[CVE-2026-89760][MODERATE 7.0] mm, swap: don't free a hibernation slot that is in the swap cache

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

CVE: CVE-2026-89760
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mm, swap: don't free a hibernation slot that is in the swap cache
Commit: a6df73156f2d85746c69adbf13d0f5ea200e0626
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a6df73156f2d85746c69adbf13d0f5ea200e0626
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89760
Analysis date: Sat, 12 Sep 2026 04:27:56 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89760 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89760

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-2026-89760	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89760 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-416;*CWE-672;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:H/A:H';BEST CVSS score: '7';DESCR 'A swap slot lifetime bug can occur when swap_free_hibernation_slot() frees a hibernation slot even though cluster readahead has placed a folio for that slot in the swap cache. The folio can remain on the LRU with a stale swap offset while the slot is returned to the allocator and later reused for unrelated data. Later reclaim can use the stale offset from the folio and overwrite the current swap table entry, causing silent memory corruption, process crashes, or data instability across unrelated userspace applications. For the CVSS the PR:L is used for the paranoid score because some deployments may allow a local logged in user or a reduced capability service to request hibernation through policy, while direct hibernation and swap control is often administrative. The issue is not network reachable. Impact is at least local denial of service and data corruption, and worst case may allow confidentiality or integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)  SKIP CVE-2026-89760 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER INIT UAF KERNEL_PANIC_PLUS_UAF LINUS KPANIC MEMORY  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6. No floor or cap changed the score.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap changed the score.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF or equivalent lifetime violation. A hibernation swap slot can be freed while a folio in the swap cache still references that slot through folio->swap.
* +1 Secondary index or swap-table staleness. The swap table entry is cleared and the offset returns to the allocator while the folio still carries the old offset, so later reclaim can act on a stale association.
* +1 Integrity impact is plausible and directly supported. The commit states that reclaim may overwrite a swap table entry that may already belong to someone else, causing silent memory corruption and data instability across unrelated userspace applications.
* +1 Important MM or storage path. The bug is in core swap table accounting and hibernation slot handling, not a device-local or diagnostic-only path.
* +1 Availability impact is realistic. The supplied text explicitly mentions process crashes and data instability.

Paranoid additional signal:

* +1 Weak LPE concern. The established primitive is active swap metadata corruption across unrelated userspace state. Controlled reclaim, arbitrary write, or credential overwrite is not demonstrated, but the primitive is stronger than crash-only behavior and merits Important-vs-Moderate review.

Non-awarded or withheld signals:

* +0 Remote reachability. No network trigger is established.
* +0 Local unprivileged trigger. Some deployments may expose hibernation through policy, but the supplied evidence does not prove complete ordinary-user reachability.
* +0 Strong LPE leverage. No controlled target, controlled payload, arbitrary kernel write, controlled reclaim, or credential manipulation is demonstrated.
* +0 Confidentiality. Data corruption is supported, but no read-back or disclosure path is established.
* +0 Concrete repeated release/refcount. This is not a double put or repeated refcount mutation on the same object.
* +0 Extra availability. Process crashes and instability are counted once.
* No race penalty. The issue depends on readahead and hibernation state, but the supplied evidence does not establish a narrow externally uncontrollable timing race.

Repeated release/refcount check:

* First release can end lifetime: not applicable.
* Exact same reference survives to a second release: not established.
* Second lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no. Raw score already exceeds 5.

3. Reachability analysis

The most direct trigger is the hibernation path, typically when uswsusp is preparing a hibernation image. Direct control over hibernation and swap management is often administrative, but host-admin-equivalent privilege is not positively established by the supplied text because policy-mediated hibernation may exist on some systems. Therefore HostAdminRequired is UNKNOWN rather than YES.

The issue is local, not network reachable. It is not namespace-scoped. Swap and hibernation slot management are host-global MM facilities and there is no evidence that an attacker-created user or mount namespace can perform the complete vulnerable operation.

Prior host setup may be needed in practice, such as configured swap and enabled hibernation support. No special hardware is required. No hard one-shot race penalty is applied because the described failure is a state/lifetime invariant violation involving hibernation slots, swap cache readahead, and later reclaim, not merely an extremely narrow timing window.

