Fix use-after-free of ETCP_LINK in keepalive_timer_cb

src/transport_layer/etcp_keepalive.c

@@ -122,7 +122,9 @@ static void keepalive_timer_cb(void* arg) {
             int old_link_status = link->link_status;
             link->link_status = 0;
             etcp_fire_link_status_cbk(link, link->link_state, old_link_status);
-            etcp_on_link_down(link->etcp, link);
+            struct ETCP_CONN *etcp = link->etcp;   /* сохранить до каскада: etcp_on_link_down может закрыть conn и освободить link */
+            etcp_on_link_down(etcp, link);
+            if (etcp->state == 2) return;          /* conn+link освобождены каскадом, link трогать нельзя */
             if (link->is_tcp && link->tcp_link) { stcp_link_close(link->tcp_link); link->tcp_link = NULL; }
             if (old_link_status) {
                 DEBUG_INFO(DEBUG_CATEGORY_CONNECTION, "[%s] Link %d down: addr=%s ka=%d remote_ka=%d state=%d init=%d tmo: %llu>%llu els=%llums", link->etcp->log_name, link->local_link_id, sockaddr_storage_to_str(&link->remote_addr).str, link->recv_keepalive, link->remote_keepalive, link->link_state, link->initialized, (unsigned long long)timeout_units, (unsigned long long)elapsed, (unsigned long long)(elapsed/10));