From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-89558][MODERATE 7.0] md/raid10: fix still_degraded being inverted in raid10_sync_request()
Date: Sat, 12 Sep 2026 00:52:05 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-89558
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: md/raid10: fix still_degraded being inverted in raid10_sync_request()
Commit: 9bb8da6ecb330a5b1ac9b96f1e55f134a7aef1d4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9bb8da6ecb330a5b1ac9b96f1e55f134a7aef1d4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89558
Analysis date: Sat, 12 Sep 2026 00:52:05 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89558 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89558
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: MODERATE 7.0
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89558 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89558 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:H/A:H';CWE-682;CWE-670;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.3';DESCR 'A logic error in md/raid10 recovery can clear bitmap bits too early when one mirror is being recovered while another mirror is still missing. A later re add of the missing device can then skip regions written while the array was degraded, causing the device to be marked In_sync while it still contains stale data. This is silent storage corruption rather than a kernel memory corruption bug. For the CVSS the PR:L is used for the paranoid score because a reduced capability storage admin, container root, or service account with md control could trigger recovery operations without full host administration. The issue is not directly network reachable. Impact is high integrity loss and possible availability impact through corrupted filesystems or application data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES DISK WARNONLY HARDWARE LINUS KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed the score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2: Persistent storage integrity primitive. The RAID10 bitmap can incorrectly clear regions that a still-missing device later needs for recovery, causing stale data to be marked In_sync.
* +1: Integrity impact. The supplied reproducer shows silent data corruption and differing file contents after degraded writes and recovery.
* +1: Important storage path. md/raid10 recovery and bitmap-based resync protect persistent block-device data.
* +1: Practical demonstrated corruption chain. The commit describes a concrete sequence ending in mismatch_cnt and stale recovered data.
* +1: Availability impact from persistent corrupted storage state. Corrupted filesystems or application data can create operational unavailability beyond a transient kernel error.
* -2: Host-admin-equivalent md control is required for the direct reproducer: failing/removing/re-adding RAID devices and driving recovery.
Paranoid difference:
* -1 instead of -2: The supplied hint reasonably treats delegated storage administration, reduced-capability root, or a service account with md control as a plausible practical attacker role below full host administration.
Non-awarded signals:
* RealUAF not awarded. No memory lifetime violation is shown.
* Controlled kernel memory corruption not awarded. The bug corrupts persistent storage recovery state, not kernel heap or object memory.
* Arbitrary write not demonstrated.
* Remote reachability not established.
* Local unprivileged trigger not established.
* Namespace-scoped privilege not established.
* Privilege escalation not demonstrated.
* Reliable kernel crash not awarded. The main demonstrated outcome is silent persistent data corruption, not panic.
* No repeated release/refcount operation exists.
3. Reachability analysis
The direct trigger requires control over md RAID10 device state: failing and removing disks, writing while degraded, and re-adding devices so bitmap-based recovery runs. That is normally host-root or host CAP_SYS_ADMIN level storage administration, so HostAdminRequired=YES for the direct kernel interface.
The supplied prior analysis gives a defensible paranoid deployment model where a reduced storage administrator, container root with delegated block-device control, or service account controlling md recovery could trigger the sequence without being full host admin. That supports a higher paranoid ActionableScore, but it does not prove ordinary unprivileged reachability.
No network trigger is established. No namespace-scoped complete trigger chain is established. No special rare hardware is required beyond an md/raid10 setup with an internal bitmap and the relevant degraded recovery sequence. This is not a race in the usual timing-window sense; it is an ordered logic error in degraded-state bookkeeping.
4. Primitive and severity interpretation
The exact primitive is a RAID10 recovery logic error: `still_degraded` is inverted, so `md_bitmap_start_sync()` can be called as if the array is no longer degraded while another mirror member is still missing. This prematurely clears bitmap bits needed by the later-returning device.
This is not a UAF, not an OOB access, not a refcount bug, and not a kernel memory corruption primitive. It is a persistent storage integrity violation: a device can be marked In_sync while holding stale data. The demonstrated consequence is silent data corruption with possible downstream filesystem or application data damage.
PrimitiveClass=CLASS_A is used because the patch establishes a strong persistent storage integrity primitive, not merely a crash or warning. ImportantCandidate=YES because silent data corruption in md/raid10 recovery should not be automatically downgraded despite the likely administrative trigger. AutoDowngradeAllowed=NO because automatic closure would miss a concrete high-integrity persistent-data corruption issue.
Operationally, this is at least Actionable Moderate. It can become Important in environments where md management is delegated to less-trusted automation or service roles, or where the affected RAID10 configuration protects high-value production data.
5. One-sentence report phrase
A RAID10 degraded-recovery logic error can prematurely clear bitmap regions and later mark a re-added device In_sync while it still contains stale data, causing silent persistent storage corruption.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the issue is not memory corruption or remote code execution, but it has a concrete silent data corruption primitive in an important storage recovery path and should not be auto-closed based only on administrative trigger requirements.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: md/raid10: fix still_degraded being inverted in raid10_sync_request()
Commit: 9bb8da6ecb330a5b1ac9b96f1e55f134a7aef1d4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9bb8da6ecb330a5b1ac9b96f1e55f134a7aef1d4
Commit description:
Commit fe6a19d ("md/md-bitmap: merge md_bitmap_start_sync() into
bitmap_operations") converted still_degraded from int to bool, but
inverted the assignment in the loop that checks whether the array will
still be degraded after the current device is recovered:
"still_degraded = 1" became "still_degraded = false".
As a result, recovering a device while another mirror is still missing
calls md_bitmap_start_sync() with degraded == false, which clears bitmap
bits that the still-missing device needs. When that device is re-added,
its bitmap-based recovery finds the bits already cleared and skips every
region written while the array was degraded, so it is marked In_sync
while holding stale data: silent corruption.
Reproducer (raid10 near=2, 4 disks, internal bitmap):
- fail and remove one disk of each mirror pair
- write to the degraded array
- re-add both disks and let recovery finish
- "check" reports mismatch_cnt=262272 after 256 MiB of degraded
writes and file contents differ; the second disk's "recovery"
completes in milliseconds because everything is skipped
The same conversion in raid1 got it right (still_degraded = true).
Restore the correct value.
Fixes: fe6a19d ("md/md-bitmap: merge md_bitmap_start_sync() into bitmap_operations")
Cc: [email protected]
Signed-off-by: Yunye Zhao <[email protected]>
Reviewed-by: Mykola Marzhan <[email protected]>
Reviewed-by: Paul Menzel <[email protected]>
Reviewed-by: Yu Kuai <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Yu Kuai <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/md/raid10.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=9bb8da6ecb330a5b1ac9b96f1e55f134a7aef1d4
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89558 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89558
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:H/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
The Best / paranoid CVSS score: 6.3
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: 4
Paranoid ActionableScore: 5
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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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