linux-kernel - Re: [PATCH] kernel/kmod: fix use-after-free of the sub

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Message-ID: <20141017152156.GA6519@redhat.com>
Date:	Fri, 17 Oct 2014 17:21:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] kernel/kmod: fix use-after-free of the
	sub_infostructure

On 10/17, Martin Schwidefsky wrote:
>
> On Thu, 16 Oct 2014 23:58:34 +0200
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > I also agree that the changelog could mention exec_mmap. Plus a comment
> > about UMH_NO_WAIT && sub_info->complete == NULL. So yes, perhaps v2 makes
> > sense if Martin agrees.
>
> Version 2 of the patch.

Thanks!

> All change requests have gone in except for the
> mention of exec_mmap. I don't quite get the relevance of it, do_execve
> can fail for the various reasons.

Yes. But if it fails before exec_mmap() (which in particular calls
mm_release()->complete_vfork_done()) we are safe; sub_info can't go away
because the parent sleeps in sys_wait4() if UMH_WAIT_PROC, or it sleeps
in wait_for_vfork_done() otherwise.

But this is minor, and this only relates to the changelog. So still/again

Reviewed-by: Oleg Nesterov <oleg@...hat.com>

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