Re: [PATCH] mm/mempolicy.c: do not put mempolicy before using its nodemask

[David Rientjes]

On Wed, 18 Jan 2017, Vlastimil Babka wrote:

> Since commit be97a41b291e ("mm/mempolicy.c: merge alloc_hugepage_vma to
> alloc_pages_vma") alloc_pages_vma() can potentially free a mempolicy by
> mpol_cond_put() before accessing the embedded nodemask by
> __alloc_pages_nodemask(). The commit log says it's so "we can use a single
> exit path within the function" but that's clearly wrong. We can still do that
> when doing mpol_cond_put() after the allocation attempt.
> 
> Make sure the mempolicy is not freed prematurely, otherwise
> __alloc_pages_nodemask() can end up using a bogus nodemask, which could lead
> e.g. to premature OOM.
> 
> Fixes: be97a41b291e ("mm/mempolicy.c: merge alloc_hugepage_vma to alloc_pages_vma")
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>

I think this deserves Cc: stable@xxxxxxxxxxxxxxx [4.0+]