linux-kernel - Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand

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Message-ID: <20170405181103.GA19444@redhat.com>
Date:   Wed, 5 Apr 2017 20:11:03 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     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>, Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a
        shared sighand_struct

On 04/05, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> I agree that changing userspace semantics is something to be very
> careful with.  But at least for purposes of discussion I think this is a
> good patch.

I agree that we need it with your approach,

but imo it would be much better to not depend on the subtle changes
like this. My 2/2 or your 1/5 are already bad enough.

> I can avoid this change but it requires moving sighand->siglock
> into signal_struct and introducing a new spinlock into sighand_struct
> to just guard the signal handlers.

Oh, this looks much, much worse to me.

Oleg.