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SubjectRe: [PATCH] zsmalloc: fix a null pointer dereference in destroy_handle_cache()
On Mon, Jun 08, 2015 at 01:55:32PM -0700, Andrew Morton wrote:
> On Fri, 5 Jun 2015 20:11:30 +0900 Sergey Senozhatsky <sergey.senozhatsky@gmail.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.

Hello, Andrew.

I'm not sure if doing the check in kmem_cache_destroy() is better.
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. I think that it's general convention that proper
pool pointer should be passed to pool based function APIs.

Thanks.


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