[PATCH 2/2] platform/surface: surfacepro3_button: Check ACPI companion before use

[Linmao Li]

Since every platform driver can be forced to match a device that doesn't
match its list of device IDs because of device_match_driver_override(),
platform drivers that rely on the existence of a device's ACPI companion
object should verify its presence.

surface_button_probe() passes the result of ACPI_COMPANION() to
acpi_device_hid(), which dereferences it, so force-binding the driver to
a device without an ACPI companion leads to a NULL pointer dereference.
The driver has been exposed to this since it was converted from an ACPI
driver to a platform driver.

Check the ACPI companion against NULL and return -ENODEV when it is
missing, like commit e4865a56d013 ("ACPI: driver: Check ACPI_COMPANION()
against NULL during probe") does for the core ACPI platform drivers.

Fixes: d913a5a12b40 ("platform/surface: surfacepro3_button: Convert to a platform driver")
Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>
---
 drivers/platform/surface/surfacepro3_button.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/surface/surfacepro3_button.c b/drivers/platform/surface/surfacepro3_button.c
index 0293bc517b54..29a10e6c3a3f 100644
--- a/drivers/platform/surface/surfacepro3_button.c
+++ b/drivers/platform/surface/surfacepro3_button.c
@@ -185,12 +185,17 @@ static bool surface_button_check_MSHW0040(struct device *dev, acpi_handle handle
 
 static int surface_button_probe(struct platform_device *pdev)
 {
-	struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
 	struct surface_button *button;
+	struct acpi_device *device;
 	struct input_dev *input;
-	const char *hid = acpi_device_hid(device);
+	const char *hid;
 	int error;
 
+	device = ACPI_COMPANION(&pdev->dev);
+	if (!device)
+		return -ENODEV;
+
+	hid = acpi_device_hid(device);
 	if (strncmp(acpi_device_bid(device), SURFACE_BUTTON_OBJ_NAME,
 	    strlen(SURFACE_BUTTON_OBJ_NAME)))
 		return -ENODEV;
-- 
2.25.1