linux-kernel - Re: [PATCH v2 1/3] hwmon: (w83791d) Fix NULL pointer dereference by removing unnecessary structure field

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Date:   Sat, 2 Oct 2021 05:07:49 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Nadezda Lutovinova <lutovinova@...ras.ru>
Cc:     Marc Hulsman <m.hulsman@...elft.nl>,
        Rudolf Marek <r.marek@...embler.cz>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org
Subject: Re: [PATCH v2 1/3] hwmon: (w83791d) Fix NULL pointer dereference by
 removing unnecessary structure field

On Tue, Sep 21, 2021 at 06:51:51PM +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@...ras.ru>

Applied, after fixing multi-line alignments.

Guenter

> ---
> v2: 
>  - split one file per patch 
>  - remove lm75[] instead of adding checking  
> ---
>  drivers/hwmon/w83791d.c | 32 ++++++++++++++------------------
>  1 file changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/hwmon/w83791d.c b/drivers/hwmon/w83791d.c
> index 37b25a1474c4..b4eae45859c1 100644
> --- a/drivers/hwmon/w83791d.c
> +++ b/drivers/hwmon/w83791d.c
> @@ -273,9 +273,6 @@ struct w83791d_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];
> -
>  	/* volts */
>  	u8 in[NUMBER_OF_VIN];		/* Register value */
>  	u8 in_max[NUMBER_OF_VIN];	/* Register value */
> @@ -1257,7 +1254,6 @@ static const struct attribute_group w83791d_group_fanpwm45 = {
>  static int w83791d_detect_subclients(struct i2c_client *client)
>  {
>  	struct i2c_adapter *adapter = client->adapter;
> -	struct w83791d_data *data = i2c_get_clientdata(client);
>  	int address = client->addr;
>  	int i, id;
>  	u8 val;
> @@ -1280,21 +1276,21 @@ static int w83791d_detect_subclients(struct i2c_client *client)
>  	}
>  
>  	val = w83791d_read(client, W83791D_REG_I2C_SUBADDR);
> +
> +	if (!(val & 0x88) && (val & 0x7) == ((val >> 4) & 0x7)) {
> +		dev_err(&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(&client->dev, adapter,
> -							  0x48 + (val & 0x7));
> -	if (!(val & 0x80)) {
> -		if (!IS_ERR(data->lm75[0]) &&
> -				((val & 0x7) == ((val >> 4) & 0x7))) {
> -			dev_err(&client->dev,
> -				"duplicate addresses 0x%x, "
> -				"use force_subclient\n",
> -				data->lm75[0]->addr);
> -			return -ENODEV;
> -		}
> -		data->lm75[1] = devm_i2c_new_dummy_device(&client->dev, adapter,
> -							  0x48 + ((val >> 4) & 0x7));
> -	}
> +		devm_i2c_new_dummy_device(&client->dev, adapter,
> +						0x48 + (val & 0x7));
> +
> +	if (!(val & 0x80))
> +		devm_i2c_new_dummy_device(&client->dev, adapter,
> +						0x48 + ((val >> 4) & 0x7));
>  
>  	return 0;
>  }