[CVE-2026-89576][LOW] dm-era: fix shadowed superblock leak on take-snap failure

[CVE-2026-89576][LOW] dm-era: fix shadowed superblock leak on take-snap failure

[AL-KERNEL]

CVE: CVE-2026-89576
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dm-era: fix shadowed superblock leak on take-snap failure
Commit: d66ceeefb87ddb097b0546bafc581380b816b048
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d66ceeefb87ddb097b0546bafc581380b816b048
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89576
Analysis date: Fri, 11 Sep 2026 21:35:51 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89576 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89576

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-2026-89576	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89576 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-772;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'dm-era can leak one shadow metadata block when metadata_take_snap() fails after dm_tm_shadow_block() succeeds but dm_sm_inc_block() fails for writeset_tree_root or era_array_root. The leak is persistent in the metadata space map, so repeated failures can gradually exhaust metadata space and make the dm-era device fail or become unavailable. For the CVSS the PR:L is used in the paranoid score because a non administrative local workload with access to an already configured dm-era device may be able to exercise the checkpoint path once the failure condition exists, while creating the dm target or forcing the low level metadata error is normally administrative. The issue is not network reachable and does not indicate UAF, OOB access, arbitrary write, or information disclosure. Impact is denial of service through metadata resource exhaustion.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	DISK SIMPLEFIX LEAK ERRORPATH LINUS 	NO	NO	checked

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

ActionableScore=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. metadata_take_snap() allocates a shadow metadata block via dm_tm_shadow_block(), and the failing dm_sm_inc_block() error paths previously returned without returning that block to the metadata space map.
* +1 Availability impact through persistent metadata resource loss. Repeated failed take-snap attempts can gradually exhaust dm-era metadata space and make the dm-era device unavailable.

Negative or non-awarded signals:

* Real UAF not awarded. The patch shows a leaked metadata block, not post-lifetime use of a freed object.
* Concrete repeated release/refcount not awarded. The bug is missing dm_sm_dec_block(), not a second lifetime mutation on an already released reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity impact not awarded. The established consequence is resource loss in dm-era metadata space, not data disclosure or unauthorized modification of another object.
* Remote reachability not established.
* Strong LPE or weak LPE concern not awarded. No memory corruption, ownership bypass, or attacker-controlled post-free primitive is shown.
* Extra availability point not awarded beyond the persistent metadata exhaustion consequence.
* Manual review preserving Class B logic does not apply because there is no UAF, double release, RCU lifetime bug, active-state reinterpretation, or authorization bypass.

3. Reachability analysis

The affected code is in the dm-era device mapper target. Creating or configuring dm targets normally involves host administrative control, but the supplied input does not fully establish whether every practical trigger of metadata_take_snap() after prior setup requires host-admin-equivalent privilege. Therefore HostAdminRequired is UNKNOWN rather than YES.

A prior configured dm-era device is likely needed. The vulnerable path also requires a narrow error condition where dm_tm_shadow_block() succeeds and a later dm_sm_inc_block() for writeset_tree_root or era_array_root fails. This is an ordered error path, not a race. The issue is not network reachable. No namespace-scoped complete trigger chain is established, and device mapper management is not shown to be attacker-obtainable inside namespaces.

4. Primitive and severity interpretation

The exact primitive is a persistent metadata block leak in the dm-era metadata space map. It is not an active structured UAF, not fixed stale storage, and not a cleanup stale dereference. There is no concrete repeated release/refcount operation because the fix adds a missing decrement of the newly allocated shadow block rather than preventing a second decrement.

The demonstrated consequence is local or configuration-dependent denial of service through gradual metadata space exhaustion for the affected dm-era device. The speculative worst case is device unavailability after repeated failures, but the patch does not support kernel memory corruption, privilege escalation, arbitrary read/write, or a broader security-boundary bypass. ImportantCandidate is NO because the established primitive is a resource leak without unresolved corruption leverage. AutoDowngradeAllowed is YES because no meaningful Important-preserving primitive remains unresolved.

5. One-sentence report phrase

dm-era can permanently leak one shadow metadata block on specific metadata_take_snap() failure paths, allowing repeated failures to exhaust dm-era metadata space and cause device-level denial of service.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a persistent metadata resource leak without UAF, double release, memory corruption, authorization bypass, or network reachability.

7. Call-site confidence

Call-site confidence: high

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

Patch: dm-era: fix shadowed superblock leak on take-snap failure
Commit: d66ceeefb87ddb097b0546bafc581380b816b048
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d66ceeefb87ddb097b0546bafc581380b816b048

Commit description:

metadata_take_snap() bumps the live superblock refcount and then
dm_tm_shadow_block() allocates a new block for the metadata snapshot.
If the subsequent dm_sm_inc_block() of writeset_tree_root or
era_array_root fails, the function only unlocks the clone and
returns.  The newly allocated shadow block is never returned to the
metadata space map, so each failed take-snap permanently leaks one
metadata block.

Free the clone with dm_sm_dec_block() on those error paths, matching
the final step of metadata_drop_snap().

Fixes: eec4057 ("dm: add era target")
Cc: stable@vger.kernel.org
Signed-off-by: liyouhong <liyouhong@kylinos.cn>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/md/dm-era-target.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=d66ceeefb87ddb097b0546bafc581380b816b048

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

The original Linux kernel CVE announcement for CVE-2026-89576 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89576

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: 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).