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>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

diff --git a/mm/slub.c b/mm/slub.c
index d2a54fe..78f1a20 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2429,9 +2429,11 @@ 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)
@@ -2446,6 +2448,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
                }
        }
        slab_unlock(page);
+       kfree(map);
 #endif
 }
 
@@ -3651,10 +3654,10 @@ 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);
@@ -3673,11 +3676,14 @@ 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);
 
@@ -3691,9 +3697,9 @@ 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);
        }
 
@@ -3744,6 +3750,7 @@ 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;