linux-hardening - Re: [PATCH v2] p54: Replace zero-length array of trailing structs with flex-array

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Message-ID: <db584852-b6a6-f479-d073-1236ba1f3c0c@gmail.com>
Date:   Sat, 19 Nov 2022 02:36:40 +0100
From:   Christian Lamparter <chunkeey@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Kalle Valo <kvalo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] p54: Replace zero-length array of trailing structs
 with flex-array

On 11/19/22 00:42, Kees Cook wrote:
> Zero-length 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 zero-length array with flexible-array member.
> 
> This results in no differences in binary output (most especially because
> struct pda_antenna_gain is unused). The struct is kept for future
> reference.
> 
> [1] https://github.com/KSPP/linux/issues/78
> 

Thank you!

> Cc: Christian Lamparter <chunkeey@...glemail.com>
> Cc: Kalle Valo <kvalo@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: linux-wireless@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: Christian Lamparter <chunkeey@...il.com>
> ---
> v2:
> - convert normally (chunkeey)
> v1: https://lore.kernel.org/lkml/20221118210639.never.072-kees@kernel.org/
> ---
>   drivers/net/wireless/intersil/p54/eeprom.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/intersil/p54/eeprom.h b/drivers/net/wireless/intersil/p54/eeprom.h
> index 1d0aaf54389a..641c4e79879e 100644
> --- a/drivers/net/wireless/intersil/p54/eeprom.h
> +++ b/drivers/net/wireless/intersil/p54/eeprom.h
> @@ -108,10 +108,10 @@ struct pda_country {
>   } __packed;
>   
>   struct pda_antenna_gain {
> -	struct {
> +	DECLARE_FLEX_ARRAY(struct {
>   		u8 gain_5GHz;	/* 0.25 dBi units */
>   		u8 gain_2GHz;	/* 0.25 dBi units */
> -	} __packed antenna[0];
> +	} __packed, antenna);
>   } __packed;
>   
>   struct pda_custom_wrapper {