Re: [PATCH] soc: qcom: aoss: Fix the out of bound usage of cooling_devs

[Matthias Kaehlcke <mka@chromium.org>]

On Mon, Jun 28, 2021 at 10:57:41PM +0530, Manivannan Sadhasivam wrote:
> In "qmp_cooling_devices_register", the count value is initially
> QMP_NUM_COOLING_RESOURCES, which is 2. Based on the initial count value,
> the memory for cooling_devs is allocated. Then while calling the
> "qmp_cooling_device_add" function, count value is post-incremented for
> each child node.
> 
> This makes the out of bound access to the cooling_dev array. Fix it by
> resetting the count value to zero before adding cooling devices.
> 
> While at it, let's also free the memory allocated to cooling_dev if no
> cooling device is found in DT and during unroll phase.
> 
> Cc: stable@vger.kernel.org # 5.4
> Fixes: 05589b30b21a ("soc: qcom: Extend AOSS QMP driver to support resources that are used to wake up the SoC.")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
> 
> Bjorn: I've just compile tested this patch.
> 
>  drivers/soc/qcom/qcom_aoss.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/soc/qcom/qcom_aoss.c b/drivers/soc/qcom/qcom_aoss.c
> index 934fcc4d2b05..98c665411768 100644
> --- a/drivers/soc/qcom/qcom_aoss.c
> +++ b/drivers/soc/qcom/qcom_aoss.c
> @@ -488,6 +488,7 @@ static int qmp_cooling_devices_register(struct qmp *qmp)
>  	if (!qmp->cooling_devs)
>  		return -ENOMEM;
>  
> +	count = 0;
>  	for_each_available_child_of_node(np, child) {
>  		if (!of_find_property(child, "#cooling-cells", NULL))
>  			continue;
> @@ -497,12 +498,16 @@ static int qmp_cooling_devices_register(struct qmp *qmp)
>  			goto unroll;
>  	}
>  
> +	if (!count)
> +		devm_kfree(qmp->dev, qmp->cooling_devs);
> +
>  	return 0;
>  
>  unroll:
>  	while (--count >= 0)
>  		thermal_cooling_device_unregister
>  			(qmp->cooling_devs[count].cdev);
> +	devm_kfree(qmp->dev, qmp->cooling_devs);
>  
>  	return ret;
>  }


A few more previous lines of code for context:

  int count = QMP_NUM_COOLING_RESOURCES;

  qmp->cooling_devs = devm_kcalloc(qmp->dev, count,
                                   sizeof(*qmp->cooling_devs),
                                   GFP_KERNEL);

I would suggest to initialize 'count' to 0 from the start and pass
QMP_NUM_COOLING_RESOURCES to devm_kcalloc() rather than 'count',
instead of resetting 'count' afterwards.