linux-kernel - Re: [PATCH v2 1/2] hwmon: (lm90) Prevent integer overflow of temperature calculations

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Date:   Mon, 21 Jun 2021 05:12:29 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 1/2] hwmon: (lm90) Prevent integer overflow of
 temperature calculations

On Mon, Jun 21, 2021 at 12:14:07AM +0300, Dmitry Osipenko wrote:
> The minimum temperature value that is passed to the driver is unlimited
> and value that is close to INT_MIN results in integer overflow of
> temperature calculations made by the driver. Limit the value in order
> to prevent the overflow. For now the overflow condition is harmless,
> but thermal framework won't work properly once we will support the
> set_trips() callback because it will pass INT_MIN value to the driver.
> 

AFAICS that should only happen for lm99 because all other values
are bound in the temp_to_xxx functions. Where else do you see an
overflow (or underflow) ?

Thanks,
Guenter

> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/hwmon/lm90.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
> index b53f17511b05..6e2fa976098f 100644
> --- a/drivers/hwmon/lm90.c
> +++ b/drivers/hwmon/lm90.c
> @@ -1028,6 +1028,9 @@ static int lm90_set_temp11(struct lm90_data *data, int index, long val)
>  	struct reg *regp = &reg[index];
>  	int err;
>  
> +	/* prevent integer overflow */
> +	val = max(val, -128000l);
> +
>  	/* +16 degrees offset for temp2 for the LM99 */
>  	if (data->kind == lm99 && index <= 2)
>  		val -= 16000;
> @@ -1088,6 +1091,9 @@ static int lm90_set_temp8(struct lm90_data *data, int index, long val)
>  	struct i2c_client *client = data->client;
>  	int err;
>  
> +	/* prevent integer overflow */
> +	val = max(val, -128000l);
> +
>  	/* +16 degrees offset for temp2 for the LM99 */
>  	if (data->kind == lm99 && index == 3)
>  		val -= 16000;
> -- 
> 2.30.2
>