[CVE-2026-53153][IMPORTANT] mm/list_lru: drain before clearing xarray entry on reparent

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

CVE: CVE-2026-53153
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: mm/list_lru: drain before clearing xarray entry on reparent
Commit: c19ff4351214f059349788e13e70e74325831ff6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c19ff4351214f059349788e13e70e74325831ff6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53153
Analysis date: Fri, 26 Jun 2026 03:43:57 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in memcg `list_lru` reparenting can let concurrent list operations modify the same physical list under different locks, corrupting kernel list pointers and causing at least local DoS with plausible privilege-escalation concern.

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

The original Linux kernel CVE announcement for CVE-2026-53153 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53153

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: IMPORTANT
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
======================================================================

CVE-2026-53153	IMPORTANT	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-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in mm list_lru memcg reparenting can corrupt kernel list pointers because the dying memcg xarray entry was cleared before its per node list_lru items were drained into the parent. A concurrent list_lru_del can then lock the parent list while the item is still physically linked on the dying memcg list, while another thread may modify the same list under the dying memcg lock. This creates unsynchronized updates to next and prev pointers on the same physical list and can lead to kernel memory corruption or a crash. For the CVSS the PR:L is used for the paranoid score because a local user or delegated service with cgroup or container level control may be able to create and remove memcgs while generating list_lru activity. The issue is not network reachable and requires a local race window. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	DANGER LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local unprivileged or delegated trigger: +1**
  Triggering may be possible by a local user or container workload that can create and remove delegated memcgs while generating list_lru activity.

* **Weak LPE concern: +1**
  The patch describes corruption of kernel list `next` and `prev` pointers, but does not show a controlled overwrite or reclaim primitive.

* **Memory corruption, weak or indirect corruption candidate: +1**
  The bug corrupts linked list metadata through concurrent modification under different locks.

* **Reliable kernel crash or strong DoS: +1**
  Corrupted kernel list pointers can realistically lead to BUG, Oops, panic, or list corruption detection.

* **Broad or common subsystem exposure: +1**
  `list_lru` and memcg are common kernel memory-management paths used by filesystem and shrinker infrastructure.

* **Hard race or special timing required: -1**
  The issue requires a race between memcg reparenting and concurrent list_lru operations.

Paranoid additional interpretation:

* **Privilege escalation plausible, stronger interpretation: +2 instead of +1**
  Kernel list pointer corruption can sometimes become more than DoS if object placement and list operations are sufficiently influenced.

* **Generic memory corruption, stronger interpretation: +2 instead of +1**
  The commit explicitly states that adjacent items can corrupt each others links, which is real kernel memory metadata corruption.

Result:

* Conservative: `1 + 1 + 1 + 1 + 1 - 1 = 5`
* Paranoid: `1 + 2 + 2 + 1 + 1 - 1 = 7`

## 3. Reachability analysis

The bug is **not network reachable**. It is triggered through local kernel memory-management and cgroup activity.

A realistic trigger requires a dying memcg being reparented while concurrent `list_lru_del()` or `list_lru_walk_one()` activity touches the same physical list. In typical host deployments, creating and deleting cgroups may require privileges or delegation. In containerized or service-managed environments, cgroup control may be delegated to less privileged workloads, so treating this only as full host-root is too conservative for triage.

The path is not a rare driver or special hardware path. It is in core mm/list_lru and memcg infrastructure, so the affected code is relevant on many modern systems using cgroups.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch describes **actual kernel list metadata corruption**, not only a warning or accounting mismatch.

Realistically, the most likely demonstrated impact is **local DoS through kernel crash or list corruption**. Theoretical LPE is plausible because corrupted `list_head` links can become security relevant in kernel heap metadata and object lifetime paths, but the patch does not demonstrate a controlled write, UAF reclaim, or stable exploit primitive.

Therefore, conservative handling is **Actionable Moderate**. Paranoid handling is **Strong Important candidate** and should not be auto-closed.

## 5. One-sentence report phrase

A race in memcg `list_lru` reparenting can let concurrent list operations modify the same physical list under different locks, corrupting kernel list pointers and causing at least local DoS with plausible privilege-escalation concern.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a race in core memory-management code with explicit kernel list pointer corruption. Even though exploitation beyond DoS is not demonstrated, the bug class and affected subsystem justify manual review.

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

Patch: mm/list_lru: drain before clearing xarray entry on reparent
Commit: c19ff4351214f059349788e13e70e74325831ff6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c19ff4351214f059349788e13e70e74325831ff6

Commit description:

memcg_reparent_list_lrus() clears the dying memcg's xarray entry with
xas_store(&xas, NULL) before reparenting its per-node lists into the
parent.  This opens a window where a concurrent list_lru_del() arriving
for the dying memcg sees xa_load() == NULL, walks to the parent in
lock_list_lru_of_memcg(), takes the parent's per-node lock, and calls
list_del_init() on an item still physically linked on the dying memcg's
list.

If another in-flight thread holds the dying memcg's per-node lock at the
same moment (another list_lru_del, or a list_lru_walk_one running an
isolate callback), both threads modify ->next/->prev pointers on the same
physical list under different locks.  Adjacent items can corrupt each
other's links.

Fix it by reversing the order: reparent each per-node list and mark the
child's list lru dead and then clear the xarray entry.  Any concurrent
list_lru op that finds the still-set xarray entry either takes the dying
memcg's per-node lock (synchronizing with the drain) or sees LONG_MIN and
walks to the parent, where the items now live.

Link: https://lore.kernel.org/20260601161501.1444829-1-shakeel.butt@linux.dev
Fixes: fb56fdf ("mm/list_lru: split the lock to per-cgroup scope")
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reported-by: Chris Mason <clm@fb.com>
Reviewed-by: Kairui Song <kasong@tencent.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/list_lru.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=c19ff4351214f059349788e13e70e74325831ff6

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

The original Linux kernel CVE announcement for CVE-2026-53153 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53153

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: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: 5
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).