[CVE-2026-53278][LOW] arm_mpam: Check whether the config array is allocated before destroying it

[CVE-2026-53278][LOW] arm_mpam: Check whether the config array is allocated before destroying it

[AL-KERNEL]

CVE: CVE-2026-53278
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: arm_mpam: Check whether the config array is allocated before destroying it
Commit: 8eb6dc76eeae5302c0d885906a0e469ef9630a59
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8eb6dc76eeae5302c0d885906a0e469ef9630a59
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53278
Analysis date: Fri, 26 Jun 2026 16:08:53 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
ARM MPAM may dereference a NULL configuration pointer during disable or reset cleanup before allocation has completed, causing a local platform-specific kernel crash without evidence of UAF, OOB access, information disclosure, or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53278 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53278

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: LOW
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-2026-53278	LOW	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:N/I:N/A:H';**CWE-476;CWE-703;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'ARM MPAM can dereference a NULL cfg pointer in __destroy_component_cfg() when mpam_disable() calls the destroy path before the component configuration array was allocated. This is a local lifecycle and error handling bug in the MPAM driver rather than a packet or remote input issue. For the CVSS the PR:L is used only for the paranoid score because some systems may delegate limited resctrl or platform management actions to a local service account, while the base case is PR:H because reliable triggering usually needs administrative control over MPAM enable disable or driver lifecycle. Impact is denial of service via kernel crash only. There is no concrete UAF, OOB access, info leak, or write primitive in the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DANGER SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1
  `__destroy_component_cfg()` can dereference `comp->cfg` when it is NULL, causing a kernel NULL pointer dereference.
* Requires admin/root/platform control in typical deployments: -2
  Reliable triggering appears tied to MPAM disable/reset or driver/platform lifecycle handling, not to an ordinary unprivileged userspace API.
* Rare AND difficult-to-reach subsystem/configuration: -1
  ARM MPAM is hardware and platform specific and is not a broadly exposed default Linux attack surface.

Conservative total is below zero, rounded to 0 for practical triage.

Paranoid signals:

* Reliable kernel crash / strong DoS: +1
  If a local service or delegated platform-management path can trigger MPAM disable before configuration allocation, the crash is plausible.
* No memory corruption bonus.
  The patch shows a NULL pointer dereference only. There is no UAF, OOB write, stale callback, refcount issue, or attacker-controlled reuse.
* No confidentiality or integrity bonus.
  The failure mode is a crash, not disclosure or modification of protected data.

Paranoid total: 1.

## 3. Reachability analysis

The bug is local and platform specific. It requires an ARM system with MPAM support and a code path where `mpam_disable()` can run before the component configuration array is allocated. In normal deployments this is likely reachable only through privileged platform, driver, or resource-control lifecycle operations. Namespace or container delegation could lower the practical privilege level in some specialized environments, but the patch does not show a normal unprivileged userspace trigger. There is no network reachability and no firmware-mediated attacker input shown by the patch.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate kernel DoS issue, not an Important-class vulnerability. The theoretical impact is a kernel crash from a NULL pointer dereference. Realistic exploitation evidence does not support privilege escalation, information disclosure, arbitrary write, object lifetime corruption, or a reusable memory-corruption primitive. The main reason to patch is stability on affected ARM MPAM systems.

## 5. One-sentence report phrase

ARM MPAM may dereference a NULL configuration pointer during disable or reset cleanup before allocation has completed, causing a local platform-specific kernel crash without evidence of UAF, OOB access, information disclosure, or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent security triage because it is a local NULL pointer dereference in a rare platform-specific subsystem, with typical privileged trigger requirements and no concrete memory corruption or security-boundary bypass primitive.

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

Patch: arm_mpam: Check whether the config array is allocated before destroying it
Commit: 8eb6dc76eeae5302c0d885906a0e469ef9630a59
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8eb6dc76eeae5302c0d885906a0e469ef9630a59

Commit description:

__destroy_component_cfg() is called to free the configuration array.
It uses the embedded 'garbage' structure, which means the array has
to be allocated.

If __destroy_component_cfg() is called from mpam_disable() before the
configuration was ever allocated, then a NULL pointer is dereferenced.

Check for this case and return early if the configuration is not
allocated.

__destroy_component_cfg() also frees the mbwu_state as this is allocated
by __allocate_component_cfg(). As the mbwu_state is allocated after
comp->cfg is set, and is also under mpam_list_lock, only the first
pointer needs checking.

Fixes: 3bd04fe ("arm_mpam: Extend reset logic to allow devices to be reset any time")
Cc: <stable@vger.kernel.org>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/resctrl/mpam_devices.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=8eb6dc76eeae5302c0d885906a0e469ef9630a59

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

The original Linux kernel CVE announcement for CVE-2026-53278 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53278

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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).