Re: [PATCHv2 2/2] hwmon: core: fix potential memory leak in *hwmon_device_register*

[Eduardo Valentin]

On Wed, Jun 05, 2019 at 01:38:38PM -0700, Guenter Roeck wrote:
> On Wed, May 29, 2019 at 07:56:05PM -0700, Eduardo Valentin wrote:
> > When registering a hwmon device with HWMON_C_REGISTER_TZ flag
> > in place, the hwmon subsystem will attempt to register the device
> > also with the thermal subsystem. When the of-thermal registration
> > fails, __hwmon_device_register jumps to ida_remove, leaving
> > the locally allocated hwdev pointer.
> > 
> > This patch fixes the leak by jumping to a new label that
> > will first unregister hdev and then fall into the kfree of hwdev
> > to finally remove the idas and propagate the error code.
> > 
> 
> Hah, actually this is wrong. hwdev is freed indirectly with the
> device_unregister() call. See commit 74e3512731bd ("hwmon: (core)
> Fix double-free in __hwmon_device_register()").

heh.. I see it now. Well, it is not a straight catch though. 

> 
> It may make sense to add a respective comment to the code, though.
> 

I agree. Or a simple comment saying "dont worry about freeing hwdev
because hwmon_dev_release() takes care of it".

Are you patching it ?

> Guenter
> 
> > Cc: Jean Delvare <jdelvare@xxxxxxxx>
> > Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Cc: linux-hwmon@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Signed-off-by: Eduardo Valentin <eduval@xxxxxxxxxx>
> > ---
> > V1->V2: removed the device_unregister() before jumping
> > into the new label, as suggested in the first review round.
> > 
> >  drivers/hwmon/hwmon.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
> > index 429784edd5ff..620f05fc412a 100644
> > --- a/drivers/hwmon/hwmon.c
> > +++ b/drivers/hwmon/hwmon.c
> > @@ -652,10 +652,8 @@ __hwmon_device_register(struct device *dev, const char *name, void *drvdata,
> >  				if (info[i]->config[j] & HWMON_T_INPUT) {
> >  					err = hwmon_thermal_add_sensor(dev,
> >  								hwdev, j);
> > -					if (err) {
> > -						device_unregister(hdev);
> > -						goto ida_remove;
> > -					}
> > +					if (err)
> > +						goto device_unregister;
> >  				}
> >  			}
> >  		}
> > @@ -663,6 +661,8 @@ __hwmon_device_register(struct device *dev, const char *name, void *drvdata,
> >  
> >  	return hdev;
> >  
> > +device_unregister:
> > +	device_unregister(hdev);
> >  free_hwmon:
> >  	kfree(hwdev);
> >  ida_remove:

-- 
All the best,
Eduardo Valentin