4. Primitive and severity interpretation

The exact primitive is a stale swap-slot lifetime and ownership violation. A swap cache folio can remain live and reachable from the LRU while the swap table entry backing its stored offset has been freed and returned to the allocator. Later reclaim can use the stale folio->swap offset and overwrite a swap table entry that may now belong to unrelated data.

This is active kernel metadata corruption, not fixed stale storage and not a shallow cleanup-only crash. It affects the relationship between the swap cache, folio state, and swap table allocator state. The demonstrated consequences include silent memory corruption, process crashes, and data instability across unrelated userspace applications.

PrimitiveClass is CLASS_B because a real kernel lifetime and metadata corruption primitive is established, but the patch and supplied context do not demonstrate controlled reclaim, arbitrary write, credential overwrite, or a complete privilege-escalation chain. RealUAF is YES in the broader lifetime sense because a stale post-lifetime swap-slot reference remains in an active folio and is later consumed.

ImportantCandidate is YES because this is core MM/swap active metadata corruption with cross-process effects and unresolved exploitation leverage beyond ordinary DoS. AutoDowngradeAllowed is NO because automatically closing this as ordinary Moderate would lose a concrete kernel lifetime/ownership corruption primitive with meaningful integrity impact.

Likely operational severity is at least Actionable Moderate and plausibly Important, depending on whether a below-host-admin user or service can trigger hibernation and whether the stale swap-table overwrite can be shaped into a more controlled corruption primitive.

5. One-sentence report phrase

A hibernation swap-slot lifetime bug can leave a swap-cache folio with a stale offset after the slot is freed and reused, allowing later reclaim to overwrite unrelated swap table state and cause silent memory corruption, process crashes, or data instability.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug establishes real active MM/swap metadata corruption across unrelated userspace state, with plausible integrity impact and unresolved exploitation leverage beyond crash-only behavior.

7. Call-site confidence

Call-site confidence: medium

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

Patch: mm, swap: don't free a hibernation slot that is in the swap cache
Commit: a6df73156f2d85746c69adbf13d0f5ea200e0626
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a6df73156f2d85746c69adbf13d0f5ea200e0626

Commit description:

A slot with a folio in the swap cache is freed when the folio leaves the
cache, not when its count drops.  swap_put_entries_cluster() follows that
rule.  swap_free_hibernation_slot() does not, it calls
__swap_cluster_free_entries() whether or not a folio sits on the slot.

Cluster readahead can put one there.  It walks a raw page_cluster sized
window of offsets around the faulting entry, and a hibernation slot passes
__swap_cache_add_check() because it is not a folio and its count is not
zero.  Freeing the slot then clears the entry under that folio.

The folio is now unreachable from the swap table, and the offset goes back
to the allocator.  The folio is still on the LRU though, so reclaim can
pick it up later.  It then takes the old offset out of folio->swap and
overwrites the table entry there, which by then may belong to someone
else.

This bug can trigger silent memory corruption, process crashes, or data
instability across completely unrelated userspace applications - typically
occurring when uswsusp is preparing the hibernation image.

I found this while working on giving hibernation slots their own marker in
the swap table, which I had discussed with Kairui.
( https://lore.kernel.org/linux-mm/abp7aDgYLrxF3Me8@KASONG-MC4/ ) As far as
I know there are no reports, so there is no Reported-by/Closes to add.

Check for a cached folio before freeing.  The slot is then left in the
ordinary state where only the swap cache holds it, and it is freed when
the folio leaves the cache, either through the reclaim below or through
normal reclaim later.

Link: https://lore.kernel.org/20260811132209.2862708-2-youngjun.park@lge.com
Fixes: 0d6af9b ("mm, swap: use the swap table to track the swap count")
Signed-off-by: Youngjun Park <youngjun.park@lge.com>
Acked-by: Kairui Song <kasong@tencent.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/swapfile.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=a6df73156f2d85746c69adbf13d0f5ea200e0626

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

The original Linux kernel CVE announcement for CVE-2026-89760 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89760

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:H/UI:N/S:U/C:L/I:H/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: 6
  Paranoid ActionableScore: 7

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).