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

[Jonathan Cameron]

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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