Re: [PATCH v2 1/2] kasan: catch invalid free before SLUB reinitializes the object

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 24 Jul 2024 18:34:12 +0200 Jann Horn <jannh@google.com> wrote:

> Currently, when KASAN is combined with init-on-free behavior, the
> initialization happens before KASAN's "invalid free" checks.
> 
> More importantly, a subsequent commit will want to use the object metadata
> region to store an rcu_head, and we should let KASAN check that the object
> pointer is valid before that. (Otherwise that change will make the existing
> testcase kmem_cache_invalid_free fail.)
> 
> So add a new KASAN hook that allows KASAN to pre-validate a
> kmem_cache_free() operation before SLUB actually starts modifying the
> object or its metadata.

I added this, to fix the CONFIG_KASAN=n build

--- a/include/linux/kasan.h~kasan-catch-invalid-free-before-slub-reinitializes-the-object-fix
+++ a/include/linux/kasan.h
@@ -381,6 +381,12 @@ static inline void *kasan_init_slab_obj(
 {
 	return (void *)object;
 }
+
+static inline bool kasan_slab_pre_free(struct kmem_cache *s, void *object)
+{
+	return false;
+}
+
 static inline bool kasan_slab_free(struct kmem_cache *s, void *object, bool init)
 {
 	return false;
_