Unity Linux 20.1050a Security Update: kernel (UTSA-2026-146609)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
##

include('compat.inc');

if (description)
{
  script_id(373201);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/10/28");

  script_cve_id("CVE-2026-89708");

  script_name(english:"Unity Linux 20.1050a Security Update: kernel (UTSA-2026-146609)");

  script_set_attribute(attribute:"synopsis", value:
"The Unity Linux host is missing one or more security updates.");
  script_set_attribute(attribute:"description", value:
"The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the
UTSA-2026-146609 advisory.

    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.

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version
number.");
  # https://src.uniontech.com/#/security_advisory_detail?utsa_id=UTSA-2026-146609
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?e2765004");
  # https://lore.kernel.org/linux-cve-announce/2026091157-CVE-2026-89708-f3f2@gregkh
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?2b6ac386");
  script_set_attribute(attribute:"see_also", value:"https://nvd.nist.gov/vuln/detail/CVE-2026-89708");
  script_set_attribute(attribute:"solution", value:
"Update the affected kernel package.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-89708");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/09/11");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/10/28");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/10/28");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Unity Linux Local Security Checks");

  script_copyright(english:"This script is Copyright (C) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info2.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/UOS-Server/release", "Host/UOS-Server/rpm-list", "Host/cpu");

  exit(0);
}
include('rpm2.inc');

if (!get_kb_item('Host/local_checks_enabled')) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
var os_product = get_kb_item('installed_os/local/SSH/0/product');
if (isnull(os_product) || 'UOS Server' >!< os_product) audit(AUDIT_OS_NOT, 'UOS Server');
var os_version = get_kb_item('installed_os/local/SSH/0/version');
if (isnull(os_version)) audit(AUDIT_UNKNOWN_APP_VER, 'UOS Server');
if (! preg(pattern:"^(20.1050a)([^0-9]|$)", string:os_version)) audit(AUDIT_OS_NOT, 'UOS Server 20.1050a', 'UOS Server ' + os_version);

if (!get_kb_item('Host/UOS-Server/rpm-list')) audit(AUDIT_PACKAGE_LIST_MISSING);

var cpu = get_kb_item('Host/cpu');
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ('aarch64' >!< cpu && 'amd64' >!< cpu && 'loongarch64' >!< cpu && 'x86_64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'UOS Server', cpu);


var constraints = [
  {
    'release': '20',
    'sp': '1050a',
    'pkgs': [
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'aarch64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'amd64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'loongarch64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'x86_64', 'rpm_spec_vers_cmp':TRUE}
    ]
  }
];

var os_release = get_one_kb_item('installed_os/local/SSH/0/release');
var os_sp = get_one_kb_item('Host/*/minor_release');

var flag = 0;
var reference;
var sp;
var _cpu;
var el_string;
var rpm_spec_vers_cmp;
var epoch;
var allowmaj;
var exists_check;
var cves;
foreach var constraint ( constraints ) {
  # Check that the target release is equal to the affected release
  if (!empty_or_null(constraint['release'])){
    if (constraint['release'] != os_release) continue;
  }
  if (!empty_or_null(constraint['sp'])){
    if (constraint['sp'] != os_sp) continue;
  }
  foreach var pkg ( constraint['pkgs'] ) {
    reference = NULL;
    sp = NULL;
    _cpu = NULL;
    el_string = NULL;
    rpm_spec_vers_cmp = NULL;
    epoch = NULL;
    allowmaj = NULL;
    exists_check = NULL;
    cves = NULL;
    if (!empty_or_null(pkg['reference'])) reference = pkg['reference'];
    if (!empty_or_null(pkg['sp'])) sp = pkg['sp'];
    if (!empty_or_null(pkg['cpu'])) _cpu = pkg['cpu'];
    if (!empty_or_null(pkg['el_string'])) el_string = pkg['el_string'];
    if (!empty_or_null(pkg['rpm_spec_vers_cmp'])) rpm_spec_vers_cmp = pkg['rpm_spec_vers_cmp'];
    if (!empty_or_null(pkg['epoch'])) epoch = pkg['epoch'];
    if (!empty_or_null(pkg['allowmaj'])) allowmaj = pkg['allowmaj'];
    if (!empty_or_null(pkg['exists_check'])) exists_check = pkg['exists_check'];
    if (!empty_or_null(pkg['cves'])) cves = pkg['cves'];
    if (reference &&
        ## (no known rpm to check OR known rpm_exists)
        (!exists_check || rpm_exists(rpm:exists_check)) &&
        rpm_check(sp:sp, cpu:_cpu, reference:reference, epoch:epoch, el_string:el_string, rpm_spec_vers_cmp:rpm_spec_vers_cmp, allowmaj:allowmaj, cves:cves)) flag++;
  }
}


if (flag)
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_HOLE,
      extra      : rpm_report_get()
  );
  exit(0);
}
else
{
  var tested = pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, 'kernel');
}