Re: [PATCH 1/1] mm_for_maps: simplify, use ptrace_may_access()

From: Roland McGrath <roland@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
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()
Date: Wed, 24 Jun 2009 02:25:47 -0700 (PDT)	[thread overview]
Message-ID: <20090624092547.D6B684059B@magilla.sf.frob.com> (raw)
In-Reply-To: Oleg Nesterov's message of  Tuesday, 23 June 2009 21:25:32 +0200 <20090623192532.GB27853@redhat.com>

> 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