[CVE-2026-89540][MODERATE 7.0] sunrpc: init gssp_lock before publishing proc entry

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-89540
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sunrpc: init gssp_lock before publishing proc entry
Commit: f15b87521168c2a92cb1931f532cba422f856f01
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f15b87521168c2a92cb1931f532cba422f856f01
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89540
Analysis date: Sat, 12 Sep 2026 01:14:36 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89540 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89540

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89540	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89540 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;CWE-667;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in SUNRPC gssproxy setup can expose /proc/net/rpc/use-gss-proxy before sn gssp_lock is initialized. A local writer that reaches the proc file in this narrow window can enter set_gssp_clnt() and lock a zero initialized mutex. On debug kernels this can trigger a lock used without init warning. On production kernels the mutex fast path may treat the zeroed object as unlocked, allowing concurrent set_gssp_clnt() execution and a possible shutdown of an rpc client while it is still in use. For the CVSS the PR:L is used because reliable triggering can be possible from a local user or service context that can access the per net proc entry, especially with namespace based setups, rather than requiring full host root in every deployment. The issue is not directly network reachable. Impact is at least local denial of service and in the paranoid case may include confidentiality or integrity impact due to a plausible use-after-free candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	REMOTE INIT RACE LEAK NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Applied conservative floor/cap: Real UAF floor 5 applied because the bug is an active structured lifetime violation involving rpc_clnt shutdown while still in use, not just a shallow cleanup dereference.
* Raw paranoid score: 6
* Paranoid score: 6
* Applied paranoid floor/cap: none.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / active lifetime violation: concurrent set_gssp_clnt() execution can shut down the first writer's rpc_clnt while it is still in use.
* +1 Concrete persistent kernel resource/reference leak: the description states that the losing writer's clnt can be leaked.
* +1 Reliable kernel crash / strong DoS concern: CONFIG_DEBUG_MUTEXES catches lock used without init, and production kernels can proceed with broken mutex exclusion and unsafe object lifetime behavior.
* +1 Weak exploitation concern: this is more than a NULL dereference because the broken locking can allow concurrent manipulation of an active rpc_clnt object.
* -1 Hard or unreliable race: the primary window is explicitly narrow, between proc_create_data() publication and init_gssp_clnt(), and requires preemption plus a writer arriving in that window.

Paranoid signals:

* +2 Real UAF / active lifetime violation: same as conservative.
* +1 Concrete persistent kernel resource/reference leak: same as conservative.
* +1 Reliable kernel crash / strong DoS concern: same as conservative.
* +1 Weak exploitation concern: same as conservative.
* +1 Attacker-influenced active-object lifetime manipulation: a local writer can influence concurrent writes to the freshly published proc file, and the described production behavior permits competing set_gssp_clnt() executions that manipulate rpc_clnt lifetime.
* +0 Race penalty withheld in paranoid score: although the statement window is narrow, module load creates the proc entry for every live net namespace and can widen practical exposure enough that the race should not be treated as an automatic downgrade for triage.

Important non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Remote reachability not established.
* Concrete repeated release/refcount on the exact same dangling reference is not established.
* Structured stale-object leverage is not separately awarded beyond weak exploitation concern because no attacker-shaped replacement object or callback consumption is shown.
* Strong LPE leverage +2 is not awarded because no controlled replacement, arbitrary R/W, credential manipulation, or demonstrated privilege escalation is shown.
* Extra Availability is not awarded because the same crash/unsafe lifetime behavior is already counted once.
* Confidentiality and integrity are not independently awarded as ActionableScore signals merely because paranoid CVSS could use C:H/I:H.

Repeated-release/refcount checklist:

* First release can end lifetime: not established as a repeated-release sequence on the exact same reference.
* Exact same reference survives to a second release: not established.
* Second operation is a real lifetime/refcount mutation on the same dangling reference: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due active structured UAF/lifetime violation, not due repeated release/refcount.

3. Reachability analysis

The vulnerable proc entry is published before the mutex inside struct sunrpc_net is initialized. Once published, it is reachable from userspace, and a local writer that reaches /proc/net/rpc/use-gss-proxy in the race window can enter set_gssp_clnt().

The complete privilege boundary is not fully resolved from the supplied diff because the exact proc file mode and capability checks are not shown. Therefore HostAdminRequired is UNKNOWN rather than YES or NO. The evidence does not positively prove host-admin-equivalent privilege, but it also does not fully prove ordinary unprivileged reachability.

The affected object is per-network-namespace state, and module load can create the proc entry for every live net namespace. However, the supplied evidence does not fully establish that the complete trigger chain is attacker-created namespace scoped. NamespaceScopedPrivilege is therefore UNKNOWN.

Prior setup may involve auth_rpcgss module load or an environment where the proc entry is created for live namespaces. No special hardware or direct network packet trigger is involved. The issue is local and timing-sensitive. The race is narrow, but the module-load across live namespaces makes it more relevant than a purely theoretical one-shot race.

