⚪ HID: pidff: fix OOB write when hid->inputs is empty (Linux Linux)

Description

In the Linux kernel, the following vulnerability has been resolved: HID: pidff: fix OOB write when hid->inputs is empty hid_pidff_init_with_quirks() derives its input_dev from list_entry(hid->inputs.next, struct hid_input, list) without first checking that hid->inputs is non-empty. The list member of struct hid_input is at offset 0, so on an empty list list_entry() yields &hid->inputs itself and the following hidinput->input load reads an unrelated member of struct hid_device. dev is then a type-confused pointer, and force-feedback init writes through it: each set_bit(FF_*, dev->ffbit) stores 8 bytes at dev + 192, past the end of the object dev actually aliases, and input_ff_create() adds further writes of a heap pointer and two function pointers. Until hid-universal-pidff the only caller was hid_pidff_init() from usbhid, which runs under HID_CLAIMED_INPUT and therefore always has at least one hid_input. universal_pidff_probe() starts the device with HID_CONNECT_DEFAULT & ~HID_CONNECT_FF and then calls hid_pidff_init_with_quirks() directly whenever the descriptor carries a PID usage page, bypassing that gate. A report descriptor whose only application collection is on HID_UP_PID leaves hid->inputs empty while hid_connect() still succeeds through the hidraw claim, so probe reaches the unguarded list_entry(). The write happens in the USB probe path, on the hotplug workqueue, so plugging in a malicious device is enough to trigger it; no attacker software and no logged-in user are required. KASAN reports an 8-byte out-of-bounds write in hid_pidff_init_with_quirks() reached from universal_pidff_probe(). Check for an empty list before deriving dev and return -ENODEV, as the other HID force-feedback drivers already do. universal_pidff_probe() propagates the error and unwinds. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>