hwmon: (w83793) Fix NULL pointer dereference by removing unnecessary structure field

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).

Cc: stable@vger.kernel.org
Signed-off-by: Nadezda Lutovinova <lutovinova@ispras.ru>
Link: https://lore.kernel.org/r/20210921155153.28098-3-lutovinova@ispras.ru
[groeck: Dropped unnecessary continuation lines, fixed multi-line alignments]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/w83793.c b/drivers/hwmon/w83793.c
index e7d0484eabe4c2a8b59470c69b8aac4def755c5a..1d2854de1cfc961b705516fc3f50b90865eac64e 100644 (file)
--- 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) {
@@ -1586,21 +1584,19 @@ w83793_detect_subclients(struct i2c_client *client)
        }
 
        tmp = w83793_read_value(client, W83793_REG_I2C_SUBADDR);
-       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));
+
+       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))
+               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;
 }