[CVE-2026-72437][LOW] md/raid1: free r1_bio when REQ_NOWAIT is set and read would block on retry [ Upstream

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

CVE: CVE-2026-72437
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: md/raid1: free r1_bio when REQ_NOWAIT is set and read would block on retry [ Upstream
Commit: d1eda529a4bf6b866d02755723ee0eb1f037a5ed
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1eda529a4bf6b866d02755723ee0eb1f037a5ed
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72437
Analysis date: Sat, 15 Aug 2026 12:40:18 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72437 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72437

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-2026-72437	LOW	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:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A resource leak in md raid1 can occur when a retried REQ_NOWAIT read reuses a pre allocated r1_bio and wait_read_barrier reports that the operation would block. The bio is completed with a would block error, but the existing r1_bio is not released, so repeated hits can accumulate leaked kernel objects. For the CVSS the PR:L is used because a local user or local process able to issue NOWAIT reads against data backed by md raid1 may reach the affected path without full administrative privileges. The issue is not network reachable and does not provide a direct memory corruption primitive. Impact is denial of service through local resource exhaustion only. For the paranoid score, the highest still defensible interpretation is sustained local availability impact with A:H, while C:N and I:N remain unchanged.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	DISK SIMPLEFIX LEAK LINUS 	NO	NO	checked

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

ActionableScore=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like**

2. Signal breakdown
* Local unprivileged trigger: +1. A local process that can issue NOWAIT reads against data backed by md RAID1 may reach the affected retry path.
* Availability impact realistic: +1. Repeated leaks of r1_bio objects can cause resource exhaustion in a sustained abuse scenario.
* Important filesystem/storage path: +1. md RAID1 is a storage reliability path, but the bug affects an error/retry cleanup path rather than persistent metadata integrity.
* Hard or special triggering conditions: -1. The leak requires REQ_NOWAIT, a retried read with pre allocated r1_bio, and wait_read_barrier returning would block.
* No generic memory corruption signal. The patch fixes a leak, not UAF, double free, OOB write, stale callback, refcount takeover, or attacker controlled object reuse.
* Paranoid score reaches 3 only if sustained repeated triggering is treated as a stronger local resource exhaustion DoS.

3. Reachability analysis
The bug is local and requires access to workloads or files backed by md RAID1 with NOWAIT read behavior. Creating or configuring md RAID1 is privileged, but triggering reads may be possible by an unprivileged local user if they can access a filesystem hosted on the affected array. It is not network reachable by itself. Containers or namespaces do not materially improve reachability unless the container workload has access to storage backed by the host md RAID1 device. The path is configuration dependent and requires a specific retry and barrier condition, so exploitation is not a simple default local crash primitive.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like resource leak. The realistic impact is local availability degradation through accumulated kernel object leaks. There is no supported privilege escalation path and no confidentiality or integrity impact. Theoretical sustained DoS is possible, but the patch does not show memory corruption, ownership bypass, page-cache corruption, or a strong exploit primitive.

5. One-sentence report phrase
A local resource leak in md RAID1 can occur when a retried REQ_NOWAIT read reuses a pre allocated r1_bio and exits on a would block condition without releasing it, allowing sustained local resource exhaustion under specific storage conditions.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is a constrained resource leak without memory corruption, network reachability, privilege escalation evidence, or cross-boundary impact.

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

Patch: md/raid1: free r1_bio when REQ_NOWAIT is set and read would block on retry [ Upstream
Commit: d1eda529a4bf6b866d02755723ee0eb1f037a5ed
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1eda529a4bf6b866d02755723ee0eb1f037a5ed

Changed files:
  drivers/md/raid1.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=d1eda529a4bf6b866d02755723ee0eb1f037a5ed

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

The original Linux kernel CVE announcement for CVE-2026-72437 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72437

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:N/A:L
  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: 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).