DPP2: Allow station to require or not allow PFS

The new wpa_supplicant network profile parameter dpp_pfs can be used to
specify how PFS is applied to associations. The default behavior
(dpp_pfs=0) remains same as it was previously, i.e., try to use PFS if
the AP supports it. PFS use can now be required (dpp_pfs=1) or disabled
(dpp_pfs=2).

This is also working around an interoperability issue of DPP R2 STA with
certain hostapd builds that included both OWE and DPP functionality.
That issue was introduced by commit 09368515d1 ("OWE: Process
Diffie-Hellman Parameter element in AP mode") and removed by commit
16a4e931f0 ("OWE: Allow Diffie-Hellman Parameter element to be
included with DPP"). hostapd builds between those two commits would
reject DPP association attempt with PFS. The new wpa_supplicant default
(dpp_pfs=0) behavior is to automatically try to connect again with PFS
disabled if that happens.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

wpa_supplicant/config.c

@@ -2570,6 +2570,7 @@ static const struct parse_data ssid_fields[] = {
 	{ STR_LEN(dpp_netaccesskey) },
 	{ INT(dpp_netaccesskey_expiry) },
 	{ STR_LEN(dpp_csign) },
+	{ INT_RANGE(dpp_pfs, 0, 2) },
 #endif /* CONFIG_DPP */
 	{ INT_RANGE(owe_group, 0, 65535) },
 	{ INT_RANGE(owe_only, 0, 1) },

wpa_supplicant/config_file.c

@@ -928,6 +928,7 @@ static void wpa_config_write_network(FILE *f, struct wpa_ssid *ssid)
 	STR(dpp_netaccesskey);
 	INT(dpp_netaccesskey_expiry);
 	STR(dpp_csign);
+	INT(dpp_pfs);
 #endif /* CONFIG_DPP */
 	INT(owe_group);
 	INT(owe_only);

wpa_supplicant/config_ssid.h

@@ -1002,6 +1002,22 @@ struct wpa_ssid {
 	 */
 	size_t dpp_csign_len;
 
+	/**
+	 * dpp_pfs - DPP PFS
+	 * 0: allow PFS to be used or not used
+	 * 1: require PFS to be used (note: not compatible with DPP R1)
+	 * 2: do not allow PFS to be used
+	 */
+	int dpp_pfs;
+
+	/**
+	 * dpp_pfs_fallback - DPP PFS fallback selection
+	 *
+	 * This is an internally used variable (i.e., not used in external
+	 * configuration) to track state of the DPP PFS fallback mechanism.
+	 */
+	int dpp_pfs_fallback;
+
 	/**
 	 * owe_group - OWE DH Group
 	 *

wpa_supplicant/ctrl_iface.c

@@ -8106,6 +8106,7 @@ static void wpa_supplicant_ctrl_iface_flush(struct wpa_supplicant *wpa_s)
 	wpa_s->dpp_resp_retry_time = 0;
 #ifdef CONFIG_DPP2
 	wpas_dpp_chirp_stop(wpa_s);
+	wpa_s->dpp_pfs_fallback = 0;
 #endif /* CONFIG_DPP2 */
 #ifdef CONFIG_TESTING_OPTIONS
 	os_memset(dpp_pkex_own_mac_override, 0, ETH_ALEN);

wpa_supplicant/events.c

@@ -3196,6 +3196,10 @@ static void wpa_supplicant_event_assoc(struct wpa_supplicant *wpa_s,
 #ifdef CONFIG_MBO
 	wpas_mbo_check_pmf(wpa_s, bss, wpa_s->current_ssid);
 #endif /* CONFIG_MBO */
+
+#ifdef CONFIG_DPP2
+	wpa_s->dpp_pfs_fallback = 0;
+#endif /* CONFIG_DPP2 */
 }
 
 
@@ -4364,6 +4368,39 @@ static void wpas_event_assoc_reject(struct wpa_supplicant *wpa_s,
 	}
 #endif /* CONFIG_OWE */
 
