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=-2.5 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 A12DFC10F0E for ; Thu, 18 Apr 2019 14:10:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7682021479 for ; Thu, 18 Apr 2019 14:10:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389220AbfDROK0 (ORCPT ); Thu, 18 Apr 2019 10:10:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41766 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388346AbfDROKZ (ORCPT ); Thu, 18 Apr 2019 10:10:25 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 82D048046F; Thu, 18 Apr 2019 14:10:24 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.38]) by smtp.corp.redhat.com (Postfix) with SMTP id 2FE5E1001E8A; Thu, 18 Apr 2019 14:10:21 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 18 Apr 2019 16:10:24 +0200 (CEST) Date: Thu, 18 Apr 2019 16:10:20 +0200 From: Oleg Nesterov To: Christian Brauner Cc: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, jannh@google.com, dhowells@redhat.com, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, serge@hallyn.com, luto@kernel.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, tglx@linutronix.de, mtk.manpages@gmail.com, akpm@linux-foundation.org, cyphar@cyphar.com, joel@joelfernandes.org, dancol@google.com Subject: Re: [PATCH v2 2/5] clone: add CLONE_PIDFD Message-ID: <20190418141019.GD13701@redhat.com> References: <20190418101841.4476-1-christian@brauner.io> <20190418101841.4476-3-christian@brauner.io> <20190418131206.GB13701@redhat.com> <20190418132822.untjt7erfvbbiz7a@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190418132822.untjt7erfvbbiz7a@brauner.io> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 18 Apr 2019 14:10:25 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/18, Christian Brauner wrote: > > On Thu, Apr 18, 2019 at 03:12:07PM +0200, Oleg Nesterov wrote: > > Should we allow CLONE_THREAD | CLONE_PIDFD ? > > I think so, yes. I have thought about this. OK, I won't insist. But let me explain why did I ask. > Yes, due to CLONE_FILES | > CLONE_VM you'd necessarily hand the pidfd to the child but threads are > no security boundary in the first place. No, no, I am not not worried about security. CLONE_PARENT | CLONE_PIDFD looks more problematic to me, but I see nothing dangerous security-wise.. I agree that CLONE_THREAD | CLONE_PIDFD may be usefule, but I am not sure we should allow this from the very begining, until we have a "real" use-case. IIUC, we are going to make it pollable soon. OK, but proc_tgid_base_poll() (which should be turned into pidfd_poll) simply can't work if pid_task() is not a group leader. poll(pidfd) will hang forever if pidfd was created by CLONE_THREAD | CLONE_PIDFD. Sure, we can (should?) improve pidfd_poll() but this will need more nasty changes in the core kernel code. Do we really need/want this? Right now it is not clear to me. Instead, we can simply disallow CLONE_THREAD|CLONE_PIDFD until we decide that yes, we want to poll sub-threads. But again, I am fine with CLONE_THREAD | CLONE_PIDFD. Oleg.