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>
---
 drivers/hid/hid-magicmouse.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hid/hid-magicmouse.c b/drivers/hid/hid-magicmouse.c
index 6e7c189f4d1d..b8932f02b6ee 100644
--- a/drivers/hid/hid-magicmouse.c
+++ b/drivers/hid/hid-magicmouse.c
@@ -726,6 +726,11 @@ 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);
-- 
2.52.0.457.g6b5491de43-goog

On Fri, 9 Jan 2026, Günther Noack wrote:

> 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 N=
> ULL,
> 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.

Applied to hid.git#for-6.19/upstream-fixes, thanks Guenther.

-- 
Jiri Kosina
SUSE Labs