On Thu, Jan 25, 2024 at 11:36PM +0100, Andrey Konovalov wrote:
[...]
>
> Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
>
> But I'm wondering if we should also stop resetting metadata when the
> object is fully freed (from quarantine or bypassing quarantine).
>
> With stack_depot_put, I had to put the stack handles on free, as
> otherwise we would leak the stack depot references. And I also chose
> to memset meta at that point, as its gets invalid anyway. But without
> stack_depot_put, this is not required.
>
> Before the stack depot-related changes, the code was inconsistent in
> this regard AFAICS: for quarantine, free meta was marked as invalid
> via KASAN_SLAB_FREE but alloc meta was kept; for no quarantine, both
> alloc and free meta were kept.
>
> So perhaps we can just keep both metas on full free. I.e. drop both
> kasan_release_object_meta calls. This will go back to the old behavior
> + keeping free meta for the quarantine case (I think there's no harm
> in that). This will give better reporting for uaf-before-realloc bugs.
>
> WDYT?
Yes, that makes sense.
You mean this on top?
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index ad32803e34e9..0577db1d2c62 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -264,12 +264,6 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object,
if (kasan_quarantine_put(cache, object))
return true;
- /*
- * If the object is not put into quarantine, it will likely be quickly
- * reallocated. Thus, release its metadata now.
- */
- kasan_release_object_meta(cache, object);
-
/* Let slab put the object onto the freelist. */
return false;
}
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 8bfb52b28c22..fc9cf1860efb 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -510,20 +510,6 @@ static void release_free_meta(const void *object, struct kasan_free_meta *meta)
*(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE;
}
-void kasan_release_object_meta(struct kmem_cache *cache, const void *object)
-{
- struct kasan_alloc_meta *alloc_meta;
- struct kasan_free_meta *free_meta;
-
- alloc_meta = kasan_get_alloc_meta(cache, object);
- if (alloc_meta)
- release_alloc_meta(alloc_meta);
-
- free_meta = kasan_get_free_meta(cache, object);
- if (free_meta)
- release_free_meta(object, free_meta);
-}
-
size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
{
struct kasan_cache *info = &cache->kasan_info;
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 216ae0ef1e4b..fb2b9ac0659a 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -390,10 +390,8 @@ struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
struct kasan_free_meta *kasan_get_free_meta(struct kmem_cache *cache,
const void *object);
void kasan_init_object_meta(struct kmem_cache *cache, const void *object);
-void kasan_release_object_meta(struct kmem_cache *cache, const void *object);
#else
static inline void kasan_init_object_meta(struct kmem_cache *cache, const void *object) { }
-static inline void kasan_release_object_meta(struct kmem_cache *cache, const void *object) { }
#endif
depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags);
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 3ba02efb952a..a758c2e10703 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -145,8 +145,6 @@ static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
void *object = qlink_to_object(qlink, cache);
struct kasan_free_meta *free_meta = kasan_get_free_meta(cache, object);
- kasan_release_object_meta(cache, object);
-
/*
* If init_on_free is enabled and KASAN's free metadata is stored in
* the object, zero the metadata. Otherwise, the object's memory will
