[CVE-2026-64415][LOW] mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup

[CVE-2026-64415][LOW] mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup

[AL-KERNEL]

CVE: CVE-2026-64415
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup
Commit: 60cbe67d1342f34b66df1c2ee328e3cd333767d7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=60cbe67d1342f34b66df1c2ee328e3cd333767d7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64415
Analysis date: Sat, 25 Jul 2026 12:45:41 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like. Not an Important candidate.
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-64415 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64415

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64415	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-400;*CWE-835;CWE-770;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'swap_reclaim_full_clusters can run for too long while reclaiming many full swap clusters, causing a CPU soft lockup in a kworker and possible kernel panic through the watchdog. The trigger requires heavy memory and swap pressure on systems with many full clusters, and the reported case needed a large arm64 machine under stress for several days. For the CVSS the PR:L is used because a local user or process can contribute to memory and swap pressure, while reliable triggering still depends on system configuration and sustained workload. The issue is not network reachable and has no evidence of UAF, OOB access, or arbitrary write. Impact is denial of service only through CPU stall or kernel crash.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Not an Important candidate. (with actual score 2)  SKIP CVE-2026-64415 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 5168a68eb78fa1c67a8b2d31d0642c7fd866cc12 YES  NO NO unknown 	MAYBE	DEADLOCK DANGER HARDWARE LINUS TEST MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like. Not an Important candidate.**

2. Signal breakdown
* Local unprivileged trigger: +1. A local process can create memory and swap pressure, but reliable triggering depends on sustained workload and system state.
* Reliable kernel crash / strong DoS: +1. The report shows a real watchdog panic from a kworker stuck in swap reclaim.
* Hard or unreliable race / special timing required: -1. The observed trigger required a large arm64 system, heavy LTP memory/swap stress, many full clusters, and about 3 days of runtime.
* Broad/default/common subsystem: +1. Swap reclaim is core mm code, but the exact vulnerable state is workload and configuration dependent.
* No memory corruption signal: +0. The patch only adds cond_resched() and does not indicate UAF, OOB access, double free, stale pointer reuse, or arbitrary write.
* No confidentiality or integrity impact: +0. The demonstrated impact is scheduler starvation and watchdog panic only.

Paranoid score reaches 3 if AC is treated as lower on already stressed swap-heavy systems with many full clusters.

3. Reachability analysis
A local user or workload can contribute to memory pressure and swap activity, so PR:L is reasonable for CVSS-style thinking. The issue is not remotely reachable and is not triggered by network packets. Namespaces or containers may help generate memory pressure, but cgroup limits can also reduce practical reachability. Swap must be enabled and the system must accumulate many full clusters under heavy reclaim pressure.

Call-site confidence: high. The trace and patch identify swap_reclaim_full_clusters() directly, and the fix is a single scheduler yield inside the long reclaim loop.

4. Severity interpretation
This behaves like an ordinary Moderate / Low-like resource-exhaustion DoS. It is not an Important-class kernel vulnerability because there is no memory corruption primitive, no security-boundary bypass, no page-cache or filesystem metadata corruption, and no privilege-escalation path. The realistic impact is system availability loss through soft lockup or watchdog panic under sustained stress.

5. One-sentence report phrase
A long-running swap_reclaim_full_clusters() loop can monopolize CPU during heavy swap reclaim and trigger a watchdog panic, causing local denial of service under sustained memory and swap pressure.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This can be handled as a DoS-only scheduler latency issue with no evidence of memory corruption or privilege escalation.

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

Patch: mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup
Commit: 60cbe67d1342f34b66df1c2ee328e3cd333767d7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=60cbe67d1342f34b66df1c2ee328e3cd333767d7

Commit description:

We hit a real softlockup in an internal stress test environment.  The
workload was LTP memory/swap stress on a large arm64 machine, with 320
CPUs, about 1TB memory and an 8.6GB swap device.  The system was under
heavy load and the swap device had a large number of full clusters.  The
softlockup was triggered during a stress test after about 3 days.

So, add periodic cond_resched() calls during large full_clusters
reclaim operations to prevent softlockup issues.

Detailed call trace as follow:

PID: 3817773  TASK: ffff0883bb28b780  CPU: 48   COMMAND: "kworker/48:7"
   #0 [ffff800080183d10] __crash_kexec at ffffa4c1361e5de4
   #1 [ffff800080183d90] panic at ffffa4c1360d5e9c
   #2 [ffff800080183e20] watchdog_timer_fn at ffffa4c136231fa8
   ...
  #16 [ffff8000c4ad3cb0] swap_cache_del_folio at ffffa4c1363e1614
  #17 [ffff8000c4ad3ce0] __try_to_reclaim_swap at ffffa4c1363e4bfc
  #18 [ffff8000c4ad3d40] swap_reclaim_full_clusters at ffffa4c1363e5474
  #19 [ffff8000c4ad3da0] swap_reclaim_work at ffffa4c1363e550c
  #20 [ffff8000c4ad3dc0] process_one_work at ffffa4c136102edc
  #21 [ffff8000c4ad3e10] worker_thread at ffffa4c136103398
  #22 [ffff8000c4ad3e70] kthread at ffffa4c13610d95c

Link: https://lore.kernel.org/20260506130919.2298807-1-kerayhuang@tencent.com
Fixes: 5168a68 ("mm, swap: avoid over reclaim of full clusters")
Signed-off-by: Zijiang Huang <kerayhuang@tencent.com>
Reviewed-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Reviewed-by: albinwyang <albinwyang@tencent.com>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Barry Song <baohua@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Youngjun Park <youngjun.park@lge.com>
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/swapfile.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=60cbe67d1342f34b66df1c2ee328e3cd333767d7

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

The original Linux kernel CVE announcement for CVE-2026-64415 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64415

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).