[CVE-2026-98217][MODERATE 7.0] IB/mlx4: Fix use-after-free on pkey sysfs registration failure

[CVE-2026-98217][MODERATE 7.0] IB/mlx4: Fix use-after-free on pkey sysfs registration failure

[AL-KERNEL]

CVE: CVE-2026-98217
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: IB/mlx4: Fix use-after-free on pkey sysfs registration failure
Commit: 791471421d848ce13e84f4b21c9e19973d471c4e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=791471421d848ce13e84f4b21c9e19973d471c4e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98217
Analysis date: Fri, 09 Oct 2026 07:15:39 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98217 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98217

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-2026-98217	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98217 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC)	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-672;CWE-415;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur in the IB mlx4 pkey sysfs registration path when register_one_pkey_tree() fails for one slave. The error path releases the pkey parent kobjects but leaves their pointers stored in the device, while registration continues for the remaining slaves. A later device cleanup can pass one of these stale pointers to kobject_put(), causing a second operation on an object that may already have been freed or reused. The demonstrated impact is at least a local denial of service through a kernel crash. Because this is a real stale pointer and lifetime violation, allocator reuse may also permit confidentiality or integrity impact in a worst case scenario and requires manual review. For the CVSS the PR:L value in the paranoid score applies when a local user, container, or service account has delegated control over an RDMA device, VF, or device lifecycle. Typical systems without such delegation instead require administrative privileges and are better represented by PR:H. AC:H applies because exploitation depends on a pkey sysfs registration failure followed by later device cleanup. The issue is not directly network reachable and requires an affected mlx4 device and the vulnerable registration path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	ERRORPATH UAF NETWORK HARDWARE LINUS KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* Applied conservative floor: 4 -> 5 under the REAL UAF FLOOR 5 rule for a concrete second lifetime mutation on the same potentially dangling reference.
* No cap or other floor changed the paranoid score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF and lifetime violation. The registration failure path drops the parent kobject references but leaves their addresses stored in the device.
* +1 Concrete repeated release or refcount operation. Later device cleanup passes the same stored references to kobject_put(), performing another lifetime mutation after the earlier puts may have destroyed the objects.
* +1 Reliable kernel crash or strong DoS. A second kobject_put() through a dangling pointer can access or modify freed kobject storage and plausibly cause an Oops or kernel crash.
* 0 Privilege penalty. The supplied evidence does not establish either host-admin-only triggering or a complete below-host-admin trigger.
* 0 Hardware penalty. An affected mlx4 device is required, but the evidence does not establish that the hardware is sufficiently rare or physical-only to justify a numeric penalty.

Paranoid-only signal:

* +1 Unresolved post-free refcount corruption. The second kobject_put() itself performs a write-like refcount or lifetime mutation through storage whose original object lifetime may already have ended. This is based on the concrete stale operation, not generic allocator-reuse speculation.

Repeated-release checks:

* The first release can end lifetime: yes. kobject_put() may invoke the release path when the reference count reaches zero.
* The exact references survive: yes. The released pointers remain in dev_ports_parent[slave] and pkeys.device_parent[slave].
* The second operation is lifetime-mutating: yes. Device cleanup performs another kobject_put() on the stored stale references.
* Concrete repeated release or refcount +1: awarded.
* Paranoid repeated-refcount leverage +1: awarded because the stale operation itself can modify lifetime metadata after object destruction.
* FLOOR 5: applied to the conservative score.
* Structured stale-object leverage: not separately awarded. No distinct stale field consumption beyond the repeated kobject lifetime mutation is established.
* Weak LPE: not separately awarded for the same repeated-release fact.
* Controlled reclaim, refcount takeover, callback control, arbitrary read or write, disclosure, and demonstrated LPE: not established.
* Additional Availability: not awarded because it would double-count the same potential kernel crash.
* Confidentiality and Integrity: not awarded merely from theoretical reuse of the freed kobject.
* Remote reachability: not established.
* B5-R retry-accumulated heap OOB: not applicable. The patch establishes no OOB write, retry-accumulated index, or later consumption of OOB-corrupted descriptor state.

3. Reachability analysis

The vulnerable sequence requires an affected mlx4 RDMA device, failure while registering a per-slave pkey sysfs tree, continued best-effort registration, and later device cleanup. The supplied evidence does not establish that an ordinary user, container, or namespace-scoped actor can force the registration failure and subsequent cleanup.

The previous PR:L hypothesis based on delegated RDMA, VF, or device-lifecycle control is possible in some deployments but is not proven for the complete sequence. Conversely, the patch does not positively establish that host-admin-equivalent privilege is mandatory. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN, with no privilege penalty or local-unprivileged bonus.

Prior device provisioning and mlx4 hardware are prerequisites. This is an ordered error-path and cleanup sequence, not a timing race. No race penalty applies.

4. Primitive and severity interpretation

The exact primitive is a stale post-lifetime kobject reference followed by a second kobject_put(). The affected kobject is an active structured kernel object, but the demonstrated stale use is specifically a cleanup-time lifetime operation.

This is category B rather than an ordinary stale cleanup read. The first kobject_put() sequence can destroy the object, the exact pointer remains stored, and later cleanup performs another refcount or lifetime mutation through that potentially dangling pointer.

The primitive is CLASS_B, not CLASS_A. Controlled reclaim, attacker-shaped replacement contents, directed corruption, callback influence, or a completed privilege-escalation chain is not demonstrated. The practical supported consequence is kernel crash or DoS. The theoretical consequence is post-free refcount corruption with unresolved exploitation leverage.

ImportantCandidate is YES because a concrete repeated lifetime mutation remains unresolved and should not be collapsed into an ordinary cleanup crash. AutoDowngradeAllowed is NO for the same reason. The likely operational severity is Actionable Moderate, with Important classification requiring manual analysis of kobject allocation, release callbacks, slab reuse, and actual trigger privileges.

5. One-sentence report phrase

A failed mlx4 pkey sysfs registration can leave freed parent kobject pointers stored in the device, allowing later cleanup to perform a second kobject_put() on potentially freed storage and requiring manual exploitation-leverage review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a real UAF and a concrete second refcount or lifetime mutation on the exact stale references, while trigger privileges and post-free exploitation leverage remain unresolved.

7. Call-site confidence

Call-site confidence: high

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

Patch: IB/mlx4: Fix use-after-free on pkey sysfs registration failure
Commit: 791471421d848ce13e84f4b21c9e19973d471c4e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=791471421d848ce13e84f4b21c9e19973d471c4e

Commit description:

register_pkey_tree() ignores errors from register_one_pkey_tree() and
continues registering the remaining slaves. The per-slave error path has
already released the pkey parent kobjects, but their pointers remain
stored in the device. A later device cleanup therefore passes the stale
pointers to kobject_put(), causing a use-after-free.

Clear the parent pointers after releasing a failed slave tree and skip
unregistered trees during device cleanup. This preserves the existing
best-effort registration behavior while preventing a second cleanup of
the failed tree.

Fixes: c1e7e46 ("IB/mlx4: Add iov directory in sysfs under the ib device")
Cc: stable@vger.kernel.org
Signed-off-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
Link: https://patch.msgid.link/20260816044510.3848996-1-shuangpeng.kernel@gmail.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/hw/mlx4/sysfs.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=791471421d848ce13e84f4b21c9e19973d471c4e

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

The original Linux kernel CVE announcement for CVE-2026-98217 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98217

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:H
  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: unknown
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).