[3/3] media: venus: don't de-reference NULL pointers at IRQ time

Smatch is warning that:
	drivers/media/platform/qcom/venus/hfi_venus.c:1100 venus_isr() warn: variable dereferenced before check 'hdev' (see line 1097)

The logic basically does:
	hdev = to_hfi_priv(core);

with is translated to:
	hdev = core->priv;

If the IRQ code can receive a NULL pointer for hdev, there's
a bug there, as it will first try to de-reference the pointer,
and then check if it is null.

After looking at the code, it seems that this indeed can happen:
Basically, the venus IRQ thread is started with:
	devm_request_threaded_irq()
So, it will only be freed after the driver unbinds.

In order to prevent the IRQ code to work with freed data,
the logic at venus_hfi_destroy() sets core->priv to NULL,
which would make the IRQ code to ignore any pending IRQs.

There is, however a race condition, as core->priv is set
to NULL only after being freed. So, we need also to move the
core->priv = NULL to happen earlier.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
---
 drivers/media/platform/qcom/venus/hfi_venus.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Hi Mauro,

On 4/8/21 10:40 AM, Mauro Carvalho Chehab wrote:
> Smatch is warning that:
> 	drivers/media/platform/qcom/venus/hfi_venus.c:1100 venus_isr() warn: variable dereferenced before check 'hdev' (see line 1097)
> 
> The logic basically does:
> 	hdev = to_hfi_priv(core);
> 
> with is translated to:
> 	hdev = core->priv;
> 
> If the IRQ code can receive a NULL pointer for hdev, there's
> a bug there, as it will first try to de-reference the pointer,
> and then check if it is null.
> 
> After looking at the code, it seems that this indeed can happen:
> Basically, the venus IRQ thread is started with:
> 	devm_request_threaded_irq()
> So, it will only be freed after the driver unbinds.
> 
> In order to prevent the IRQ code to work with freed data,
> the logic at venus_hfi_destroy() sets core->priv to NULL,
> which would make the IRQ code to ignore any pending IRQs.
> 
> There is, however a race condition, as core->priv is set
> to NULL only after being freed. So, we need also to move the
> core->priv = NULL to happen earlier.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> ---
>  drivers/media/platform/qcom/venus/hfi_venus.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Acked-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>

> 
> diff --git a/drivers/media/platform/qcom/venus/hfi_venus.c b/drivers/media/platform/qcom/venus/hfi_venus.c
> index cebb20cf371f..ce98c523b3c6 100644
> --- a/drivers/media/platform/qcom/venus/hfi_venus.c
> +++ b/drivers/media/platform/qcom/venus/hfi_venus.c
> @@ -1094,12 +1094,15 @@ static irqreturn_t venus_isr(struct venus_core *core)
>  {
>  	struct venus_hfi_device *hdev = to_hfi_priv(core);
>  	u32 status;
> -	void __iomem *cpu_cs_base = hdev->core->cpu_cs_base;
> -	void __iomem *wrapper_base = hdev->core->wrapper_base;
> +	void __iomem *cpu_cs_base;
> +	void __iomem *wrapper_base;
>  
>  	if (!hdev)
>  		return IRQ_NONE;
>  
> +	cpu_cs_base = hdev->core->cpu_cs_base;
> +	wrapper_base = hdev->core->wrapper_base;
> +
>  	status = readl(wrapper_base + WRAPPER_INTR_STATUS);
>  	if (IS_V6(core)) {
>  		if (status & WRAPPER_INTR_STATUS_A2H_MASK ||
> @@ -1650,10 +1653,10 @@ void venus_hfi_destroy(struct venus_core *core)
>  {
>  	struct venus_hfi_device *hdev = to_hfi_priv(core);
>  
> +	core->priv = NULL;
>  	venus_interface_queues_release(hdev);
>  	mutex_destroy(&hdev->lock);
>  	kfree(hdev);
> -	core->priv = NULL;
>  	core->ops = NULL;
>  }
>  
>