[CVE-2026-97487][LOW] jfs: handle set_blocksize failures [ Upstream

[CVE-2026-97487][LOW] jfs: handle set_blocksize failures [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97487
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: jfs: handle set_blocksize failures [ Upstream
Commit: a0ac22af8acca6ea6c57aff72662086cb3243b1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a0ac22af8acca6ea6c57aff72662086cb3243b1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97487
Analysis date: Thu, 24 Sep 2026 19:23:16 -0400
ActionableScore: 0
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-2026-97487 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97487

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-2026-97487	LOW	https://www.kernelcve.org/list/?q=CVE-2026-97487 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-252;CWE-703;CWE-617;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'JFS can continue mounting after sb_set_blocksize() fails when the underlying device block size is larger than PAGE_SIZE. The first __bread_gfp operation can then reach a BUG_ON in folio_set_bh because buffer heads do not safely support this block size configuration. The realistic impact is a failed mount or kernel Oops. A kernel panic and system wide denial of service are possible when panic_on_oops is enabled or when the failure leaves the kernel in an unstable state. For the CVSS the PR:L value in the paranoid assessment represents environments where mounting prepared images or virtual block devices is delegated to a container, service account, or restricted administrator. Normal host mounting typically requires CAP_SYS_ADMIN and therefore supports PR:H for the base assessment. The issue is not network reachable and there is no supported UAF, OOB access, information leak, or write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)  SKIP CVE-2026-97487 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE DISK SIMPLEFIX LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: -1
* Paranoid score: 0
* Applied score lower bound: -1 -> 0
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash or strong DoS. Continuing after `sb_set_blocksize()` fails reaches the documented `BUG_ON()` during the first `__bread_gfp()` call. This can produce an Oops or panic depending on kernel configuration.
* -2 Full host-admin-equivalent privilege. Triggering requires mounting JFS from a block device with an incompatible logical block size. JFS block-device mounting is not an ordinary user-namespace mount operation and requires host-level mount and device access.
* No extra Availability point. An Oops and a panic are alternative manifestations of the same fault.
* No filesystem integrity point. The patch establishes a mount-time assertion, not persistent metadata corruption or cross-file ownership violation.
* No rare-subsystem penalty. JFS usage and the unusual block-size condition reduce practical exposure, but no additional penalty is needed beyond the established host-admin requirement.
* No UAF, OOB access, overwrite, information disclosure, authorization bypass, or attacker-useful corruption primitive is established.
* No paranoid escalation. A hypothetical delegated mount service is not supplied as an established deployment fact.

3. Reachability analysis

The trigger requires mounting a JFS filesystem on a block device for which setting the JFS block size to `PSIZE` fails, principally because the device block size exceeds `PAGE_SIZE`. The complete operation requires mount authority and access to a suitable block device. An ordinary local user cannot perform this operation through an attacker-created user namespace because JFS block-device mounts are not established as user-namespace mountable.

No network path exists. No race or timing condition is involved. The unusual block-size device is a prerequisite, but it does not create a below-host-admin attack path. A separately provisioned service that mounts attacker-supplied devices could change the operational model, but such delegation is not established by the supplied evidence.

4. Primitive and severity interpretation

The exact defect is an unchecked failure return from `sb_set_blocksize()`. JFS continues with an unsupported buffer-head block-size configuration until `folio_set_bh()` detects that the buffer offset is outside the folio and executes `BUG_ON()`.

This is CLASS_C invalid-state and crash behavior. The assertion prevents continuation into the unsupported state and does not establish an out-of-bounds memory access. There is no stale object, post-lifetime access, repeated release, or memory corruption primitive.

The demonstrated consequence is a failed mount, kernel Oops, or possible panic. Stronger confidentiality, integrity, privilege-escalation, or persistent filesystem-corruption consequences are unsupported. ImportantCandidate is therefore NO, and automatic downgrade is safe because no unresolved corruption or security-boundary primitive remains.

5. One-sentence report phrase

JFS failed to handle an unsuccessful block-size change during mount, allowing an incompatible block device to reach a kernel BUG in folio_set_bh, but exploitation requires host-level mount and device control and no memory-corruption primitive is established.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a host-admin-triggered mount-time assertion with no UAF, overwrite, disclosure, authorization bypass, or unresolved ownership primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: jfs: handle set_blocksize failures [ Upstream
Commit: a0ac22af8acca6ea6c57aff72662086cb3243b1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a0ac22af8acca6ea6c57aff72662086cb3243b1c

Changed files:
  fs/jfs/super.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=a0ac22af8acca6ea6c57aff72662086cb3243b1c

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

The original Linux kernel CVE announcement for CVE-2026-97487 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97487

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:H/UI:N/S:U/C:N/I:N/A:L
  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: 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: 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).