* [CVE-2026-23097][MODERATE REGULAR] migrate: correct lock ordering for hugetlb file folios
@ 2026-09-27 4:02 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-27 4:02 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-23097
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: migrate: correct lock ordering for hugetlb file folios
Commit: 526394af4e8ade89cacd1a9ce2b97712712fcc34
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=526394af4e8ade89cacd1a9ce2b97712712fcc34
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-23097
Analysis date: Sun, 27 Sep 2026 00:02:43 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-23097 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-23097
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-23097 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-23097 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:N/I:N/A:H';*CWE-833;CWE-667;CWE-362;BEST CVSS score: '4.7';DESCR 'A lock ordering race in hugetlb folio migration can deadlock the kernel because the migration path holds folio_lock and then waits for i_mmap_rwsem while hugetlbfs hole punching can hold i_mmap_rwsem and wait for the same folio_lock. A local user may trigger the condition by operating on an accessible hugetlbfs file while its folios are being migrated, although reliable reproduction depends on hugetlbfs availability, file permissions, concurrent migration, and a narrow timing window. For the CVSS the PR:L value is used because a local user context and access to the affected hugetlbfs object are required, but full administrative control is not necessarily required. The issue is not network reachable. Impact is denial of service through blocked tasks and a possible persistent kernel deadlock. No UAF, out of bounds access, information disclosure, or write primitive is supported by the analyzed code, so confidentiality and integrity remain unaffected.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE READ DEADLOCK DANGER RACE UAF SYZBOT MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable strong DoS. The inverted `folio_lock` and `i_mmap_rwsem` acquisition order establishes an ABBA deadlock that can leave the participating tasks blocked indefinitely.
* +0 Local unprivileged trigger. Hole punching may be available to a user with write access to the hugetlbfs file, but the supplied evidence does not establish that the same below-host-admin actor can initiate the required file-folio migration.
* +0 Memory corruption. The patch changes lock scope and passes `RMP_LOCKED`. It does not establish a UAF, stale post-lifetime access, OOB operation, overwrite, or invalid free.
* +0 Confidentiality and integrity. No disclosure, unauthorized modification, ownership violation, or security-boundary bypass is shown.
* +0 Additional availability. The same deadlock is not counted again as a separate availability consequence.
* +0 Hard-race penalty. Concurrency is required, but the evidence does not establish a genuinely one-shot or externally uncontrollable race. Repeated hole-punch attempts may enlarge the opportunity.
* +0 Rare-subsystem penalty. Hugetlbfs requires relevant configuration and available huge pages, but specialization alone does not justify a negative point.
* Controlled reclaim, arbitrary write, privilege escalation, remote reachability, and persistent data corruption are not demonstrated.
3. Reachability analysis
The vulnerable sequence requires a file-backed hugetlb folio to undergo migration while another task performs partial hole punching through `hugetlbfs_fallocate()`. A user with write access to the file can plausibly control the hole-punch side, but the supplied context does not prove who controls the migration side or whether an ordinary user can complete both stages in the affected deployment.
Hugetlbfs must be available, huge pages must have been provisioned, and the attacker must have access to a suitable file. Some deployments therefore involve prior administrative setup, but that setup is not equivalent to proof that host-admin privilege is required for every trigger. `HostAdminRequired` remains `UNKNOWN`.
No user-namespace or network-namespace capability path is involved, and the issue is not network reachable. The timing requires concurrent operations, but repeated attempts appear possible and no concrete hard-race penalty is supported.
4. Primitive and severity interpretation
The exact primitive is an ABBA lock-order inversion:
`folio_lock` to `i_mmap_rwsem`
versus:
`i_mmap_rwsem` to `folio_lock`
This is a synchronization defect producing deadlock, not a lifetime or memory-corruption primitive. There is no first operation that frees an object, no dangling reference, and no second release or refcount mutation.
The demonstrated consequence is blocked migration and hole-punch tasks, with possible broader availability degradation if dependent kernel work also stalls. Privilege escalation and memory corruption are unsupported speculative consequences.
`PrimitiveClass=CLASS_C` is appropriate because the behavior is DoS-oriented without an independently useful exploitation primitive. `ImportantCandidate=NO` follows from the absence of corruption, authorization bypass, ownership violation, or cross-boundary impact. `AutoDowngradeAllowed=YES` is appropriate, although deployment-specific reachability should be checked before closure.
5. One-sentence report phrase
An ABBA lock-order inversion between hugetlb folio migration and hugetlbfs hole punching can deadlock kernel tasks, causing a local denial of service without an established memory-corruption or privilege-escalation primitive.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm whether an unprivileged user can both access a hugetlbfs file and induce migration of its file-backed huge folios in the evaluated product.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: migrate: correct lock ordering for hugetlb file folios
Commit: 526394af4e8ade89cacd1a9ce2b97712712fcc34
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=526394af4e8ade89cacd1a9ce2b97712712fcc34
Commit description:
Syzbot has found a deadlock (analyzed by Lance Yang):
1) Task (5749): Holds folio_lock, then tries to acquire i_mmap_rwsem(read lock).
2) Task (5754): Holds i_mmap_rwsem(write lock), then tries to acquire
folio_lock.
migrate_pages()
-> migrate_hugetlbs()
-> unmap_and_move_huge_page() <- Takes folio_lock!
-> remove_migration_ptes()
-> __rmap_walk_file()
-> i_mmap_lock_read() <- Waits for i_mmap_rwsem(read lock)!
hugetlbfs_fallocate()
-> hugetlbfs_punch_hole() <- Takes i_mmap_rwsem(write lock)!
-> hugetlbfs_zero_partial_page()
-> filemap_lock_hugetlb_folio()
-> filemap_lock_folio()
-> __filemap_get_folio <- Waits for folio_lock!
The migration path is the one taking locks in the wrong order according to
the documentation at the top of mm/rmap.c. So expand the scope of the
existing i_mmap_lock to cover the calls to remove_migration_ptes() too.
This is (mostly) how it used to be after commit c0d0381 . That was
removed by 336bf30 for both file & anon hugetlb pages when it should
only have been removed for anon hugetlb pages.
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Fixes: 336bf30 ("hugetlbfs: fix anon huge page migration race")
Reported-by: [email protected]
Link: https://lore.kernel.org/all/[email protected]
Debugged-by: Lance Yang <[email protected]>
Acked-by: David Hildenbrand (Red Hat) <[email protected]>
Acked-by: Zi Yan <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Ying Huang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
mm/rmap.c
mm/migrate.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=526394af4e8ade89cacd1a9ce2b97712712fcc34
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-23097 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-23097
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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: unknown
Paranoid ActionableScore: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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