When 'orig_size' of kmalloc object is enabled by debug option, it
should either contains the actual requested size or the cache's
'object_size'.

But it's not true if that object is a kfence-allocated one, and the
data at 'orig_size' offset of metadata could be zero or other values.
This is not a big issue for current 'orig_size' usage, as init_object()
and check_object() during alloc/free process will be skipped for kfence
addresses. But it could cause trouble for other usage in future.

Use the existing kfence helper kfence_ksize() which can return the
real original request size.

Signed-off-by: Feng Tang <feng.tang@intel.com>
---
 mm/slub.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index af9a80071fe0..1d348899f7a3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -768,6 +768,9 @@ static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
 {
 	void *p = kasan_reset_tag(object);
 
+	if (is_kfence_address(object))
+		return kfence_ksize(object);
+
 	if (!slub_debug_orig_size(s))
 		return s->object_size;
 
-- 
2.27.0

On Thu, Oct 17, 2024 at 12:42 AM Feng Tang <feng.tang@intel.com> wrote:
>
> When 'orig_size' of kmalloc object is enabled by debug option, it
> should either contains the actual requested size or the cache's
> 'object_size'.
>
> But it's not true if that object is a kfence-allocated one, and the
> data at 'orig_size' offset of metadata could be zero or other values.
> This is not a big issue for current 'orig_size' usage, as init_object()
> and check_object() during alloc/free process will be skipped for kfence
> addresses. But it could cause trouble for other usage in future.
>
> Use the existing kfence helper kfence_ksize() which can return the
> real original request size.
>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

>  mm/slub.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index af9a80071fe0..1d348899f7a3 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -768,6 +768,9 @@ static inline unsigned int get_orig_size(struct kmem_cache *s, void *object)
>  {
>         void *p = kasan_reset_tag(object);
>
> +       if (is_kfence_address(object))
> +               return kfence_ksize(object);
> +
>         if (!slub_debug_orig_size(s))
>                 return s->object_size;
>
> --
> 2.27.0
>