wpa_auth: Fix race in rejecting 4-way handshake for entropy

When there is not enough entropy and there are two station associating
at the same time, one of the stations will be rejected, but during
that rejection, the "reject_4way_hs_for_entropy" flag gets cleared. This
may allow the second station to avoid rejection and complete a 4-Way
Handshake with a GTK that will be cleared as soon as more entropy is
available and another station connects.

This reworks the logic to ban all 4-way handshakes until enough entropy
is available.

Signed-hostap: Nicolas Cavallari <cavallar@lri.fr>

src/ap/wpa_auth.c

@@ -966,9 +966,7 @@ continue_processing:
 			wpa_printf(MSG_DEBUG, "WPA: Reject 4-way handshake to "
 				   "collect more entropy for random number "
 				   "generation");
-			sm->group->reject_4way_hs_for_entropy = FALSE;
 			random_mark_pool_ready();
-			sm->group->first_sta_seen = FALSE;
 			wpa_sta_disconnect(wpa_auth, sm->addr);
 			return;
 		}
@@ -1614,9 +1612,11 @@ SM_STATE(WPA_PTK, AUTHENTICATION)
 }
 
 
-static void wpa_group_first_station(struct wpa_authenticator *wpa_auth,
-				    struct wpa_group *group)
+static void wpa_group_ensure_init(struct wpa_authenticator *wpa_auth,
+				  struct wpa_group *group)
 {
+	if (group->first_sta_seen)
+		return;
 	/*
 	 * System has run bit further than at the time hostapd was started
 	 * potentially very early during boot up. This provides better chances
@@ -1630,7 +1630,11 @@ static void wpa_group_first_station(struct wpa_authenticator *wpa_auth,
 		wpa_printf(MSG_INFO, "WPA: Not enough entropy in random pool "
 			   "to proceed - reject first 4-way handshake");
 		group->reject_4way_hs_for_entropy = TRUE;
+	} else {
+		group->first_sta_seen = TRUE;
+		group->reject_4way_hs_for_entropy = FALSE;
 	}
+
 	wpa_group_init_gmk_and_counter(wpa_auth, group);
 	wpa_gtk_update(wpa_auth, group);
 	wpa_group_config_group_keys(wpa_auth, group);
@@ -1641,10 +1645,7 @@ SM_STATE(WPA_PTK, AUTHENTICATION2)
 {
 	SM_ENTRY_MA(WPA_PTK, AUTHENTICATION2, wpa_ptk);
 
-	if (!sm->group->first_sta_seen) {
-		wpa_group_first_station(sm->wpa_auth, sm->group);
-		sm->group->first_sta_seen = TRUE;
-	}
+	wpa_group_ensure_init(sm->wpa_auth, sm->group);
 
 	os_memcpy(sm->ANonce, sm->group->Counter, WPA_NONCE_LEN);
 	wpa_hexdump(MSG_DEBUG, "WPA: Assign ANonce", sm->ANonce,