[CVE-2026-52965][LOW] drm/ttm: Fix ttm_bo_swapout() infinite LRU walk on swapout failure

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

CVE: CVE-2026-52965
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/ttm: Fix ttm_bo_swapout() infinite LRU walk on swapout failure
Commit: 0124a09e3e5f5f6080efe9663b27af27933f8382
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0124a09e3e5f5f6080efe9663b27af27933f8382
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52965
Analysis date: Thu, 25 Jun 2026 09:03:00 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-52965 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52965

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
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CVE-2026-52965	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A logic error in the DRM TTM swapout path can make ttm_bo_swapout_cb revisit the same LRU resource forever when ttm_tt_swapout fails. The failure path moves the resource relative to the LRU walk hitch cursor in a way that lets the next continue operation find the same object again, causing an infinite LRU walk and possible CPU soft lockup. For the CVSS the PR:L is used because a local user or process with access to a DRM render device may be able to create buffer objects and influence memory pressure, but reliable triggering still depends on swapout failure conditions and driver state. The issue is not network reachable and is triggered through local GPU memory management activity rather than remote traffic. Impact is denial of service only via CPU hang or stalled reclaim path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	LOCK SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process with DRM render device access may be able to create TTM buffer objects and influence memory pressure or swapout activity.
* Reliable kernel crash / strong DoS: +1. The bug can cause an infinite LRU walk and CPU soft lockup when ttm_tt_swapout() fails.
* Hard or unreliable race / special condition: -1. Triggering depends on swapout failure conditions, memory pressure, driver state, and TTM reclaim behavior.
* Broad/default/common subsystem: +1. DRM/TTM is common on GPU systems, but exposure still depends on affected drivers and accessible render nodes.
* No memory corruption signal: +0. The patch shows list cursor logic causing repeated traversal, not UAF, OOB write, double free, or attacker-controlled overwrite.

3. Reachability analysis
A local user or process with access to a DRM render node is the realistic trigger. Containers may inherit render device access if explicitly passed through, but this is not a network path and not a default container capability. The affected path requires GPU memory management activity and a failed ttm_tt_swapout(), so exploitation is plausible as local DoS but not straightforward or universally reachable.

4. Severity interpretation
This behaves like an ordinary Moderate DoS issue rather than an Important-class vulnerability. The realistic impact is CPU hang or stalled reclaim due to an infinite LRU walk. There is no supported evidence of memory corruption, privilege escalation, information disclosure, or cross-boundary security bypass.

5. One-sentence report phrase
A logic error in DRM TTM swapout handling can cause ttm_bo_swapout_cb() to revisit the same LRU resource after swapout failure, leading to an infinite LRU walk and local denial of service.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The issue is DoS-only, local, condition-dependent, and the patch does not indicate a memory corruption or privilege escalation primitive.

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

Patch: drm/ttm: Fix ttm_bo_swapout() infinite LRU walk on swapout failure
Commit: 0124a09e3e5f5f6080efe9663b27af27933f8382
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0124a09e3e5f5f6080efe9663b27af27933f8382

Commit description:

When ttm_tt_swapout() fails, the current code calls
ttm_resource_add_bulk_move() followed by ttm_resource_move_to_lru_tail()
to restore the resource's bulk_move membership.

However, ttm_resource_move_to_lru_tail() places the resource at the tail
of the LRU list which, relative to the walk cursor's hitch node (placed
immediately after the resource when it was yielded), puts the resource
*in front of the* the hitch. The next list_for_each_entry_continue() from
the hitch finds the same resource again, causing an infinite loop.

Fix by deferring del_bulk_move to the success path only.

On the success path, TTM_TT_FLAG_SWAPPED has just been set by
ttm_tt_swapout() but the resource is still tracked in the bulk_move range,
so ttm_resource_del_bulk_move()'s !ttm_resource_unevictable() guard would
incorrectly skip the removal. Introduce
ttm_resource_del_bulk_move_unevictable() which bypasses that guard.

Reported-by: Jatin Kataria <jkataria@netflix.com>
Fixes: fc5d966 ("drm/ttm: Move swapped objects off the manager's LRU list")
Cc: Christian König <christian.koenig@amd.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
Cc: <stable@vger.kernel.org> # v6.13+
Assisted-by: GitHub_Copilot:claude-sonnet-4.6
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Tested-by: Boqun Feng <boqun@kernel.org>
Link: https://patch.msgid.link/20260428094442.16985-1-thomas.hellstrom@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/ttm/ttm_bo.c
  drivers/gpu/drm/ttm/ttm_resource.c
  include/drm/ttm/ttm_resource.h

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=0124a09e3e5f5f6080efe9663b27af27933f8382

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

The original Linux kernel CVE announcement for CVE-2026-52965 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52965

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: unknown
  Paranoid ActionableScore: 2

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).