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>

diff --git a/src/ap/wpa_auth.c b/src/ap/wpa_auth.c
index c4d77bf80d89a4e1f8df069fa8b1c560beee8797..34e366492fd63343f1080c1a9cf728b2c8dee1e5 100644 (file)
--- a/src/ap/wpa_auth.c
+++ b/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,