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From:   Andy Lutomirski <luto@kernel.org>
Date:   Wed, 31 Jul 2019 22:29:45 -0700
Message-ID: <CALCETrWHEcaG9gZe6ACt5H1H+P8D0RobrJ_bf4Wf9ts40NMM9w@mail.gmail.com>
Subject: Re: [PATCHv5 01/37] ns: Introduce Time Namespace
To:     Dmitry Safonov <dima@arista.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Andrei Vagin <avagin@openvz.org>,
        Adrian Reber <adrian@lisas.de>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Jann Horn <jannh@google.com>, Jeff Dike <jdike@addtoit.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Linux Containers <containers@lists.linux-foundation.org>,
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        X86 ML <x86@kernel.org>
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On Mon, Jul 29, 2019 at 2:58 PM Dmitry Safonov <dima@arista.com> wrote:
>
> From: Andrei Vagin <avagin@openvz.org>
>
> Time Namespace isolates clock values.

> +static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
> +{
> +       struct time_namespace *ns = to_time_ns(new);
> +
> +       if (!thread_group_empty(current))
> +               return -EINVAL;

You also need to check for other users of the mm.

> +
> +       if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
> +           !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
> +               return -EPERM;
> +
> +       get_time_ns(ns);
> +       get_time_ns(ns);
> +       put_time_ns(nsproxy->time_ns);
> +       put_time_ns(nsproxy->time_ns_for_children);
> +       nsproxy->time_ns = ns;
> +       nsproxy->time_ns_for_children = ns;
> +       ns->initialized = true;

I really really wish that setns() took an explicit flag for "change
now" or "change for children", since the semantics are different.  Oh
well.