linux-kernel - Re: [PATCH] slub: make sure struct kmem_cache

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Date:   Fri, 7 Jul 2017 13:23:51 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     dvyukov@...gle.com, kcc@...gle.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] slub: make sure struct kmem_cache_node is initialized
 before publication

On Fri,  7 Jul 2017 10:34:08 +0200 Alexander Potapenko <glider@...gle.com> wrote:

> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3389,8 +3389,8 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
>  			return 0;
>  		}
>  
> -		s->node[node] = n;
>  		init_kmem_cache_node(n);
> +		s->node[node] = n;
>  	}
>  	return 1;
>  }

If this matters then I have bad feelings about free_kmem_cache_nodes():

static void free_kmem_cache_nodes(struct kmem_cache *s)
{
	int node;
	struct kmem_cache_node *n;

	for_each_kmem_cache_node(s, node, n) {
		kmem_cache_free(kmem_cache_node, n);
		s->node[node] = NULL;
	}
}

Inviting a use-after-free?  I guess not, as there should be no way
to look up these items at this stage.

Could the slab maintainers please take a look at these and also have a
think about Alexander's READ_ONCE/WRITE_ONCE question?