rtc: snvs: fix possible race condition

[ Upstream commit 6fd4fe9b496d9ba3382992ff4fde3871d1b6f63d ]

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 before requesting
the RTC IRQ using devm_rtc_allocate_device, and use rtc_register_device
to register the RTC device.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Link: https://lore.kernel.org/r/20190716071858.36750-1-Anson.Huang@nxp.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/rtc/rtc-snvs.c

@@ -273,6 +273,10 @@ 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)) {
@@ -335,10 +339,9 @@ 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);
+	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;
 	}