* [CVE-2026-90219][MODERATE REGULAR] RDMA/cxgb4: Free debugfs on registration failure [ Upstream
@ 2026-09-18 6:38 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 6:38 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90219
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/cxgb4: Free debugfs on registration failure [ Upstream
Commit: 459b59f7ed56511d6529311cb4e5e482ebfcfb8e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=459b59f7ed56511d6529311cb4e5e482ebfcfb8e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90219
Analysis date: Fri, 18 Sep 2026 02:38:38 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90219 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90219
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 REGULAR
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-2026-90219 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90219 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;*CWE-772;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7';DESCR 'RDMA cxgb4 can leave per device debugfs dentries alive when RDMA device registration fails because the failure path calls c4iw_dealloc directly and bypasses the remove path that used to delete debugfs. Those dentries can outlive the freed c4iw_dev object, creating a stale reference pattern and a possible use-after-free candidate if a later debugfs operation reaches data stored under that device tree. For the CVSS the PR:L is used in the paranoid score because a reduced capability administrator, service account, or delegated device management context may be able to trigger driver registration failure or interact with debugfs without being full system root in practical deployments. The issue is local and is not directly network reachable. Impact is at least local denial of service or resource leakage, and in the worst defensible case may include confidentiality and integrity impact due to stale debugfs references to freed kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES LEAK UAF NETWORK HARDWARE DEBUGFS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::
No floor or cap was applied.
2. Signal breakdown
Conservative positive signals:
* +2 Real UAF / lifetime violation: debugfs dentries can outlive the freed `c4iw_dev`, leaving stale post-lifetime debugfs state tied to a freed per-device object.
* +1 Concrete persistent kernel resource/reference leak: the per-device debugfs tree is created but not removed on the registration-failure path that calls `c4iw_dealloc()` directly.
Paranoid additional signal:
* +1 Realistic crash / DoS concern: if the stale debugfs entries remain reachable and a later debugfs operation reaches per-device data, the stale `c4iw_dev` reference can plausibly cause a kernel fault.
Negative signals:
* No host-admin penalty: host-admin-equivalent privilege is not positively established from the supplied evidence, even though driver registration failure and debugfs access may often be privileged in practice.
* No race penalty: the issue is an ordered error-path cleanup/lifetime bug, not a demonstrated narrow timing race.
* No rare-hardware penalty applied: the code is cxgb4 RDMA hardware-specific, but the prompt requires concrete evidence before subtracting merely because this is a driver path.
Important non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary read or arbitrary write not demonstrated.
* Callback or function-pointer control not demonstrated.
* Confidentiality and integrity impact not awarded because stale debugfs references alone do not establish disclosure or unauthorized modification.
* Structured stale-object leverage not awarded because attacker-controlled replacement, attacker-shaped post-free contents, or meaningful field-consumption after reuse is not established.
* Concrete repeated release/refcount signal not awarded. The patch moves `debugfs_remove_recursive()`, but it does not show first release -> exact same reference survives -> second lifetime/refcount mutation.
* Extra availability point not awarded because no distinct availability mechanism beyond possible crash/resource leak is established.
* Strong LPE leverage not awarded because no exploit chain, refcount takeover, controlled reclaim, or directed corruption is shown.
Repeated release/refcount checklist:
* First release can end lifetime: not established for the same exact debugfs-related object reference.
* Exact same reference survives and reaches a second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The vulnerable state is reached when `c4iw_alloc()` creates the per-device debugfs tree and RDMA device registration later fails. The registration worker then takes an error path that calls `c4iw_dealloc()` directly, bypassing `c4iw_remove()` where debugfs cleanup previously lived.
The complete attacker model is unresolved. Triggering the registration-failure path likely depends on cxgb4 RDMA device presence, driver/device state, and possibly privileged device-management conditions. Interacting with debugfs may also be restricted by mount and file permissions. The supplied evidence does not prove ordinary unprivileged reachability, but it also does not positively prove that full host-admin-equivalent privilege is required.
