In the Linux kernel, the following vulnerability has been resolved:
HID: bpf: abort dispatch if device destroyed
The current HID bpf implementation assumes no output report/request will go through it after hid_bpf_destroy_device() has been called. This leads to a bug that unplugging certain types of HID devices causes a cleaned- up SRCU to be accessed. The bug was previously a hidden failure until a recent x86 percpu change [1] made it access not-present pages.
The bug will be triggered if the conditions below are met:
A) a device under the driver has some LEDs on B) hid_ll_driver->request() is uninplemented (e.g., logitech-djreceiver)
If condition A is met, hidinput_led_worker() is always scheduled *after* hid_bpf_destroy_device().
hid_destroy_device
hid_bpf_destroy_device
cleanup_srcu_struct(&hdev->bpf.srcu)
hid_remove_device
...
led_classdev_unregister
led_trigger_set(led_cdev, NULL)
led_set_brightness(led_cdev, LED_OFF)
...
input_inject_event
input_event_dispose
hidinput_input_event
schedule_work(&hid->led_work) [hidinput_led_worker]
This is fine when condition B is not met, where hidinput_led_worker() calls hid_ll_driver->request(). This is the case for most HID drivers, which implement it or use the generic one from usbhid. The driver itself or an underlying driver will then abort processing the request.
Otherwise, hidinput_led_worker() tries hid_hw_output_report() and leads to the bug.
hidinput_led_worker
hid_hw_output_report
dispatch_hid_bpf_output_report
srcu_read_lock(&hdev->bpf.srcu)
srcu_read_unlock(&hdev->bpf.srcu, idx)
The bug has existed since the introduction [2] of dispatch_hid_bpf_output_report(). However, the same bug also exists in dispatch_hid_bpf_raw_requests(), and I've reproduced (no visible effect because of the lack of [1], but confirmed bpf.destroyed == 1) the bug against the commit (i.e., the Fixes:) introducing the function. This is because hidinput_led_worker() falls back to hid_hw_raw_request() when hid_ll_driver->output_report() is uninplemented (e.g., logitech- djreceiver).
hidinput_led_worker
hid_hw_output_report: -ENOSYS
hid_hw_raw_request
dispatch_hid_bpf_raw_requests
srcu_read_lock(&hdev->bpf.srcu)
` srcu_read_unlock(&hdev->bpf.srcu, idx)
Fix the issue by returning early in the two mentioned functions if hid_bpf has been marked as destroyed. Though dispatch_hid_bpf_device_event() handles input events, and there is no evidence that it may be called after the destruction, the same check, as a safety net, is also added to it to maintain the consistency among all dispatch functions.
The impact of the bug on other architectures is unclear. Even if it acts as a hidden failure, this is still dangerous because it corrupts whatever is on the address calculated by SRCU. Thus, CC'ing the stable list.
[1]: commit 9d7de2aa8b41 ("x86/percpu/64: Use relative percpu offsets") [2]: commit 9286675a2aed ("HID: bpf: add HID-BPF hooks for hid_hw_output_report")