PASN: Derive KDK only when required

When a PTK derivation is done as part of PASN authentication flow, a KDK
derivation should be done if and only if the higher layer protocol is
supported by both parties.

Fix the code accordingly, so KDK would be derived if and only if both
sides support Secure LTF.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>

src/ap/ieee802_11.c

@@ -2646,7 +2646,7 @@ static void pasn_fils_auth_resp(struct hostapd_data *hapd,
 			      wpabuf_head(pasn->secret),
 			      wpabuf_len(pasn->secret),
 			      &sta->pasn->ptk, sta->pasn->akmp,
-			      sta->pasn->cipher, WPA_KDK_MAX_LEN);
+			      sta->pasn->cipher, sta->pasn->kdk_len);
 	if (ret) {
 		wpa_printf(MSG_DEBUG, "PASN: FILS: Failed to derive PTK");
 		goto fail;
@@ -2883,7 +2883,7 @@ pasn_derive_keys(struct hostapd_data *hapd, struct sta_info *sta,
 	ret = pasn_pmk_to_ptk(pmk, pmk_len, sta->addr, hapd->own_addr,
 			      wpabuf_head(secret), wpabuf_len(secret),
 			      &sta->pasn->ptk, sta->pasn->akmp,
-			      sta->pasn->cipher, WPA_KDK_MAX_LEN);
+			      sta->pasn->cipher, sta->pasn->kdk_len);
 	if (ret) {
 		wpa_printf(MSG_DEBUG, "PASN: Failed to derive PTK");
 		return -1;
@@ -3151,6 +3151,15 @@ static void handle_auth_pasn_1(struct hostapd_data *hapd, struct sta_info *sta,
 	sta->pasn->akmp = rsn_data.key_mgmt;
 	sta->pasn->cipher = rsn_data.pairwise_cipher;
 
+	if (hapd->conf->force_kdk_derivation ||
+	    ((hapd->iface->drv_flags2 & WPA_DRIVER_FLAGS2_SEC_LTF) &&
+	     elems.rsnxe && elems.rsnxe_len >= 2 &&
+	     (WPA_GET_LE16(elems.rsnxe) & BIT(WLAN_RSNX_CAPAB_SECURE_LTF))))
+		sta->pasn->kdk_len = WPA_KDK_MAX_LEN;
+	else
+		sta->pasn->kdk_len = 0;
+	wpa_printf(MSG_DEBUG, "PASN: kdk_len=%zu", sta->pasn->kdk_len);
+
 	if (!elems.pasn_params || !elems.pasn_params_len) {
 		wpa_printf(MSG_DEBUG,
 			   "PASN: No PASN Parameters element found");

src/ap/sta_info.h

@@ -88,6 +88,7 @@ struct pasn_data {
 	u16 group;
 	u8 trans_seq;
 	u8 wrapped_data_format;
+	size_t kdk_len;
 
 	u8 hash[SHA384_MAC_LEN];
 	struct wpa_ptk ptk;

wpa_supplicant/pasn_supplicant.c

@@ -1052,6 +1052,17 @@ static int wpas_pasn_start(struct wpa_supplicant *wpa_s, const u8 *bssid,
 	pasn->cipher = cipher;
 	pasn->group = group;
 	pasn->freq = freq;
+
+	if (wpa_s->conf->force_kdk_derivation ||
+	    (wpa_s->drv_flags2 & WPA_DRIVER_FLAGS2_SEC_LTF &&
+	     beacon_rsnxe && beacon_rsnxe_len >= 4 &&
+	     (WPA_GET_LE16(beacon_rsnxe + 2) &
+	      BIT(WLAN_RSNX_CAPAB_SECURE_LTF))))
+		pasn->kdk_len = WPA_KDK_MAX_LEN;
+	else
+		pasn->kdk_len = 0;
+	wpa_printf(MSG_DEBUG, "PASN: kdk_len=%zu", pasn->kdk_len);
+
 	os_memcpy(pasn->bssid, bssid, ETH_ALEN);
 
 	wpa_printf(MSG_DEBUG,
@@ -1480,7 +1491,7 @@ int wpas_pasn_auth_rx(struct wpa_supplicant *wpa_s,
 			      wpa_s->own_addr, pasn->bssid,
 			      wpabuf_head(secret), wpabuf_len(secret),
 			      &pasn->ptk, pasn->akmp, pasn->cipher,
-			      WPA_KDK_MAX_LEN);
+			      pasn->kdk_len);
 	if (ret) {
 		wpa_printf(MSG_DEBUG, "PASN: Failed to derive PTK");
 		goto fail;

wpa_supplicant/wpa_supplicant_i.h

@@ -539,6 +539,7 @@ struct wpas_pasn {
 	int cipher;
 	u16 group;
 	int freq;
+	size_t kdk_len;
 
 	u8 trans_seq;
 	u8 status;