[CVE-2026-53156][MODERATE 7.0] nvmem: core: fix use-after-free bugs in error paths

[CVE-2026-53156][MODERATE 7.0] nvmem: core: fix use-after-free bugs in error paths

[AL-KERNEL]

CVE: CVE-2026-53156
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nvmem: core: fix use-after-free bugs in error paths
Commit: e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53156
Analysis date: Thu, 25 Jun 2026 05:06:21 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
The nvmem core error paths could drop the final reference to an nvmem device and then continue using the freed object, creating a local kernel use-after-free that is most likely a crash risk but deserves manual review for possible memory corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53156 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53156

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53156	MODERATE	CHECK	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-416;*CWE-672;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'nvmem core has use after free error paths because __nvmem_device_put can drop the last reference and free the nvmem object while the same code path still reads nvmem layout or calls nvmem_layout_module_put with that pointer. A local trigger would normally need to drive nvmem consumer lookup or cell release error paths, for example through driver probe, device removal, module handling, or other platform management paths that reach of_nvmem_cell_get or nvmem_cell_put. For the CVSS the PR:L is used for the paranoid score because some systems may expose device management or probe paths to a reduced capability root, container root, service account, or delegated local management context rather than full host administrator control. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in worst case may allow confidentiality or integrity impact because the bug class is explicit use after free in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	NVME ERRORPATH UAF HARDWARE LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Memory corruption, strong corruption primitive: +2. The patch explicitly fixes use-after-free paths where `__nvmem_device_put()` may free `nvmem`, after which the same pointer was still used.
* Real lifetime corruption: +1. This is a reference/lifetime ordering bug involving a possible final put followed by later object access.
* Reliable kernel crash / strong DoS: +1. A freed `nvmem` object being dereferenced or passed to `nvmem_layout_module_put()` can plausibly crash the kernel.
* Privileged kernel/device-management memory corruption path: +1. The bug is in nvmem core device-management and cell lifecycle handling.
* Corruption primitive highly constrained or metadata-only: -1. The patch does not show attacker-controlled reclaim, object replacement, write-after-free, callback dispatch, or arbitrary write.
* Requires admin/root/device-management in typical deployments: conservative -2. Typical triggering likely requires driver probe/remove, module/device lifecycle manipulation, or platform-device paths.
* Paranoid reachability adjustment: +1 instead of full admin penalty. Some systems may expose relevant probe or device-management paths to reduced-capability root, container root, service accounts, or delegated local management contexts.

Not counted:

* Remote reachable: +0. No network path is shown.
* Strong LPE plausibility: +0. UAF exists, but no reclaim, overwrite, stale callback, type confusion, or refcount takeover is demonstrated.
* Confidentiality / integrity impact: +0 for the main score. They are theoretically possible for UAF class, but not supported by a concrete primitive in this patch.

## 3. Reachability analysis

The realistic trigger is local and likely tied to nvmem consumer lookup, cell creation failure, cell release, driver probe, device removal, module handling, or platform management paths that reach `of_nvmem_cell_get()` or `nvmem_cell_put()`. In ordinary deployments this is not a direct unprivileged syscall-style attack surface and may require administrator-level device control. Namespaces or containers can matter if device management, module loading, sysfs/configuration access, or service-level probe actions are delegated to less-than-full-root contexts. The path is not network reachable and does not appear default-exposed to arbitrary local users on a normal system.

## 4. Severity interpretation

This is not an ordinary cleanup bug because the fixed behavior is an explicit use-after-free in kernel memory. However, the demonstrated primitive is constrained: the patch shows use-after-put on an error path, but does not show attacker-controlled reuse, write-after-free, function pointer control, or a direct LPE chain. Realistically it behaves like a local DoS or constrained kernel-memory lifetime bug. Paranoid handling should keep it as Actionable Moderate because explicit UAF bugs are unsafe to auto-close without manual review.

## 5. One-sentence report phrase

The nvmem core error paths could drop the final reference to an nvmem device and then continue using the freed object, creating a local kernel use-after-free that is most likely a crash risk but deserves manual review for possible memory corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Explicit kernel use-after-free is present, even though the current patch does not demonstrate a practical privilege-escalation primitive. This should not be auto-closed without checking realistic triggerability on affected platforms and whether delegated device-management paths can make the bug reachable below full host-root privileges.

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

Patch: nvmem: core: fix use-after-free bugs in error paths
Commit: e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7

Commit description:

Fix several instances of error paths in which we call
__nvmem_device_put() - which may end up freeing the underlying memory
and other resources - and then keep on using the nvmem structure. Always
put the reference to the nvmem device as the last step before returning
the error code.

Cc: stable@vger.kernel.org
Fixes: 7ae6478 ("nvmem: core: rework nvmem cell instance creation")
Fixes: e888d44 ("nvmem: resolve cells from DT at registration time")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://patch.msgid.link/20260530204340.116743-3-srini@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/nvmem/core.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=e0d38bf47a72da2f02c9fa6f752cd66d977cd7f7

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

The original Linux kernel CVE announcement for CVE-2026-53156 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53156

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).