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

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Message-ID: <0ca5ee14-a382-0935-66be-820975501f45@wanadoo.fr>
Date:   Fri, 17 Jun 2022 07:01:27 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Liang He <windhl@....com>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org
Cc:     nick.child@....com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: powernv: Fix refcount leak bug in opal-powercap

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.


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

> 
> 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);
>   }