[CVE-2026-97593][LOW] iommu/s390: Fix NULL dereference in iova_to_phys() with ZPCI_TABLE_TYPE_RFX

[CVE-2026-97593][LOW] iommu/s390: Fix NULL dereference in iova_to_phys() with ZPCI_TABLE_TYPE_RFX

[AL-KERNEL]

CVE: CVE-2026-97593
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iommu/s390: Fix NULL dereference in iova_to_phys() with ZPCI_TABLE_TYPE_RFX
Commit: d0502ed0a1aae97e2ab7a21545903ba612d9f02e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d0502ed0a1aae97e2ab7a21545903ba612d9f02e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97593
Analysis date: Sat, 26 Sep 2026 14:24:16 -0400
ActionableScore: 0
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-2026-97593 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97593

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-2026-97593	LOW	https://www.kernelcve.org/list/?q=CVE-2026-97593 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:N/I:N/A:H';**CWE-476;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL-pointer dereference in the s390 IOMMU translation path occurs when iova_to_phys processes an unmapped IOVA using a 5-level ZPCI_TABLE_TYPE_RFX table. An invalid region-first entry causes get_rso_from_iova to return NULL, but get_rto_from_iova can dereference that NULL result while looking up the region-second entry. This can crash the host kernel and cause a local denial of service on affected s390 systems with the relevant ZPCI configuration. For the CVSS the PR:L value is used for the paranoid score because delegated device access or a restricted service context may be able to trigger IOVA translation activity without full host administration. Reliable triggering also requires specialized s390 hardware and a matching IOMMU configuration, so AC:H is appropriate. No confidentiality or integrity impact is supported because the observed primitive is a NULL-pointer dereference rather than memory corruption.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	NULLPTR SIMPLEFIX  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: -1
* Paranoid score: 0
* Applied score lower bound: -1 -> 0
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash or strong DoS. The missing NULL check deterministically dereferences a NULL region-second origin pointer when iova_to_phys reaches an unmapped IOVA through the affected RFX or RSX table path.
* -2 Physical-only or rare hardware requirement. The vulnerable path requires IBM s390 hardware using zPCI IOMMU translation with the 5-level ZPCI_TABLE_TYPE_RFX configuration. This is a concrete architecture and hardware-specific prerequisite from the patch context.
* No local unprivileged trigger awarded. The supplied patch does not establish that an ordinary local user can create the required IOMMU domain, submit the relevant IOVA lookup, or control a device path that invokes iova_to_phys.
* No remote reachability awarded. The operation is an internal IOMMU translation lookup and no network-facing call path is shown.
* No corruption primitive awarded. The dereference is a NULL-pointer read/access fault, not a UAF, OOB access, arbitrary write, refcount mutation, or ownership violation.
* No confidentiality or integrity points awarded. There is no patch-supported disclosure, unauthorized modification, DMA ownership violation, or active mapping corruption.
* No additional availability point awarded. The same NULL dereference already accounts for the single crash or DoS signal.
* No privilege penalty awarded. Host-admin-equivalent privilege is not positively established by the supplied evidence, so HostAdminRequired remains UNKNOWN rather than YES.

3. Reachability analysis

The visible trigger is an internal call to iova_to_phys on an unmapped IOVA in an s390 IOMMU domain using the affected five-level zPCI translation-table mode. The immediate cause is an invalid region-first entry, which makes get_rso_from_iova return NULL before get_rto_from_iova indexes rso[rsx].

The supplied patch does not show the external caller, device assignment path, IOMMU-domain setup operation, or capability checks needed to reach this lookup. Therefore, it does not establish whether the complete trigger is available to an ordinary user, a delegated device-management service, a VM guest, or only a host administrator. HostAdminRequired is UNKNOWN.

No namespace-scoped capability analysis can be completed from this patch. The existence of an IOMMU domain or a possible delegated-device deployment does not prove that all required operations are available in an attacker-controlled namespace. NamespaceScopedPrivilege is UNKNOWN.

The path requires s390 zPCI support and an affected RFX translation-table configuration. This is a specialized hardware and configuration prerequisite, not a broadly exposed default kernel path. No race is involved.

4. Primitive and severity interpretation

The exact primitive is an invalid NULL-pointer dereference. get_rso_from_iova can return NULL for an invalid region-first entry, and get_rto_from_iova subsequently accesses rso[rsx] without first checking rso. The demonstrated consequence is a kernel fault or crash when the relevant internal translation lookup is reached.

This is neither an active structured-object UAF nor fixed stale storage. No object is freed, no stale reference survives a lifetime transition, and no repeated release, put, refcount decrement, or post-free mutation occurs. RealUAF is therefore NO.

The patch establishes a crash-only invalid-state condition. It does not establish controlled memory corruption, controlled DMA, a stale translation remaining active, arbitrary read or write, information disclosure, privilege escalation, or an authorization-boundary bypass. The primitive is CLASS_C.

ImportantCandidate is NO because no meaningful exploitation leverage beyond a NULL-pointer crash is established. AutoDowngradeAllowed is YES because the issue is constrained to a specialized IOMMU lookup path and no unresolved kernel-corruption or security-boundary primitive remains.

Likely operational severity is low to ordinary Moderate. Systems without affected s390 zPCI hardware or without the RFX translation-table mode are not exposed to this specific path.

5. One-sentence report phrase

A missing NULL check in the s390 zPCI IOMMU five-level translation path can dereference a NULL region table pointer for an unmapped IOVA and cause a kernel crash on affected systems.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch demonstrates a constrained NULL-pointer dereference with crash-only impact and does not establish a UAF, memory corruption, privilege-boundary bypass, or attacker-controlled kernel-state primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: iommu/s390: Fix NULL dereference in iova_to_phys() with ZPCI_TABLE_TYPE_RFX
Commit: d0502ed0a1aae97e2ab7a21545903ba612d9f02e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d0502ed0a1aae97e2ab7a21545903ba612d9f02e

Commit description:

When using a 5-level translation table via ZPCI_TABLE_TYPE_RFX
get_rso_from_iova() returns NULL when the region-first entry is invalid.
Yet in get_rto_from_iova() the region-second origin rso is not checked
to be non-NULL before accessing rso[rsx] leading to a NULL pointer
dereference instead of a NULL return when iova_to_phys() is called on
a unmapped IOVA. Fix this by adding the missing NULL check.

Cc: stable@vger.kernel.org
Fixes: 8124407 ("iommu/s390: allow larger region tables")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/iommu/s390-iommu.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=d0502ed0a1aae97e2ab7a21545903ba612d9f02e

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

The original Linux kernel CVE announcement for CVE-2026-97593 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97593

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: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: 0

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).