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

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Date:	Wed, 24 Mar 2010 16:25:47 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Pekka J Enberg <penberg@...helsinki.fi>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] slub: Potential stack overflow

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?

V1->V2 Fix missing kfree

Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>

---
 mm/slub.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2010-03-24 16:23:19.000000000 -0500
+++ linux-2.6/mm/slub.c	2010-03-24 16:24:21.000000000 -0500
@@ -3648,10 +3648,10 @@ static int add_location(struct loc_track
 }

 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,
+		unsigned long *map)
 {
 	void *addr = page_address(page);
-	DECLARE_BITMAP(map, page->objects);
 	void *p;

 	bitmap_zero(map, page->objects);
@@ -3670,8 +3670,10 @@ static int list_locations(struct kmem_ca
 	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),
+	if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
 			GFP_TEMPORARY))
 		return sprintf(buf, "Out of memory\n");

@@ -3688,11 +3690,12 @@ static int list_locations(struct kmem_ca

 		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);
 	}
+	kfree(map);

 	for (i = 0; i < t.count; i++) {
 		struct location *l = &t.loc[i];
--
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