linux-kernel - Re: [PATCH] zsmalloc: fix a null pointer dereference in destroy_handle

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Message-Id: <20150608135532.ac913746b6394217e92a229a@linux-foundation.org>
Date:	Mon, 8 Jun 2015 13:55:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] zsmalloc: fix a null pointer dereference in
 destroy_handle_cache()

On Fri,  5 Jun 2015 20:11:30 +0900 Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:

> zs_destroy_pool()->destroy_handle_cache() invoked from
> zs_create_pool() can pass a NULL ->handle_cachep pointer
> to kmem_cache_destroy(), which will dereference it.
>

That's slightly lacking in details (under what circumstances will it
crash) so I changed it to

: If zs_create_pool()->create_handle_cache()->kmem_cache_create() fails,
: zs_create_pool()->destroy_handle_cache() will dereference the NULL
: pool->handle_cachep.
:
: Modify destroy_handle_cache() to avoid this.


> ...
>
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -285,7 +285,8 @@ static int create_handle_cache(struct zs_pool *pool)
>  
>  static void destroy_handle_cache(struct zs_pool *pool)
>  {
> -	kmem_cache_destroy(pool->handle_cachep);
> +	if (pool->handle_cachep)
> +		kmem_cache_destroy(pool->handle_cachep);
>  }
>  
>  static unsigned long alloc_handle(struct zs_pool *pool)

I'll apply this, but...  from a bit of grepping I'm estimating that we
have approximately 200 instances of

	if (foo)
		kmem_cache_destroy(foo);

so obviously kmem_cache_destroy() should be doing the check.
--
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