Google: sys-kernel/cchost-kernel-6_18, sys-kernel/csql-kernel-6_18, sys-kernel/lakitu-kernel-6_18, sys-kernel/lakitu-nc-kernel-6_18: security update to 20162.0.0

critical Tenable Self-Hosted Container Security Plugin ID 475748

Description

There are packages installed that are affected by a vulnerability referenced in the following CVE:

- In the Linux kernel, the following vulnerability has been resolved: nfsd: RCU-protect cl_cb_session to fix
use-after-free on session teardown After a DESTROY_SESSION the per-session teardown path can free a
session while rpciod still holds an inflight callback rpc_task that dereferences clp->cl_cb_session.
nfsd4_probe_callback_sync() flushes cl_callback_wq, but once nfsd4_run_cb_work() has called
rpc_call_async() the rpc_task lives on rpciod; flushing the workqueue does not wait for it.
rpc_shutdown_client() does drain rpciod tasks, but uses a 1-second wait_event_timeout — tasks stuck in
rpc_delay() (e.g. 2-second NFS4ERR_DELAY retries) can outlive the drain. destroy path rpciod ------------
------ unhash_session(ses) nfsd4_probe_callback_sync(clp) flush_workqueue(cl_callback_wq) /* returns;
rpc_task still live */ nfsd4_put_session_locked(ses) free_session(ses) -> kfree(ses)
nfsd4_cb_sequence_done() reads cb_clp->cl_cb_session /* freed slab */ A second window exists in
nfsd4_process_cb_update(). When __nfsd4_find_backchannel() returns NULL because unhash_session() has
already removed the destroyed session from cl_sessions, setup_callback_client() takes the v4.1 early
return so clp->cl_cb_session = ses never fires and the field retains a pointer to the about-to-be-freed
session. Fix both by converting cl_cb_session to an RCU-protected pointer: - Move the cl_cb_session = ses
assignment in setup_callback_client() to after rpc_create() succeeds, so it is only published when a
working backchannel exists. Clear cl_cb_session on the error return in nfsd4_process_cb_update(). Both
stores use rcu_assign_pointer(). - Annotate cl_cb_session with __rcu. All rpciod-side readers use
rcu_read_lock()/rcu_dereference() and check for NULL, bailing to the appropriate error or requeue path:
encode_cb_sequence4args(), decode_cb_sequence4resok(), nfsd41_cb_get_slot(), nfsd41_cb_release_slot(),
nfsd4_cb_prepare(), and nfsd4_cb_sequence_done(). - Switch __free_session() from kfree() to kfree_rcu() so
the session slab is not reclaimed until after an RCU grace period, guaranteeing that rpciod readers inside
rcu_read_lock() never dereference freed memory. - Pass the session pointer to the nfsd_cb_seq_status and
nfsd_cb_free_slot tracepoints instead of having them re-read cl_cb_session. - nfsd4_cb_prepare() calls
rpc_exit() when the session is NULL, routing through the done/release path to requeue the callback.
(CVE-2026-89708)

Solution

Update the sys-kernel/cchost-kernel-6_18 library and its related packages to version 20162.0.0 or later.

Plugin Details

Severity: Critical

ID: 475748

Version: Revision 1.1

Type: Local

Family: Google COS Security Checks

Published: 10/16/2026

Updated: 10/16/2026

Risk Information

VPR

Risk Factor: Medium

Score: 4.9

Percentile: 58.23

Vendor

Vendor Severity: LOW

CVSS v2

Risk Factor: Critical

Base Score: 10

Temporal Score: 7.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

CVSS Score Source: CVE-2026-89708

CVSS v3

Risk Factor: Critical

Base Score: 9.8

Temporal Score: 8.5

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 9/11/2026

Reference Information

CVE: CVE-2026-89708

Detections

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