[PATCH V2] rtc: snvs: fix possible race condition

[PATCH V2] rtc: snvs: fix possible race condition

[Anson.Huang]

From: Anson Huang <Anson.Huang@nxp.com>

The RTC IRQ is requested before the struct rtc_device is allocated,
this may lead to a NULL pointer dereference in IRQ handler.

To fix this issue, allocating the rtc_device struct and register rtc
device before requesting the RTC IRQ.

Using devm_rtc_allocate_device/rtc_register_device instead of
devm_rtc_device_register.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
---
Changes since V1:
	- move devm_request_irq() to after rtc device register done, make sure everything
	  is ready before enabling IRQ.
---
 drivers/rtc/rtc-snvs.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/rtc/rtc-snvs.c b/drivers/rtc/rtc-snvs.c
index 7ee673a2..d9650e7 100644
--- a/drivers/rtc/rtc-snvs.c
+++ b/drivers/rtc/rtc-snvs.c
@@ -279,6 +279,10 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 	if (!data)
 		return -ENOMEM;
 
+	data->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(data->rtc))
+		return PTR_ERR(data->rtc);
+
 	data->regmap = syscon_regmap_lookup_by_phandle(pdev->dev.of_node, "regmap");
 
 	if (IS_ERR(data->regmap)) {
@@ -335,6 +339,13 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 	if (ret)
 		dev_err(&pdev->dev, "failed to enable irq wake\n");
 
+	data->rtc->ops = &snvs_rtc_ops;
+	ret = rtc_register_device(data->rtc);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to register rtc: %d\n", ret);
+		goto error_rtc_device_register;
+	}
+
 	ret = devm_request_irq(&pdev->dev, data->irq, snvs_rtc_irq_handler,
 			       IRQF_SHARED, "rtc alarm", &pdev->dev);
 	if (ret) {
@@ -343,14 +354,6 @@ static int snvs_rtc_probe(struct platform_device *pdev)
 		goto error_rtc_device_register;
 	}
 
-	data->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
-					&snvs_rtc_ops, THIS_MODULE);
-	if (IS_ERR(data->rtc)) {
-		ret = PTR_ERR(data->rtc);
-		dev_err(&pdev->dev, "failed to register rtc: %d\n", ret);
-		goto error_rtc_device_register;
-	}
-
 	return 0;
 
 error_rtc_device_register:
-- 
2.7.4

Re: [PATCH V2] rtc: snvs: fix possible race condition

[Alexandre Belloni]

On 19/07/2019 11:01:02+0800, Anson.Huang@nxp.com wrote:
> From: Anson Huang <Anson.Huang@nxp.com>
> 
> The RTC IRQ is requested before the struct rtc_device is allocated,
> this may lead to a NULL pointer dereference in IRQ handler.
> 
> To fix this issue, allocating the rtc_device struct and register rtc
> device before requesting the RTC IRQ.
> 
> Using devm_rtc_allocate_device/rtc_register_device instead of
> devm_rtc_device_register.
> 
> Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
> ---
> Changes since V1:
> 	- move devm_request_irq() to after rtc device register done, make sure everything
> 	  is ready before enabling IRQ.

This opens another race condition, the first version of the patch was
correct.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

RE: [PATCH V2] rtc: snvs: fix possible race condition

[Anson Huang]

Hi, Alexandre

> On 19/07/2019 11:01:02+0800, Anson.Huang@nxp.com wrote:
> > From: Anson Huang <Anson.Huang@nxp.com>
> >
> > The RTC IRQ is requested before the struct rtc_device is allocated,
> > this may lead to a NULL pointer dereference in IRQ handler.
> >
> > To fix this issue, allocating the rtc_device struct and register rtc
> > device before requesting the RTC IRQ.
> >
> > Using devm_rtc_allocate_device/rtc_register_device instead of
> > devm_rtc_device_register.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
> > ---
> > Changes since V1:
> > 	- move devm_request_irq() to after rtc device register done, make
> sure everything
> > 	  is ready before enabling IRQ.
> 
> This opens another race condition, the first version of the patch was correct.

Hmm, OK, then we should go with V1.

Thanks,
Anson.