In the Linux kernel, the following vulnerability has been resolved: HID: magicmouse: do not keep a stale msc->input if no input is claimed

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:

 1if ((connect_mask & HID_CONNECT_HIDINPUT) && !hidinput_connect(hdev,
 2			connect_mask & HID_CONNECT_HIDINPUT_FORCE))
 3	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.