1 files changed, 18 insertions, 7 deletions

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index ed4873e18c75..9142964ab9c9 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -230,16 +230,12 @@ static bool check_slab_allocation(struct kmem_cache *cache, void *object,
 }
 
 static inline void poison_slab_object(struct kmem_cache *cache, void *object,
-				      bool init, bool still_accessible)
+				      bool init)
 {
 	void *tagged_object = object;
 
 	object = kasan_reset_tag(object);
 
-	/* RCU slabs could be legally used after free within the RCU period. */
-	if (unlikely(still_accessible))
-		return;
-
 	kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE),
 			KASAN_SLAB_FREE, init);
 
@@ -261,7 +257,22 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
 	if (!kasan_arch_is_ready() || is_kfence_address(object))
 		return false;
 
-	poison_slab_object(cache, object, init, still_accessible);
+	/*
+	 * If this point is reached with an object that must still be
+	 * accessible under RCU, we can't poison it; in that case, also skip the
+	 * quarantine. This should mostly only happen when CONFIG_SLUB_RCU_DEBUG
+	 * has been disabled manually.
+	 *
+	 * Putting the object on the quarantine wouldn't help catch UAFs (since
+	 * we can't poison it here), and it would mask bugs caused by
+	 * SLAB_TYPESAFE_BY_RCU users not being careful enough about object
+	 * reuse; so overall, putting the object into the quarantine here would
+	 * be counterproductive.
+	 */
+	if (still_accessible)
+		return false;
+
+	poison_slab_object(cache, object, init);
 
 	/*
 	 * If the object is put into quarantine, do not let slab put the object
@@ -519,7 +530,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
 	if (check_slab_allocation(slab->slab_cache, ptr, ip))
 		return false;
 
-	poison_slab_object(slab->slab_cache, ptr, false, false);
+	poison_slab_object(slab->slab_cache, ptr, false);
 	return true;
 }