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SubjectRe: [PATCH] slub: Potential stack overflow
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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@linux-foundation.org>

Sure, here is third version :

Thanks

[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@gmail.com>
Signed-off-by: Christoph Lameter <cl@linux-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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