linux-kernel - Re: scope of cred_guard

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Message-ID: <CAGXu5j+ngHnxcauv1aJYZke0TQ8LxMxt9nv-=q+EjG33dPzyrA@mail.gmail.com>
Date:   Wed, 5 Apr 2017 09:11:18 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <asarai@...e.com>,
        Andy Lutomirski <luto@...capital.net>,
        Attila Fazekas <afazekas@...hat.com>,
        Jann Horn <jann@...jh.net>, Michal Hocko <mhocko@...nel.org>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: scope of cred_guard_mutex.

On Wed, Apr 5, 2017 at 9:08 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 04/03, Eric W. Biederman wrote:
>>
>> You have asked why I have problems with your patch and so I am going to
>> try to explain.  Partly I want to see a clean set of patches that we
>> can merge into Linus's tree before we make any compromises.  Because the
>> work preparing a clean patchset may inform us of something better.  Plus
>> we need to make something clean and long term maintainable in any event.
>>
>> Partly I object because your understanding and my understanding of
>> cred_guard_mutex are very different.
>
> And I think there is another problem, your understanding and my understanding
> of "clean" differ too much and it seems that we can not convince each other ;)
>
> The last series looks buggy (I'll send more emails later today), but the
> main problem is that - in my opinion! - your approach is "obviously wrong
> and much less clean". But yes, yes, I understand that this is my opinion,
> and I can be wrong.
>
> Eric, I think we need more CC's. Linus, probably security list, the more
> the better.
>
> I am going to resend my series with more CC's, then you can nack it and
> explain what you think we should do. Perhaps someone else will suggest
> a better solution, or at least review the patches. OK?

I've been following along, but it seems like there are a lot of edge
cases in these changes. I'll try to meaningfully comment on the coming
emails... having code examples of why various things will/won't work
go a long way for helping understand what's safe or not...

-Kees

-- 
Kees Cook
Pixel Security