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From: Roland McGrath <roland@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
       Christoph Hellwig <hch@infradead.org>, James Morris <jmorris@namei.org>,
       Ingo Molnar <mingo@elte.hu>, Chris Wright <chrisw@sous-sol.org>,
       linux-kernel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>,
       linux-security-module@vger.kernel.org
Subject: Re: [PATCH 1/1] mm_for_maps: simplify, use ptrace_may_access()
In-Reply-To: Oleg Nesterov's message of  Tuesday, 23 June 2009 21:25:32 +0200 <20090623192532.GB27853@redhat.com>
References: <20090507083851.GA19133@elte.hu>
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	<alpine.LRH.2.00.0905071951530.29219@tundra.namei.org>
	<20090507102015.GB8901@elte.hu>
	<alpine.LRH.2.00.0905072135580.29806@tundra.namei.org>
	<20090623141451.GA8133@redhat.com>
	<20090623174918.GA24430@infradead.org>
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Emacs: it's not slow --- it's stately.
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Date: Wed, 24 Jun 2009 02:25:47 -0700 (PDT)
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> Also, we do not need to take ->mmap_sem in advance. In fact I think
> mm_for_maps() should not play with ->mmap_sem at all, the caller should
> take this lock.

Agreed.  It has only one caller (though two forks of it) in
fs/proc/task_{no,}mmu.c and it looks easy to change.

> With or without this patch, without ->cred_guard_mutex held we can race
> with exec() and get the new ->mm but check old creds.

It looks safe and proper for mm_for_maps() to take that mutex around its
check.  Your patch looks good to me as it is, and taking cred_guard_mutex
can be another security fix patch on top.


Thanks,
Roland