[CVE-2026-98920][MODERATE REGULAR] netfs: Fix missing alloc tagging of direct mempool allocations

[CVE-2026-98920][MODERATE REGULAR] netfs: Fix missing alloc tagging of direct mempool allocations

[AL-KERNEL]

CVE: CVE-2026-98920
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfs: Fix missing alloc tagging of direct mempool allocations
Commit: 5c03da745171485fd181f17b69213464f6d05f3d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c03da745171485fd181f17b69213464f6d05f3d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98920
Analysis date: Mon, 26 Oct 2026 21:41:08 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Direct netfs mempool callback allocations skipped profiling hooks, causing debug warnings and allocation-accounting omissions without a demonstrated security primitive.

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

The original Linux kernel CVE announcement for CVE-2026-98920 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98920

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-2026-98920	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98920 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE RESULT=SAME V39_AEGIS_ONE_STEP_UP=LOW->MODERATE (final reconciliation agrees; DECISION: both 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-665;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:N';BEST CVSS score: '4.7';DESCR 'Direct netfs mempool callback calls bypass alloc_hooks, leaving current alloc_tag unset under CONFIG_MEM_ALLOC_PROFILING_DEBUG. This produces allocation and free warnings and omits the affected objects from /proc/allocinfo, but it does not provide a UAF, OOB access, information leak, or write primitive. For the CVSS the PR:L value reflects that a local user or process must initiate a netfs operation such as reading a CIFS file. The issue is not established as directly network reachable. Normal impact is diagnostic and accounting inaccuracy. A kernel panic is plausible only in a special debug environment that converts warnings into fatal failures. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to MODERATE because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class NONE and manual review REQUIRED. Its independently reconciled impact was MODERATE. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	REMOTE DISK LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0.
* Conservative score: 0; no floor or cap applied.
* Raw paranoid score: 0.
* Paranoid score: 0; a fatal-warning configuration is not evidence of a reliable crash.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +0 allocation-tagging/accounting defect: direct mempool callbacks bypass `alloc_hooks()`, leaving `current->alloc_tag` unset and allocations absent from `/proc/allocinfo`.
* +0 WARN evidence: warnings occur with `CONFIG_MEM_ALLOC_PROFILING_DEBUG`, but the patch does not show memory corruption or a normally fatal failure.
* No UAF, OOB access, invalid free, lifetime mutation, shared-backing write, authorization bypass, disclosure, or protected-state modification is shown.
* NEW52/B5-R does not apply: there is no retry-accumulated index or heap OOB write.
* B3-PENDING does not apply: no write into shared or file-backed storage is shown.
* B4-PENDING does not apply: no security guard or DENY-to-ALLOW authorization transition exists.
* No crash/availability point: panic requires an unproven special policy that makes warnings fatal.

3. Reachability analysis

A user able to read an accessible CIFS/netfs file can plausibly exercise the affected allocation path, so host-administrator privilege and host UID 0 are not required. This does not establish any namespace-scoped capability chain. CIFS mounting or provisioning may require prior administration, but the later read itself can be performed by an ordinary authorized user. No race, special hardware, or attacker-controlled allocation contents are involved.

4. Primitive and severity reading

The defect is missing allocation profiling metadata around otherwise valid, failable allocations. The fix preserves allocation semantics and only adds the expected `alloc_hooks()` wrapper. The shown effects are diagnostic warnings and inaccurate `/proc/allocinfo` accounting. There is no material security primitive, corrupted active state, or downstream privileged consumer. Important-candidate preservation is therefore unwarranted, and automatic downgrade is safe.

5. One-sentence report phrase

Direct netfs mempool callback allocations skipped profiling hooks, causing debug warnings and allocation-accounting omissions without a demonstrated security primitive.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch establishes a profiling instrumentation defect only.

7. Call-site confidence

Call-site confidence: high

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

Patch: netfs: Fix missing alloc tagging of direct mempool allocations
Commit: 5c03da745171485fd181f17b69213464f6d05f3d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c03da745171485fd181f17b69213464f6d05f3d

Commit description:

Commit 1d78d56 ("netfs: Fix folio_queue ENOMEM in writeback by
adding a mempool") added a mempool for the folio_queues and made the
request, subrequest and folio_queue allocations distinguish between
writeback and everything else.  Writeback is part of memory reclaim
and must not fail due to ENOMEM, so it allocates under GFP_NOFS
through mempool_alloc(), which may dip into the pool's reserve and,
if that runs empty, wait for elements to be returned.  The
GFP_KERNEL paths, which can return -ENOMEM to their callers, invoke
the pool's ->alloc() callback directly instead.

The direct call, however, skips the alloc_hooks() wrapper that the
mempool_alloc() macro provides.  The pool callbacks, mempool_alloc_slab()
and mempool_kmalloc(), call kmem_cache_alloc_noprof() and kmalloc_noprof()
and rely on current->alloc_tag having been set by the caller.  With
CONFIG_MEM_ALLOC_PROFILING_DEBUG=y this leads to

    current->alloc_tag not set
    WARNING: ./include/linux/alloc_tag.h:161 at __alloc_tagging_slab_alloc_hook
    alloc_tag was not set
    WARNING: ./include/linux/alloc_tag.h:166 at __alloc_tagging_slab_free_hook

at allocation and free time respectively, as reported when reading
files on a CIFS mount.  The allocations are also missing from
/proc/allocinfo.

Wrap the direct ->alloc() invocations in alloc_hooks() with a new
mempool_alloc_noreserve() helper in include/linux/mempool.h, next to
the other alloc_hooks()-wrapped macros such as mempool_alloc().  The
GFP_KERNEL paths keep their failable allocation semantics, they just
get tagged now.

Fixes: 1d78d56 ("netfs: Fix folio_queue ENOMEM in writeback by adding a mempool")
Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Closes: https://lore.kernel.org/all/0b004319-9ef7-437c-a4dd-174d6a9a83db@mailbox.org/
Tested-by: Erhard Furtner <erhard_f@mailbox.org>
Suggested-by: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>
Link: https://patch.msgid.link/20260923063759.34667-1-hao.ge@linux.dev
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/linux/alloc_tag.h
  include/linux/mempool.h
  fs/netfs/objects.c
  fs/netfs/rolling_buffer.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=5c03da745171485fd181f17b69213464f6d05f3d

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

The original Linux kernel CVE announcement for CVE-2026-98920 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98920

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:L/PR:L/UI:N/S:U/C:N/I:N/A:N
  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: 0

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).