[CVE-2026-74472][MODERATE 7.0] ublk: reset kernel-owned dev_info fields in ublk_ctrl_add_dev()

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

CVE: CVE-2026-74472
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ublk: reset kernel-owned dev_info fields in ublk_ctrl_add_dev()
Commit: ee41b00858ca65b4428e99efe39a4277c1f043d2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee41b00858ca65b4428e99efe39a4277c1f043d2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74472
Analysis date: Sat, 15 Aug 2026 17:26:49 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74472 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74472

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: NO

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-2026-74472	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:L/A:H';*CWE-20;CWE-665;**CWE-476;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'ublk_ctrl_add_dev copied userspace supplied dev_info into the kernel object and did not reset driver owned fields such as state and ublksrv_pid. A local user with access to the ublk control interface could add a device with a poisoned state that makes it look live before ub_disk is allocated, then remove it and trigger a NULL pointer dereference in del_gendisk. For the CVSS the PR:L is used because reliable triggering requires a local process with access to the ublk control interface, but not necessarily full administrator privileges in deployments that delegate ublk usage. The issue is not network reachable and is triggered through local block device control operations. Impact is primarily denial of service via kernel crash. The paranoid score keeps availability high and integrity low because userspace controlled driver owned state can disturb the ublk device lifecycle, but there is no clear arbitrary write or UAF primitive in the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74472 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 6d9e6dfdf3b207701471f364121c67eefb000682 YES  NO NO unknown 	MAYBE	DANGER HARDWARE TEST IO_URING  KPANIC INCREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN5	-	-	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
* Local unprivileged trigger: +1. A local process with access to the ublk control interface can supply the poisoned dev_info fields during ADD_DEV.
* Memory corruption, weak/indirect corruption candidate: +1. The primitive is not a demonstrated UAF or overwrite, but userspace controls kernel-owned lifecycle state and can drive invalid object state transitions.
* Reliable kernel crash / strong DoS: +1. The commit explicitly describes ADD_DEV followed by DEL_DEV reaching del_gendisk() with ub_disk == NULL and causing an oops.
* Important filesystem/storage path: +1. ublk is a block/storage subsystem path and device lifecycle corruption can affect kernel block device management.
* Integrity impact plausible, paranoid only: +1. Poisoned state can route START_USER_RECOVERY and char device read/write paths onto a device that was never started, but no arbitrary write or privilege escalation primitive is shown.

3. Reachability analysis
The bug is local and is triggered through the ublk control interface, not through the network. Typical reachability depends on whether untrusted users can access ublk device-management ioctls or whether access is delegated by policy, service configuration, container setup, or device node permissions. If ublk control is restricted to full host root only, practical severity is lower. If a reduced-privilege service account or container-like environment can create ublk devices, PR:L is the more useful triage interpretation. The path is not universally default-exposed, but it is reachable through ordinary local block device control once ublk is enabled.

4. Severity interpretation
This behaves primarily as a local kernel crash / DoS caused by unsanitized userspace-controlled state in a kernel device object. The realistic exploitation evidence supports a reliable oops, not arbitrary code execution. Theoretical privilege escalation is weak because the patch does not show UAF reclaim, attacker-controlled overwrite, type confusion, callback control, or refcount takeover. However, because userspace can poison driver-owned lifecycle state in a storage control path, it should not be auto-closed as an ordinary low-risk Moderate without review.

5. One-sentence report phrase
A local actor with access to the ublk control interface can poison kernel-owned dev_info state during ADD_DEV so the device appears live before disk allocation, allowing DEL_DEV or recovery paths to trigger a NULL pointer dereference and kernel DoS.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED. The demonstrated impact is DoS, but the bug affects kernel-owned lifecycle state in a block device interface and has enough state-machine ambiguity to justify manual review before closure.

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

Patch: ublk: reset kernel-owned dev_info fields in ublk_ctrl_add_dev()
Commit: ee41b00858ca65b4428e99efe39a4277c1f043d2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee41b00858ca65b4428e99efe39a4277c1f043d2

Commit description:

ublk_ctrl_add_dev() memcpy()s the userspace ublksrv_ctrl_dev_info into
ub->dev_info and then fixes up the fields the driver owns, but misses
->state and ->ublksrv_pid.

A device added with ->state = UBLK_S_DEV_LIVE passes the
"->state != UBLK_S_DEV_DEAD" test that ublk_stop_dev_unlocked() uses as its
proxy for "a disk is attached", while ->ub_disk is still NULL, so DEL_DEV
right after ADD_DEV oopses in del_gendisk().  UBLK_S_DEV_QUIESCED plus
UBLK_F_USER_RECOVERY dies one step earlier, in ublk_force_abort_dev().  A
poisoned ->state also gets START_USER_RECOVERY and the char device
read/write path onto a device that was never started, and wedges START_DEV
at -EEXIST.  A poisoned ->ublksrv_pid just makes GET_DEV_INFO report an
unrelated task as the ublk server.

Reset both after the memcpy(), as ublk_detach_disk() does.  Userspace only
ever reads these back, so correcting them silently breaks nothing.

ADD_DEV has copied ->state in unsanitized since ublk was merged, but back
then it was harmless: the gendisk was allocated during ADD_DEV, and both
teardown and the START_DEV -EEXIST check keyed off disk_live() rather than
->state.  The oops became reachable once the disk allocation moved to
START_DEV and those checks switched to ->state.

Fixes: 6d9e6df ("ublk: defer disk allocation")
Cc: stable@vger.kernel.org
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://patch.msgid.link/20260726145025.1507383-1-tom.leiming@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/block/ublk_drv.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=ee41b00858ca65b4428e99efe39a4277c1f043d2

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

The original Linux kernel CVE announcement for CVE-2026-74472 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74472

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:L/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:L/A:H
  The Best / paranoid CVSS score: 6.1

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).