* [CVE-2026-90396][LOW] block: fix dio leak on metadata mapping error [ Upstream
@ 2026-09-17 22:34 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-17 22:34 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90396
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: block: fix dio leak on metadata mapping error [ Upstream
Commit: d29c5a88d5703afb6286038e86e1b88daa4962a9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d29c5a88d5703afb6286038e86e1b88daa4962a9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90396
Analysis date: Thu, 17 Sep 2026 18:34:13 -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-2026-90396 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90396
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-2026-90396 LOW https://www.kernelcve.org/list/?q=CVE-2026-90396 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A DIO reference leak in the block direct I/O path can occur when bio_integrity_map_iter fails while IOCB_HAS_METADATA is set. The failed integrity metadata mapping can leave a bio with an extra dio reference instead of completing it through the normal bio end path, which can hang or leak direct I/O state when earlier bios in the same sequence were already submitted. For the CVSS the PR:L is used because an attacker needs local code execution and access to issue direct I/O with metadata to an affected block device, but full administrative privileges are not inherent if such device access is delegated. The issue is not network reachable. Impact is denial of service through hung I/O or resource leakage, with no supported path to information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES SIMPLEFIX LEAK INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
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. The commit states that a failed integrity mapping holds a DIO reference and the old error path skipped the normal bio ending path.
* +1 Important storage path. The bug is in block direct I/O handling with integrity metadata, which is an important kernel storage path.
Negative or non-awarded signals:
* RealUAF not awarded. The patch establishes a leaked reference, not a use-after-free or stale post-lifetime object use.
* Concrete repeated release/refcount not awarded. The issue is missing completion/release of a held DIO reference, not a second put/release on the same dangling reference.
* Reliable kernel crash not awarded. The supplied evidence supports DIO reference leak or hung I/O state, not a kernel panic.
* Extra availability not awarded. Resource leakage or hung I/O is the consequence of the same missing bio completion and is not counted again as an independent signal.
* Confidentiality and integrity not awarded. No disclosure, unauthorized write, ownership violation, or privilege escalation primitive is established.
* Controlled reclaim, arbitrary write, OOB access, and semantic reinterpretation are not demonstrated.
* Remote reachability not established. This is a local block I/O path, not a network-triggered path.
* Manual Important-grade review signal not awarded. The primitive is resource/reference leak only, without memory corruption or security-boundary bypass.
3. Reachability analysis
The trigger requires a local process that can issue direct I/O with integrity metadata on an affected block device or file path using the block direct I/O path. Ordinary unprivileged reachability is not fully established from the supplied patch because access to suitable block devices and metadata-capable I/O may depend on local permissions and deployment. Host-admin-equivalent privilege is also not positively established, so HostAdminRequired is UNKNOWN rather than YES.
The issue is not namespace-scoped in the relevant sense. No evidence shows that an attacker-created namespace provides the complete required access to an affected metadata-capable block I/O path. Prior setup may be needed in practice, such as a block device and stack supporting integrity metadata, but the prompt does not establish a rare or physical-only prerequisite strong enough for a scoring penalty. There is no race requirement.
4. Primitive and severity interpretation
The exact primitive is a missing normal completion path after bio_integrity_map_iter fails while IOCB_HAS_METADATA is set. The failed integrity mapping holds a DIO reference, and skipping bio_endio_status can leave the DIO state unreleased when earlier bios in the sequence were already submitted.
This is not active structured UAF and not fixed stale storage. It is a resource/reference leak in the block direct I/O completion path. There is no concrete repeated release/refcount mutation. The first operation does not free an object followed by a second lifetime mutation on the same dangling reference.
PrimitiveClass is CLASS_C because the demonstrated behavior is primarily DoS or invalid completion state without an independently useful corruption primitive. Demonstrated consequence is local hung I/O or resource leakage. Speculative consequence would be broader resource exhaustion under repeated triggering, but no memory corruption, LPE, or data exposure is supported. ImportantCandidate is NO because the patch does not establish meaningful exploitation leverage beyond resource/reference leak. AutoDowngradeAllowed is YES because this can be handled as ordinary Moderate or Low-like triage unless separate evidence shows a stronger consequence.
5. One-sentence report phrase
A block direct I/O metadata mapping error can leak a DIO reference by skipping the normal bio completion path, causing local hung I/O or resource leakage when an attacker can issue suitable metadata direct I/O, with no evidence of memory corruption or privilege escalation.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: this is a local resource/reference leak in a storage I/O error path, with no UAF, no repeated stale refcount mutation, no controlled corruption, no security-boundary bypass, and no demonstrated LPE.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: block: fix dio leak on metadata mapping error [ Upstream
Commit: d29c5a88d5703afb6286038e86e1b88daa4962a9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d29c5a88d5703afb6286038e86e1b88daa4962a9
Changed files:
block/fops.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=d29c5a88d5703afb6286038e86e1b88daa4962a9
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90396 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90396
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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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