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

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Message-ID: <7c4622e7-d7a8-ae5d-e381-f726cb511228@gmail.com>
Date:   Fri, 23 Jun 2023 17:38:09 +0200
From:   Christian Lamparter <chunkeey@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>, Kalle Valo <kvalo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Shiji Yang <yangshiji66@...look.com>,
        Nick Kossifidis <mickflemm@...il.com>, jirislaby@...nel.org,
        Ansuel Smith <ansuelsmth@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] carl9170: re-fix fortified-memset warning

On 6/23/23 17:23, 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")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>


Wait! I want to point out this funny thing is happening in ath too!

https://lore.kernel.org/linux-wireless/TYAP286MB03154F9AAFD4C35BEEDE4A99BC4CA@TYAP286MB0315.JPNP286.PROD.OUTLOOK.COM/T/#mf1b8919a000fe661803c17073f48b3c410888541

And that patch got NACK by Jiri Slaby because like me he suspects that
this is a compiler bug.

so, what's going wrong with fortified there?

Thanks,
Christian