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Subject: Re: RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add CLONE_PIDFD]
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <87v9zc6cz2.fsf@oldenburg2.str.redhat.com>
Date:   Wed, 17 Apr 2019 09:46:49 -0700
Cc:     Andy Lutomirski <luto@kernel.org>,
        Aleksa Sarai <cyphar@cyphar.com>,
        "Enrico Weigelt, metux IT consult" <lkml@metux.net>,
        Christian Brauner <christian@brauner.io>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jann Horn <jannh@google.com>,
        David Howells <dhowells@redhat.com>,
        Linux API <linux-api@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Daniel Colascione <dancol@google.com>
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References: <20190414201436.19502-1-christian@brauner.io> <dc05ffe3-c2ff-8b3e-d181-e0cc620bf91d@metux.net> <20190415195911.z7b7miwsj67ha54y@yavin> <CALCETrWxMnaPvwicqkMLswMynWvJVteazD-bFv3ZnBKWp-1joQ@mail.gmail.com> <87v9zc6cz2.fsf@oldenburg2.str.redhat.com>
To:     Florian Weimer <fweimer@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Apr 17, 2019, at 5:19 AM, Florian Weimer <fweimer@redhat.com> wrote:
>=20
> * Andy Lutomirski:
>=20
>> I would personally *love* it if distros started setting no_new_privs
>> for basically all processes.
>=20
> Wouldn't no_new_privs inhibit all security transitions, including those
> that reduce privileges?  And therefore effectively reduce security?

In principle, you still can reduce privileges with no_new_privs.  SELinux ha=
s a whole mechanism for privilege-reducing transitions on exec that works in=
 no_new_privs mode. Also, all the traditional privilege dropping techniques w=
ork =E2=80=94 setresuid(), unshare(), etc are all unaffected.

>=20
>> There seems to be some demand to be able to do large
> parts of container setup using posix_spawn, so we'll probably add
> support for things like writing to arbitrary files eventually.  And of
> course, proper error reporting, so that you can figure out which file
> creation action failed.
>=20

ISTM the way to handle this is to have a way to make a container, set it up,=
 and then clone/spawn into it.  The current unshare() API is severely awkwar=
d.

Maybe the new better kernel spawn API shouldn=E2=80=99t support unshare-like=
 semantics at all and should instead work like setns().=