linux-hardening - Re: [PATCH 2/2] wifi: ath9k: work around memset overflow warning

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Message-ID: <202403281450.CAD08A9B@keescook>
Date: Thu, 28 Mar 2024 14:50:47 -0700
From: Kees Cook <keescook@...omium.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Kalle Valo <kvalo@...nel.org>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	linux-hardening@...r.kernel.org, linux-wireless@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Jeff Johnson <quic_jjohnson@...cinc.com>,
	Dmitry Antipov <dmantipov@...dex.ru>,
	Hancheng Yang <hyang@...ebox.fr>, Remi Pommarel <repk@...plefau.lt>,
	Johannes Berg <johannes.berg@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] wifi: ath9k: work around memset overflow warning

On Thu, Mar 28, 2024 at 02:55:05PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc-9 and some other older versions produce a false-positive warning
> for zeroing two fields
> 
> In file included from include/linux/string.h:369,
>                  from drivers/net/wireless/ath/ath9k/main.c:18:
> In function 'fortify_memset_chk',
>     inlined from 'ath9k_ps_wakeup' at drivers/net/wireless/ath/ath9k/main.c:140:3:
> include/linux/fortify-string.h:462:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>   462 |                         __write_overflow_field(p_size_field, size);
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Using a struct_group seems to reliably avoid the warning and
> not make the code much uglier. The combined memset() should even
> save a couple of cpu cycles.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook