Re: [PATCH v2 3/3] hwmon: (w83793) Fix NULL pointer dereference by removing unnecessary structure field

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Sep 21, 2021 at 06:51:53PM +0300, Nadezda Lutovinova wrote:
> If driver read tmp 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)
> Also lm75[] does not serve a purpose anymore after switching to
> devm_i2c_new_dummy_device() in w83791d_detect_subclients().
> 
> The patch fixes possible NULL pointer dereference by removing lm75[].
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Nadezda Lutovinova <lutovinova@ispras.ru>

Applied, after fixing multi-line alignments

Thanks,
Guenter

> ---
> v2: 
>  - split one file per patch 
>  - remove lm75[] instead of adding checking  
> ---
>  drivers/hwmon/w83793.c | 29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/hwmon/w83793.c b/drivers/hwmon/w83793.c
> index e7d0484eabe4..4ee96756ed49 100644
> --- a/drivers/hwmon/w83793.c
> +++ b/drivers/hwmon/w83793.c
> @@ -202,7 +202,6 @@ static inline s8 TEMP_TO_REG(long val, s8 min, s8 max)
>  }
>  
>  struct w83793_data {
> -	struct i2c_client *lm75[2];
>  	struct device *hwmon_dev;
>  	struct mutex update_lock;
>  	char valid;			/* !=0 if following fields are valid */
> @@ -1566,7 +1565,6 @@ w83793_detect_subclients(struct i2c_client *client)
>  	int address = client->addr;
>  	u8 tmp;
>  	struct i2c_adapter *adapter = client->adapter;
> -	struct w83793_data *data = i2c_get_clientdata(client);
>  
>  	id = i2c_adapter_id(adapter);
>  	if (force_subclients[0] == id && force_subclients[1] == address) {
> @@ -1586,20 +1584,21 @@ w83793_detect_subclients(struct i2c_client *client)
>  	}
>  
>  	tmp = w83793_read_value(client, W83793_REG_I2C_SUBADDR);
> +
> +	if (!(tmp & 0x88) && (tmp & 0x7) == ((tmp >> 4) & 0x7)) {
> +		dev_err(&client->dev,
> +			"duplicate addresses 0x%x, use force_subclient\n",
> +				0x48 + (tmp & 0x7));
> +		return -ENODEV;
> +	}
> +
>  	if (!(tmp & 0x08))
> -		data->lm75[0] = devm_i2c_new_dummy_device(&client->dev, adapter,
> -							  0x48 + (tmp & 0x7));
> -	if (!(tmp & 0x80)) {
> -		if (!IS_ERR(data->lm75[0])
> -		    && ((tmp & 0x7) == ((tmp >> 4) & 0x7))) {
> -			dev_err(&client->dev,
> -				"duplicate addresses 0x%x, "
> -				"use force_subclients\n", data->lm75[0]->addr);
> -			return -ENODEV;
> -		}
> -		data->lm75[1] = devm_i2c_new_dummy_device(&client->dev, adapter,
> -							  0x48 + ((tmp >> 4) & 0x7));
> -	}
> +		devm_i2c_new_dummy_device(&client->dev, adapter,
> +						0x48 + (tmp & 0x7));
> +
> +	if (!(tmp & 0x80))
> +		devm_i2c_new_dummy_device(&client->dev, adapter,
> +						0x48 + ((tmp >> 4) & 0x7));
>  
>  	return 0;
>  }