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.
CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 7.8
AV:L - HID-BPF attach and unreg are reached only through local bpf() syscalls (BPF_MAP_TYPE_STRUCT_OPS / BPF_PROG_TYPE_STRUCT_OPS). Concurrent hid_destroy_device() is also local (uhid UHID_DESTROY/close or HID teardown), not a network or adjacent-radio packet path.
AC:L - The attacker controls both sides of the TOCTOU race: attach HID-BPF, then concurrently delete the struct_ops map (hid_bpf_unreg) and destroy the HID device (e.g. uhid close). Destroy never took prog_list_lock, so unreg does not block on it and the double-put is reliably hittable.
PR:L - Loading STRUCT_OPS maps/programs requires CAP_BPF and CAP_PERFMON, which can be delegated via BPF tokens into user namespaces rather than init-namespace root. /dev/uhid is also granted to the seat user on typical desktop systems, so real root is not required.
UI:N - The attacker creates their own uhid HID device, loads and attaches HID-BPF struct_ops, then races map delete against device destroy in their own processes. No victim action such as plugging in hardware or mounting a filesystem is required.
S:U - The double-put use-after-free of struct hid_device stays inside the host kernel HID/BPF authority and is a standard local privilege-escalation primitive, not a VM, IOMMU, or sandbox boundary crossing.
C:H - Double-putting struct hid_device frees it while hid_destroy_device() still uses it. Use-after-free of this large kobject, which holds driver callbacks and pointers, enables an attacker-controlled kernel memory read primitive.
I:H - The same use-after-free lets the attacker reclaim the freed hid_device via heap spray and corrupt ll_driver/hiddev function pointers or adjacent heap objects, yielding arbitrary kernel writes and control-flow hijacking.
A:H - Even without full exploitation, dropping the hid_device refcount to zero while hid_remove_device()/put_device() still run causes a kernel oops, panic, or hang on the subsequent use of freed memory.
| Attack Vector |
Local |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
Low |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:L - HID-BPF attach and unreg are reached only through local bpf() syscalls (BPF_MAP_TYPE_STRUCT_OPS / BPF_PROG_TYPE_STRUCT_OPS). Concurrent hid_destroy_device() is also local (uhid UHID_DESTROY/close or HID teardown), not a network or adjacent-radio packet path.
AC:L - The attacker controls both sides of the TOCTOU race: attach HID-BPF, then concurrently delete the struct_ops map (hid_bpf_unreg) and destroy the HID device (e.g. uhid close). Destroy never took prog_list_lock, so unreg does not block on it and the double-put is reliably hittable.
PR:L - Loading STRUCT_OPS maps/programs requires CAP_BPF and CAP_PERFMON, which can be delegated via BPF tokens into user namespaces rather than init-namespace root. /dev/uhid is also granted to the seat user on typical desktop systems, so real root is not required.
UI:N - The attacker creates their own uhid HID device, loads and attaches HID-BPF struct_ops, then races map delete against device destroy in their own processes. No victim action such as plugging in hardware or mounting a filesystem is required.
S:U - The double-put use-after-free of struct hid_device stays inside the host kernel HID/BPF authority and is a standard local privilege-escalation primitive, not a VM, IOMMU, or sandbox boundary crossing.
C:H - Double-putting struct hid_device frees it while hid_destroy_device() still uses it. Use-after-free of this large kobject, which holds driver callbacks and pointers, enables an attacker-controlled kernel memory read primitive.
I:H - The same use-after-free lets the attacker reclaim the freed hid_device via heap spray and corrupt ll_driver/hiddev function pointers or adjacent heap objects, yielding arbitrary kernel writes and control-flow hijacking.
A:H - Even without full exploitation, dropping the hid_device refcount to zero while hid_remove_device()/put_device() still run causes a kernel oops, panic, or hang on the subsequent use of freed memory.
CVSS 3.1