linux-kernel - Re: [PATCH, v2] arm: omap2: timer: fix a kmemleak caused in omap_get_timer

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Date:   Tue, 9 Jan 2018 12:52:22 +0100
From:   Ladislav Michl <ladis@...ux-mips.org>
To:     Qi Hou <qi.hou@...driver.com>
Cc:     tony@...mide.com, linux@...linux.org.uk,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, v2] arm: omap2: timer: fix a kmemleak caused in
 omap_get_timer_dt

On Tue, Jan 09, 2018 at 05:24:21PM +0800, Qi Hou wrote:
> When more than one GP timers are used as kernel system timers and the
> corresponding nodes in device-tree are marked with the same "disabled"
> property, then the "attr" field of the property will be initialized
> more than once as the property being added to sys file system via
> __of_add_property_sysfs().
> 
> In __of_add_property_sysfs(), the "name" field of pp->attr.attr is set
> directly to the return value of safe_name(), without taking care of
> whether it's already a valid pointer to a memory block. If it is, its
> old value will always be overwritten by the new one and the memory block
> allocated before will a "ghost", then a kmemleak happened.

As timers does not seem to be deallocated, this does not matter in practice.
Fix eats a bit more from heap.

> That the same "disabled" property being added to different nodes of device
> tree would cause that kind of kmemleak overhead, at leat once.
> 
> To fix it, allocate the property dynamically, and delete static one.
>
> Signed-off-by: Qi Hou <qi.hou@...driver.com>
> ---
>  arch/arm/mach-omap2/timer.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/mach-omap2/timer.c b/arch/arm/mach-omap2/timer.c
> index ece09c9..206ae8d 100644
> --- a/arch/arm/mach-omap2/timer.c
> +++ b/arch/arm/mach-omap2/timer.c
> @@ -156,12 +156,6 @@ static struct clock_event_device clockevent_gpt = {
>  	.tick_resume		= omap2_gp_timer_shutdown,
>  };
>  
> -static struct property device_disabled = {
> -	.name = "status",
> -	.length = sizeof("disabled"),
> -	.value = "disabled",
> -};
> -
>  static const struct of_device_id omap_timer_match[] __initconst = {
>  	{ .compatible = "ti,omap2420-timer", },
>  	{ .compatible = "ti,omap3430-timer", },
> @@ -203,8 +197,17 @@ static struct device_node * __init omap_get_timer_dt(const struct of_device_id *
>  				  of_get_property(np, "ti,timer-secure", NULL)))
>  			continue;
>  
> -		if (!of_device_is_compatible(np, "ti,omap-counter32k"))
> -			of_add_property(np, &device_disabled);
> +		if (!of_device_is_compatible(np, "ti,omap-counter32k")) {
> +			struct property *prop;
> +
> +			prop = kzalloc(sizeof(*prop), GFP_KERNEL);
> +			if (!prop)
> +				return NULL;
> +			prop->name = "status";
> +			prop->length = sizeof("disabled");
> +			prop->value = "disabled";

How about (see drivers/of/unittest.c)?
prop->value = "disabled";
prop->length = strlen(prop->value);

> +			of_add_property(np, prop);
> +		}
>  		return np;
>  	}
>  
> -- 
> 2.7.4
> 
> --
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