linux-hardening - Re: [PATCH 1/2] [RESEND] wifi: carl9170: re-fix fortified-memset warning

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Message-ID: <202403281451.6E8EB15E0@keescook>
Date: Thu, 28 Mar 2024 14:51:32 -0700
From: Kees Cook <keescook@...omium.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Christian Lamparter <chunkeey@...glemail.com>,
	Kalle Valo <kvalo@...nel.org>,
	Johannes Berg <johannes.berg@...el.com>,
	linux-hardening@...r.kernel.org,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	linux-wireless@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Colin Ian King <colin.i.king@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] [RESEND] wifi: carl9170: re-fix fortified-memset
 warning

On Thu, Mar 28, 2024 at 02:55:04PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The carl9170_tx_release() function sometimes triggers a fortified-memset
> warning in my randconfig builds:
> 
> In file included from include/linux/string.h:254,
>                  from drivers/net/wireless/ath/carl9170/tx.c:40:
> In function 'fortify_memset_chk',
>     inlined from 'carl9170_tx_release' at drivers/net/wireless/ath/carl9170/tx.c:283:2,
>     inlined from 'kref_put' at include/linux/kref.h:65:3,
>     inlined from 'carl9170_tx_put_skb' at drivers/net/wireless/ath/carl9170/tx.c:342:9:
> include/linux/fortify-string.h:493:25: 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]
>   493 |                         __write_overflow_field(p_size_field, size);
> 
> Kees previously tried to avoid this by using memset_after(), but it seems
> this does not fully address the problem. I noticed that the memset_after()
> here is done on a different part of the union (status) than the original
> cast was from (rate_driver_data), which may confuse the compiler.
> 
> Unfortunately, the memset_after() trick does not work on driver_rates[]
> because that is part of an anonymous struct, and I could not get
> struct_group() to do this either. Using two separate memset() calls
> on the two members does address the warning though.
> 
> Fixes: fb5f6a0e8063b ("mac80211: Use memset_after() to clear tx status")
> Link: https://lore.kernel.org/lkml/20230623152443.2296825-1-arnd@kernel.org/
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

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

-- 
Kees Cook