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

[Jonathan Cameron <jic23@kernel.org>]

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@samsung.com>
>> 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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