linux-kernel - Re: [PATCH] hwmon: (w83791d) Convert macros to functions to avoid TOCTOU

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Message-ID: <695c582d-308f-4960-84fa-cbf6f08c909b@roeck-us.net>
Date: Thu, 4 Dec 2025 20:02:54 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Gui-Dong Han <hanguidong02@...il.com>
Cc: m.hulsman@...elft.nl, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] hwmon: (w83791d) Convert macros to functions to avoid
 TOCTOU

On Wed, Dec 03, 2025 at 02:01:05AM +0800, Gui-Dong Han wrote:
> The macro FAN_FROM_REG evaluates its arguments multiple times. When used
> in lockless contexts involving shared driver data, this leads to
> Time-of-Check to Time-of-Use (TOCTOU) race conditions, potentially
> causing divide-by-zero errors.
> 
> Convert the macro to a static function. This guarantees that arguments
> are evaluated only once (pass-by-value), preventing the race
> conditions.
> 
> Additionally, in store_fan_div, move the calculation of the minimum
> limit inside the update lock. This ensures that the read-modify-write
> sequence operates on consistent data.
> 
> Adhere to the principle of minimal changes by only converting macros
> that evaluate arguments multiple times and are used in lockless
> contexts.
> 
> Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/
> Fixes: 9873964d6eb2 ("[PATCH] HWMON: w83791d: New hardware monitoring driver for the Winbond W83791D") 
> Cc: stable@...r.kernel.org
> Signed-off-by: Gui-Dong Han <hanguidong02@...il.com>

Applied.

Thanks,
Guenter