mm, slub: fix mismatch between reconstructed freelist depth and cnt

If object's reuse is delayed, it will be excluded from the reconstructed
freelist.  But we forgot to adjust the cnt accordingly.  So there will
be a mismatch between reconstructed freelist depth and cnt.  This will
lead to free_debug_processing() complaining about freelist count or a
incorrect slub inuse count.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: c389539 ("kasan, slub: fix handling of kasan_slab_free hook")
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Faiyaz Mohammed <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/slub.c

@@ -1701,7 +1701,8 @@ static __always_inline bool slab_free_hook(struct kmem_cache *s,
 }
 
 static inline bool slab_free_freelist_hook(struct kmem_cache *s,
-					   void **head, void **tail)
+					   void **head, void **tail,
+					   int *cnt)
 {
 
 	void *object;
@@ -1728,6 +1729,12 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
 			*head = object;
 			if (!*tail)
 				*tail = object;
+		} else {
+			/*
+			 * Adjust the reconstructed freelist depth
+			 * accordingly if object's reuse is delayed.
+			 */
+			--(*cnt);
 		}
 	} while (object != old_tail);
 
@@ -3480,7 +3487,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
 	 * With KASAN enabled slab_free_freelist_hook modifies the freelist
 	 * to remove objects, whose reuse must be delayed.
 	 */
-	if (slab_free_freelist_hook(s, &head, &tail))
+	if (slab_free_freelist_hook(s, &head, &tail, &cnt))
 		do_slab_free(s, page, head, tail, cnt, addr);
 }