[CVE-2026-64356][LOW] xfs: fix memory leak in xfs_dqinode_metadir_create()

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-64356
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xfs: fix memory leak in xfs_dqinode_metadir_create()
Commit: c3d3d2212c2966973dd7d603c6c6e6ed6fc7fbe1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3d3d2212c2966973dd7d603c6c6e6ed6fc7fbe1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64356
Analysis date: Sat, 25 Jul 2026 14:01:18 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
XFS quota metadir inode creation can leak metadir update state or inode references on create or commit failure, causing local resource leakage or mount setup stall in privileged quota-enabled mount scenarios.

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

The original Linux kernel CVE announcement for CVE-2026-64356 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64356

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: YES

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
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CVE-2026-64356	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-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: '4.7';DESCR 'XFS quota metadir inode creation can leak metadir update or transaction state when xfs_metadir_create fails and can leak an inode reference when xfs_metadir_commit fails. The failure path is reachable during quota setup for metadir XFS mounts, for example during mount -o uquota when metadata creation or commit returns an error. The practical impact is resource leakage and possible mount setup stall rather than a direct memory corruption primitive. For the CVSS the PR:L is used for the paranoid score because a delegated mount helper, container root, or service account with mount control could trigger the path, while typical host deployments require CAP_SYS_ADMIN. The issue is not network reachable. Impact is denial of service or resource exhaustion only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DISK WARNONLY LEAK LINUS 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScoreLower=0
ActionableScore=2

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Important filesystem/storage path: +1. The bug is in XFS quota metadir inode creation during mount setup.
* Availability impact realistic: +1. The described failure can leak update or inode references and leave mount setup stuck.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Triggering requires mounting or configuring an XFS filesystem with quota, normally a privileged operation.
* Special failure path required: -1. The issue requires xfs_metadir_create() or xfs_metadir_commit() failure, demonstrated via kprobe fault injection rather than a normal easy trigger.

Conservative total is capped at 0 after negative adjustments.

Paranoid signals:

* Important filesystem/storage path: +1.
* Availability impact realistic: +1.
* No memory corruption primitive is shown. The patch fixes cleanup and reference-release paths, not UAF, OOB write, double free, or attacker-controlled overwrite.
* No LPE signal. The leaked inode reference and metadir update state support DoS or stuck mount behavior, not a privilege escalation primitive.
* No network reachability.

Paranoid total: 2.

## 3. Reachability analysis

The realistic trigger is local and privileged: mounting a metadir-enabled XFS filesystem with quota options such as `mount -o uquota`, followed by an error in quota metadir inode creation or commit. In normal host deployments this requires CAP_SYS_ADMIN or equivalent mount control.

Namespaces or containers may lower practical privilege if a container root, mount helper, or service account can mount attacker-supplied XFS images or control quota-enabled XFS setup. Even then, the observed result is resource leakage or mount setup stall, not a demonstrated kernel memory corruption primitive.

The path is not network reachable. It is also not a broad default runtime data path. It is an error/unwind path in a relatively specific XFS quota metadir mount scenario.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource leak, not an Important-class vulnerability. The patch context supports a cleanup bug causing leaked update state and leaked inode references. It does not support arbitrary write, UAF reclaim, type confusion, page-cache corruption, credential exposure, or practical LPE.

The theoretical worst case is a local availability issue if the failure path can be triggered repeatedly or causes mount setup to become stuck. Realistic exploitation evidence remains limited to fault-injection validation and privileged mount setup.

## 5. One-sentence report phrase

XFS quota metadir inode creation can leak metadir update state or inode references on create or commit failure, causing local resource leakage or mount setup stall in privileged quota-enabled mount scenarios.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

Reason: this is a local privileged resource-leak and cleanup-path issue without evidence of UAF, OOB access, arbitrary write, information disclosure, network reachability, or privilege escalation.

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

Patch: xfs: fix memory leak in xfs_dqinode_metadir_create()
Commit: c3d3d2212c2966973dd7d603c6c6e6ed6fc7fbe1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3d3d2212c2966973dd7d603c6c6e6ed6fc7fbe1

Commit description:

If xfs_metadir_create() fails in xfs_dqinode_metadir_create(), the current
code returns directly, leaking the allocated update and transaction state.
If the subsequent commit fails, the caller-owned inode reference is left
behind.

Fix this memory leak by routing the create failure path through
xfs_metadir_cancel().  For both create and commit failures, finish and
release any inode returned to the caller, mirroring the unwind pattern in
xfs_metadir_mkdir().

The bug was first flagged by an experimental analysis tool we are
developing for kernel memory-management bugs while analyzing
v6.13-rc1. The tool is still under development and is not yet publicly
available. Manual inspection confirms that the bug is still
present in v7.1.1.

An x86_64 allyesconfig build showed no new warnings. Runtime validation
used kprobe fault injection during `mount -o uquota` on a metadir XFS
image. Injecting xfs_metadir_create() reproduced the old active-update path
that left mount stuck later in mount setup; after this change, the same
injection reported cancel_hits=1 and irele_hits=1. Injecting
xfs_metadir_commit() exercised the old inode-reference leak path; after
this change, it reported irele_hits=1.

Fixes: e80fbe1 ("xfs: use metadir for quota inodes")
Cc: stable@vger.kernel.org # v6.13
Signed-off-by: Dawei Feng <dawei.feng@seu.edu.cn>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/xfs/libxfs/xfs_dquot_buf.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=c3d3d2212c2966973dd7d603c6c6e6ed6fc7fbe1

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

The original Linux kernel CVE announcement for CVE-2026-64356 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64356

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: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: 0
  Paranoid ActionableScore: 2

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).