Re: [PATCH] powerpc: powernv: Fix refcount leak bug in opal-powercap

[Christophe JAILLET]

Le 17/06/2022 à 07:42, Liang He a écrit :
> At 2022-06-17 13:01:27, "Christophe JAILLET" <christophe.jaillet@xxxxxxxxxx> wrote:
> > Le 17/06/2022 à 06:20, Liang He a écrit :
> > > In opal_powercap_init(), of_find_compatible_node() will return
> > > a node pointer with refcount incremented. We should use of_node_put()
> > > in fail path or when it is not used anymore.
> > >
> > > Besides, for_each_child_of_node() will automatically *inc* and *dec*
> > > refcount during iteration. However, we should add the of_node_put()
> > > if there is a break.
> >
> > Hi,
> >
> > I'm not sure that your patch is right here. Because of this *inc* and
> > *dec* things, do we still need to of_node_put(powercap) once we have
> > entered for_each_child_of_node?
> >
> > I think that this reference will be released on the first iteration of
> > the loop.
>
> Hi, CJ,
>
> Thanks for your reply and I want have a discuss.
>
> Based on my review on the src of 'of_get_next_child',  there is only
> *inc* for next and *dec* for pre as follow.
>
> (|node| == powercap)
> ======__of_get_next_child( |node|, prev)======
>       ...
>          next = prev? prev->sibling:|node|->child;
> 	of_node_get(next);
> 	of_node_put(prev);
>       ...
> =========================
>
> However, there is no any code to release the |node| (i.e., *powercap*).
>
> Am I right?   If I am wrong, please correct me, thanks.

You are right.
I mis-read __of_get_next_child(().

CJ


> > Maybe of_node_put(powercap) should be duplicated everywhere it is
> > relevant and removed from the error handling path?
> > Or an additional reference should be taken before the loop?
> > Or adding a new label with "powercap = NULL" and branching there when
> > needed?
> >
> > CJ
>
> If my understanding is right, I think current patch is right.
>
> Otherwise, I will make a new patch to handle that, Thanks.
>
> Liang
>
> > > Signed-off-by: Liang He <windhl@xxxxxxx>
> > > ---
> > >    arch/powerpc/platforms/powernv/opal-powercap.c | 5 ++++-
> > >    1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/powerpc/platforms/powernv/opal-powercap.c b/arch/powerpc/platforms/powernv/opal-powercap.c
> > > index 64506b46e77b..b102477d3f95 100644
> > > --- a/arch/powerpc/platforms/powernv/opal-powercap.c
> > > +++ b/arch/powerpc/platforms/powernv/opal-powercap.c
> > > @@ -153,7 +153,7 @@ void __init opal_powercap_init(void)
> > >    	pcaps = kcalloc(of_get_child_count(powercap), sizeof(*pcaps),
> > >    			GFP_KERNEL);
> > >    	if (!pcaps)
> > > -		return;
> > > +		goto out_powercap;
> > >    
> > >    	powercap_kobj = kobject_create_and_add("powercap", opal_kobj);
> > >    	if (!powercap_kobj) {
> > > @@ -236,6 +236,9 @@ void __init opal_powercap_init(void)
> > >    		kfree(pcaps[i].pg.name);
> > >    	}
> > >    	kobject_put(powercap_kobj);
> > > +	of_node_put(node);
> > >    out_pcaps:
> > >    	kfree(pcaps);
> > > +out_powercap:
> > > +	of_node_put(powercap);
> > >    }