[CVE-2026-98223][LOW] mm: filemap: retain mapped dropbehind folios

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

CVE: CVE-2026-98223
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm: filemap: retain mapped dropbehind folios
Commit: 2897601dffe576fcd87a4259102f41f7fb0cbfc8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2897601dffe576fcd87a4259102f41f7fb0cbfc8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98223
Analysis date: Fri, 09 Oct 2026 09:19:38 -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-2026-98223 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98223

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-2026-98223	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98223 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both 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:N/A:H';CWE-667;*CWE-833;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A mapped dropbehind folio can reach folio_unmap_invalidate when writeback completes because fault around may map the folio without clearing its dropbehind state. The invalidation path can call unmap_mapping_folio which takes i_mmap_rwsem and may sleep while filemap_end_dropbehind is running in non preemptible task context. The demonstrated result is a sleeping in atomic warning. A more severe but still defensible result is a task stall or denial of service if the sleeping operation blocks progress in a sensitive execution context. For the CVSS the PR:L value is used because a local unprivileged process may create and map file backed pages and generate the required I O activity, although reliable triggering depends on kernel timing and writeback behavior. AC:H is used because the vulnerable state requires fault around, a mapped dropbehind folio, and writeback completion in the affected context. The issue is not directly network reachable. C:N and I:N are retained because source analysis shows no UAF, OOB access, information leak, or write primitive. Impact is limited to availability.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	READ SIMPLEFIX MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
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

Positive signals:

* +1 Important filesystem and page-cache path. The defect occurs during filemap writeback completion and mapped-folio invalidation.
* +0 WARN_ON behavior. The demonstrated result is a sleeping-in-atomic warning, which does not qualify as a reliable kernel crash.
* +0 B5-R. No heap or slab OOB write, retry-accumulated offset, corrupted descriptor, or later consumption of corrupted state is present.

Negative signals:

* No negative points were applied. The required state combination does not by itself establish a hard or uncontrollable race.
* No host-admin penalty was applied because the supplied evidence does not establish such a requirement.
* No rarity penalty was applied because no unusual hardware or rare subsystem is required.

Important non-awarded signals:

* No UAF, OOB access, repeated release, refcount mutation, resource leak, or ownership violation is established.
* No arbitrary or constrained kernel write is demonstrated.
* No reliable crash point was awarded because only a warning is documented.
* No additional availability point was awarded for a speculative stall.
* Local unprivileged trigger was not awarded because ordinary file access is plausible, but the supplied evidence does not establish that an ordinary user controls the complete dropbehind and writeback trigger sequence.
* Broad/default exposure was not separately awarded because the exact mapped-dropbehind path is more specific than ordinary page-cache use.
* No confidentiality, integrity, privilege-escalation, or remote-reachability signal applies.

3. Reachability analysis

The vulnerable operation is reached through local file-backed memory activity involving fault-around, a mapped dropbehind folio, and writeback completion. No capability check, namespace requirement, privileged sysctl, boot option, or special hardware is visible in the supplied evidence.

An ordinary user can generally map and access permitted files, but it is not shown here whether that user can reliably drive the complete dropbehind state transition and affected writeback context. Host-admin necessity and below-host-admin completeness are therefore unresolved. No namespace-scoped privilege participates in the visible path.

The trigger depends on a specific state and execution context, but the patch does not establish a narrow race or one-shot timing requirement. No timing penalty is applied.

4. Primitive and severity interpretation

The exact defect is an execution-context violation. `filemap_end_dropbehind()` can call `folio_unmap_invalidate()` for a mapped folio, and the downstream `unmap_mapping_folio()` path can take `i_mmap_rwsem` and sleep while execution is non-preemptible.

This is CLASS_C behavior rather than memory corruption. The demonstrated consequence is a sleeping-in-atomic warning. A stall or deadlock-like availability effect is conceivable if lock contention prevents progress, but it is not demonstrated strongly enough to score as reliable host-wide DoS.

The folio is still mapped and therefore has a legitimate competing user. Retaining it is not a reference leak or post-lifetime use. There is no first lifetime-ending operation, no dangling reference, and no second release or refcount mutation.

The NEW52 B5-R profile does not apply because its first mandatory condition, a confirmed heap or slab OOB write, is absent. There is also no retry-accumulated index and no later consumption of corrupted structured state.

ImportantCandidate is NO because no corruption, lifetime, ownership, authorization, or security-boundary primitive is established. AutoDowngradeAllowed is YES because the evidence supports a warning-class context bug without unresolved exploitation leverage. Likely operational severity is Low-like to ordinary Moderate.

5. One-sentence report phrase

A mapped dropbehind folio could enter a sleep-capable invalidation path from non-preemptible context, producing a sleeping-in-atomic warning without evidence of memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a context-safety defect and warning, but no UAF, OOB write, reliable crash, security-boundary bypass, or B5-R preservation primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: mm: filemap: retain mapped dropbehind folios
Commit: 2897601dffe576fcd87a4259102f41f7fb0cbfc8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2897601dffe576fcd87a4259102f41f7fb0cbfc8

Commit description:

Fault-around can map ready dropbehind folios without going through the
normal page-cache lookup that clears dropbehind.  A mapping represents a
competing cached user, so retain the folio instead of forcibly unmapping
it when writeback completes.

For a mapped folio, folio_unmap_invalidate() can call
unmap_mapping_folio(), which takes i_mmap_rwsem and may sleep.  Retaining
mapped folios avoids this path when folio_end_dropbehind() runs in
non-preemptible task context.

Tal was able to trigger a sleeping-in-atomic warning due to this [1].

Unmapped dropbehind folios continue through the existing invalidation path.

Link: https://lore.kernel.org/4aba05e1a2c3b61cb337d373eb9b7a8db4ddd822.1788024049.git.qiwenjie@xiaomi.com
Link: https://lore.kernel.org/076bb01b-6fcf-4691-be8c-0e8507c9fe64@columbia.edu [1]
Fixes: fb7d3bc ("mm/filemap: drop streaming/uncached pages when writeback completes")
Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Tal Zussman <tz2294@columbia.edu>
Tested-by: Tal Zussman <tz2294@columbia.edu>
Cc: Barry Song <baohua@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Trond Myklebust <trond.myklebust@hammerspace.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/filemap.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=2897601dffe576fcd87a4259102f41f7fb0cbfc8

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

The original Linux kernel CVE announcement for CVE-2026-98223 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98223

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: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: 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).