linux-kernel - Re: [PATCH 1/1] mm_for_maps: simplify, use ptrace_may

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Message-Id: <20090624092547.D6B684059B@magilla.sf.frob.com>
Date:	Wed, 24 Jun 2009 02:25:47 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	James Morris <jmorris@...ei.org>, Ingo Molnar <mingo@...e.hu>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/1] mm_for_maps: simplify, use ptrace_may_access()

> 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
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