[CVE-2026-46046][LOW] ext4: fix missing brelse() in ext4_xattr_inode_dec_ref_all()

[CVE-2026-46046][LOW] ext4: fix missing brelse() in ext4_xattr_inode_dec_ref_all()

[AL-KERNEL]

CVE: CVE-2026-46046
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ext4: fix missing brelse() in ext4_xattr_inode_dec_ref_all()
Commit: 1bc1107a3a403a6d440673ed6666f7b07ef868a8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1bc1107a3a403a6d440673ed6666f7b07ef868a8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46046
Analysis date: Wed, 27 May 2026 10:48:53 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missing `brelse()` in ext4 xattr inode cleanup can leak a buffer_head reference under specific filesystem conditions, allowing local resource-pressure DoS only after repeated triggering.

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

The original Linux kernel CVE announcement for CVE-2026-46046 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46046

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-2026-46046	LOW	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:N/A:H';*CWE-772;CWE-404;*CWE-401;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A resource leak can occur in ext4_xattr_inode_dec_ref_all() because ext4_get_inode_loc() obtains iloc.bh but the function did not release it with brelse(). A local user may influence this path through repeated extended attribute cleanup operations on an ext4 filesystem that uses xattr inodes, but reliable triggering depends on filesystem features and the block_csum false case. For the CVSS the PR:L is used because local file and xattr operations may be available to an unprivileged user on files they own. The issue is not network reachable and does not involve UAF, out of bounds access, arbitrary write, information disclosure, or privilege escalation. Impact is denial of service only through buffer_head reference retention or resource pressure after repeated operations.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	DISK SIMPLEFIX LEAK 	YES	NO	checked

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

ActionableScore=2

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user may influence xattr creation/removal or cleanup paths on files they own, if the filesystem supports the relevant ext4 xattr inode configuration.

* Important filesystem/storage path: +1
  The issue is in ext4 xattr inode cleanup and buffer_head lifetime handling.

* Availability impact plausible: +1
  Repeated triggering can retain buffer_head references and cause resource pressure.

Subtracting signals:

* Configuration and path dependent: -1
  The leak depends on ext4 xattr inode handling and the `block_csum == false` case.

* Constrained resource leak only: -1
  The bug is a missing `brelse()` reference drop, not memory corruption or persistent metadata corruption.

No signals apply for remote reachability, UAF, OOB access, arbitrary write, page-cache corruption, confidentiality impact, integrity impact, privilege escalation, or security-boundary bypass.

## 3. Reachability analysis

The reachable path is local ext4 xattr inode cleanup. A local user may trigger related xattr operations on files they control, but reliable exploitation requires the affected ext4 feature set and the specific block checksum condition described in the commit.

Namespaces and containers do not materially increase severity unless they can operate on a host ext4 filesystem with the affected features. The issue is not network reachable.

## 4. Severity interpretation

This behaves like a Low-like local resource leak. It is in an important filesystem subsystem, but the supported impact is only buffer_head reference retention and possible resource pressure after repeated operations.

There is no evidence of memory corruption, metadata corruption, information disclosure, or privilege escalation. Theoretical impact remains DoS-only.

## 5. One-sentence report phrase

A missing `brelse()` in ext4 xattr inode cleanup can leak a buffer_head reference under specific filesystem conditions, allowing local resource-pressure DoS only after repeated triggering.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a constrained ext4 resource leak with local, configuration-dependent reachability and no supported memory corruption or privilege-escalation primitive.

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

Patch: ext4: fix missing brelse() in ext4_xattr_inode_dec_ref_all()
Commit: 1bc1107a3a403a6d440673ed6666f7b07ef868a8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1bc1107a3a403a6d440673ed6666f7b07ef868a8

Commit description:

The commit c8e008b ("ext4: ignore xattrs past end")
introduced a refcount leak in when block_csum is false.

ext4_xattr_inode_dec_ref_all() calls ext4_get_inode_loc() to
get iloc.bh, but never releases it with brelse().

Fixes: c8e008b ("ext4: ignore xattrs past end")
Signed-off-by: Sohei Koyama <skoyama@ddn.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>
Link: https://patch.msgid.link/20260406074830.8480-1-skoyama@ddn.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/ext4/xattr.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=1bc1107a3a403a6d440673ed6666f7b07ef868a8

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

The original Linux kernel CVE announcement for CVE-2026-46046 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46046

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: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: unknown
  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).