[CVE-2026-74392][MODERATE REGULAR] dm: limit target bio polling to one shot [ Upstream

[CVE-2026-74392][MODERATE REGULAR] dm: limit target bio polling to one shot [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74392
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dm: limit target bio polling to one shot [ Upstream
Commit: 6c4ede3b771adbb3bf21ad4e8b8f2f6f6120c4f7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c4ede3b771adbb3bf21ad4e8b8f2f6f6120c4f7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74392
Analysis date: Sat, 15 Aug 2026 06:22:32 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / not an Important candidate
Manual review required: NO

Summary:
A local DoS can occur when device mapper forwards a spinning poll policy to target bios, allowing io_uring IOPOLL on affected dm stacks to keep a task in blk_mq_poll long enough to trigger an RCU CPU stall.

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

The original Linux kernel CVE announcement for CVE-2026-74392 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74392

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 REGULAR
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-2026-74392	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-834;*CWE-835;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in device mapper polling because dm_poll_bio() forwarded the callers spinning poll policy to the mapped target bio. With io_uring IOPOLL on a dm-stripe target, a task can remain in dm_poll_bio() to bio_poll() to blk_mq_poll() long enough to trigger an RCU CPU stall before io_uring reaches its reschedule check. For the CVSS the PR:L is used for the higher paranoid score because a local user or process needs access to an IOPOLL capable file or block device on the affected dm stack, but full administrator privileges are not necessarily required in delegated storage environments. The issue is not network reachable and is triggered through local storage I/O rather than remote packets. Impact is denial of service from CPU stall or degraded scheduler responsiveness. No UAF, OOB access, information leak, or privilege escalation primitive is indicated by the code change.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / not an Important candidate (with actual score 3)  SKIP CVE-2026-74392 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: f22ecf9c14c12918e30f2179ef516e99eb8b2e49 YES  NO NO unknown 	MAYBE	DISK SIMPLEFIX HARDWARE LINUS IO_URING  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / not an Important candidate**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process may trigger the issue if it can perform io_uring IOPOLL against an affected dm-backed block device.
* Reliable kernel crash / strong DoS: +1
  The commit describes an RCU CPU stall caused by prolonged spinning in dm_poll_bio() -> bio_poll() -> blk_mq_poll().
* Important filesystem/storage path: +1
  The affected code is in device mapper polling, part of the block/storage I/O stack.
* Hard or configuration-specific trigger: -1
  The described reproducer depends on io_uring IOPOLL, a dm-stripe target, and conditions where target queue polling spins long enough to stall RCU.

Paranoid difference:

* Paranoid score removes the -1 configuration penalty when the evaluated environment already exposes dm-stripe or similar dm-backed IOPOLL storage to untrusted local users.

Not counted:

* No generic memory corruption.
  The patch bounds polling behavior and does not indicate UAF, OOB access, double free, type confusion, or stale pointer reuse.
* No privilege escalation plausible.
  The bug is a CPU stall / scheduling starvation issue, not a corruption primitive.
* No confidentiality or integrity impact.
  There is no evidence of data disclosure, unauthorized writes, page-cache corruption, or storage metadata corruption.
* No remote reachability.
  The trigger is local storage I/O, not network packet processing.

## 3. Reachability analysis

The bug is locally reachable by a process that can submit I/O using io_uring IOPOLL to an affected dm-backed device. Creating or configuring dm-stripe targets usually requires administrative privileges, but triggering the issue may not require full root if the device is already configured and accessible to a local user or service.

Namespaces and containers do not normally make this broadly reachable unless the block device or equivalent I/O access is delegated into the container. The affected subsystem is common, but the exact trigger conditions are not fully default because they require IOPOLL-capable storage usage and a stacked dm target where polling can spin for too long.

## 4. Severity interpretation

This behaves like an ordinary Moderate local DoS. The realistic impact is an RCU CPU stall or degraded system responsiveness caused by unbounded polling. There is no supported memory corruption, privilege escalation, information leak, or cross-boundary write primitive. It should not be treated as an Important-class kernel vulnerability based on the provided patch.

## 5. One-sentence report phrase

A local DoS can occur when device mapper forwards a spinning poll policy to target bios, allowing io_uring IOPOLL on affected dm stacks to keep a task in blk_mq_poll long enough to trigger an RCU CPU stall.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as a non-urgent Moderate unless the product specifically exposes dm-backed IOPOLL block devices to untrusted local tenants.

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

Patch: dm: limit target bio polling to one shot [ Upstream
Commit: 6c4ede3b771adbb3bf21ad4e8b8f2f6f6120c4f7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c4ede3b771adbb3bf21ad4e8b8f2f6f6120c4f7

Changed files:
  drivers/md/dm.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=6c4ede3b771adbb3bf21ad4e8b8f2f6f6120c4f7

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

The original Linux kernel CVE announcement for CVE-2026-74392 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74392

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).