Namespace-scoped privilege is not established. This is not a netns-created object path, and no evidence shows that the full registration-failure plus stale-debugfs access chain can be performed inside attacker-created namespaces.
Prior host setup exists in the practical sense that the system must have the cxgb4 RDMA driver/device path active and debugfs support available. However, this is not scored as a negative because the supplied evidence does not establish a restrictive deployment prerequisite sufficient for a penalty.
No direct network trigger is established. Remote RDMA or network traffic is not shown to reach the vulnerable cleanup path directly. The bug is local/device-management/debugfs lifetime exposure, not packet-processing exposure.
Race repeatability is not relevant. This is not presented as a timing race.
4. Primitive and severity interpretation
The exact primitive is a stale lifetime/reference-management bug: per-device debugfs dentries can survive after the associated `c4iw_dev` has been freed. This is a real Class B lifetime issue because kernel-visible debugfs state may retain access paths associated with an object whose lifetime has ended.
The stale object is an active structured driver object rather than a fixed DMA buffer. However, the supplied patch does not show that an attacker can control the freed object replacement, shape post-free contents, influence callbacks, or direct reads/writes through the stale reference. The demonstrated root cause is therefore stronger than a mere resource leak, but weaker than a proven Important-class exploitation primitive.
This is not a concrete repeated release/refcount case. The fix ensures debugfs cleanup happens from `c4iw_dealloc()`, but the supplied control flow does not show a second `put`, `free`, `kref_put`, or equivalent lifetime mutation through the same dangling reference after an earlier lifetime-ending operation.
PrimitiveClass is CLASS_B because a real lifetime/stale-reference condition is established. It is not CLASS_A because controlled reclaim, arbitrary kernel R/W, callback control, LPE, or a security-boundary bypass is not established. It is not CLASS_C because the problem is not merely an immediate invalid dereference or passive warning. It involves escaping stale debugfs lifetime state.
The demonstrated consequence is resource/reference leakage and possible stale debugfs exposure after device-registration failure. The speculative consequence is a local kernel crash or stronger UAF effect if a later debugfs operation dereferences the stale per-device object after memory reuse. The evidence does not justify scoring confidentiality, integrity, or privilege escalation.
ImportantCandidate is NO because meaningful exploitation leverage beyond stale debugfs lifetime exposure is not established. Manual review is still recommended because leaked debugfs dentries outliving a freed device object are a real kernel lifetime issue and downstream debugfs callbacks should be inspected.
AutoDowngradeAllowed is YES because this is a constrained Class B lifetime cleanup bug with no demonstrated repeated lifetime mutation, controlled reclaim, arbitrary R/W, boundary bypass, or LPE. It should not be treated as a strong Important candidate from the supplied evidence alone.
Likely operational severity: borderline Moderate. It is worth manual review, but the supplied evidence does not support automatic Important classification.
5. One-sentence report phrase
RDMA cxgb4 can leave per-device debugfs entries alive after a registration-failure path frees the associated c4iw_dev, creating stale debugfs state that may lead to local resource leakage or a possible kernel crash if later accessed.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
The stale debugfs tree outliving `c4iw_dev` is a real lifetime issue, but the supplied evidence does not demonstrate controlled reclaim, repeated refcount mutation, arbitrary R/W, privilege escalation, or a concrete non-crash exploitation primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: RDMA/cxgb4: Free debugfs on registration failure [ Upstream
Commit: 459b59f7ed56511d6529311cb4e5e482ebfcfb8e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=459b59f7ed56511d6529311cb4e5e482ebfcfb8e
Changed files:
drivers/infiniband/hw/cxgb4/device.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=459b59f7ed56511d6529311cb4e5e482ebfcfb8e
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90219 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90219
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:H/I:H/A:H
The Best / paranoid CVSS score: 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: 3
Paranoid ActionableScore: 4
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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
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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