Re: [PATCH 9/9] mm: introduce VM_POPULATE flag to better deal withracy userspace programs

From: Rik van Riel
Date: Thu Jan 03 2013 - 01:26:53 EST

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@xxxxxxxxxx>

Acked-by: Rik van Riel <ri

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