Re: [PATCH] sctp: annotate struct sctp_assoc_ids with __counted_by()

[Justin Stitt]

Hi,

On Wed, May 01, 2024 at 07:01:22PM +0200, Erick Archer wrote:
> Prepare for the coming implementation by GCC and Clang of the
> __counted_by attribute. Flexible array members annotated with
> __counted_by can have their accesses bounds-checked at run-time via
> CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE
> (for strcpy/memcpy-family functions).
> 
> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Erick Archer <erick.archer@xxxxxxxxxxx>
> ---
>  include/uapi/linux/sctp.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> index b7d91d4cf0db..836173e73401 100644
> --- a/include/uapi/linux/sctp.h
> +++ b/include/uapi/linux/sctp.h
> @@ -1007,7 +1007,7 @@ enum sctp_sstat_state {
>   */
>  struct sctp_assoc_ids {
>  	__u32		gaids_number_of_ids;
> -	sctp_assoc_t	gaids_assoc_id[];
> +	sctp_assoc_t	gaids_assoc_id[] __counted_by(gaids_number_of_ids);

Crucially, gaids_number_of_ids is assigned before any accesses to
gaids_assoc_id[] are made.

|	ids->gaids_number_of_ids = num;
|	num = 0;
|	list_for_each_entry(asoc, &(sp->ep->asocs), asocs) {
|		ids->gaids_assoc_id[num++] = asoc->assoc_id;
|	}

So this looks good to me.

Reviewed-by: Justin Stitt <justinstitt@xxxxxxxxxx>

>  };
>  
>  /*
> -- 
> 2.25.1
> 

Thanks
Justin