linux-kernel - Re: [PATCH] slub: Potential stack overflow

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Date:	Thu, 25 Mar 2010 21:29:06 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] slub: Potential stack overflow

Eric Dumazet wrote:
> Le mercredi 24 mars 2010 à 16:14 -0500, Christoph Lameter a écrit :
>> Here is a patch for the second case. I think its better since it results
>> in an error display and it avoids the alloc for each slab. Add this piece
>> to your patch?
>>
>> Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
> 
> Sure, here is third version :

Christoph, does this look OK to you? I think Eric has all your later 
additions and kfree() fixlets here.

> [PATCH] slub: Potential stack overflow
> 
> I discovered that we can overflow stack if CONFIG_SLUB_DEBUG=y and use
> slabs with many objects, since list_slab_objects() and process_slab()
> use DECLARE_BITMAP(map, page->objects);
> 
> With 65535 bits, we use 8192 bytes of stack ...
> 
> Switch these allocations to dynamic allocations.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
> ---
>  mm/slub.c |   25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> diff --git a/mm/slub.c b/mm/slub.c
> index b364844..7dc8e73 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2426,9 +2426,11 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
>  #ifdef CONFIG_SLUB_DEBUG
>  	void *addr = page_address(page);
>  	void *p;
> -	DECLARE_BITMAP(map, page->objects);
> +	long *map = kzalloc(BITS_TO_LONGS(page->objects) * sizeof(long),
> +			    GFP_ATOMIC);
>  
> -	bitmap_zero(map, page->objects);
> +	if (!map)
> +		return;
>  	slab_err(s, page, "%s", text);
>  	slab_lock(page);
>  	for_each_free_object(p, s, page->freelist)
> @@ -2443,6 +2445,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
>  		}
>  	}
>  	slab_unlock(page);
> +	kfree(map);
>  #endif
>  }
>  
> @@ -3648,10 +3651,10 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
>  }
>  
>  static void process_slab(struct loc_track *t, struct kmem_cache *s,
> -		struct page *page, enum track_item alloc)
> +		struct page *page, enum track_item alloc,
> +		long *map)
>  {
>  	void *addr = page_address(page);
> -	DECLARE_BITMAP(map, page->objects);
>  	void *p;
>  
>  	bitmap_zero(map, page->objects);
> @@ -3670,11 +3673,14 @@ static int list_locations(struct kmem_cache *s, char *buf,
>  	unsigned long i;
>  	struct loc_track t = { 0, 0, NULL };
>  	int node;
> +	unsigned long *map = kmalloc(BITS_TO_LONGS(oo_objects(s->max)) *
> +				     sizeof(unsigned long), GFP_KERNEL);
>  
> -	if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> -			GFP_TEMPORARY))
> +	if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
> +				     GFP_TEMPORARY)) {
> +		kfree(map);
>  		return sprintf(buf, "Out of memory\n");
> -
> +	}
>  	/* Push back cpu slabs */
>  	flush_all(s);
>  
> @@ -3688,9 +3694,9 @@ static int list_locations(struct kmem_cache *s, char *buf,
>  
>  		spin_lock_irqsave(&n->list_lock, flags);
>  		list_for_each_entry(page, &n->partial, lru)
> -			process_slab(&t, s, page, alloc);
> +			process_slab(&t, s, page, alloc, map);
>  		list_for_each_entry(page, &n->full, lru)
> -			process_slab(&t, s, page, alloc);
> +			process_slab(&t, s, page, alloc, map);
>  		spin_unlock_irqrestore(&n->list_lock, flags);
>  	}
>  
> @@ -3741,6 +3747,7 @@ static int list_locations(struct kmem_cache *s, char *buf,
>  	}
>  
>  	free_loc_track(&t);
> +	kfree(map);
>  	if (!t.count)
>  		len += sprintf(buf, "No data\n");
>  	return len;
> 
> 

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