[CVE-2026-97993][LOW] vhost-vdpa: don't install the eventfd_ctx_fdget() error in config_ctx [ Upstream

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

CVE: CVE-2026-97993
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: vhost-vdpa: don't install the eventfd_ctx_fdget() error in config_ctx [ Upstream
Commit: 388c678639a0cebfd936b3e56c64ac6a371efec2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=388c678639a0cebfd936b3e56c64ac6a371efec2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97993
Analysis date: Sat, 26 Sep 2026 13:54:30 -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-2026-97993 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97993

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-2026-97993	LOW	https://www.kernelcve.org/list/?q=CVE-2026-97993 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-362;**CWE-476;CWE-252;BEST CVSS score: '4.7';DESCR 'A race in vhost_vdpa_set_config_call can temporarily install an ERR_PTR returned by eventfd_ctx_fdget into config_ctx. If a device configuration interrupt arrives in this window, vhost_vdpa_config_cb can pass the invalid pointer to eventfd_signal and cause a kernel crash. For the CVSS the PR:L because an attacker needs local access to a vhost vdpa device interface and must issue the relevant ioctl. Exploitation also requires precise timing of a concurrent configuration interrupt, so AC:H is appropriate. The issue is not directly network reachable. Impact is denial of service through a host kernel crash. The patch context does not demonstrate a use after free, out of bounds access, information leak, or write primitive that would support privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	HARDWARE LINUS TEST  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	guess

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

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

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

The patch establishes a narrow invalid-pointer crash path, but does not establish a UAF, post-free reuse, refcount mutation, attacker-controlled overwrite, disclosure, authorization bypass, or privilege-escalation primitive.

2. Signal breakdown

Positive signals:

* +1 Reliable kernel crash or strong DoS. An ERR_PTR returned by eventfd_ctx_fdget can temporarily be stored in config_ctx. A concurrent configuration callback checks only for non-NULL and can pass the ERR_PTR to eventfd_signal, plausibly causing a host kernel Oops or panic.

Negative signals:

* -1 Hard or unreliable race. The invalid ERR_PTR exists only between swap and the later error cleanup. A configuration interrupt must arrive during this very narrow interval.

Important non-awarded signals:

* +0 Real UAF. No object is freed while a stale reference remains in use. The invalid value is an ERR_PTR returned by eventfd_ctx_fdget.
* +0 Strong or weak exploitation leverage. The pointer value is an error pointer derived from a failed file descriptor lookup, not a reclaimed or attacker-shaped active kernel object.
* +0 Controlled reclaim or object replacement. Not demonstrated.
* +0 Arbitrary or directed kernel write. Not demonstrated.
* +0 Confidentiality or integrity impact. No disclosure, write, ownership violation, or security-policy modification is established.
* +0 Remote reachability. The vulnerable operation is a local vhost-vdpa ioctl and callback path. Network traffic does not directly reach it.
* +0 Local unprivileged trigger. Access controls for the complete vhost-vdpa device and ioctl sequence are not established by the supplied patch.
* +0 Extra availability impact. The same potential kernel crash is counted once and no independent persistent availability consequence is demonstrated.

3. Reachability analysis

The evaluated attacker is a local userspace process that can access the relevant vhost-vdpa instance and issue vhost_vdpa_set_config_call with an invalid or closed eventfd file descriptor. The attacker must also cause or coincide with a device configuration interrupt during the brief interval after config_ctx is replaced with an ERR_PTR and before it is cleared.

The patch does not establish whether the required vhost-vdpa file descriptor is available to an ordinary user, a delegated virtualization service account, a VMM process, or only a host administrator. Therefore HostAdminRequired is UNKNOWN. The patch also does not show that all required operations can be performed from an attacker-created namespace, so NamespaceScopedPrivilege is UNKNOWN.

A vDPA device and vhost-vdpa instance must already exist or be provisioned. This may be a meaningful deployment prerequisite, but the supplied evidence does not establish that it necessarily requires host-admin privilege for the attacker. No special physical hardware requirement is proven because vDPA can be implemented by hardware or software-backed devices. The race is narrow because it depends on asynchronous configuration interrupt timing during a small error-handling window.

4. Primitive and severity interpretation

The exact primitive is temporary publication of an invalid ERR_PTR as config_ctx. The callback treats every non-NULL config_ctx as a valid eventfd context and sends the invalid pointer to eventfd_signal. This is an invalid-pointer dereference and a crash-capable invalid-state bug.

This is neither active structured-object UAF nor fixed stale storage. No object lifetime ends before a stale reference is consumed. No concrete repeated release, put, free, or refcount operation exists. The old valid eventfd context can be released after a failed replacement attempt, causing configuration interrupts to stop, but this is a functional availability failure rather than a second mutation through a dangling reference.

PrimitiveClass is CLASS_C because the established behavior is crash or DoS through an invalid pointer. The demonstrated consequence is host kernel crash or device configuration interrupt loss. A stronger consequence such as controlled memory corruption, disclosure, integrity impact, or privilege escalation is speculative and unsupported by the patch. ImportantCandidate is NO and AutoDowngradeAllowed is YES because no meaningful unresolved corruption or lifetime primitive remains after excluding the crash.

Likely operational severity is low to ordinary Moderate depending on actual device exposure and whether a less-privileged VMM or service account can access the affected interface.

5. One-sentence report phrase

A narrow race in vhost_vdpa_set_config_call can publish an eventfd ERR_PTR as config_ctx, allowing a concurrent configuration interrupt callback to pass the invalid pointer to eventfd_signal and crash the host kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the permissions on the deployed vhost-vdpa device node and determine whether a non-host-admin VMM or service account can issue the affected ioctl and influence configuration interrupt timing.

7. Call-site confidence

Call-site confidence: medium

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

Patch: vhost-vdpa: don't install the eventfd_ctx_fdget() error in config_ctx [ Upstream
Commit: 388c678639a0cebfd936b3e56c64ac6a371efec2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=388c678639a0cebfd936b3e56c64ac6a371efec2

Changed files:
  drivers/vhost/vdpa.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=388c678639a0cebfd936b3e56c64ac6a371efec2

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

The original Linux kernel CVE announcement for CVE-2026-97993 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97993

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: Not available
  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).