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

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Date:   Tue, 21 Sep 2021 18:51:52 +0300
From:   Nadezda Lutovinova <lutovinova@...ras.ru>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Nadezda Lutovinova <lutovinova@...ras.ru>,
        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: [PATCH v2 2/3] hwmon: (w83792d) 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).

Signed-off-by: Nadezda Lutovinova <lutovinova@...ras.ru>
---
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;
 }
-- 
2.17.1