linux-kernel - Re: [PATCH 9/9] mm: introduce VM_POPULATE flag to better deal with racy userspace programs

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Date:	Thu, 03 Jan 2013 01:20:06 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
CC:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>, Jorn_Engel <joern@...fs.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] mm: introduce VM_POPULATE flag to better deal with
 racy userspace programs

On 12/20/2012 07:49 PM, Michel Lespinasse wrote:
> The vm_populate() code populates user mappings without constantly
> holding the mmap_sem. This makes it susceptible to racy userspace
> programs: the user mappings may change while vm_populate() is running,
> and in this case vm_populate() may end up populating the new mapping
> instead of the old one.
>
> In order to reduce the possibility of userspace getting surprised by
> this behavior, this change introduces the VM_POPULATE vma flag which
> gets set on vmas we want vm_populate() to work on. This way
> vm_populate() may still end up populating the new mapping after such a
> race, but only if the new mapping is also one that the user has
> requested (using MAP_SHARED, MAP_LOCKED or mlock) to be populated.
>
> Signed-off-by: Michel Lespinasse <walken@...gle.com>

Acked-by: Rik van Riel <ri

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