linux-kernel - Re: RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add CLONE

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Message-ID: <c783a83a-01a1-9813-e2f7-0516cf7a1c16@metux.net>
Date:   Tue, 16 Apr 2019 20:45:43 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Andy Lutomirski <luto@...nel.org>, Aleksa Sarai <cyphar@...har.com>
Cc:     Christian Brauner <christian@...uner.io>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jann Horn <jannh@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Colascione <dancol@...gle.com>
Subject: Re: RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add
 CLONE_PIDFD]

On 15.04.19 22:29, Andy Lutomirski wrote:

<snip>

> I would personally *love* it if distros started setting no_new_privs> for basically all processes.

Maybe a pam module for that would be fine.
But this should be configurable per-user, as so many things still rely
on suid.

Actually, I'd like to move all authentication / privilege switching
to factotum (login(1), sshd, etc then also could run as unprivileged
users).

> And pidfd actually gets us part of the> way toward a straightforward way to make sudo and su still work in a>
no_new_privs world: su could call into a daemon that would spawn the>
privileged task, and su would get a (read-only!) pidfd back and then>
wait for the fd and exit.

How exactly would the pidfd improve this scenario ?
IMHO, would just need to pass the inherited fd's to that daemon (eg.
via unix socket) which then sets them up in the new child process.

> I suppose that, done naively, this might> cause some odd effects with respect to tty handling, but I bet it's>
solveable.

Yes, signals and process groups would be a bit tricky. Some signals
could be transmitted in a similar way as ssh does.

But: how can we handle things like cgroups ?


--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287