Re: [PATCH] overflow: Clarify expectations for getting DEFINE_FLEX variable sizes

[Gustavo A. R. Silva]

On 16/04/25 11:29, Kees Cook wrote:
> Mention the use of __member_size() for DEFINE_FLEX variables as a hint
> for getting at the compile-time size of the resulting flexible array
> member.
>
> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks!
--
Gustavo

> ---
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> ---
>   include/linux/overflow.h | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 0c7e3dcfe867..6ee67c20b575 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -419,6 +419,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
>    * Define a zeroed, on-stack, instance of @type structure with a trailing
>    * flexible array member.
>    * Use __struct_size(@name) to get compile-time size of it afterwards.
> + * Use __member_size(@name->member) to get compile-time size of @name members.
>    */
>   #define DEFINE_RAW_FLEX(type, name, member, count)	\
>   	_DEFINE_FLEX(type, name, member, count, = {})
> @@ -436,6 +437,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
>    * Define a zeroed, on-stack, instance of @TYPE structure with a trailing
>    * flexible array member.
>    * Use __struct_size(@NAME) to get compile-time size of it afterwards.
> + * Use __member_size(@NAME->member) to get compile-time size of @NAME members.
>    */
>   #define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT)	\
>   	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })