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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 54675C34021 for ; Mon, 17 Feb 2020 14:59:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 31ECF20679 for ; Mon, 17 Feb 2020 14:59:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729349AbgBQO7P (ORCPT ); Mon, 17 Feb 2020 09:59:15 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:46123 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729206AbgBQO7O (ORCPT ); Mon, 17 Feb 2020 09:59:14 -0500 Received: from ip5f5bf7ec.dynamic.kabel-deutschland.de ([95.91.247.236] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1j3hra-0006Ab-1U; Mon, 17 Feb 2020 14:59:10 +0000 Date: Mon, 17 Feb 2020 15:59:08 +0100 From: Christian Brauner To: Michael Kerrisk Cc: Dmitry Safonov , Andrei Vagin , Linux Kernel , Dmitry Safonov <0x7f454c46@gmail.com>, Adrian Reber , Andy Lutomirski , Arnd Bergmann , Cyrill Gorcunov , "Eric W. Biederman" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jeff Dike , Oleg Nesterov , Pavel Emelyanov , Shuah Khan , Thomas Gleixner , Vincenzo Frascino , containers , criu@openvz.org, Linux API , x86@kernel.org, Andrei Vagin Subject: Re: Time Namespaces: CLONE_NEWTIME and clone3()? Message-ID: <20200217145908.7epzz5nescccwvzv@wittgenstein> References: <20191112012724.250792-1-dima@arista.com> <20191112012724.250792-4-dima@arista.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 Mon, Feb 17, 2020 at 03:20:55PM +0100, Michael Kerrisk wrote: > Hello Dmitry, Andrei, > > Is the CLONE_NEWTIME flag intended to be usable with clone3()? The > mail quoted below implies (in my reading) that this should be possible > once clone3() is available, which it is by now. (See also [1].) > > If the answer is yes, CLONE_NEWTIME should be usable with clone3(), > then I have a bug report and a question. > > I successfully used CLONE_NEWTIME with unshare(). But if I try to use > CLONE_NEWSIGNAL with clone3(), it errors out with EINVAL, because of s/CLONE_NEWSIGNAL/CLONE_NEWTIME/ > the following check in clone3_args_valid(): > > /* > * - make the CLONE_DETACHED bit reuseable for clone3 > * - make the CSIGNAL bits reuseable for clone3 > */ > if (kargs->flags & (CLONE_DETACHED | CSIGNAL)) > return false; > > The problem is that CLONE_NEWTIME matches one of the bits in the > CSIGNAL mask. If the intention is to allow CLONE_NEWTIME with > clone3(), then either the bit needs to be redefined, or the error > checking in clone3_args_valid() needs to be reworked. If this is intended to be useable with clone3() the check should be adapted to allow for CLONE_NEWTIME. (I asked about this a while ago I think.) But below rather sounds like it should simply be an unshare() flag. The code seems to set frozen_offsets to true right after copy_namespaces() in timens_on_fork(new_ns, tsk) and so the offsets can't be changed anymore unless I'm reading this wrong. Alternatives seem to either make timens_offsets writable once after fork and before exec, I guess - though that's probably not going to work with the vdso judging from timens_on_fork(). The other alternative is that Andrei and Dmitry send me a patch to enable CLONE_NEWTIME with clone3() by exposing struct timens_offsets (or a version of it) in the uapi and extend struct clone_args to include a pointer to a struct timens_offset that is _only_ set when CLONE_NEWTIME is set. Though the unshare() way sounds way less invasive simpler. Christian