[CVE-2026-64435][LOW] audit: Fix data races of skb_queue_len() readers on audit_queue

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

CVE: CVE-2026-64435
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: audit: Fix data races of skb_queue_len() readers on audit_queue
Commit: 69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64435
Analysis date: Sat, 25 Jul 2026 13:00:02 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A data race in Linux audit queue length readers can cause inconsistent audit backlog accounting and limited local denial of service effects, but the patch does not indicate memory corruption, remote reachability, or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-64435 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64435

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: LOW
Manual review required: NO

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

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

CVE-2026-64435	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';CWE-362;CWE-662;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.6';DESCR 'An unsynchronized data race in the Linux audit queue length readers can make skb_queue_len() observe audit_queue.qlen while kauditd updates it through skb_dequeue and __skb_unlink. The affected reads are used in the kauditd wait condition, AUDIT_GET backlog reporting, audit_receive backlog checks, and audit_log_start backlog checks and warnings. For the CVSS the PR:L is used because reliable triggering requires a local process that can generate audit activity or interact with audit netlink paths, not a remote network packet. The issue is not network reachable. Impact is mainly limited denial of service or audit accounting inconsistency, such as delayed processing or incorrect backlog based decisions, with no evidence of UAF, OOB access, arbitrary write, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	KASAN RACE SKB LOG HARDWARE DEBUGFS LINUS 	NO	NO	checked

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

ActionableScore=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process can plausibly generate audit activity through normal syscall paths or audit-relevant events.

* Availability impact realistic: +1
  The race can cause incorrect audit backlog accounting, delayed processing, unnecessary backlog warnings, or audit event loss under pressure.

Not triggered:

* Remote reachable: +0
  This is not reachable from network packets.

* Generic memory corruption: +0
  The patch only changes unlocked qlen reads to skb_queue_len_lockless(). No UAF, OOB access, double free, stale pointer, or arbitrary write is shown.

* Privilege escalation plausible: +0
  No LPE primitive is supported by the patch or described behavior.

* Reliable kernel crash / strong DoS: +0
  KCSAN reports a data race, but the described effect is accounting inconsistency, not a reliable panic or Oops.

Subtractors:

* Hard or unreliable race / special timing required: effectively neutralized in final score
  The issue is a race, but the impact is already low and limited to qlen observation consistency.

## 3. Reachability analysis

The bug is locally reachable through audit-producing activity or audit netlink paths. Some audit control operations may require privileges, but audit events themselves can be generated by ordinary local workloads. Namespaces do not materially turn this into a stronger boundary bypass based on the provided patch. The affected path is a core audit subsystem path, but the vulnerable operation is only an unsynchronized queue length read.

Realistic exploitation conditions are weak. An attacker would need to influence timing around audit_queue.qlen updates and readers, and the likely outcome is incorrect backlog decisions rather than memory corruption or privilege gain.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate concurrency correctness issue. Theoretical impact is limited to inconsistent audit backlog accounting and possible audit logging degradation. There is no evidence of memory corruption, attacker-controlled object reuse, stale pointer access, kernel write primitive, information disclosure, or privilege escalation.

## 5. One-sentence report phrase

A data race in Linux audit queue length readers can cause inconsistent audit backlog accounting and limited local denial of service effects, but the patch does not indicate memory corruption, remote reachability, or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a low-severity KCSAN-reported data race fixed by READ_ONCE-style lockless queue length access, with no supported memory corruption or security-boundary bypass primitive.

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

Patch: audit: Fix data races of skb_queue_len() readers on audit_queue
Commit: 69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0

Commit description:

Multiple readers access audit_queue.qlen via skb_queue_len() without
holding the queue lock or using READ_ONCE(), while kauditd writes to
this field via the skb_dequeue() → __skb_unlink() path with WRITE_ONCE()
protected by a spinlock. This constitutes data races.

All affected skb_queue_len(&audit_queue) call sites:
  - kauditd_thread() wait_event_freezable() condition
  - audit_receive_msg() AUDIT_GET handler (s.backlog assignment)
  - audit_receive() backlog check
  - audit_log_start() backlog check and pr_warn()

KCSAN reports the following conflicting access pattern (one example):
==================================================================
BUG: KCSAN: data-race in audit_log_start / skb_dequeue

write (marked) to 0xffffffff8512ee20 of 4 bytes by task 661 on cpu 57:
 skb_dequeue+0x70/0xf0
 kauditd_send_queue+0x71/0x220
 kauditd_thread+0x1cb/0x430
 kthread+0x1c2/0x210
 ret_from_fork+0x162/0x1a0
 ret_from_fork_asm+0x1a/0x30

read to 0xffffffff8512ee20 of 4 bytes by task 36586 on cpu 1:
 audit_log_start+0x2a0/0x6b0
 audit_core_dumps+0x64/0xa0
 do_coredump+0x14b/0x1260
 get_signal+0xeb2/0xf70
 arch_do_signal_or_restart+0x41/0x170
 exit_to_user_mode_loop+0xa2/0x1c0
 do_syscall_64+0x1a3/0x1c0
 entry_SYSCALL_64_after_hwframe+0x76/0xe0

value changed: 0x00000001 -> 0x00000000
==================================================================

Resolve the race by switching to lockless helper skb_queue_len_lockless(),
which internally uses READ_ONCE() and properly pairs with the WRITE_ONCE()
write accesses already present on the writer side.

Cc: stable@vger.kernel.org
Fixes: 3197542 ("audit: rework audit_log_start()")
Signed-off-by: Chi Wang <wangchi@kylinos.cn>
Reviewed-by: Ricardo Robaina <rrobaina@redhat.com>
[PM: line length tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/audit.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=69f98fff30bdaa72b0cb0e7e078ab6456a0a59b0

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

The original Linux kernel CVE announcement for CVE-2026-64435 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64435

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS score: 3.6

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).