[CVE-2026-46061][LOW] jbd2: fix deadlock in jbd2_journal_cancel_revoke()

[CVE-2026-46061][LOW] jbd2: fix deadlock in jbd2_journal_cancel_revoke()

[AL-KERNEL]

CVE: CVE-2026-46061
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: jbd2: fix deadlock in jbd2_journal_cancel_revoke()
Commit: dff07cc98fdf6af57a7c054dc09b2050a9d5c287
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dff07cc98fdf6af57a7c054dc09b2050a9d5c287
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46061
Analysis date: Wed, 27 May 2026 14:45:32 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-46061 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46061

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-2026-46061	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-833;CWE-667;CWE-362;BEST CVSS score: '4.7';DESCR 'A lock ordering regression in jbd2_journal_cancel_revoke can cause an ABBA deadlock between the buffer lock and the folio lock when ext4 uses a filesystem block size smaller than the page size. A local process that can create or modify files on the affected filesystem may trigger the issue together with concurrent writeback or sync activity, causing filesystem operations to hang and potentially requiring administrative recovery or reboot. For the CVSS the PR:L is used because reliable triggering only requires local execution with access to the mounted filesystem, not full administrator privileges. The issue is not network reachable by itself and there is no supported memory corruption primitive in this patch context. Impact is denial of service via hung kernel filesystem paths, with C:N and I:N.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	DEADLOCK DISK  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	guess

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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
* Local unprivileged trigger: +1. A local process that can create or modify files on the mounted ext4 filesystem may participate in the triggering workload.
* Availability impact realistic: +1. The bug can cause an ABBA deadlock and hang filesystem or writeback paths.
* Important filesystem/storage path: +1. jbd2/ext4 journaling and writeback are important storage paths.
* Hard or unreliable race / special timing required: -1. The deadlock requires a specific lock ordering race with concurrent writeback or sync activity and blocksize smaller than pagesize.
* Rare or configuration-dependent condition: -1. The described issue depends on filesystem blocksize being smaller than pagesize, which is not the most common default ext4 setup on typical x86 systems.
* No memory corruption signal. No UAF, OOB write, arbitrary write, page-cache corruption, or privilege-escalation primitive is indicated.

3. Reachability analysis
A local user or process with ordinary write/create access to the affected filesystem may trigger the relevant ext4/jbd2 paths, but reliable reproduction also needs concurrent writeback or sync activity. No network reachability is indicated. Containers or namespaces do not materially raise severity unless they can write to an affected host-mounted ext4 filesystem and influence writeback timing. The path is in a common filesystem subsystem, but the vulnerable condition is configuration-dependent.

4. Severity interpretation
This behaves like an ordinary Moderate storage DoS issue, not an Important-class vulnerability. The realistic impact is a filesystem or kernel path hang that may require administrative recovery or reboot. There is no supported evidence of confidentiality impact, integrity corruption, or privilege escalation.

5. One-sentence report phrase
A jbd2 lock ordering regression can cause an ABBA deadlock between folio and buffer locks during ext4 journal revoke handling, allowing a local filesystem workload with concurrent writeback to trigger a denial of service.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is a DoS-only lock ordering bug with no memory corruption or security-boundary bypass primitive shown by the patch context.

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

Patch: jbd2: fix deadlock in jbd2_journal_cancel_revoke()
Commit: dff07cc98fdf6af57a7c054dc09b2050a9d5c287
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dff07cc98fdf6af57a7c054dc09b2050a9d5c287

Commit description:

Commit f76d4c2 ("fs/jbd2: use sleeping version of
__find_get_block()") changed jbd2_journal_cancel_revoke() to use
__find_get_block_nonatomic() which holds the folio lock instead of
i_private_lock. This breaks the lock ordering (folio -> buffer) and
causes an ABBA deadlock when the filesystem blocksize < pagesize:

     T1                                T2
ext4_mkdir()
 ext4_init_new_dir()
  ext4_append()
   ext4_getblk()
    lock_buffer()    <- A
                                   sync_blockdev()
                                    blkdev_writepages()
                                     writeback_iter()
                                      writeback_get_folio()
                                       folio_lock()   <- B
     ext4_journal_get_create_access()
      jbd2_journal_cancel_revoke()
       __find_get_block_nonatomic()
        folio_lock()  <- B
                                     block_write_full_folio()
                                      lock_buffer()   <- A

This can occasionally cause generic/013 to hang.

Fix by only calling __find_get_block_nonatomic() when the passed
buffer_head doesn't belong to the bdev, which is the only case that we
need to look up its bdev alias. Otherwise, the lookup is redundant since
the found buffer_head is equal to the one we passed in.

Fixes: f76d4c2 ("fs/jbd2: use sleeping version of __find_get_block()")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20260409114204.917154-1-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/jbd2/revoke.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=dff07cc98fdf6af57a7c054dc09b2050a9d5c287

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

The original Linux kernel CVE announcement for CVE-2026-46061 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46061

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: Not available
  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).