From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5114CC433E0 for ; Thu, 28 May 2020 09:57:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3359D20DD4 for ; Thu, 28 May 2020 09:57:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387673AbgE1J5u (ORCPT ); Thu, 28 May 2020 05:57:50 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:46311 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387660AbgE1J5p (ORCPT ); Thu, 28 May 2020 05:57:45 -0400 Received: from ip5f5af183.dynamic.kabel-deutschland.de ([95.90.241.131] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1jeFIF-0002s4-9R; Thu, 28 May 2020 09:57:43 +0000 Date: Thu, 28 May 2020 11:57:42 +0200 From: Christian Brauner To: Jann Horn Cc: kernel list , Kees Cook , Andy Lutomirski , Tycho Andersen , Matt Denton , Sargun Dhillon , Chris Palmer , Aleksa Sarai , Robert Sesek , Jeffrey Vander Stoep , Linux Containers Subject: Re: [PATCH 1/2] seccomp: notify user trap about unused filter Message-ID: <20200528095742.cjwemtucwgvhxnxv@wittgenstein> References: <20200527111902.163213-1-christian.brauner@ubuntu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 28, 2020 at 06:04:48AM +0200, Jann Horn wrote: > On Wed, May 27, 2020 at 1:19 PM Christian Brauner > wrote: > > We've been making heavy use of the seccomp notifier to intercept and > > handle certain syscalls for containers. This patch allows a syscall > > supervisor listening on a given notifier to be notified when a seccomp > > filter has become unused. > [...] > > To fix this, we introduce a new "live" reference counter that tracks the > > live tasks making use of a given filter and when a notifier is > > registered waiting tasks will be notified that the filter is now empty > > by receiving a (E)POLLHUP event. > > The concept in this patch introduces is the same as for signal_struct, > > i.e. reference counting for life-cycle management is decoupled from > > reference counting live taks using the object. > [...] > > + * @live: tasks that actually use this filter, only to be altered > > + * during fork(), exit()/free_task(), and filter installation > > This comment is a bit off. Actually, @live counts the number of tasks > that use the filter directly plus the number of dependent filters that > have non-zero @live. I'll update the comment. > > [...] > > +void seccomp_filter_notify(const struct task_struct *tsk) > > +{ > > + struct seccomp_filter *orig = tsk->seccomp.filter; > > + > > + while (orig && refcount_dec_and_test(&orig->live)) { > > + if (waitqueue_active(&orig->wqh)) > > + wake_up_poll(&orig->wqh, EPOLLHUP); > > + orig = orig->prev; > > + } > > +} > > /me fetches the paint bucket > > Maybe name this seccomp_filter_unuse() or > seccomp_filter_unuse_notify() or something like that? The current name > isn't very descriptive. I think seccomp_filter_release() might be the right color. It would also line-up nicely with: - cgroup_release() - exit_mm_release() - exec_mm_release() - futex_exec_release() - ptrace_release_task() and others. Christian