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SubjectRe: [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@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;

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
>

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