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

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Message-ID: <87v9zc6cz2.fsf@oldenburg2.str.redhat.com>
Date:   Wed, 17 Apr 2019 14:19:29 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Aleksa Sarai <cyphar@...har.com>,
        "Enrico Weigelt\, metux IT consult" <lkml@...ux.net>,
        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]

* Andy Lutomirski:

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

Wouldn't no_new_privs inhibit all security transitions, including those
that reduce privileges?  And therefore effectively reduce security?

> Anyway, clone(2) is an enormous mess.  Surely the right solution here
> is to have a whole new process creation API that takes a big,
> extensible struct as an argument, and supports *at least* the full
> abilities of posix_spawn() and ideally covers all the use cases for
> fork() + do stuff + exec().  It would be nifty if this API also had a
> way to say "add no_new_privs and therefore enable extra functionality
> that doesn't work without no_new_privs".  This functionality would
> include things like returning a future extra-privileged pidfd that
> gives ptrace-like access.

I agree that consistent replacement for the clone system call makes
sense.  I'm not sure if covering everything that posix_spawn could do
would make sense.  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.

Thanks,
Florian