kasan: unify code between kasan_slab_free() and kasan_poison_kfree()

Both of these functions deal with freeing of slab objects.
However, kasan_poison_kfree() mishandles SLAB_TYPESAFE_BY_RCU
(must also not poison such objects) and does not detect double-frees.

Unify code between these functions.

This solves both of the problems and allows to add more common code
(e.g. detection of invalid frees).

Link: http://lkml.kernel.org/r/385493d863acf60408be219a021c3c8e27daa96f.1514378558.git.dvyukov@google.com
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>a
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kasan/kasan.c

@@ -489,21 +489,11 @@ void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
 	kasan_kmalloc(cache, object, cache->object_size, flags);
 }
 
-static void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
-{
-	unsigned long size = cache->object_size;
-	unsigned long rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
-
-	/* RCU slabs could be legally used after free within the RCU period */
-	if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
-		return;
-
-	kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
-}
-
-bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
+static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
+			      unsigned long ip, bool quarantine)
 {
 	s8 shadow_byte;
+	unsigned long rounded_up_size;
 
 	/* RCU slabs could be legally used after free within the RCU period */
 	if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
@@ -515,9 +505,10 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
 		return true;
 	}
 
-	kasan_poison_slab_free(cache, object);
+	rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
+	kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
 
-	if (unlikely(!(cache->flags & SLAB_KASAN)))
+	if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
 		return false;
 
 	set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
@@ -525,6 +516,11 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
 	return true;
 }
 
+bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
+{
+	return __kasan_slab_free(cache, object, ip, true);
+}
+
 void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
 		   gfp_t flags)
 {
@@ -602,7 +598,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
 		kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
 				KASAN_FREE_PAGE);
 	} else {
-		kasan_poison_slab_free(page->slab_cache, ptr);
+		__kasan_slab_free(page->slab_cache, ptr, ip, false);
 	}
 }