CVE-2026-90001

In the Linux kernel, the following vulnerability has been resolved:

HID: bpf: serialize device reference release in struct_ops destroy path

__hid_bpf_ops_destroy_device() and hid_bpf_unreg() can race on the

same registration reference, double-putting struct hid_device and

freeing it while hid_destroy_device() still uses it. Serialize the

remove/NULL decision under hdev->bpf.prog_list_lock so exactly one

path releases each registration reference: unreg re-checks ops->hdev

under the lock and returns without putting when the destroy path

already cleared it; all put_device() calls happen after the lock is

dropped, which is safe because a concurrent unreg then observes

ops->hdev == NULL under the lock.

Background: each successful attach (hid_bpf_ops_reg) acquires one

device reference (hid_get_device()). Two paths can release it:

- device destruction: hid_destroy_device() -> hid_bpf_destroy_device()

-> __hid_bpf_ops_destroy_device(), which walks hdev->bpf.prog_list

under rcu_read_lock() and drops one reference per attached program;

- BPF link release: bpf map delete (no BPF_F_LINK) synchronously calls

st_ops->unreg() -> hid_bpf_unreg(), which drops the reference for

its own registration.

The coordination handshake (e->hdev = NULL on the destroy side vs

"if (!hdev) return" on the unreg side) is a TOCTOU check: the two

paths run under different lock domains (rcu_read_lock vs

prog_list_lock), so a concurrent unreg can read ops->hdev as

non-NULL, block on prog_list_lock, and then proceed while the

destroy traversal executes - both paths then drop the same

reference. The refcount reaches zero legitimately (each decrement

is individually valid), so no refcount_t saturation fires: the

device is simply freed while the transport is still inside

hid_destroy_device(), and subsequent teardown touches freed memory.

The fix serializes the remove/NULL decision under prog_list_lock on

both sides and moves the destroy-side puts outside the lock. With

the lock held, plain reads/writes of ops->hdev are sufficient; no

READ_ONCE/WRITE_ONCE are added, keeping the patch minimal.

Unlocked-read safety: the unlocked read of ops->hdev at the top of

hid_bpf_unreg() cannot touch a freed device, because the unreg path

itself still holds this registration's reference (released only by

its own hid_put_device() after the lock is dropped), and a destroy

traversal that already cleared ops->hdev makes the lock-internal

re-check return early without any put. At most one of the two

paths releases each registration reference.