HID: magicmouse: do not keep a stale msc->input if no input is claimed

Summary

In the Linux kernel, the following vulnerability has been resolved: HID: magicmouse: do not keep a stale msc->input if no input is claimed magicmouse_input_mapping() caches the first hid_input's input_dev in msc->input while the report descriptor is parsed, and the rest of the driver treats a non-NULL msc->input as proof that an input device was registered. That does not hold on the hid-input error path. If hidinput_connect() fails -- for instance because input_register_device() returns an error -- it unwinds through hidinput_disconnect(), which frees every input_dev it created, including the one cached in msc->input. The failure does not abort the probe. hid_connect() only skips the claim: if ((connect_mask & HID_CONNECT_HIDINPUT) && !hidinput_connect(hdev, connect_mask & HID_CONNECT_HIDINPUT_FORCE)) hdev->claimed |= HID_CLAIMED_INPUT; and the "device has no listeners" bailout below it does not fire for this driver, which sets ->raw_event; on the USB Magic Mouse 2 / Magic Trackpad 2 paths hidraw and hiddev are claimed as well. hid_hw_start() therefore returns 0 and magicmouse_probe() continues with msc->input pointing at freed memory. Being non-NULL, it passes the "input not registered" check in probe and the NULL checks in ->raw_event and ->event, so the next input report dereferences freed memory. Clear msc->input when the HID core did not claim an input device, so the existing NULL checks cover this case as well.