linux-kernel - Re: [PATCH] regulator: vctrl: Fix out of bounds array access for vctrl->vtable

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Message-ID: <20170414171137.GK28657@google.com>
Date:   Fri, 14 Apr 2017 10:11:37 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Axel Lin <axel.lin@...ics.com>
Cc:     Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regulator: vctrl: Fix out of bounds array access for
 vctrl->vtable

Hi Axel,

El Fri, Apr 14, 2017 at 10:50:43AM +0800 Axel Lin ha dit:

> Current code only allocates rdesc->n_voltages entries for vctrl->vtable.
> Thus use rdesc->n_voltages instead of n_voltages in the for loop.

This is intended. n_voltages is the number of voltages of the control
regulator. In the first loop of the function we determine how many of
these voltages are usable by the vctrl regulator (=> rdesc->n_voltages).
The loop that populates vctrl->vtable iterates over n_voltages,
however it skips those that are outside of the voltage range for the
control regulator.

> While at it, also switch to use devm_kcalloc instead of devm_kmalloc_array
> + __GFP_ZERO flag and fix the argument order.

This looks good to me.

Thanks

Matthias

> Signed-off-by: Axel Lin <axel.lin@...ics.com>
> ---
>  drivers/regulator/vctrl-regulator.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/regulator/vctrl-regulator.c b/drivers/regulator/vctrl-regulator.c
> index 6baadef..78de002 100644
> --- a/drivers/regulator/vctrl-regulator.c
> +++ b/drivers/regulator/vctrl-regulator.c
> @@ -345,9 +345,9 @@ static int vctrl_init_vtable(struct platform_device *pdev)
>  		return -EINVAL;
>  	}
>  
> -	vctrl->vtable = devm_kmalloc_array(
> -		&pdev->dev, sizeof(struct vctrl_voltage_table),
> -		rdesc->n_voltages, GFP_KERNEL | __GFP_ZERO);
> +	vctrl->vtable = devm_kcalloc(&pdev->dev, rdesc->n_voltages,
> +				     sizeof(struct vctrl_voltage_table),
> +				     GFP_KERNEL);
>  	if (!vctrl->vtable)
>  		return -ENOMEM;
>  
> @@ -371,7 +371,7 @@ static int vctrl_init_vtable(struct platform_device *pdev)
>  	     NULL);
>  
>  	/* pre-calculate OVP-safe downward transitions */
> -	for (i = n_voltages - 1; i > 0; i--) {
> +	for (i = rdesc->n_voltages - 1; i > 0; i--) {
>  		int j;
>  		int ovp_min_uV = (vctrl->vtable[i].out *
>  				  (100 - vctrl->ovp_threshold)) / 100;