linux-kernel - Re: [CFT][PATCH 6/7] userns: Add a knob to disable setgroups on a per user namespace basis

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Message-ID: <87r3w8liw4.fsf@x220.int.ebiederm.org>
Date:	Tue, 09 Dec 2014 13:31:39 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	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\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Richard Weinberger <richard@....at>,
	Kenton Varda <kenton@...dstorm.io>,
	stable <stable@...r.kernel.org>
Subject: Re: [CFT][PATCH 6/7] userns: Add a knob to disable setgroups on a per user namespace basis

ebiederm@...ssion.com (Eric W. Biederman) writes:

> Andy Lutomirski <luto@...capital.net> writes:
>
>>
>> This text was actually my suggested comment text.
>
> Now I see.
>
>> If you put smp_rmb() in this function with a comment like that, then I
>> think it will all make sense and be obviously correct (even with most
>> of the other barriers removed).
>
> Right.
>
> Given that we have to be careful when using these things anyway what
> I was hoping to achieve with the barriers appears impossible, and
> confusing so I will see about just adding barriers where we need them
> for real.  Sigh.

Doh.  The code has been entirely too clever.

There are no need for atomics or other cleverness, I just need to
generalize id_map_mutex.  I knew that had to be a trivially correct
way of handling this mess.

Eric
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