[CVE-2026-68450][LOW] btrfs: free mapping node on duplicate reloc root insert [ Upstream

[CVE-2026-68450][LOW] btrfs: free mapping node on duplicate reloc root insert [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68450
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: btrfs: free mapping node on duplicate reloc root insert [ Upstream
Commit: 92bedc0455552b42ada1a1f42b0e3a8593cdfccc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92bedc0455552b42ada1a1f42b0e3a8593cdfccc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68450
Analysis date: Tue, 11 Aug 2026 21:58:44 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like. Autoclose candidate
Manual review required: NO

Summary:
A defensive btrfs relocation error path leaked an unlinked mapping_node on an unexpected duplicate reloc root insert, with impact limited to possible local resource exhaustion under privileged filesystem-management conditions.

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

The original Linux kernel CVE announcement for CVE-2026-68450 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68450

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-68450	LOW	CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;CWE-404;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'A memory leak can occur in the btrfs relocation path when __add_reloc_root allocates a mapping_node and rb_simple_insert reports a duplicate relocation root. The newly allocated node is not inserted into reloc_root_tree, so later relocation cleanup cannot find it and the allocation is lost. For the CVSS the PR:H is used because reliable triggering is expected to require administrative control over btrfs relocation or similarly privileged filesystem operations. The issue is not network reachable and there is no evidence of a UAF, OOB access, or arbitrary write primitive. Impact is limited to local denial of service through possible resource exhaustion if the unexpected duplicate insert path can be reached repeatedly.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Autoclose candidate (with actual score 1)	YES	DANGER DISK SIMPLEFIX ERRORPATH SKIP 	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like. Autoclose candidate**::

## 2. Signal breakdown

Triggered signals:

* Important filesystem/storage path: +1
  Btrfs relocation is a filesystem metadata path, so the affected code is in an important storage subsystem.

Subtracting signals:

* Requires admin/root/CAP capable filesystem management in typical deployments: -2
  Reliable triggering is expected to require btrfs relocation activity such as balance or similarly privileged filesystem-management operations.

* Rare AND difficult-to-reach condition: -1
  The duplicate insert path is described as unexpected, and callers currently assert that EEXIST should not happen.

Not awarded:

* No generic memory corruption.
  The patch fixes a missing kfree on an unlinked allocation. There is no UAF, double free, OOB write, arbitrary write, stale callback, or refcount takeover.

* No privilege escalation signal.
  The leaked node is simply lost from cleanup visibility. There is no supported path to control kernel memory or cross a security boundary.

* No strong DoS signal in the conservative score.
  The leak is small and on an unexpected defensive error path. Sustained resource exhaustion is only a weak paranoid concern.

## 3. Reachability analysis

The bug is local only and not network reachable. Triggering requires reaching btrfs relocation code and specifically causing a duplicate reloc root insertion in `__add_reloc_root()`. In normal deployments, relocation operations are administrative and not directly available to an unprivileged user. Namespaces or containers do not obviously lower the privilege requirement unless the container has delegated access to manage the underlying btrfs filesystem, which would already be a privileged storage-management role.

Call-site confidence: medium. The patch gives the allocation, failed insert, and cleanup consequence directly, but not a full external trigger path.

## 4. Severity interpretation

This behaves like a low-risk resource leak, not an Important-class kernel vulnerability. The theoretical worst case is local availability impact if the unexpected duplicate insertion path can be reached repeatedly, but the patch does not support memory corruption, privilege escalation, confidentiality impact, or integrity impact. Conservative triage should treat it as ordinary Moderate or Low-like.

## 5. One-sentence report phrase

A defensive btrfs relocation error path leaked an unlinked mapping_node on an unexpected duplicate reloc root insert, with impact limited to possible local resource exhaustion under privileged filesystem-management conditions.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a straightforward memory leak fix in a privileged and unexpected btrfs relocation error path, with no supported memory corruption or security-boundary bypass primitive.

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

Patch: btrfs: free mapping node on duplicate reloc root insert [ Upstream
Commit: 92bedc0455552b42ada1a1f42b0e3a8593cdfccc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92bedc0455552b42ada1a1f42b0e3a8593cdfccc

Changed files:
  fs/btrfs/relocation.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=92bedc0455552b42ada1a1f42b0e3a8593cdfccc

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

The original Linux kernel CVE announcement for CVE-2026-68450 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68450

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.1

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: 0
  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).