linux-hardening - Re: [PATCH] bcachefs: Annotate struct bucket_array with __counted

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Message-ID: <202408221035.5464B1E0@keescook>
Date: Thu, 22 Aug 2024 10:35:57 -0700
From: Kees Cook <kees@...nel.org>
To: Thorsten Blum <thorsten.blum@...lux.com>
Cc: kent.overstreet@...ux.dev, gustavoars@...nel.org,
	linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] bcachefs: Annotate struct bucket_array with
 __counted_by()

On Wed, Aug 21, 2024 at 06:29:22PM +0200, Thorsten Blum wrote:
> Add the __counted_by compiler attribute to the flexible array member
> bucket to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
> ---
>  fs/bcachefs/buckets_types.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/bcachefs/buckets_types.h b/fs/bcachefs/buckets_types.h
> index c9698cdf866f..a19460a1bb7c 100644
> --- a/fs/bcachefs/buckets_types.h
> +++ b/fs/bcachefs/buckets_types.h
> @@ -24,7 +24,7 @@ struct bucket_array {
>  	u16			first_bucket;
>  	size_t			nbuckets;
>  	size_t			nbuckets_minus_first;
> -	struct bucket		b[];
> +	struct bucket		b[] __counted_by(nbuckets);
>  };
>  
>  struct bucket_gens {

I only see this being allocated in one place and nbuckets is immediately
assigned to the count of "b" elements, so this looks correct to me.

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook