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Date: Wed, 1 May 2024 20:04:11 +0000
From: Justin Stitt <justinstitt@google.com>
To: Erick Archer <erick.archer@outlook.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>, 
	Xin Long <lucien.xin@gmail.com>, Kees Cook <keescook@chromium.org>, 
	"Gustavo A. R. Silva" <gustavoars@kernel.org>, Nathan Chancellor <nathan@kernel.org>, 
	Nick Desaulniers <ndesaulniers@google.com>, Bill Wendling <morbo@google.com>, linux-sctp@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH] sctp: annotate struct sctp_assoc_ids with __counted_by()
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In-Reply-To: <AS8PR02MB723728DA244A82D97342D6498B192@AS8PR02MB7237.eurprd02.prod.outlook.com>

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@chromium.org>
> Signed-off-by: Erick Archer <erick.archer@outlook.com>
> ---
>  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@google.com>

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

Thanks
Justin