[CVE-2026-45984][IMPORTANT] gfs2: Fix use-after-free in iomap inline data write path [ Upstream

[CVE-2026-45984][IMPORTANT] gfs2: Fix use-after-free in iomap inline data write path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45984
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: gfs2: Fix use-after-free in iomap inline data write path [ Upstream
Commit: 1403989d1b502f4a2c0d0b42ccf1c25748442eff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1403989d1b502f4a2c0d0b42ccf1c25748442eff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45984
Analysis date: Wed, 27 May 2026 18:09:36 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-45984 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45984

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: IMPORTANT
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-2026-45984	IMPORTANT	CHECK	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-787;*CWE-664;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'GFS2 inline data writes can keep iomap inline_data pointing into a buffer head that is released by release_metapath() before iomap_write_end_inline() later writes to it. If reclaim frees the underlying page in between, the inline write becomes a use after free write into freed kernel memory. For the CVSS the PR:L is used because a local user with write access to an affected GFS2 file can exercise the inline data write path, although reliable triggering requires reclaim timing and specific filesystem state. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	WRITE OOB DEADLOCK DISK LEAK UAF IMPROVEONLY LINUS SYZBOT 	-	-	checked

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

ActionableScore=8
ActionableScoreLower=6

1. ActionableScore
* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local user with write access to an affected GFS2 filesystem can exercise the inline data write path.
* Generic memory corruption, strong primitive: +2. The bug is an explicit use-after-free write detected by KASAN.
* Real lifetime corruption: +1. `iomap->inline_data` points into a buffer head that was released before later write completion.
* Reliable kernel crash / strong DoS: +1. The UAF write can crash the kernel under reclaim timing.
* Important filesystem/storage path: +1. The bug is in GFS2 iomap inline data write handling.
* Integrity impact plausible: +1. A write into freed memory can corrupt reclaimed kernel memory or filesystem metadata buffers.
* Paranoid LPE plausibility: +1. UAF write in a filesystem write path may be exploitable beyond DoS, but no controlled reclaim or overwrite primitive is demonstrated.
* Hard timing required: -1. Exploitation requires reclaim to free the buffer page between iomap begin and write end, and no standalone C reproducer is available.

3. Reachability analysis
The issue is local and requires write access to a GFS2 file using inline data. It is not network reachable by itself. Containers may matter if untrusted workloads can write to a host GFS2 mount. Reliable exploitation depends on reclaim timing and filesystem state, but the syzbot/KASAN report confirms the lifetime bug and UAF write path.

4. Severity interpretation
This is a real memory corruption issue, not only a filesystem warning or resource leak. Conservative handling is Actionable Moderate due to local trigger and timing constraints. Paranoid handling reaches Strong Important candidate because it is a UAF write in a filesystem write path, which historically can be underestimated even when a practical LPE chain is not yet demonstrated.

5. One-sentence report phrase
GFS2 inline writes can retain `iomap->inline_data` pointing into a released buffer head, allowing reclaim to turn the later inline memcpy into a local use-after-free write.

6. Manual review recommendation
MANUAL CHECK REQUIRED. The patch fixes an explicit KASAN-confirmed UAF write in a filesystem write path, with plausible impact beyond DoS despite timing constraints.

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

Patch: gfs2: Fix use-after-free in iomap inline data write path [ Upstream
Commit: 1403989d1b502f4a2c0d0b42ccf1c25748442eff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1403989d1b502f4a2c0d0b42ccf1c25748442eff

Changed files:
  fs/gfs2/bmap.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=1403989d1b502f4a2c0d0b42ccf1c25748442eff

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

The original Linux kernel CVE announcement for CVE-2026-45984 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45984

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:L/I:L/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: 8

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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT

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).