[CVE-2026-99036][MODERATE 7.0] dm: fix reading free memory in do_resume

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

CVE: CVE-2026-99036
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: dm: fix reading free memory in do_resume
Commit: 281f68d6cf8acb2547ebf0a849b8beae8fb0ec3c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=281f68d6cf8acb2547ebf0a849b8beae8fb0ec3c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99036
Analysis date: Mon, 26 Oct 2026 23:07:42 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A host administrator can race device-mapper resume operations to cause a stale `dm_table` mode read, potentially crashing the kernel or selecting an incorrect disk read-only state.

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

The original Linux kernel CVE announcement for CVE-2026-99036 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99036

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
======================================================================

CVE-2026-99036	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99036 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.2';DESCR 'A race in device mapper do_resume can cause dm_table_get_mode to read a new_map object after a concurrent ioctl has replaced the table and freed that object. The demonstrated primitive is a use after free read whose result controls the disk read only state. A kernel crash is the clearest impact. Reuse of the freed allocation could also produce an incorrect mode value and limited integrity impact, but no arbitrary write or reliable privilege escalation primitive is established. For the CVSS the PR:H value reflects that concurrent device mapper table management normally requires root or equivalent administrative capability. AC:H reflects the need to win a concurrency window between dm_swap_table and the mode read. YES REQUIRES MANUAL CHECK because the issue contains a confirmed race based use after free even though practical triggering requires privileged local access. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.2 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.2 and ActionableScore 0 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	DANGER DISK RACE UAF HARDWARE LINUS SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=YES
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1; no additional technically supported leverage.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 Real UAF: after `dm_swap_table(md, new_map)`, a concurrent privileged table swap can free the table still referenced by local `new_map`; `dm_table_get_mode(new_map)` then reads it.
* +1 Reliable kernel crash/DoS: dereferencing the freed table plausibly faults; syzbot triggered the race.
* -2 Host-administrator prerequisite: the commit positively states that only root can issue the required concurrent device-mapper management operations.
* No hard-race penalty: a concurrency window exists, but the evidence does not establish that repeated attempts are exceptionally narrow or uncontrollable.
* No structured-reuse or weak-LPE bonus: only a stale mode read is shown. Attacker-controlled reclaim, replacement contents, arbitrary write, callback use, disclosure, or privilege escalation is not shown.
* No integrity point: the stale value can alter `set_disk_ro()`, but no unauthorized protected-state change exists against an attacker already holding device-mapper administration authority.
* No repeated release/refcount operation exists; FLOOR 5 is inapplicable.
* No extra availability point is awarded for the same possible crash.

3. Reachability analysis

The complete trigger requires concurrent device-mapper ioctls on the same mapped device. Supplied evidence identifies root or equivalent host-administrative authority, not an ordinary user or namespace-delegated capability. No user-namespace-complete path is shown. The actor can repeat the ioctls, but common tools reportedly do not issue this sequence accidentally.

4. Primitive and severity reading

This is a real CLASS_B UAF read of an active structured `dm_table`, followed by consumption of the stale mode in disk read-only configuration. The patch proves neither a write through freed memory nor controlled reuse. The shown consequences are crash and possibly an incorrect mode decision under host-admin control. Therefore it is not an Important candidate, and normal Moderate downgrade remains permissible.

5. One-sentence report phrase

A host administrator can race device-mapper resume operations to cause a stale `dm_table` mode read, potentially crashing the kernel or selecting an incorrect disk read-only state.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm product-specific device-mapper ioctl delegation and crash behavior, although the supplied evidence supports a host-admin-only constrained UAF.

7. Call-site confidence

Call-site confidence: high

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

Patch: dm: fix reading free memory in do_resume
Commit: 281f68d6cf8acb2547ebf0a849b8beae8fb0ec3c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=281f68d6cf8acb2547ebf0a849b8beae8fb0ec3c

Commit description:

When do_resume calls dm_table_get_mode(new_map), the call is done without
holding any locks (it only holds a reference to the md). It may be
possible that another concurrent ioctl on the same device will swap table
after dm_swap_table and before dm_table_get_mode. In this case,
dm_table_get_mode(new_map) reads freed memory.

This race condition was triggered by syzbot.

This commit fixes the race by reading mode of the new table before
dm_swap_table. Note that new_map is also passed to dm_ima_need_measure,
but this function doesn't attempt to dereference it, so this call should
be safe.

Note that this is not a security bug because only root can trigger it and
the commonly used tools such as lvm or cryptsetup do not call the ioctls
concurrently, so that they can't trigger it acceidentally.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: syzbot+bdff1ecf726d2af66afd@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/md/dm-ioctl.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=281f68d6cf8acb2547ebf0a849b8beae8fb0ec3c

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

The original Linux kernel CVE announcement for CVE-2026-99036 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99036

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:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.2

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: 1

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).