[CVE-2026-68416][MODERATE 7.0] mtd: fix double free and WARN_ON in add_mtd_device() error paths [ Upstream

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

CVE: CVE-2026-68416
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mtd: fix double free and WARN_ON in add_mtd_device() error paths [ Upstream
Commit: ffe21a3545b439e7b11578a701c22a847c149561
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ffe21a3545b439e7b11578a701c22a847c149561
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68416
Analysis date: Mon, 10 Aug 2026 10:26:30 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A double free in the MTD partition add error path can occur when `add_mtd_device()` failure handling releases the partition object while caller cleanup later frees the same object, causing kernel memory corruption and at least a local DoS risk.

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

The original Linux kernel CVE announcement for CVE-2026-68416 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68416

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-2026-68416	MODERATE	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:H/I:H/A:H';CWE-415;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A double free can occur in the MTD partition add error path because add_mtd_device may drop the device reference and call mtd_release while the caller still owns the same mtd_info object and later frees it through free_partition. This is a kernel memory corruption class issue rather than a simple warning because the same partition object can be released through two different cleanup paths. For the CVSS the PR:L paranoid interpretation covers environments where a reduced capability root, container root, or delegated device management service can create or reconfigure MTD partitions and trigger the failing add path. The issue is not network reachable and normally requires local control of MTD device or partition management. Impact is at least local denial of service via kernel crash or allocator corruption and in worst case may allow confidentiality or integrity impact due to double free based memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-68416 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 19bfa9ebebb5ec0695def57eb1d80de7e9cab369 YES  NO NO unknown 	MAYBE	INIT WARNONLY ERRORPATH HARDWARE LINUS SYZBOT  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, Strong corruption primitive: +2. The patch fixes a real double free of the same `mtd_info` partition object.
* Real lifetime corruption: +1. The bug is caused by inconsistent ownership between `mtd_release()` and caller cleanup paths.
* Reliable kernel crash / strong DoS: +1. Double free and the linked-list `WARN_ON` can plausibly crash or destabilize the kernel.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in MTD device registration and partition lifetime handling.
* Requires admin/root/CAP_* in typical deployments: -2. Creating or reconfiguring MTD partitions is normally privileged.
* Hard or special failure path required: -1. Triggering requires failure of `device_register()` or `mtd_nvmem_add()` during partition add.
* Rare/configuration-dependent subsystem: -1. MTD is common in embedded systems but not broadly exposed on general-purpose servers.

Paranoid differences:

* Do not apply the full admin penalty in delegated-management or containerized embedded environments where reduced-privilege services may control MTD setup.
* Do not apply the rare-subsystem penalty if the evaluated product is an embedded or storage appliance where MTD is part of the normal device model.
* Weak LPE concern: +1. Double free is a memory-corruption class that may become exploitable if allocator reuse is controllable, although no reclaim primitive is shown.

## 3. Reachability analysis

The bug is local and not network reachable. A realistic trigger requires the ability to add or configure MTD partitions and to hit an error path inside `add_mtd_device()`. In typical Linux deployments this implies administrative or device-management privileges. In embedded products, init scripts, management daemons, containerized maintenance tools, or reduced-capability root contexts may make this closer to PR:L in practical triage terms. The vulnerable path is not default-exposed to ordinary users on most systems.

Call-site confidence: high. The commit explicitly describes the caller cleanup paths, `mtd_add_partition()` and `add_mtd_partitions()`, and the conflicting release path through `put_device()` or `device_unregister()`.

## 4. Severity interpretation

This is not an ordinary warning-only bug. It is a real kernel object lifetime bug with double free semantics. Realistic impact is most likely local DoS or allocator corruption under constrained error-path conditions. Theoretical privilege escalation is possible because double free can sometimes be converted into UAF-style exploitation, but the patch does not show attacker-controlled reclaim, replacement object control, callback control, or arbitrary write. Therefore the conservative score remains borderline, while the paranoid score reaches Actionable Moderate and should not be auto-closed.

## 5. One-sentence report phrase

A double free in the MTD partition add error path can occur when `add_mtd_device()` failure handling releases the partition object while caller cleanup later frees the same object, causing kernel memory corruption and at least a local DoS risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is a concrete double free in kernel lifetime handling. Even though the trigger is privileged and error-path dependent, memory corruption bugs in object cleanup paths should receive manual review to determine whether allocator reuse or delegated device-management access makes exploitation more practical.

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

Patch: mtd: fix double free and WARN_ON in add_mtd_device() error paths [ Upstream
Commit: ffe21a3545b439e7b11578a701c22a847c149561
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ffe21a3545b439e7b11578a701c22a847c149561

Changed files:
  drivers/mtd/mtdcore.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=ffe21a3545b439e7b11578a701c22a847c149561

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

The original Linux kernel CVE announcement for CVE-2026-68416 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68416

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: 3
  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).