Re: [PATCH] iio: cm36651: Fix i2c client leak and possible NULL pointer dereference

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On 17/03/14 08:01, Krzysztof Kozlowski wrote:
Hi,

On Sat, 2014-03-15 at 16:24 +0000, Jonathan Cameron wrote:
On 06/03/14 09:33, Krzysztof Kozlowski wrote:
During probe the driver allocates dummy I2C devices (i2c_new_dummy())
but they aren't unregistered during driver remove or probe failure.

Additionally driver does not check the return value of i2c_new_dummy().
In case of error (i2c_new_device(): memory allocation failure or I2C
address cannot be used) this function returns NULL which is later
dereferenced by i2c_smbus_{read,write}_data() functions.

Fix issues by properly checking for i2c_new_dummy() return value and
unregistering I2C devices on driver remove or probe failure.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
Good catch, but the error path needs more care.
---
   drivers/iio/light/cm36651.c |   12 ++++++++++++
   1 file changed, 12 insertions(+)

diff --git a/drivers/iio/light/cm36651.c b/drivers/iio/light/cm36651.c
index a45e07492db3..e7e9a597159f 100644
--- a/drivers/iio/light/cm36651.c
+++ b/drivers/iio/light/cm36651.c
@@ -653,6 +653,11 @@ static int cm36651_probe(struct i2c_client *client,
   	cm36651->ps_client = i2c_new_dummy(client->adapter,
   						     CM36651_I2C_ADDR_PS);
   	cm36651->ara_client = i2c_new_dummy(client->adapter, CM36651_ARA);
+	if (!cm36651->ps_client || !cm36651->ara_client) {
+		dev_err(&client->dev, "%s: new i2c device failed\n", __func__);
+		ret = -ENODEV;
+		goto error_i2c_unregister;
+	}
The two failures need to be handled independently as we only want to unregister
those that succeeded.  i2c_new_dummy will not return an error and leave a device
registered.  This is particularly true given the first thing that i2c_unregister_device
does is to derefence the client pointer.  That will cause a segfault if you do it
for NULL as here.


Where the segfault would occur? If i2c_new_dummy fails then
i2c_unregister_device() will be called only on NON-null values:
	+error_i2c_unregister:
	+	if (cm36651->ps_client)
	+		i2c_unregister_device(cm36651->ps_client);
	+	if (cm36651->ara_client)
	+		i2c_unregister_device(cm36651->ara_client);

If probe() succeeds (both i2c_new_dummy return proper pointer) then
remove() will unregister two i2c devices.

Oops, I missed that.  Still, the form of this is unusual so please
change it to the more conventional option of a goto per error rather
than grouping them.  That will also allow you to drop the null checks
below leading to a more obviously correct error path.

   	mutex_init(&cm36651->lock);
   	indio_dev->dev.parent = &client->dev;
   	indio_dev->channels = cm36651_channels;
@@ -687,6 +692,11 @@ error_free_irq:
   	free_irq(client->irq, indio_dev);
   error_disable_reg:
   	regulator_disable(cm36651->vled_reg);
+error_i2c_unregister:
+	if (cm36651->ps_client)
+		i2c_unregister_device(cm36651->ps_client);
+	if (cm36651->ara_client)
+		i2c_unregister_device(cm36651->ara_client);
   	return ret;
   }

@@ -698,6 +708,8 @@ static int cm36651_remove(struct i2c_client *client)
   	iio_device_unregister(indio_dev);
   	regulator_disable(cm36651->vled_reg);
   	free_irq(client->irq, indio_dev);
+	i2c_unregister_device(cm36651->ps_client);
+	i2c_unregister_device(cm36651->ara_client);
Good catch.

   	return 0;
   }


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