linux-kernel - Re: [PATCH] kthread: fix use-after-free if kthread fork fails

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Message-ID: <20170506195136.GB21726@redhat.com>
Date:   Sat, 6 May 2017 21:51:36 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Vegard Nossum <vegard.nossum@...cle.com>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Jamie Iles <jamie.iles@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] kthread: fix use-after-free if kthread fork fails

On 05/05, Vegard Nossum wrote:
>
> On 05/05/17 18:44, Oleg Nesterov wrote:
> >
> >Can't we just move both
> >
> >	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
> >	/*
> >	 * Clear TID on mm_release()?
> >	 */
> >	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
> >
> >lines here?
>
> clone_flags is not available in dup_task_struct(), but we could move
> those lines higher in copy_process().

Yes, yes, this is what I meant.

> The newly attached patch has been tested and seems to work, if you
> prefer it.

Yes, please, this loos a bit better simply because we do not need to set it twice.

And I agree this needs cleanups. Even if we forget about this particular problem
and the usage of set_child_tid, we should add copy_misc() which should absorb a
lot of chaotic initializations from copy_process() imo.

Oleg.