linux-kernel - Re: [PATCH 05/10] user namespace: clamp down users of cap

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Message-ID: <CALQRfL7ZNv9+7tooJC8x8Pmz62QtnJ+-pVFRy_YspCG1BhZKzg@mail.gmail.com>
Date:	Mon, 24 Oct 2011 17:43:25 -0700
From:	"Andrew G. Morgan" <morgan@...nel.org>
To:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, oleg@...hat.com, richard@....at,
	mikevs@...all.net, segoon@...nwall.com, gregkh@...e.de,
	eparis@...hat.com
Subject: Re: [PATCH 05/10] user namespace: clamp down users of cap_raised

On Mon, Oct 24, 2011 at 10:28 AM, Serge E. Hallyn
<serge.hallyn@...onical.com> wrote:
> Quoting Andrew G. Morgan (morgan@...nel.org):
>> Serge,
>>
>> It seems as if this whole thing is really idiomatic. How about?
>>
>> #define IN_ROOT_USER_NS_CAPABLE(cap)  \
>>    ((current_user_ns() == &init_user_ns) && cap_raised(current_cap(), cap))
>
> My objection to this was that it seems to encourage others to use it :)  I'm
> not sure we want that.  Also, IN_ROOT_USER_NS seems more generally useful.

What is driving the choice of when its appropriate? How can a
developer determine this? If you make it hard, presumably folk won't
do it by default, but will that create a burdon on others to go round
patching things like this up?

> But if I'm the only one who feels this way I'll go ahead and do it...

I'm more of a optimize for a human to read the source code (ie. debug
a problem) kind of person. If IN_ROOT_USER_NS is useful, you could
always define IN_ROOT_USER_NS_CAPABLE in terms of IN_ROOT_USER_NS &&
... and provide both.

I guess I'm unclear, however, when you want developers to use one or
the other variant of the basic capable() functionality. Since I'm not
clear, I'm suspecting this is a fragile situation.

Cheers

Andrew
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