[CVE-2026-46168][MODERATE REGULAR] mptcp: fix scheduling with atomic in timestamp sockopt

[CVE-2026-46168][MODERATE REGULAR] mptcp: fix scheduling with atomic in timestamp sockopt

[AL-KERNEL]

CVE: CVE-2026-46168
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mptcp: fix scheduling with atomic in timestamp sockopt
Commit: ebeb70e29e37cfce899309cc2665a3bfe960ed94
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ebeb70e29e37cfce899309cc2665a3bfe960ed94
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46168
Analysis date: Thu, 28 May 2026 11:16:52 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
MPTCP timestamp socket option propagation used `lock_sock_fast()` around helpers that may sleep, allowing a local user to trigger `scheduling while atomic` and potentially panic the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-46168 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46168

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 REGULAR
Manual review required: YES

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

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

CVE-2026-46168	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-703;CWE-754;BEST CVSS score: '5.5';DESCR 'MPTCP timestamp socket option propagation used lock_sock_fast around helpers that may sleep, which can trigger scheduling while atomic when a local process changes timestamp or timestamping options on an MPTCP socket with subflows. For the CVSS the PR:L is used because the attacker needs local socket API access but does not need full administrative privileges. The issue is not network reachable by itself and is triggered through local setsockopt control plane operations. Impact is availability only through a kernel BUG or panic. There is no supported memory corruption, information disclosure, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) 	MAYBE	REMOTE DANGER SIMPLEFIX NETWORK LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1. A local process can create/use an MPTCP socket and call timestamp or timestamping `setsockopt()`.
* Reliable kernel crash / strong DoS: +1. Calling sleepable helpers under `lock_sock_fast()` atomic context can trigger `scheduling while atomic` and panic.
* Availability impact realistic: +1. The supported impact is local kernel BUG or panic.

Not counted:

* No memory corruption.
* No UAF, double free, OOB write, arbitrary write, or information leak.
* No privilege escalation primitive.
* No direct network trigger. The issue is reached through local socket control-plane operations, not by remote packets alone.

## 3. Reachability analysis

The trigger is local. An attacker needs local socket API access and the ability to create or operate an MPTCP socket with subflows, then change timestamp-related socket options.

Namespaces may matter if untrusted workloads can create MPTCP sockets inside a network namespace. No administrative privilege is normally required for basic socket option use, but MPTCP availability depends on kernel configuration and system policy.

The issue is not remotely reachable by itself.

## 4. Severity interpretation

This behaves like a borderline Moderate local DoS issue. It is security-relevant if untrusted local users can trigger kernel panic, but it is not an Important-class memory corruption issue.

The theoretical impact is limited to availability based on the patch. There is no evidence of confidentiality, integrity, or privilege-escalation impact.

## 5. One-sentence report phrase

MPTCP timestamp socket option propagation used `lock_sock_fast()` around helpers that may sleep, allowing a local user to trigger `scheduling while atomic` and potentially panic the kernel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review whether MPTCP is enabled and available to untrusted local users. The issue is DoS-only, but local unprivileged kernel panic paths should generally not be auto-closed without checking exposure.

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

Patch: mptcp: fix scheduling with atomic in timestamp sockopt
Commit: ebeb70e29e37cfce899309cc2665a3bfe960ed94
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ebeb70e29e37cfce899309cc2665a3bfe960ed94

Commit description:

Using lock_sock_fast() (atomic context) around sock_set_timestamp()
and sock_set_timestamping() is unsafe, as both helpers can sleep.

Replace lock_sock_fast() with sleepable lock_sock()/release_sock()
to avoid scheduling while atomic panic.

Fixes: 9061f24 ("mptcp: sockopt: propagate timestamp request to subflows")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260420093343.16443-1-gang.yan@linux.dev
Signed-off-by: Gang Yan <yangang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260427-net-mptcp-misc-fixes-7-1-rc2-v1-2-7432b7f279fa@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/mptcp/sockopt.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=ebeb70e29e37cfce899309cc2665a3bfe960ed94

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

The original Linux kernel CVE announcement for CVE-2026-46168 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46168

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).