hwmon: (w83791d) Fix NULL pointer dereference by removing unnecessary structure field

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).

Cc: stable@vger.kernel.org
Signed-off-by: Nadezda Lutovinova <lutovinova@ispras.ru>
Link: https://lore.kernel.org/r/20210921155153.28098-1-lutovinova@ispras.ru
[groeck: Dropped unnecessary continuation lines, fixed multi-line alignment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/w83791d.c b/drivers/hwmon/w83791d.c
index 37b25a1..3c1be2c 100644 (file)
--- 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;
@@ -1280,22 +1276,19 @@ static int w83791d_detect_subclients(struct i2c_client *client)
        }
 
        val = w83791d_read(client, W83791D_REG_I2C_SUBADDR);
-       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));
+
+       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))
+               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;
 }