[CVE-2026-45934][MODERATE 7.0] btrfs: fix EEXIST abort due to non-consecutive gaps in chunk allocation [ Upstream

[CVE-2026-45934][MODERATE 7.0] btrfs: fix EEXIST abort due to non-consecutive gaps in chunk allocation [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45934
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: btrfs: fix EEXIST abort due to non-consecutive gaps in chunk allocation [ Upstream
Commit: 7d4eadee7042d27fcea659fcdd738f463a7d2e70
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d4eadee7042d27fcea659fcdd738f463a7d2e70
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45934
Analysis date: Wed, 27 May 2026 20:36:57 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A Btrfs chunk allocation logic bug can miss non-consecutive pending extents and allocate overlapping DUP chunk mappings, allowing local allocation pressure to cause filesystem metadata inconsistency and transaction abort DoS.

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

The original Linux kernel CVE announcement for CVE-2026-45934 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45934

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 7.0
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-2026-45934	MODERATE	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:N/I:H/A:H';CWE-682;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '6.3';DESCR 'A Btrfs chunk allocation logic bug can miss non consecutive pending extents while searching a device hole, allowing a later DUP chunk allocation to overlap an already pending physical range. A local workload that creates chunk allocation pressure and races with unused block group cleanup may trigger transaction aborts or inconsistent chunk mapping state. For the CVSS the PR:L is used because a local user with write access to the mounted filesystem can influence allocation pressure, although the easiest reproducer uses privileged force_chunk_alloc controls. The issue is not network reachable. Impact is mainly filesystem availability and integrity risk, including transaction abort, possible read only failure mode, ENOSPC like behavior, or overlapping allocation metadata. Kernel memory corruption or privilege escalation is not directly supported by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6) 	MAYBE	OOB DANGER DISK RACE SKIP HARDWARE DEBUGFS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local user with write access to a mounted Btrfs filesystem can create allocation and deletion pressure that may influence chunk allocation patterns. The easiest reproducer uses privileged `force_chunk_alloc`, but the commit states the issue can theoretically happen to any DUP chunk allocation.

* Filesystem/storage metadata corruption reachable by local workload: +1
  The bug can produce overlapping physical chunk mappings due to incorrect accounting of non-consecutive pending extents.

* Integrity impact plausible: +1
  Overlapping chunk maps and incorrect device extent allocation affect Btrfs allocation metadata and can lead to inconsistent filesystem state.

* Availability impact realistic: +1
  The observed result is `EEXIST`, transaction abort, and Btrfs error state, which can cause filesystem-level DoS or read-only/failure behavior.

* Broad/default/common subsystem: +1
  Btrfs is a widely deployed Linux filesystem, even if not always the default.

* Important filesystem/storage path: +1
  This is in Btrfs chunk allocation and device extent selection, a core filesystem metadata path.

* Hard or unreliable race / special layout required: -1
  Reliable reproduction requires a specific pending-extent layout, DUP allocation, cleaner timing, and allocation/free sequencing.

* No generic kernel memory corruption: +0
  The patch supports filesystem metadata overlap and transaction abort, not UAF, heap corruption, OOB write, or arbitrary kernel memory overwrite.

* No practical privilege escalation primitive: +0
  There is no demonstrated LPE path, credential overwrite, page-cache corruption, or attacker-controlled kernel write primitive.

## 3. Reachability analysis

The bug is locally reachable through Btrfs allocation behavior when a filesystem uses affected DUP chunk allocation patterns. A normal local user with write access may influence allocation pressure, but the clearest reproducer uses privileged sysfs `force_chunk_alloc` controls and artificial cleaner-thread timing. Containers or namespaces matter only if untrusted workloads can write to a host-backed Btrfs filesystem or if management controls are delegated.

The path is not network reachable. Exploitation is realistic mainly as filesystem integrity or availability impact under specific allocation and cleanup timing, not as a direct kernel compromise.

## 4. Severity interpretation

This behaves as an actionable Moderate. It is more serious than a simple warning because it involves overlapping Btrfs chunk mappings and transaction aborts in an important filesystem metadata path. However, it should not be classified as Important solely on memory-safety grounds, because the patch does not show kernel memory corruption, UAF, arbitrary write, or a plausible privilege escalation primitive.

The paranoid score is higher because filesystem metadata overlap can have persistent integrity and availability consequences even without kernel code execution.

## 5. One-sentence report phrase

A Btrfs chunk allocation logic bug can miss non-consecutive pending extents and allocate overlapping DUP chunk mappings, allowing local allocation pressure to cause filesystem metadata inconsistency and transaction abort DoS.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this affects Btrfs core allocation metadata and can produce overlapping physical chunk mappings, but the available patch context does not justify treating it as kernel memory corruption or privilege escalation.

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

Patch: btrfs: fix EEXIST abort due to non-consecutive gaps in chunk allocation [ Upstream
Commit: 7d4eadee7042d27fcea659fcdd738f463a7d2e70
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7d4eadee7042d27fcea659fcdd738f463a7d2e70

Changed files:
  fs/btrfs/block-group.c
  fs/btrfs/volumes.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=7d4eadee7042d27fcea659fcdd738f463a7d2e70

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

The original Linux kernel CVE announcement for CVE-2026-45934 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45934

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
  The Best / paranoid CVSS score: 6.3

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: 5
  Paranoid ActionableScore: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).