Avoid a theoretical use-after-free in WPA auth sm init

wpa_sm_step() could theoretically free the statemachine, but it does
not do it in this particular case. Anyway, the code can be cleaned to
verify whether the state machine data is still available after the
wpa_sm_step() call.

src/ap/wpa_auth.c

@@ -38,7 +38,7 @@
 
 
 static void wpa_send_eapol_timeout(void *eloop_ctx, void *timeout_ctx);
-static void wpa_sm_step(struct wpa_state_machine *sm);
+static int wpa_sm_step(struct wpa_state_machine *sm);
 static int wpa_verify_key_mic(struct wpa_ptk *PTK, u8 *data, size_t data_len);
 static void wpa_sm_call_step(void *eloop_ctx, void *timeout_ctx);
 static void wpa_group_sm_step(struct wpa_authenticator *wpa_auth,
@@ -520,7 +520,8 @@ void wpa_auth_sta_associated(struct wpa_authenticator *wpa_auth,
 	sm->started = 1;
 
 	sm->Init = TRUE;
-	wpa_sm_step(sm);
+	if (wpa_sm_step(sm) == 1)
+		return; /* should not really happen */
 	sm->Init = FALSE;
 	sm->AuthenticationRequest = TRUE;
 	wpa_sm_step(sm);
@@ -2059,17 +2060,17 @@ static void wpa_group_sm_step(struct wpa_authenticator *wpa_auth,
 }
 
 
-static void wpa_sm_step(struct wpa_state_machine *sm)
+static int wpa_sm_step(struct wpa_state_machine *sm)
 {
 	if (sm == NULL)
-		return;
+		return 0;
 
 	if (sm->in_step_loop) {
 		/* This should not happen, but if it does, make sure we do not
 		 * end up freeing the state machine too early by exiting the
 		 * recursive call. */
 		wpa_printf(MSG_ERROR, "WPA: wpa_sm_step() called recursively");
-		return;
+		return 0;
 	}
 
 	sm->in_step_loop = 1;
@@ -2094,7 +2095,9 @@ static void wpa_sm_step(struct wpa_state_machine *sm)
 		wpa_printf(MSG_DEBUG, "WPA: Completing pending STA state "
 			   "machine deinit for " MACSTR, MAC2STR(sm->addr));
 		wpa_free_sta_sm(sm);
+		return 1;
 	}
+	return 0;
 }