Re: [PATCH v2 2/3] hwmon: (w83792d) Fix NULL pointer dereference by removing unnecessary structure field

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

On Tue, Sep 21, 2021 at 06:51:52PM +0300, Nadezda Lutovinova wrote:
> If driver read val value sufficient for 
> (val & 0x08) && (!(val & 0x80)) && ((val & 0x7) == ((val >> 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

> ---
> v2: 
>  - split one file per patch 
>  - remove lm75[] instead of adding checking  
> ---
>  drivers/hwmon/w83792d.c | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/hwmon/w83792d.c b/drivers/hwmon/w83792d.c
> index abd5c3a722b9..8a72be4ad74f 100644
> --- a/drivers/hwmon/w83792d.c
> +++ b/drivers/hwmon/w83792d.c
> @@ -264,9 +264,6 @@ struct w83792d_data {
>  	char valid;		/* !=0 if following fields are valid */
>  	unsigned long last_updated;	/* In jiffies */
>  
> -	/* array of 2 pointers to subclients */
> -	struct i2c_client *lm75[2];
> -
>  	u8 in[9];		/* Register value */
>  	u8 in_max[9];		/* Register value */
>  	u8 in_min[9];		/* Register value */
> @@ -927,7 +924,6 @@ w83792d_detect_subclients(struct i2c_client *new_client)
>  	int address = new_client->addr;
>  	u8 val;
>  	struct i2c_adapter *adapter = new_client->adapter;
> -	struct w83792d_data *data = i2c_get_clientdata(new_client);
>  
>  	id = i2c_adapter_id(adapter);
>  	if (force_subclients[0] == id && force_subclients[1] == address) {
> @@ -946,20 +942,21 @@ w83792d_detect_subclients(struct i2c_client *new_client)
>  	}
>  
>  	val = w83792d_read_value(new_client, W83792D_REG_I2C_SUBADDR);
> +
> +	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;
> +	}
> +
>  	if (!(val & 0x08))
> -		data->lm75[0] = devm_i2c_new_dummy_device(&new_client->dev, adapter,
> -							  0x48 + (val & 0x7));
> -	if (!(val & 0x80)) {
> -		if (!IS_ERR(data->lm75[0]) &&
> -			((val & 0x7) == ((val >> 4) & 0x7))) {
> -			dev_err(&new_client->dev,
> -				"duplicate addresses 0x%x, use force_subclient\n",
> -				data->lm75[0]->addr);
> -			return -ENODEV;
> -		}
> -		data->lm75[1] = devm_i2c_new_dummy_device(&new_client->dev, adapter,
> -							  0x48 + ((val >> 4) & 0x7));
> -	}
> +		devm_i2c_new_dummy_device(&new_client->dev, adapter,
> +						0x48 + (val & 0x7));
> +
> +	if (!(val & 0x80))
> +		devm_i2c_new_dummy_device(&new_client->dev, adapter,
> +						0x48 + ((val >> 4) & 0x7));
>  
>  	return 0;
>  }