[PATCH v2] rtc: gamecube: Check the return value of ioremap()

[Haotian Zhang <vulab@iscas.ac.cn>]

The function ioremap() in gamecube_rtc_read_offset_from_sram() can fail
and return NULL, which is dereferenced without checking, leading to a
NULL pointer dereference.

Add a check for the return value of ioremap() and return -ENOMEM on
failure.

Fixes: 86559400b3ef ("rtc: gamecube: Add a RTC driver for the GameCube, Wii and Wii U")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
---
Changes in v2:
  -Use lowercase for error message to match existing style.
---
 drivers/rtc/rtc-gamecube.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/rtc/rtc-gamecube.c b/drivers/rtc/rtc-gamecube.c
index c828bc8e05b9..045d5d45ab4b 100644
--- a/drivers/rtc/rtc-gamecube.c
+++ b/drivers/rtc/rtc-gamecube.c
@@ -242,6 +242,10 @@ static int gamecube_rtc_read_offset_from_sram(struct priv *d)
 	}
 
 	hw_srnprot = ioremap(res.start, resource_size(&res));
+	if (!hw_srnprot) {
+		pr_err("failed to ioremap hw_srnprot\n");
+		return -ENOMEM;
+	}
 	old = ioread32be(hw_srnprot);
 
 	/* TODO: figure out why we use this magic constant.  I obtained it by
-- 
2.50.1.windows.1