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Date: Sun, 18 Mar 2012 21:53:42 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Djalal Harouni <tixxdz@opendz.org>,
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        linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Greg KH <gregkh@linuxfoundation.org>, Ingo Molnar <mingo@elte.hu>,
        Stephen Wilson <wilsons@start.ca>,
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        Roland McGrath <roland@hack.frob.com>
Subject: Re: [PATCH 1/1] CLONE_PARENT shouldn't allow to set ->exit_signal
Message-ID: <20120318205342.GA14383@redhat.com>
References: <1331421919-15499-1-git-send-email-tixxdz@opendz.org> <1331421919-15499-2-git-send-email-tixxdz@opendz.org> <20120311172512.GA2729@redhat.com> <20120311174953.GB2729@redhat.com> <CA+55aFx43nZmhRg5Qv5x-4BdgcM-y80ECrgC8mCWc0RqU+_8rQ@mail.gmail.com> <20120314185510.GA14172@redhat.com> <20120314185538.GB14172@redhat.com> <CA+55aFzKc578eWYaq4+OaOM6hFjW+ePYCeC++_1p8f09YWV_hA@mail.gmail.com>
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On 03/18, Linus Torvalds wrote:
>
> On Wed, Mar 14, 2012 at 11:55 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> > +       if (clone_flags & CLONE_THREAD)
> > +               p->exit_signal = -1;
> > +       else if (clone_flags & CLONE_PARENT)
> > +               p->exit_signal = current->group_leader->exit_signal;
> > +       else
> > +               p->exit_signal = (clone_flags & CSIGNAL);
>
> So why is it "current->group_leader->exit_signal" rather than the much
> more logical (imho) and simpler "current->exit_signal"?

This would be wrong if current is not the main thread. In this
case current->exit_signal = -1. Only group_leader has the "real"
exit_signal used for notification.

Historically "exit_signal = -1" meant different things, currently
it only means "I am not the leader", see thread_group_leader().

I'll write another email tomorrow. Yes, I do remember I promised
the security fixes in this area, sorry for delay.

Oleg.