[CVE-2026-72370][LOW] iomap: release pages on atomic dio size mismatch [ Upstream

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

CVE: CVE-2026-72370
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: iomap: release pages on atomic dio size mismatch [ Upstream
Commit: 27ddd3442fc6f698fb8577c7cfb243ddd81ea8c0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=27ddd3442fc6f698fb8577c7cfb243ddd81ea8c0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72370
Analysis date: Sat, 15 Aug 2026 08:53:08 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like, autoclose candidate
Manual review required: YES

Summary:
An iomap atomic direct I/O error path can fail to release pages attached to a short bio rejected by the REQ_ATOMIC size check, allowing a local process with access to a suitable filesystem to cause resource exhaustion through repeated failed writes.

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

The original Linux kernel CVE announcement for CVE-2026-72370 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72370

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-72370	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-772;*CWE-401;**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 'An iomap direct I/O error path can leak pages attached to a bio when an atomic direct write builds a short bio and is rejected by the REQ_ATOMIC size check before submission. The leaked page references can accumulate across repeated failed atomic direct I/O attempts and may cause memory pressure or resource exhaustion. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to a writable file and an environment where atomic direct I/O is supported. The issue is not network reachable and does not provide an apparent read, write, or UAF primitive. Impact is denial of service only via resource exhaustion.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like, autoclose candidate (with actual score 2)  SKIP CVE-2026-72370 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 9e0933c21c128d6d8ac4d8aae0babaf9a43100b8 YES  NO NO unknown 	MAYBE	DISK WARNONLY SIMPLEFIX ERRORPATH IMPROVEONLY LINUS 	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like, autoclose candidate**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process with write access to a suitable file may be able to issue atomic direct I/O if the filesystem and block device support it.
* Important filesystem/storage path: +1. The bug is in iomap direct I/O and affects bio page handling.
* Availability impact realistic: +1. Leaked page references can accumulate and create memory pressure or resource exhaustion.
* Hard or special conditions required: -1. Triggering requires REQ_ATOMIC, direct I/O, a short bio after pages were attached, and rejection before submission.
* Rare or configuration-dependent exposure: -1. Atomic write support is not a broad default path on all filesystems and storage devices.

Paranoid additional signal:

* Stronger sustained DoS interpretation: +1. Repeated failed atomic direct I/O attempts could pin enough pages to cause meaningful system memory pressure.

No memory corruption signals applied:

* No UAF.
* No double free.
* No OOB write.
* No arbitrary write.
* No page-cache ownership or COW bypass.
* No privilege escalation primitive shown.

## 3. Reachability analysis

The bug is locally reachable through atomic direct I/O on a writable file, but only when the underlying filesystem and storage stack support atomic writes. No network reachability is indicated. Namespaces or containers do not inherently make this remote, but an unprivileged container workload with access to a suitable writable mount could potentially exercise the path. The trigger is configuration-dependent and requires a short bio condition before submission, so exploitation is not a simple default local DoS on most systems.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource exhaustion issue. The realistic impact is denial of service through leaked page references and memory pressure after repeated attempts. There is no supported evidence of confidentiality impact, integrity impact, memory corruption, page-cache corruption, or privilege escalation. The paranoid score only raises the issue slightly because sustained abuse may create stronger availability impact.

## 5. One-sentence report phrase

An iomap atomic direct I/O error path can fail to release pages attached to a short bio rejected by the REQ_ATOMIC size check, allowing a local process with access to a suitable filesystem to cause resource exhaustion through repeated failed writes.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

Reason: this is a local resource leak with configuration-dependent reachability and no evidence of memory corruption, ownership bypass, information disclosure, or privilege escalation.

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

Patch: iomap: release pages on atomic dio size mismatch [ Upstream
Commit: 27ddd3442fc6f698fb8577c7cfb243ddd81ea8c0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=27ddd3442fc6f698fb8577c7cfb243ddd81ea8c0

Changed files:
  fs/iomap/direct-io.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=27ddd3442fc6f698fb8577c7cfb243ddd81ea8c0

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

The original Linux kernel CVE announcement for CVE-2026-72370 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72370

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: 1
  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).