Re: [PATCH] coresight: syscfg: Fix memleak on registration failure in cscfg_create_device

From: Mathieu Poirier
Date: Thu Jan 20 2022 - 13:28:28 EST


On Thu, Jan 20, 2022 at 10:56:42AM -0700, Mathieu Poirier wrote:
> Good morning,
>
> On Mon, Jan 10, 2022 at 07:31:00AM +0000, Miaoqian Lin wrote:
> > device_register() calls device_initialize(),
> > according to doc of device_initialize:
> >
> > Use put_device() to give up your reference instead of freeing
> > * @dev directly once you have called this function.
>
> That is _if_ device_initialize() is called manually. In this instance
> @dev is registered with device_register() and unregistered with
> device_unregister(). The latter conforms to the comment you pointed out and
> calls put_device() as expected.

I originally misunderstood the context - you are referring to the failure path in
cscfg_create_device(). You are correct about needing to call put_device() but
your solution will not work when the module is unloaded properly and
device_unregister() is called by way of cscfg_clear_device(). In that case
device_unregister() is already calling put_device().

Here simply calling put_device() instead of cscfg_dev_release() in the error
path should do just fine. That will call cscfg_dev_release() and the memory
allocated for cscfg_mgr will be release.

>
> Thanks,
> Mathieu
>
> >
> > To prevent potential memleak, use put_device() instead call kfree
> > directly.
> >
> > Signed-off-by: Miaoqian Lin <linmq006@xxxxxxxxx>
> > ---
> > drivers/hwtracing/coresight/coresight-syscfg.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> > index 43054568430f..007fa1c761a7 100644
> > --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> > +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> > @@ -764,7 +764,7 @@ struct device *cscfg_device(void)
> > /* Must have a release function or the kernel will complain on module unload */
> > static void cscfg_dev_release(struct device *dev)
> > {
> > - kfree(cscfg_mgr);
> > + put_device(dev);
> > cscfg_mgr = NULL;
> > }
> >
> > --
> > 2.17.1
> >