[CVE-2026-64416][MODERATE REGULAR] mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host [ Upstream

[CVE-2026-64416][MODERATE REGULAR] mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64416
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host [ Upstream
Commit: 818416fef38759f23210de449663cd9d7e293d39
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=818416fef38759f23210de449663cd9d7e293d39
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64416
Analysis date: Sat, 25 Jul 2026 11:39:39 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A NULL pointer dereference in `lookup_swap_cgroup_id()` can crash a swapless host during process teardown when a corrupted non-present PTE is interpreted as a swap entry, but the patch does not show the source of PTE corruption or a standalone privilege-escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-64416 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64416

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 REGULAR
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-2026-64416	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:L/I:L/A:H';**CWE-476;CWE-754;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'lookup_swap_cgroup_id can dereference a NULL swap_cgroup map on a swapless host when zap_pte_range processes a non present PTE that decodes as a real swap entry. A local process exit can then reach swap_pte_batch and crash the kernel if a corrupted PTE is present. For the CVSS the PR:L is used because triggering is tied to local process memory teardown rather than a remote interface, although reliable exploitation also depends on a separate source of PTE corruption. The issue is not network reachable. Impact is at least local denial of service via kernel crash. The paranoid score keeps limited confidentiality and integrity impact because the affected path is in mm teardown and depends on corrupted PTE state, but the patch itself does not show a direct arbitrary write or standalone privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)  SKIP CVE-2026-64416 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: bea67dcc5eea0f6a213897a59b9e644977cd07e6 YES  NO NO unknown 	MAYBE	READ DANGER LINUS SYZBOT MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process exit can reach `exit_mmap()` -> `zap_pte_range()` -> `swap_pte_batch()` -> `lookup_swap_cgroup_id()`, but only if a corrupted swap-like PTE already exists.

* Reliable kernel crash / strong DoS: +1
  The commit shows a concrete kernel page fault in `lookup_swap_cgroup_id()` and says both production and syzbot hit the same stack.

* Broad/default/common subsystem: +1 in paranoid score only
  The affected path is core mm teardown, not a rare driver-only path, but the vulnerable condition itself is unusual.

* Hard or unreliable precondition: -1
  The bug requires a corrupted PTE that decodes as a real swap entry on a swapless host. The commit explicitly says the corruption source is a separate bug.

* Weak/indirect corruption candidate: +1 in paranoid score only
  The crash depends on invalid PTE state being interpreted as swap metadata, but this patch does not provide the corruption primitive itself.

Not applied:

* No remote/network trigger.
* No demonstrated arbitrary write, UAF, double-free, controlled reclaim, or type confusion.
* No strong LPE signal from this patch alone.
* No direct confidentiality or integrity impact in the conservative score.

## 3. Reachability analysis

A local process can reach the crashing teardown path during process exit, but the process must already have a corrupted non-present PTE that decodes as a valid swap entry. On swapless hosts, `swap_cgroup_ctrl[type].map` is NULL because the swap type was never registered through `swap_cgroup_swapon()`. Namespaces do not materially reduce the main precondition because the bug is in host mm teardown, but an unprivileged container workload could still be the exiting process if some separate bug corrupts its PTEs. The path is not network reachable and is not a normal standalone trigger without the separate PTE corruption source.

## 4. Severity interpretation

This behaves primarily like a local kernel crash / DoS robustness bug in the mm teardown path. The theoretical concern is higher than an ordinary NULL dereference because it involves corrupted PTE state in core memory-management code, and the separate corruption source should be investigated. Realistically, this patch alone does not show a privilege-escalation primitive, attacker-controlled memory corruption, or a way for a normal local user to create the required PTE corruption.

## 5. One-sentence report phrase

A NULL pointer dereference in `lookup_swap_cgroup_id()` can crash a swapless host during process teardown when a corrupted non-present PTE is interpreted as a swap entry, but the patch does not show the source of PTE corruption or a standalone privilege-escalation primitive.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the fixed crash depends on corrupted PTE state in the mm teardown path, and the separate source of that corruption may represent the real security-relevant primitive.

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

Patch: mm: swap_cgroup: fix NULL deref in lookup_swap_cgroup_id on swapless host [ Upstream
Commit: 818416fef38759f23210de449663cd9d7e293d39
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=818416fef38759f23210de449663cd9d7e293d39

Changed files:
  mm/swap_cgroup.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=818416fef38759f23210de449663cd9d7e293d39

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

The original Linux kernel CVE announcement for CVE-2026-64416 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64416

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:L/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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3

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 REGULAR

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).