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

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Message-ID: <6a9bcf7d.3ab8.181702f264d.Coremail.windhl@126.com>
Date:   Fri, 17 Jun 2022 13:42:27 +0800 (CST)
From:   "Liang He" <windhl@....com>
To:     "Christophe JAILLET" <christophe.jaillet@...adoo.fr>
Cc:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        nick.child@....com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH] powerpc: powernv: Fix refcount leak bug in
 opal-powercap




At 2022-06-17 13:01:27, "Christophe JAILLET" <christophe.jaillet@...adoo.fr> 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.

>
>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@....com>
>> ---
>>   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);
>>   }