[CVE-2026-64112][MODERATE 7.0] rbd: eliminate a race in lock_dwork draining on unmap

[CVE-2026-64112][MODERATE 7.0] rbd: eliminate a race in lock_dwork draining on unmap

[AL-KERNEL]

CVE: CVE-2026-64112
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: rbd: eliminate a race in lock_dwork draining on unmap
Commit: 3427d7ae38337066ce88b68302e285d344ab756b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3427d7ae38337066ce88b68302e285d344ab756b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64112
Analysis date: Sun, 19 Jul 2026 20:51:15 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in RBD unmap can allow exclusive-lock delayed work to run after image resources are released or reset, causing at least a local kernel crash and presenting a plausible workqueue lifetime UAF concern in delegated RBD management scenarios.

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

The original Linux kernel CVE announcement for CVE-2026-64112 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64112

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.

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

CVE-2026-64112	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the RBD unmap path can let lock_dwork be requeued while exclusive lock work is being drained. This can allow rbd_acquire_lock and follow up lock handling to run after rbd_dev_device_release and rbd_dev_image_release have freed or reset image resources, creating a plausible use-after-free condition or kernel crash. For the CVSS the PR:L is used in the paranoid score because reliable triggering may be possible by a local user or service account with delegated RBD map or unmap control, even though typical systems restrict this path to root or CAP_SYS_ADMIN. The issue is not directly network reachable because the trigger is local RBD device control rather than incoming Ceph traffic, although backend network timing may influence the race window. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use-after-free in kernel workqueue context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	DEADLOCK DANGER INIT RACE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak or indirect corruption candidate: +1. The commit explicitly says work may run after `rbd_dev_device_release()` and `rbd_dev_image_release()` free and/or reset resources, but no attacker-controlled reclaim, overwrite, callback hijack, or type confusion is shown.
* Real lifetime corruption: +1. This is an async workqueue lifetime bug where delayed work can survive past the expected teardown point.
* Reliable kernel crash / strong DoS: +1. The commit describes an assertion failure through `rbd_dev_header_info()` via `rbd_dev_refresh()` from `rbd_post_acquire_action()`.
* Important filesystem/storage path: +1. RBD is a block/storage driver path and the bug occurs during unmap and exclusive-lock teardown.
* Privileged kernel/device-management lifetime path: +1. The affected code is trusted block device management and workqueue teardown logic.
* Hard or unreliable race / special timing required: -1. The trigger depends on a TOCTOU race between delayed-work cancellation and requeue.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. RBD map/unmap is normally controlled by root or privileged storage-management services.

Paranoid interpretation:

* Use PR:L style practical reachability for delegated RBD management. In some environments, a local service account, containerized storage component, or reduced-privilege automation may be able to trigger map/unmap without being equivalent to full host root.
* Keep the Race-UAF downgrade. No strong LPE bonus is awarded because the patch does not show controlled reclaim, stale object replacement, write-after-free, type confusion, callback dispatch, or refcount takeover.
* Paranoid score is capped at 5 under the race-only UAF rule because this is a plausible UAF/lifetime bug but not a demonstrated privilege-escalation primitive.

Call-site confidence: high. The commit message describes the relevant call path from `lock_dwork` to `rbd_acquire_lock()` and then to post-acquire refresh after release/reset.

## 3. Reachability analysis

The bug is triggered locally through RBD device unmap and exclusive-lock teardown behavior. It is not directly network reachable from incoming Ceph traffic, although backend I/O and Ceph timing may influence the race window. In typical deployments, RBD map/unmap requires root, CAP_SYS_ADMIN, or a privileged storage-management service, which lowers the conservative score. Namespaces or containers may matter if RBD control is delegated to a reduced-privilege service or container root that is not equivalent to full host root.

The path is not a default user API for all local users. It is relevant on systems using Ceph RBD kernel mappings with exclusive-lock behavior. Realistic exploitation requires both access to RBD device control and successful timing of the workqueue race during unmap.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup because the patch addresses async work running after resource release/reset. Realistically, the demonstrated impact is local DoS through kernel assertion or crash. The theoretical memory-corruption concern is a use-after-free style lifetime window in kernel workqueue context, but the patch does not demonstrate a strong exploitation primitive.

Conservative handling is Moderate-like due to privileged trigger and hard race. Paranoid handling is Actionable Moderate and manual-review worthy because the affected class is a storage-driver lifetime race with plausible UAF after teardown.

## 5. One-sentence report phrase

A race in RBD unmap can allow exclusive-lock delayed work to run after image resources are released or reset, causing at least a local kernel crash and presenting a plausible workqueue lifetime UAF concern in delegated RBD management scenarios.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

YES REQUIRES MANUAL CHECK because the patch context explicitly describes work executing after release/free/reset in a storage driver teardown path, which is a plausible UAF class even though practical privilege escalation is not demonstrated.

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

Patch: rbd: eliminate a race in lock_dwork draining on unmap
Commit: 3427d7ae38337066ce88b68302e285d344ab756b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3427d7ae38337066ce88b68302e285d344ab756b

Commit description:

Given how rbd_lock_add_request() and rbd_img_exclusive_lock() are
written, lock_dwork may be (re)queued more than it's actually needed:
for example in case a new I/O request comes in while we are in the
middle of rbd_acquire_lock() on behalf of another I/O request.  This is
expected and with rbd_release_lock() preemptively canceling lock_dwork
is benign under normal operation.

A more problematic example is maybe_kick_acquire():

    if (have_requests || delayed_work_pending(&rbd_dev->lock_dwork)) {
            dout("%s rbd_dev %p kicking lock_dwork\n", __func__, rbd_dev);
            mod_delayed_work(rbd_dev->task_wq, &rbd_dev->lock_dwork, 0);
    }

It's not unrealistic for lock_dwork to get canceled right after
delayed_work_pending() returns true and for mod_delayed_work() to
requeue it right there anyway.  This is a classic TOCTOU race.

When it comes to unmapping the image, there is an implicit assumption
of no self-initiated exclusive lock activity past the point of return
from rbd_dev_image_unlock() which unlocks the lock if it happens to be
held.  This unlock is assumed to be final and lock_dwork (as well as
all other exclusive lock tasks, really) isn't expected to get queued
again.  However, lock_dwork is canceled only in cancel_tasks_sync()
(i.e. later in the unmap sequence) and on top of that the cancellation
can get in effect nullified by maybe_kick_acquire().  This may result
in rbd_acquire_lock() executing after rbd_dev_device_release() and
rbd_dev_image_release() run and free and/or reset a bunch of things.
One of the possible failure modes then is a violated

    rbd_assert(rbd_image_format_valid(rbd_dev->image_format));

in rbd_dev_header_info() which is called via rbd_dev_refresh() from
rbd_post_acquire_action().

Redo exclusive lock task draining to provide saner semantics and try
to meet the assumptions around rbd_dev_image_unlock().

Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/block/rbd.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=3427d7ae38337066ce88b68302e285d344ab756b

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

The original Linux kernel CVE announcement for CVE-2026-64112 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64112

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 2
  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: NO
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).