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>

1 files changed, 16 insertions, 9 deletions

diff --git a/mm/slub.c b/mm/slub.c
index d2a54fe71ea2..78f1a202ca33 100644
--- 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;