linux-kernel - Re: [PATCH] hpet: Replace one-element array with flexible-array member

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Message-ID: <Y3cB3MqiM+KFJHNm@work>
Date:   Thu, 17 Nov 2022 21:54:04 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Clemens Ladisch <clemens@...isch.de>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] hpet: Replace one-element array with flexible-array
 member

On Thu, Nov 17, 2022 at 07:42:55PM -0800, Kees Cook wrote:
> One-element arrays are deprecated[1] and are being replaced with
> flexible array members in support of the ongoing efforts to tighten the
> FORTIFY_SOURCE routines on memcpy(), correctly instrument array indexing
> with UBSAN_BOUNDS, and to globally enable -fstrict-flex-arrays=3.
> 
> Replace one-element array with flexible-array member in struct hpet.
> 
> This results in no differences in binary output. The use of struct hpet
> is never used with sizeof() and accesses via hpet_timers array are
> already done after explicit bounds checking.
> 
> [1] https://github.com/KSPP/linux/issues/79
> 
> Cc: Clemens Ladisch <clemens@...isch.de>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Such a sneaky 1-element... ~.~

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

Thanks!
--
Gustavo

> ---
>  include/linux/hpet.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/hpet.h b/include/linux/hpet.h
> index 8604564b985d..21e69eaf7a36 100644
> --- a/include/linux/hpet.h
> +++ b/include/linux/hpet.h
> @@ -30,7 +30,7 @@ struct hpet {
>  			unsigned long _hpet_compare;
>  		} _u1;
>  		u64 hpet_fsb[2];	/* FSB route */
> -	} hpet_timers[1];
> +	} hpet_timers[];
>  };
>  
>  #define	hpet_mc		_u0._hpet_mc
> -- 
> 2.34.1
>