linux-kernel - Re: [PATCH 2/2] groups: Allow unprivileged processes to use setgroups to drop groups

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Message-ID: <20141117113734.396798e6@lxorguk.ukuu.org.uk>
Date:	Mon, 17 Nov 2014 11:37:34 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	Andy Lutomirski <luto@...capital.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Linux API <linux-api@...r.kernel.org>,
	linux-man <linux-man@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] groups: Allow unprivileged processes to use
 setgroups to drop groups

> optional), I can do that too.  The security model of "having a group
> gives you less privilege than not having it" seems crazy, but
> nonetheless I can see a couple of easy ways that we can avoid breaking

It's an old pattern of use that makes complete sense in a traditional
Unix permission world because it's the only way to do "exclude {list}"
nicely. Our default IMHO shouldn't break this.

> that pattern, no_new_privs being one of them.  I'd like to make sure
> that nobody sees any other real-world corner case that unprivileged
> setgroups would break.

Barring the usual risk of people doing improper error checking I don't
see one immediately.

For containers I think it actually makes sense that the sysctl can be
applied per container anyway.

Alan
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