linux-kernel - Re: [PATCH v2] clk: Skip clk provider registration when np is NULL

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Date:   Mon, 10 May 2021 12:36:45 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>
Cc:     gregkh@...uxfoundation.org, rafael@...nel.org,
        mturquette@...libre.com, sboyd@...nel.org, nsaenz@...nel.org,
        maxime@...no.tech, khilman@...nel.org, ulf.hansson@...aro.org,
        len.brown@...el.com, pavel@....cz, robh+dt@...nel.org,
        frowand.list@...il.com, maz@...nel.org, tglx@...utronix.de,
        saravanak@...gle.com, geert@...ux-m68k.org, nsaenzjulienne@...e.de,
        guillaume.tucker@...labora.com, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, corbet@....net,
        nicolas.ferre@...rochip.com, claudiu.beznea@...rochip.com,
        linux-doc@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-acpi@...r.kernel.org,
        kernel-team@...roid.com, linux-rpi-kernel@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v2] clk: Skip clk provider registration when np is NULL

On Mon, Apr 26, 2021 at 09:56:18AM +0300, Tudor Ambarus wrote:
> commit 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
> revealed that clk/bcm/clk-raspberrypi.c driver calls
> devm_of_clk_add_hw_provider(), with a NULL dev->of_node, which resulted in a
> NULL pointer dereference in of_clk_add_hw_provider() when calling
> fwnode_dev_initialized().
> 
> Returning 0 is reducing the if conditions in driver code and is being
> consistent with the CONFIG_OF=n inline stub that returns 0 when CONFIG_OF
> is disabled. The downside is that drivers will maybe register clkdev lookups
> when they don't need to and waste some memory.
> 
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Fixes: 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
> Fixes: 3c9ea42802a1 ("clk: Mark fwnodes when their clock provider is added/removed")
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> Reviewed-by: Stephen Boyd <sboyd@...nel.org>

Tested-by: Guenter Roeck <linux@...ck-us.net>

> ---
> v2:
> - s/return 0;/return; in void of_clk_del_provider()
> - add second fixes tag and Stephen's R-b tag
> The opinions on whether to return an error or zero were split. Returning 0
> and skipping the logic was considered safer as we don't know for sure if
> other drivers are affected. See:
> https://lore.kernel.org/lkml/d24bebc5-0f78-021f-293f-e58defa32531@samsung.com/
> https://lore.kernel.org/lkml/20210423171335.262316-1-tudor.ambarus@microchip.com/
> 
>  drivers/clk/clk.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index a3b30f7de2ef..b47460b40d14 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -4552,6 +4552,9 @@ int of_clk_add_provider(struct device_node *np,
>  	struct of_clk_provider *cp;
>  	int ret;
>  
> +	if (!np)
> +		return 0;
> +
>  	cp = kzalloc(sizeof(*cp), GFP_KERNEL);
>  	if (!cp)
>  		return -ENOMEM;
> @@ -4591,6 +4594,9 @@ int of_clk_add_hw_provider(struct device_node *np,
>  	struct of_clk_provider *cp;
>  	int ret;
>  
> +	if (!np)
> +		return 0;
> +
>  	cp = kzalloc(sizeof(*cp), GFP_KERNEL);
>  	if (!cp)
>  		return -ENOMEM;
> @@ -4688,6 +4694,9 @@ void of_clk_del_provider(struct device_node *np)
>  {
>  	struct of_clk_provider *cp;
>  
> +	if (!np)
> +		return;
> +
>  	mutex_lock(&of_clk_mutex);
>  	list_for_each_entry(cp, &of_clk_providers, link) {
>  		if (cp->node == np) {
> -- 
> 2.25.1
>