[CVE-2026-64053][MODERATE 7.0] block: don't overwrite bip_vcnt in bio_integrity_copy_user() [ Upstream

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

CVE: CVE-2026-64053
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: block: don't overwrite bip_vcnt in bio_integrity_copy_user() [ Upstream
Commit: d18160c9525c63c203656fefd847e94b538cd4a4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d18160c9525c63c203656fefd847e94b538cd4a4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64053
Analysis date: Sun, 19 Jul 2026 16:01:16 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An incorrect `bip_vcnt` overwrite in `bio_integrity_copy_user()` can violate the integrity vector layout invariant and cause block gap-merge checks to read past `bip_vec[]`, making this a local block-layer OOB-read and DoS issue with limited metadata integrity concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64053 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64053

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-2026-64053	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-125;CWE-119;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '5.8';DESCR 'bio_integrity_copy_user() overwrites bip_vcnt with nr_vecs even though bio_integrity_add_page() already sets bip_vcnt to 1 for the bounce segment. On WRITE this can make bip_vcnt greater than bip_max_vcnt and make block gap merge checks read past the bip_vec flex array. On READ the access stays in bounds but can use a saved user bvec instead of the bounce vector, which can cause incorrect integrity metadata handling. For the CVSS the PR:L is used because reliable triggering requires a local process with access to a block device path that accepts user integrity metadata, not full administrator privileges in all deployments. The issue is not network reachable. Impact is primarily local denial of service via invalid kernel memory access, with limited integrity or confidentiality risk considered in the paranoid score because an out-of-bounds read primitive is present.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	IMPROVEONLY  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged or low-privileged trigger: +1. A local process with access to a suitable block device path and user integrity metadata can plausibly reach `bio_integrity_copy_user()`.
* Memory layout invariant restoration: +1. The patch restores consistency between `bip_vcnt` and `bip_max_vcnt` for the integrity payload vector layout.
* Reliable kernel crash / strong DoS: +1. On WRITE, `bip_vcnt > bip_max_vcnt` can make block gap-merge checks read past the `bip_vec[]` flex array.
* Important filesystem/storage path: +1. This is in the block integrity path, affecting storage I/O metadata handling.

Paranoid additional signal:

* Integrity or limited confidentiality concern: +1. The WRITE path has a concrete OOB read, and the READ path may use a saved user bvec instead of the bounce vector, so limited metadata integrity impact is technically defensible even without an OOB write.

Not counted:

* No strong generic memory corruption +2. The demonstrated primitive is an OOB read / wrong-vector use, not OOB write, UAF, double-free, arbitrary write, or type confusion.
* No LPE bonus. There is no demonstrated reclaim, overwrite, callback control, refcount takeover, or arbitrary write.
* No remote/network bonus. This is local block I/O, not network reachable.
* No Dirty-Pipe-like bonus. The patch does not show attacker-controlled writes into page cache or shared file-backed pages.

## 3. Reachability analysis

The bug is locally reachable through block I/O paths that use integrity metadata and `bio_integrity_copy_user()`. Reliable triggering likely requires access to a block device or storage stack configuration that accepts user integrity metadata, so this is not a default attack surface for every unprivileged user. Containers or delegated device access can reduce the practical privilege requirement if the attacker has access to the relevant block device node or storage interface. The affected code is in an important block-layer path, but the required integrity metadata configuration makes exposure narrower than ordinary filesystem reads or writes.

Call-site confidence: medium. The patch and commit describe the downstream gap-merge read past `bip_vec[]`, but the full caller chain and exact user-facing device access policy are not included.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary Low/Moderate bookkeeping bug. The core primitive is a concrete kernel out-of-bounds read caused by an invalid integrity vector count, plus incorrect integrity-vector selection on READ. Realistic impact is primarily local DoS or incorrect integrity metadata handling. Theoretical escalation is not strongly supported because there is no write primitive, UAF, type confusion, or attacker-controlled object replacement shown by the patch.

## 5. One-sentence report phrase

An incorrect `bip_vcnt` overwrite in `bio_integrity_copy_user()` can violate the integrity vector layout invariant and cause block gap-merge checks to read past `bip_vec[]`, making this a local block-layer OOB-read and DoS issue with limited metadata integrity concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not just a resource leak or warning. It is a concrete block-layer OOB read in integrity metadata handling, with storage-path impact and enough ambiguity around reachable device configurations to require manual triage.

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

Patch: block: don't overwrite bip_vcnt in bio_integrity_copy_user() [ Upstream
Commit: d18160c9525c63c203656fefd847e94b538cd4a4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d18160c9525c63c203656fefd847e94b538cd4a4

Changed files:
  block/blk.h
  block/bio-integrity.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=d18160c9525c63c203656fefd847e94b538cd4a4

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

The original Linux kernel CVE announcement for CVE-2026-64053 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64053

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:N/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4
  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).