[PATCH 1/2] platform/surface: acpi-notify: 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.

san_probe() dereferences the result of ACPI_COMPANION() when installing
the GSBUS address space handler, so force-binding the driver to a device
without an ACPI companion leads to a NULL pointer dereference.  The
dereference was introduced when the probe function was switched from
ACPI_HANDLE() to ACPI_COMPANION().

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: a9e10e587304 ("ACPI: scan: Extend acpi_walk_dep_device_list()")
Signed-off-by: Linmao Li <lilinmao@xxxxxxxxxx>
---
 drivers/platform/surface/surface_acpi_notify.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/surface/surface_acpi_notify.c b/drivers/platform/surface/surface_acpi_notify.c
index a9dcb0bbe90e..593a7aba6243 100644
--- a/drivers/platform/surface/surface_acpi_notify.c
+++ b/drivers/platform/surface/surface_acpi_notify.c
@@ -777,12 +777,16 @@ static int san_consumer_links_setup(struct platform_device *pdev)
 
 static int san_probe(struct platform_device *pdev)
 {
-	struct acpi_device *san = ACPI_COMPANION(&pdev->dev);
 	struct ssam_controller *ctrl;
+	struct acpi_device *san;
 	struct san_data *data;
 	acpi_status astatus;
 	int status;
 
+	san = ACPI_COMPANION(&pdev->dev);
+	if (!san)
+		return -ENODEV;
+
 	ctrl = ssam_client_bind(&pdev->dev);
 	if (IS_ERR(ctrl))
 		return PTR_ERR(ctrl) == -ENODEV ? -EPROBE_DEFER : PTR_ERR(ctrl);
-- 
2.25.1