SAE: Reuse previously generated PWE on a retry with the same AP

Do not start SAE authentication from scratch when the AP requests
anti-clogging token to be used. Instead, use the previously generated
PWE as-is if the retry is for the same AP and the same group. This saves
unnecessary processing on the station side in case the AP is under heavy
SAE authentiation load.

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

src/common/sae.h

@@ -41,6 +41,7 @@ struct sae_temporary_data {
 	struct wpabuf *anti_clogging_token;
 	char *pw_id;
 	int vlan_id;
+	u8 bssid[ETH_ALEN];
 };
 
 enum sae_state {

wpa_supplicant/sme.c

@@ -84,7 +84,8 @@ static int sme_set_sae_group(struct wpa_supplicant *wpa_s)
 
 static struct wpabuf * sme_auth_build_sae_commit(struct wpa_supplicant *wpa_s,
 						 struct wpa_ssid *ssid,
-						 const u8 *bssid, int external)
+						 const u8 *bssid, int external,
+						 int reuse)
 {
 	struct wpabuf *buf;
 	size_t len;
@@ -111,6 +112,12 @@ static struct wpabuf * sme_auth_build_sae_commit(struct wpa_supplicant *wpa_s,
 		return NULL;
 	}
 
+	if (reuse && wpa_s->sme.sae.tmp &&
+	    os_memcmp(bssid, wpa_s->sme.sae.tmp->bssid, ETH_ALEN) == 0) {
+		wpa_printf(MSG_DEBUG,
+			   "SAE: Reuse previously generated PWE on a retry with the same AP");
+		goto reuse_data;
+	}
 	if (sme_set_sae_group(wpa_s) < 0) {
 		wpa_printf(MSG_DEBUG, "SAE: Failed to select group");
 		return NULL;
@@ -123,7 +130,10 @@ static struct wpabuf * sme_auth_build_sae_commit(struct wpa_supplicant *wpa_s,
 		wpa_printf(MSG_DEBUG, "SAE: Could not pick PWE");
 		return NULL;
 	}
+	if (wpa_s->sme.sae.tmp)
+		os_memcpy(wpa_s->sme.sae.tmp->bssid, bssid, ETH_ALEN);
 
+reuse_data:
 	len = wpa_s->sme.sae_token ? wpabuf_len(wpa_s->sme.sae_token) : 0;
 	if (ssid->sae_password_id)
 		len += 4 + os_strlen(ssid->sae_password_id);
@@ -631,7 +641,8 @@ static void sme_send_authentication(struct wpa_supplicant *wpa_s,
 	if (!skip_auth && params.auth_alg == WPA_AUTH_ALG_SAE) {
 		if (start)
 			resp = sme_auth_build_sae_commit(wpa_s, ssid,
-							 bss->bssid, 0);
+							 bss->bssid, 0,
+							 start == 2);
 		else
 			resp = sme_auth_build_sae_confirm(wpa_s, 0);
 		if (resp == NULL) {
@@ -914,7 +925,7 @@ static void sme_external_auth_send_sae_commit(struct wpa_supplicant *wpa_s,
 {
 	struct wpabuf *resp, *buf;
 
-	resp = sme_auth_build_sae_commit(wpa_s, ssid, bssid, 1);
+	resp = sme_auth_build_sae_commit(wpa_s, ssid, bssid, 1, 0);
 	if (!resp)
 		return;
 
@@ -1065,7 +1076,7 @@ static int sme_sae_auth(struct wpa_supplicant *wpa_s, u16 auth_transaction,
 							 len - sizeof(le16));
 		if (!external)
 			sme_send_authentication(wpa_s, wpa_s->current_bss,
-						wpa_s->current_ssid, 1);
+						wpa_s->current_ssid, 2);
 		else
 			sme_external_auth_send_sae_commit(
 				wpa_s, wpa_s->sme.ext_auth.bssid,