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

[Rik van Riel]

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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