rtc: xgene: fix possible race condition

[ Upstream commit a652e00e ]

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
struct before requesting the IRQ.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/rtc/rtc-xgene.c

@@ -168,6 +168,10 @@ static int xgene_rtc_probe(struct platform_device *pdev)
 	if (IS_ERR(pdata->csr_base))
 		return PTR_ERR(pdata->csr_base);
 
+	pdata->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(pdata->rtc))
+		return PTR_ERR(pdata->rtc);
+
 	irq = platform_get_irq(pdev, 0);
 	if (irq < 0) {
 		dev_err(&pdev->dev, "No IRQ resource\n");
@@ -198,15 +202,15 @@ static int xgene_rtc_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	pdata->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
-					 &xgene_rtc_ops, THIS_MODULE);
-	if (IS_ERR(pdata->rtc)) {
-		clk_disable_unprepare(pdata->clk);
-		return PTR_ERR(pdata->rtc);
-	}
-
 	/* HW does not support update faster than 1 seconds */
 	pdata->rtc->uie_unsupported = 1;
+	pdata->rtc->ops = &xgene_rtc_ops;
+
+	ret = rtc_register_device(pdata->rtc);
+	if (ret) {
+		clk_disable_unprepare(pdata->clk);
+		return ret;
+	}
 
 	return 0;
 }