[CVE-2026-74306][MODERATE 7.0] vfio/qat: fix f_pos race in qat_vf_resume_write() [ Upstream

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

CVE: CVE-2026-74306
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vfio/qat: fix f_pos race in qat_vf_resume_write() [ Upstream
Commit: 6465af0004dc1b067129a26ef44f19cdf13bbce6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6465af0004dc1b067129a26ef44f19cdf13bbce6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74306
Analysis date: Sat, 15 Aug 2026 19:12:28 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in qat_vf_resume_write() can let concurrent local writers bypass migration-state bounds checks and write past the VFIO/QAT migration buffer, causing kernel memory corruption with realistic DoS impact and plausible privilege-escalation concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74306 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74306

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74306	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-362;*CWE-787;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'qat_vf_resume_write() checked filp f_pos before taking migf lock, then copied user data into the VFIO/QAT migration state buffer after taking the lock and using the shared file position again. Two concurrent local writers can pass the bounds check with an old offset and then one writer can advance f_pos before the other copy, causing an out of bounds write past the migration state buffer. For the CVSS the PR:L is used because an attacker needs local access to the VFIO/QAT migration file or an equivalent VM management context, but this is not full host administrator privilege in many deployments. The issue is not network reachable. Impact is at least local denial of service via kernel memory corruption and in worst case may allow confidentiality or integrity impact due to a kernel out of bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-74306 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB LOCK NOMEMCHK SIMPLEFIX RACE HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local reduced-privilege trigger: +1. Trigger requires local access to the VFIO/QAT migration file or equivalent VM management context, not network access.
* Memory corruption, strong corruption primitive: +2. The race can cause an out-of-bounds write past the migration-state buffer.
* Weak LPE concern: +1. The primitive is a kernel OOB write, but the patch does not show target selection, reclaim control, or a demonstrated privilege-escalation chain.
* Reliable kernel crash / strong DoS: +1. Kernel memory corruption in a VFIO driver path can realistically crash the host.
* Privileged kernel/device-management memory corruption path: +1. The bug is in a trusted VFIO device migration path.
* Availability impact realistic: +1. A host-wide crash is realistic if the OOB write corrupts adjacent kernel state.
* Hard or unreliable race: -1. Two concurrent writers and a timing window are required.
* Rare/configuration-dependent exposure: -1. The issue requires Intel QAT SR-IOV VFIO migration support and access to the migration interface.

Paranoid difference:

* Privilege escalation plausible is raised to +2 instead of +1 because the primitive is a user-influenced kernel OOB write.
* The rare-exposure penalty is not applied in the paranoid score once the affected VFIO/QAT migration path is delegated to a VM management user or service account.

## 3. Reachability analysis

The bug is locally reachable through the VFIO/QAT migration write path. It is not network-triggerable. A normal remote attacker cannot directly reach it unless they already control a VM management component or another local process with access to the VFIO migration file.

Typical deployments restrict VFIO device assignment and migration handling to root, libvirt, QEMU, or a service account. However, such service accounts may be reduced-privilege rather than full host root, so treating this strictly as PR:H would understate practical risk in capability-separated virtualization environments.

Namespaces and containers usually do not make this broadly reachable unless the VFIO device or migration file is explicitly delegated into that environment.

Call-site confidence: high. The patch directly shows the bounds check, shared f_pos use, locking order, and copy boundary issue in the affected write handler.

## 4. Severity interpretation

This is not an ordinary Moderate correctness issue. It is a race-driven kernel out-of-bounds write in a VFIO device migration path.

Realistic impact is likely local DoS or host crash. Theoretical impact includes privilege escalation because attacker-provided data can be copied past the end of a kernel migration-state buffer, but the patch does not demonstrate reliable target control or a complete exploitation primitive.

Overall, this should be treated as Actionable Moderate at minimum and a Strong Important candidate for manual review.

## 5. One-sentence report phrase

A race in qat_vf_resume_write() can let concurrent local writers bypass migration-state bounds checks and write past the VFIO/QAT migration buffer, causing kernel memory corruption with realistic DoS impact and plausible privilege-escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is a race-triggered kernel out-of-bounds write with user-influenced data in a privileged VFIO device-management path, so it should not be auto-closed even though exploitation depends on local VFIO/QAT migration access.

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

Patch: vfio/qat: fix f_pos race in qat_vf_resume_write() [ Upstream
Commit: 6465af0004dc1b067129a26ef44f19cdf13bbce6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6465af0004dc1b067129a26ef44f19cdf13bbce6

Changed files:
  drivers/vfio/pci/qat/main.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=6465af0004dc1b067129a26ef44f19cdf13bbce6

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

The original Linux kernel CVE announcement for CVE-2026-74306 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74306

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:L/UI:N/S:U/C:L/I:L/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: 5
  Paranoid ActionableScore: 7

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).