+#ifdef CONFIG_DPP2
+	/* Try to follow AP's PFS policy. WLAN_STATUS_ASSOC_DENIED_UNSPEC is
+	 * the status code defined in the DPP R2 tech spec.
+	 * WLAN_STATUS_AKMP_NOT_VALID is addressed in the same manner as an
+	 * interoperability workaround with older hostapd implementation. */
+	if (wpa_s->current_ssid &&
+	    wpa_s->current_ssid->key_mgmt == WPA_KEY_MGMT_DPP &&
+	    wpa_s->current_ssid->dpp_pfs == 0 &&
+	    (data->assoc_reject.status_code ==
+	     WLAN_STATUS_ASSOC_DENIED_UNSPEC ||
+	     data->assoc_reject.status_code == WLAN_STATUS_AKMP_NOT_VALID)) {
+		struct wpa_ssid *ssid = wpa_s->current_ssid;
+		struct wpa_bss *bss = wpa_s->current_bss;
+
+		wpa_s->current_ssid->dpp_pfs_fallback ^= 1;
+		if (!bss)
+			bss = wpa_supplicant_get_new_bss(wpa_s, bssid);
+		if (!bss || wpa_s->dpp_pfs_fallback) {
+			wpa_printf(MSG_DEBUG,
+				   "DPP: Updated PFS policy for next try");
+			wpas_connection_failed(wpa_s, bssid);
+			wpa_supplicant_mark_disassoc(wpa_s);
+			return;
+		}
+		wpa_printf(MSG_DEBUG, "DPP: Try again with updated PFS policy");
+		wpa_s->dpp_pfs_fallback = 1;
+		wpas_connect_work_done(wpa_s);
+		wpa_supplicant_mark_disassoc(wpa_s);
+		wpa_supplicant_connect(wpa_s, bss, ssid);
+		return;
+	}
+#endif /* CONFIG_DPP2 */
+
 #ifdef CONFIG_MBO
 	if (data->assoc_reject.status_code ==
 	    WLAN_STATUS_DENIED_POOR_CHANNEL_CONDITIONS &&

wpa_supplicant/sme.c

@@ -1793,7 +1793,9 @@ void sme_associate(struct wpa_supplicant *wpa_s, enum wpas_mode mode,
 
 #ifdef CONFIG_DPP2
 	if (wpa_s->key_mgmt == WPA_KEY_MGMT_DPP && wpa_s->current_ssid &&
-	    wpa_s->current_ssid->dpp_netaccesskey) {
+	    wpa_s->current_ssid->dpp_netaccesskey &&
+	    wpa_s->current_ssid->dpp_pfs != 2 &&
+	    !wpa_s->current_ssid->dpp_pfs_fallback) {
 		struct wpa_ssid *ssid = wpa_s->current_ssid;
 
 		dpp_pfs_free(wpa_s->dpp_pfs);

wpa_supplicant/wpa_supplicant.c

@@ -3071,7 +3071,8 @@ static u8 * wpas_populate_assoc_ies(
 
 #ifdef CONFIG_DPP2
 	if (wpa_sm_get_key_mgmt(wpa_s->wpa) == WPA_KEY_MGMT_DPP &&
-	    ssid->dpp_netaccesskey) {
+	    ssid->dpp_netaccesskey &&
+	    ssid->dpp_pfs != 2 && !ssid->dpp_pfs_fallback) {
 		dpp_pfs_free(wpa_s->dpp_pfs);
 		wpa_s->dpp_pfs = dpp_pfs_init(ssid->dpp_netaccesskey,
 					      ssid->dpp_netaccesskey_len);

wpa_supplicant/wpa_supplicant.conf

@@ -1461,6 +1461,12 @@ fast_reauth=1
 # 1-65535 = DH Group to use for FILS PFS
 #fils_dh_group=0
 
+# DPP PFS
+# 0: allow PFS to be used or not used (default)
+# 1: require PFS to be used (note: not compatible with DPP R1)
+# 2: do not allow PFS to be used
+#dpp_pfs=0
+
 # MAC address policy
 # 0 = use permanent MAC address
 # 1 = use random MAC address for each ESS connection

wpa_supplicant/wpa_supplicant_i.h

@@ -1273,6 +1273,7 @@ struct wpa_supplicant {
 	size_t dpp_last_ssid_len;
 #ifdef CONFIG_DPP2
 	struct dpp_pfs *dpp_pfs;
+	int dpp_pfs_fallback;
 	struct wpabuf *dpp_presence_announcement;
 	struct dpp_bootstrap_info *dpp_chirp_bi;
 	int dpp_chirp_freq;