4. Primitive and severity interpretation

The exact primitive is an initialization/publication race: /proc/net/rpc/use-gss-proxy becomes externally reachable before sn->gssp_lock is initialized. A writer can then take a zero-initialized mutex. On production kernels this can fail to provide real mutual exclusion, allowing concurrent set_gssp_clnt() execution.

This is an active structured object lifetime issue, not fixed stale storage. The affected object is an rpc_clnt reachable through sunrpc_net state, and the described consequence includes shutting down one writer's clnt while it is still in use and leaking another clnt.

This is not merely an ordinary stale cleanup dereference. It is closer to an active lifetime/synchronization violation where broken locking allows concurrent manipulation of a live client object. However, it is also not CLASS_A because controlled reclaim, attacker-shaped replacement contents, arbitrary read/write, callback control, or demonstrated LPE are not established.

PrimitiveClass is CLASS_B. Demonstrated consequences are warning/splat on debug kernels, unsafe concurrent object lifetime behavior on production kernels, possible DoS, and resource leak. Speculative consequences include stronger memory-safety impact or privilege escalation if the rpc_clnt lifetime violation can be turned into useful post-free object manipulation, but that is not proven.

ImportantCandidate is YES because an active rpc_clnt lifetime violation remains unresolved beyond a simple crash-only NULL dereference. AutoDowngradeAllowed is NO because automatically closing this as ordinary Moderate would lose a concrete active-object lifetime primitive with unresolved exploitation leverage.

Likely operational severity is Actionable Moderate at minimum, with Strong Important review warranted if below-host-admin reachability or practical rpc_clnt post-free leverage is confirmed.

5. One-sentence report phrase

A race in SUNRPC gssproxy setup can expose /proc/net/rpc/use-gss-proxy before sn gssp_lock is initialized, allowing a local writer to enter set_gssp_clnt() with broken mutex protection and potentially shut down an active rpc_clnt while it is still in use.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete active-object lifetime race with a plausible UAF-style rpc_clnt shutdown while in use, unresolved privilege boundary, and no safe basis for automatic downgrade.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: sunrpc: init gssp_lock before publishing proc entry
Commit: f15b87521168c2a92cb1931f532cba422f856f01
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f15b87521168c2a92cb1931f532cba422f856f01

Commit description:

create_use_gss_proxy_proc_entry() publishes /proc/net/rpc/use-gss-proxy
via proc_create_data() before init_gssp_clnt() runs mutex_init() on
sn->gssp_lock.  Once the dentry is linked under proc_subdir_lock it is
immediately reachable from userspace, so a write that lands in the
window drives set_gssp_clnt() into mutex_lock() on a zero-initialized
struct mutex.

    create_use_gss_proxy_proc_entry(net)
      proc_create_data("use-gss-proxy", ...)   /* dentry live */
      init_gssp_clnt(sn)
        mutex_init(&sn->gssp_lock)             /* too late */

    write_gssp()
      set_gssp_clnt(net)
        mutex_lock(&sn->gssp_lock)             /* uninitialized */
        gssp_rpc_create(...)
        sn->gssp_clnt = clnt
        mutex_unlock(&sn->gssp_lock)

The window spans only the two statements between proc_create_data()
returning and init_gssp_clnt(), so a writer reaches it only if the
registering thread is preempted there while another task is already
opening the freshly published file.  register_pernet_subsys() runs in
preemptible context under pernet_ops_rwsem, so that preemption is
possible, and the window widens on auth_rpcgss module load, when the
proc entry is created for every live net namespace whose tasks are
already running.  A writer that wins the race locks a zero-filled
struct mutex.  On CONFIG_DEBUG_MUTEXES the missing magic value trips a
"lock used without init" splat; on a production kernel the fast path
acquires the lock via CMPXCHG(owner, 0, current).  In the latter case
a second writer that arrives before init_gssp_clnt() re-zeroes owner
can enter set_gssp_clnt() concurrently, shut down the first writer's
clnt while it is still in use, and leak the loser's clnt.

Fix by initializing sn->gssp_lock in sunrpc_init_net() so its lifetime
matches the sunrpc_net it lives in.  sn->gssp_clnt is already NULL from
the kzalloc that backs net_generic storage, so the lazy helper is no
longer needed; drop init_gssp_clnt(), its prototype, and the call from
create_use_gss_proxy_proc_entry().  sunrpc.ko is a build-time
dependency of auth_rpcgss.ko, so sunrpc_init_net() has always run on
every netns before any auth_gss pernet init can publish the proc
entry.

Fixes: 030d794 ("SUNRPC: Use gssproxy upcall for server RPCGSS authentication.")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Signed-off-by: Chris Mason <clm@meta.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260530-tier2-local-v2-1-5a0fd532db57@oracle.com
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/sunrpc/auth_gss/gss_rpc_upcall.c
  net/sunrpc/auth_gss/gss_rpc_upcall.h
  net/sunrpc/auth_gss/svcauth_gss.c
  net/sunrpc/sunrpc_syms.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f15b87521168c2a92cb1931f532cba422f856f01

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89540 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89540

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 5
  Paranoid ActionableScore: 6

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).