linux-kernel - Re: [PATCH v2] powerpc/85xx: Fix reference leak in xes_mpc85xx_setup

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Date:   Fri, 29 Jul 2022 16:53:06 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Miaoqian Lin <linmq006@...il.com>, Scott Wood <oss@...error.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Miaoqian Lin <linmq006@...il.com>,
        Nick Child <nick.child@....com>, Nate Case <ncase@...-inc.com>,
        Kumar Gala <galak@...nel.crashing.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] powerpc/85xx: Fix reference leak in
 xes_mpc85xx_setup_arch

Miaoqian Lin <linmq006@...il.com> writes:
> of_find_node_by_path() returns remote device nodepointer with
> refcount incremented, we should use of_node_put() on it when done.
> Add missing of_node_put() to avoid refcount leak.
>
> Fixes: 3038acf9091f ("powerpc/85xx: Add platform support for X-ES MPC85xx boards")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
> changes in v2:
> - update Fixes tag.
> v1 Link: https://lore.kernel.org/all/20220603120907.19999-1-linmq006@gmail.com
> ---
>  arch/powerpc/platforms/85xx/xes_mpc85xx.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/platforms/85xx/xes_mpc85xx.c b/arch/powerpc/platforms/85xx/xes_mpc85xx.c
> index 5836e4ecb7a0..93f67b430714 100644
> --- a/arch/powerpc/platforms/85xx/xes_mpc85xx.c
> +++ b/arch/powerpc/platforms/85xx/xes_mpc85xx.c
> @@ -130,6 +130,8 @@ static void __init xes_mpc85xx_setup_arch(void)
>  	mpc85xx_smp_init();
>  
>  	fsl_pci_assign_primary();
> +
> +	of_node_put(root);
>  }

For context, here is the full function:

static void __init xes_mpc85xx_setup_arch(void)
{
	struct device_node *root;
	const char *model = "Unknown";

	root = of_find_node_by_path("/");
	if (root == NULL)
		return;

	model = of_get_property(root, "model", NULL);

	printk(KERN_INFO "X-ES MPC85xx-based single-board computer: %s\n",
	       model + strlen("xes,"));

	xes_mpc85xx_fixups();

	mpc85xx_smp_init();

	fsl_pci_assign_primary();
}


So yes it's missing an of_node_put(root).

But rather than add the of_node_put(), it would be simpler to just use
of_root directly, then it doesn't need an of_node_put() at all.

But then look closer. To begin with model is assigned "Unknown", but
then unconditionally overwritten by the of_get_property() call. So
that's a waste of space.

And then if there's no model property of_get_property() will return
NULL, and then the model + strlen("xes,") would oops.

And all of that just to print the model at boot, which is not really
necessary, anyone who cares can look it up in /proc/device-tree
after the system has booted.

So please just remove the lookup and printing of model entirely.

cheers