Re: [PATCH v2] mm: rmap: fix use-after-free in __put_anon_vma

[Peter Zijlstra]

On Fri, Jun 06, 2014 at 07:09:30PM +0400, Andrey Ryabinin wrote:
> While working address sanitizer for kernel I've discovered use-after-free
> bug in __put_anon_vma.
> For the last anon_vma, anon_vma->root freed before child anon_vma.
> Later in anon_vma_free(anon_vma) we are referencing to already freed anon_vma->root
> to check rwsem.
> This patch puts freeing of child anon_vma before freeing of anon_vma->root.
> 
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.0+

Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

> Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
> ---
> 
> Changes since v1:
>  - just made it more simple following Peter's suggestion
> 
>  mm/rmap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 9c3e773..cb5f70a 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1564,10 +1564,10 @@ void __put_anon_vma(struct anon_vma *anon_vma)
>  {
>  	struct anon_vma *root = anon_vma->root;
>  
> +	anon_vma_free(anon_vma);
> +
>  	if (root != anon_vma && atomic_dec_and_test(&root->refcount))
>  		anon_vma_free(root);
> -
> -	anon_vma_free(anon_vma);
>  }
>  
>  static struct anon_vma *rmap_walk_anon_lock(struct page *page,
> -- 
> 1.8.5.5
> 
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