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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 18B38C32789 for ; Fri, 2 Nov 2018 10:02:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB01320831 for ; Fri, 2 Nov 2018 10:02:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB01320831 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726328AbeKBTJT (ORCPT ); Fri, 2 Nov 2018 15:09:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51318 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725935AbeKBTJT (ORCPT ); Fri, 2 Nov 2018 15:09:19 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 547F388E4F; Fri, 2 Nov 2018 10:02:42 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.31]) by smtp.corp.redhat.com (Postfix) with SMTP id 6727E5EDE1; Fri, 2 Nov 2018 10:02:39 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 2 Nov 2018 11:02:40 +0100 (CET) Date: Fri, 2 Nov 2018 11:02:35 +0100 From: Oleg Nesterov To: Tycho Andersen Cc: Kees Cook , Andy Lutomirski , "Eric W . Biederman" , "Serge E . Hallyn" , Christian Brauner , Tyler Hicks , Akihiro Suda , Aleksa Sarai , linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, linux-api@vger.kernel.org Subject: Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace Message-ID: <20181102100234.GA12360@redhat.com> References: <20181029224031.29809-1-tycho@tycho.ws> <20181029224031.29809-2-tycho@tycho.ws> <20181101134001.GA23232@redhat.com> <20181101195635.GG2180@cisco> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181101195635.GG2180@cisco> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 02 Nov 2018 10:02:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/01, Tycho Andersen wrote: > > On Thu, Nov 01, 2018 at 02:40:02PM +0100, Oleg Nesterov wrote: > > > > Somehow I no longer understand why do you need to take all locks. Isn't > > the first filter's notify_lock enough? IOW, > > > > for (cur = current->seccomp.filter; cur; cur = cur->prev) { > > if (cur->notif) > > return ERR_PTR(-EBUSY); > > first = cur; > > } > > > > if (first) > > mutex_lock(&first->notify_lock); > > > > ... initialize filter->notif ... > > > > out: > > if (first) > > mutex_unlock(&first->notify_lock); > > > > return ret; > > The idea here is to prevent people from "nesting" notify filters. So > if any filter in the chain has a listener attached, it refuses to > install another filter with a listener. Yes, I understand, so we need to check cur->notif. My point was, we do not need to take all the locks in the ->prev chain, we need only one: first->notify_lock. But you know what? today I think that we do not need any locking at all, all we need is the lockless for (cur = current->seccomp.filter; cur; cur = cur->prev) if (cur->notif) return ERR_PTR(-EBUSY); at the start, nothing more. > But it just occurred to me that we don't handle the TSYNC case > correctly by doing it this way, Why? Perhaps I missed your point, but TSYNC case looks fine. I mean, if 2 threads do seccomp_set_mode_filter(NEW_LISTENER | TSYNC) then only one can win the race and succeed, but this has nothing to do with init_listener(), we rely on ->siglock and is_ancestor() check. No? Oleg.