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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8F50FC433E7 for ; Tue, 13 Oct 2020 20:05:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4247D20E65 for ; Tue, 13 Oct 2020 20:05:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732292AbgJMUFg (ORCPT ); Tue, 13 Oct 2020 16:05:36 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35700 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730198AbgJMUFf (ORCPT ); Tue, 13 Oct 2020 16:05:35 -0400 Received: from ip5f5af0a0.dynamic.kabel-deutschland.de ([95.90.240.160] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1kSQXz-0000Ge-6Z; Tue, 13 Oct 2020 20:05:23 +0000 Date: Tue, 13 Oct 2020 22:05:21 +0200 From: Christian Brauner To: Andrei Vagin Cc: Michael =?utf-8?B?V2Vpw58=?= , Thomas Gleixner , Dmitry Safonov <0x7f454c46@gmail.com>, linux-kernel@vger.kernel.org, "J. Bruce Fields" , Chuck Lever , Trond Myklebust , Anna Schumaker Subject: Re: [PATCH v2 2/4] time: make getboottime64 aware of time namespace Message-ID: <20201013200521.5dplf5ohey64qmcx@wittgenstein> References: <20201008053944.32718-1-michael.weiss@aisec.fraunhofer.de> <20201008053944.32718-3-michael.weiss@aisec.fraunhofer.de> <20201009132815.5afulu5poh5ti57m@wittgenstein> <20201010071914.GA135401@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201010071914.GA135401@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 10, 2020 at 12:19:14AM -0700, Andrei Vagin wrote: > On Fri, Oct 09, 2020 at 03:28:15PM +0200, Christian Brauner wrote: > > On Thu, Oct 08, 2020 at 07:39:42AM +0200, Michael Weiß wrote: > > > getboottime64() provides the time stamp of system boot. In case of > > > time namespaces, the offset to the boot time stamp was not applied > > > earlier. However, getboottime64 is used e.g., in /proc/stat to print > > > the system boot time to userspace. In container runtimes which utilize > > > time namespaces to virtualize boottime of a container, this leaks > > > information about the host system boot time. > > > > > > Therefore, we make getboottime64() to respect the time namespace offset > > > for boottime by subtracting the boottime offset. > > > > > > Signed-off-by: Michael Weiß > > > --- > > > kernel/time/timekeeping.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > > > index 4c47f388a83f..67530cdb389e 100644 > > > --- a/kernel/time/timekeeping.c > > > +++ b/kernel/time/timekeeping.c > > > @@ -17,6 +17,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -2154,6 +2155,8 @@ void getboottime64(struct timespec64 *ts) > > > { > > > struct timekeeper *tk = &tk_core.timekeeper; > > > ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot); > > > + /* shift boot time stamp according to the timens offset */ > > > + t = timens_ktime_to_host(CLOCK_BOOTTIME, t); > > > > Note that getbootime64() is mostly used in net/sunrpc and I don't know > > if this change has any security implications for them. > > I would prefer to not patch kernel internal functions if they are used > not only to expose time to the userspace. > > I think when kernel developers sees the getboottime64 function, they > will expect that it returns the real time of kernel boot. They will > not expect that it is aware of time namespaces and a returned time will > depend on a task in which context it will be called. > > IMHO, as a minimum, we need to update the documentation for this function or > even adjust a function name. > > And I think we need to consider an option to not change getbootime64 and > apply a timens offset right in the show_stat(fs/proc/stat.c) function. This is why I asked about this since I assumed this would break someone's use-case. :) In any case, if I understand correctly then we want the same thing: just change fs/proc/stat.c i.e. have a a specific helper that applies the correct offset. Christian