linux-kernel - Re: [PATCH] hwmon: Correct the error handling in w83793.c, w83791d.c, w83792d.c

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Date:   Wed, 11 Aug 2021 11:18:44 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Nadezda Lutovinova <lutovinova@...ras.ru>
Cc:     Marc Hulsman <m.hulsman@...elft.nl>,
        Jean Delvare <jdelvare@...e.com>,
        Rudolf Marek <r.marek@...embler.cz>,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] hwmon: Correct the error handling in w83793.c,
 w83791d.c, w83792d.c

On Wed, Aug 11, 2021 at 07:15:15PM +0300, Nadezda Lutovinova wrote:
> If driver read tmp (or val) value sufficient for 
> (tmp & 0x08) && (!(tmp & 0x80)) && ((tmp & 0x7) == ((tmp >> 4) & 0x7))
> from device then Null pointer dereference occurs. 
> (It is possible if tmp = 0b0xyz1xyz, where same literals mean same numbers)
> 
> The patch adds checking if data->lm75[0] is NULL.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 

One patch per driver, please.

> Signed-off-by: Nadezda Lutovinova <lutovinova@...ras.ru>
> ---
>  drivers/hwmon/w83791d.c | 2 +-
>  drivers/hwmon/w83792d.c | 2 +-
>  drivers/hwmon/w83793.c  | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/w83791d.c b/drivers/hwmon/w83791d.c
> index 37b25a1474c4..8b30bbfafaa7 100644
> --- a/drivers/hwmon/w83791d.c
> +++ b/drivers/hwmon/w83791d.c
> @@ -1284,7 +1284,7 @@ static int w83791d_detect_subclients(struct i2c_client *client)
>  		data->lm75[0] = devm_i2c_new_dummy_device(&client->dev, adapter,
>  							  0x48 + (val & 0x7));
>  	if (!(val & 0x80)) {
> -		if (!IS_ERR(data->lm75[0]) &&
> +		if (!IS_ERR_OR_NULL(data->lm75[0]) &&
>  				((val & 0x7) == ((val >> 4) & 0x7))) {
>  			dev_err(&client->dev,
>  				"duplicate addresses 0x%x, "

As you pointed out in te other e-mail, lm75[] does not really serve 
a purpose anymore. It might be much better to replace this code with
something like

	if (!(val & 0x88) && (val & 0x7) == ((val >> 4) & 0x7)) {
		dev_err(&new_client->dev,
		        "duplicate addresses 0x%x, use force_subclient\n",
                        0x48 + (val & 0x7));
		return -ENODEV;
	}

Same for the other chips.

Guenter

> diff --git a/drivers/hwmon/w83792d.c b/drivers/hwmon/w83792d.c
> index abd5c3a722b9..85ae12d950e1 100644
> --- a/drivers/hwmon/w83792d.c
> +++ b/drivers/hwmon/w83792d.c
> @@ -950,7 +950,7 @@ w83792d_detect_subclients(struct i2c_client *new_client)
>  		data->lm75[0] = devm_i2c_new_dummy_device(&new_client->dev, adapter,
>  							  0x48 + (val & 0x7));
>  	if (!(val & 0x80)) {
> -		if (!IS_ERR(data->lm75[0]) &&
> +		if (!IS_ERR_OR_NULL(data->lm75[0]) &&
>  			((val & 0x7) == ((val >> 4) & 0x7))) {
>  			dev_err(&new_client->dev,
>  				"duplicate addresses 0x%x, use force_subclient\n",
> diff --git a/drivers/hwmon/w83793.c b/drivers/hwmon/w83793.c
> index e7d0484eabe4..9d8c44e2fa6e 100644
> --- a/drivers/hwmon/w83793.c
> +++ b/drivers/hwmon/w83793.c
> @@ -1590,7 +1590,7 @@ w83793_detect_subclients(struct i2c_client *client)
>  		data->lm75[0] = devm_i2c_new_dummy_device(&client->dev, adapter,
>  							  0x48 + (tmp & 0x7));
>  	if (!(tmp & 0x80)) {
> -		if (!IS_ERR(data->lm75[0])
> +		if (!IS_ERR_OR_NULL(data->lm75[0])
>  		    && ((tmp & 0x7) == ((tmp >> 4) & 0x7))) {
>  			dev_err(&client->dev,
>  				"duplicate addresses 0x%x, "
> -- 
> 2.17.1
>