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

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Date:	Tue, 9 Jun 2015 12:57:17 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] zsmalloc: fix a null pointer dereference in
 destroy_handle_cache()

On (06/08/15 13:55), Andrew Morton 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.
> 

Oh, sorry I first received "+ zsmalloc-fix-a-null-pointer-dereference-in-
destroy_handle_cache.patch added to -mm tree" message, so I replied
there. fetchmail works somewhat confusing over the last weeks.

> > ...
> >
> > --- 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.

Yes, I thought about this.

A naive grepping gave me 563 occurrences

 git grep kmem_cache_destroy | wc -l
 563

So I decided to hold this activity. Well, I think I can create this
patch bomb, it's trivial.

	-ss
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