rtc: pl030: fix possible race condition

[ Upstream commit c778ec85825dc895936940072aea9fe9037db684 ]

The IRQ is requested before the struct rtc is allocated and registered, but
this struct is used in the IRQ handler. This may lead to a NULL pointer
dereference.

Switch to devm_rtc_allocate_device/rtc_register_device to allocate the rtc
before requesting the IRQ.
Signed-off-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>

drivers/rtc/rtc-pl030.c

@@ -112,6 +112,13 @@ static int pl030_probe(struct amba_device *dev, const struct amba_id *id)
 		goto err_rtc;
 	}
 
+	rtc->rtc = devm_rtc_allocate_device(&dev->dev);
+	if (IS_ERR(rtc->rtc)) {
+		ret = PTR_ERR(rtc->rtc);
+		goto err_rtc;
+	}
+
+	rtc->rtc->ops = &pl030_ops;
 	rtc->base = ioremap(dev->res.start, resource_size(&dev->res));
 	if (!rtc->base) {
 		ret = -ENOMEM;
@@ -128,12 +135,9 @@ static int pl030_probe(struct amba_device *dev, const struct amba_id *id)
 	if (ret)
 		goto err_irq;
 
-	rtc->rtc = rtc_device_register("pl030", &dev->dev, &pl030_ops,
-				       THIS_MODULE);
-	if (IS_ERR(rtc->rtc)) {
-		ret = PTR_ERR(rtc->rtc);
+	ret = rtc_register_device(rtc->rtc);
+	if (ret)
 		goto err_reg;
-	}
 
 	return 0;
 
@@ -154,7 +158,6 @@ static int pl030_remove(struct amba_device *dev)
 	writel(0, rtc->base + RTC_CR);
 
 	free_irq(dev->irq[0], rtc);
-	rtc_device_unregister(rtc->rtc);
 	iounmap(rtc->base);
 	amba_release_regions(dev);