linux-kernel - Re: [PATCH] soc: qcom: aoss: Fix the out of bound usage of cooling

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Message-ID: <YNs/o7VVh+JnbxK9@yoga>
Date:   Tue, 29 Jun 2021 10:43:31 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        thara.gopinath@...aro.org, stable@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: aoss: Fix the out of bound usage of
 cooling_devs

On Mon 28 Jun 12:27 CDT 2021, 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@...r.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@...aro.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;

This will address the immediate problem, which is that we assign
cooling_devs[2..] in this loop. But, like Matthias I don't think we
should use "count" as a constant in the first hunk and then reset it
and use it as a counter in the second hunk.

Frankly, I don't see why cooling_devs is dynamically allocated (without
being conditional on there being any children).

So, could you please make the cooling_devs an array of size
QMP_NUM_COOLING_RESOURCES, remove the dynamic allocation here, just
initialize count to 0 and add a check in the loop to generate an error
if count == QMP_NUM_COOLING_RESOURCES?

>  	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);

I presume this is just an optimization, to get some memory back when
there's no cooling devices specified in DT.  I don't think this is
necessary and this made me want the static sizing of the array..

> +
>  	return 0;
>  
>  unroll:
>  	while (--count >= 0)
>  		thermal_cooling_device_unregister
>  			(qmp->cooling_devs[count].cdev);
> +	devm_kfree(qmp->dev, qmp->cooling_devs);

I don't remember why we don't fail probe() when this happens, seems like
the DT properties should be optional but the errors adding them should
be fatal. But that's a separate issue.

Regards,
Bjorn

>  
>  	return ret;
>  }
> -- 
> 2.25.1
>