HID: magicmouse: Do not crash on missing msc->input

Fake USB devices can send their own report descriptors for which the
input_mapping() hook does not get called.  In this case, msc->input stays NULL,
leading to a crash at a later time.

Detect this condition in the input_configured() hook and reject the device.

This is not supposed to happen with actual magic mouse devices, but can be
provoked by imposing as a magic mouse USB device.

Cc: stable@vger.kernel.org
Signed-off-by: Günther Noack <gnoack@google.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

Author: gnoack

drivers/hid/hid-magicmouse.c

@@ -725,6 +725,11 @@ static int magicmouse_input_configured(struct hid_device *hdev,
 	struct magicmouse_sc *msc = hid_get_drvdata(hdev);
 	int ret;
 
+	if (!msc->input) {
+		hid_err(hdev, "magicmouse setup input failed (no input)");
+		return -EINVAL;
+	}
+
 	ret = magicmouse_setup_input(msc->input, hdev);
 	if (ret) {
 		hid_err(hdev, "magicmouse setup input failed (%d)\n", ret);