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

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Message-Id: <20150608174306.92652579.akpm@linux-foundation.org>
Date:	Mon, 8 Jun 2015 17:43:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	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>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] zsmalloc: fix a null pointer dereference in
 destroy_handle_cache()

On Tue, 9 Jun 2015 09:38:27 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:

> > > ...
> > >
> > > --- 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.
> 
> Hello, Andrew.
> 
> I'm not sure if doing the check in kmem_cache_destroy() is better.

Of course it's better - we have *hundreds* of sites doing something
which could be done at a single site.  Where's the advantage in that?

> My quick grep for other pool based allocators(ex. mempool, zpool) also
> says that they don't check whether passed pool pointer is NULL or not
> in destroy function.

Maybe some of those should be converted as well.
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