buf, size_t len, const u8 *attr, size_t attr_len);
 
+size_t add_multi_ap_ie(u8 *buf, size_t len, u8 value);
+
 struct country_op_class {
 	u8 country_op_class;
 	u8 global_op_class;

src/common/ieee802_11_defs.h

@@ -1213,6 +1213,13 @@ struct ieee80211_ampe_ie {
 #define MBO_OUI_TYPE 22
 #define OWE_IE_VENDOR_TYPE 0x506f9a1c
 #define OWE_OUI_TYPE 28
+#define MULTI_AP_OUI_TYPE 0x1B
+
+#define MULTI_AP_SUB_ELEM_TYPE 0x06
+#define MULTI_AP_TEAR_DOWN BIT(4)
+#define MULTI_AP_FRONTHAUL_BSS BIT(5)
+#define MULTI_AP_BACKHAUL_BSS BIT(6)
+#define MULTI_AP_BACKHAUL_STA BIT(7)
 
 #define WMM_OUI_TYPE 2
 #define WMM_OUI_SUBTYPE_INFORMATION_ELEMENT 0