[CVE-2026-64430][LOW] NTB: epf: Avoid calling pci_irq_vector() from hardirq context

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-64430
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: NTB: epf: Avoid calling pci_irq_vector() from hardirq context
Commit: 33bba331a4a5fee8b6026fe72eca13cceeec1b7b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=33bba331a4a5fee8b6026fe72eca13cceeec1b7b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64430
Analysis date: Sat, 25 Jul 2026 09:59:24 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
`ntb_epf_vec_isr could call pci_irq_vector from hardirq context, causing scheduling while atomic warnings and possible availability impact on NTB EPF systems, but the issue is hardware specific and does not show memory corruption or privilege escalation.`

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

The original Linux kernel CVE announcement for CVE-2026-64430 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64430

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64430	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-662;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.7';DESCR 'ntb_epf_vec_isr called pci_irq_vector from hardirq context, and pci_irq_vector can take a mutex through the MSI lookup path. This can trigger scheduling while atomic warnings when NTB EPF interrupts are handled and may cause denial of service or kernel instability, especially on systems configured to panic on such warnings. For the CVSS the PR:L in the paranoid score reflects a specialized deployment where a less privileged local actor or an adjacent NTB peer can provoke NTB interrupt activity after the device has been configured. The issue is not Internet reachable and is tied to PCIe NTB hardware rather than normal network packet processing. Impact is availability only. No confidentiality or integrity impact is supported because the patch shows an invalid sleep in atomic context rather than UAF, OOB access, or another memory corruption primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-64430 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +0
  The patch shows `scheduling while atomic` splats from taking a mutex in hardirq context, but it does not show a guaranteed panic or memory corruption.
* Availability impact realistic: +1
  The issue can cause kernel warnings or instability when NTB EPF interrupts are handled.
* Requires admin/root/device setup in typical deployments: -2
  NTB EPF setup and use normally requires privileged device configuration and specific hardware.
* Physical-only or rare hardware-only condition: -2
  The affected path is tied to PCIe NTB EPF hardware, not a broadly exposed default kernel interface.

Paranoid additional signals:

* Firmware-mediated or adjacent device influence: +1
  A peer NTB endpoint may be able to provoke interrupt activity once the device is configured.
* Reliable kernel crash / strong DoS: +1
  On systems with `panic_on_warn` or strict atomic-context diagnostics, the warning can become a host-impacting DoS.

No memory-corruption signals apply:

* No UAF.
* No OOB access.
* No double free.
* No stale callback.
* No attacker-controlled overwrite.
* No confidentiality or integrity primitive.

Call-site confidence: high. The relevant ISR call path and fixed call site are visible in the patch.

## 3. Reachability analysis

The bug is triggered when `ntb_epf_vec_isr()` handles an NTB EPF interrupt and calls `pci_irq_vector()` from hardirq context. In normal deployments, the NTB EPF device and its MSI/MSI-X setup are controlled by privileged kernel or administrator-managed device configuration. This is not Internet reachable and is not part of a normal packet-processing network path.

A paranoid interpretation allows that an adjacent NTB peer or a less privileged actor in a specialized NTB test or appliance environment may be able to provoke interrupts after setup. That still only reaches an invalid sleep in atomic context, not a memory corruption primitive.

Namespaces and containers generally do not make this broadly reachable unless device access is explicitly delegated.

## 4. Severity interpretation

This behaves like an ordinary Low-like or weak Moderate kernel reliability issue, not an Important-class vulnerability. The realistic impact is availability loss through warning, lockup risk, or panic on systems configured to panic on such diagnostics.

Theoretical impact is limited because the patch fixes an invalid blocking call in hardirq context. There is no evidence of privilege escalation, data disclosure, object lifetime corruption, or attacker-controlled memory corruption.

## 5. One-sentence report phrase

`ntb_epf_vec_isr could call pci_irq_vector from hardirq context, causing scheduling while atomic warnings and possible availability impact on NTB EPF systems, but the issue is hardware specific and does not show memory corruption or privilege escalation.`

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for ordinary environments because the issue is a rare hardware-specific DoS-only atomic-context bug with no demonstrated memory corruption, no confidentiality or integrity impact, and no realistic broad unprivileged reachability.

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

Patch: NTB: epf: Avoid calling pci_irq_vector() from hardirq context
Commit: 33bba331a4a5fee8b6026fe72eca13cceeec1b7b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=33bba331a4a5fee8b6026fe72eca13cceeec1b7b

Commit description:

ntb_epf_vec_isr() calls pci_irq_vector() in hardirq context to derive
the vector number. pci_irq_vector() calls msi_get_virq() that takes a
mutex and can therefore trigger "scheduling while atomic" splats:

  BUG: scheduling while atomic: kworker/u33:0/55/0x00010001
  ...
  Call trace:
   ...
   schedule+0x38/0x110
   schedule_preempt_disabled+0x28/0x50
   __mutex_lock.constprop.0+0x848/0x908
   __mutex_lock_slowpath+0x18/0x30
   mutex_lock+0x4c/0x60
   msi_domain_get_virq+0xe8/0x138
   pci_irq_vector+0x2c/0x60
   ntb_epf_vec_isr+0x28/0x120 [ntb_hw_epf]
   __handle_irq_event_percpu+0x70/0x3a8
   handle_irq_event+0x48/0x100
   handle_edge_irq+0x100/0x1c8
   ...

Cache the Linux IRQ number for vector 0 when vectors are allocated and
use it as a base in the ISR. Running the ISR in a threaded IRQ handler
would also avoid the problem, but that would be unnecessary here.

Fixes: 812ce2f ("NTB: Add support for EPF PCI Non-Transparent Bridge")
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Cc: stable@vger.kernel.org # v5.12+
Link: https://patch.msgid.link/20260304083028.1391068-3-den@valinux.co.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/ntb/hw/epf/ntb_hw_epf.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=33bba331a4a5fee8b6026fe72eca13cceeec1b7b

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

The original Linux kernel CVE announcement for CVE-2026-64430 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64430

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.7

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: 0
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).