[CVE-2026-68165][LOW] mm/damon/core: validate ranges in damon_set_regions()

[CVE-2026-68165][LOW] mm/damon/core: validate ranges in damon_set_regions()

[AL-KERNEL]

CVE: CVE-2026-68165
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/damon/core: validate ranges in damon_set_regions()
Commit: b585facbafbb5cf117b37b1c75819ac046646c27
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b585facbafbb5cf117b37b1c75819ac046646c27
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68165
Analysis date: Mon, 10 Aug 2026 17:25:27 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
DAMON accepted zero-length monitoring ranges through `damon_set_regions()`, allowing a privileged or delegated local actor to trigger a WARN_ONCE or divide-by-zero DoS path without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-68165 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68165

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-2026-68165	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-20;CWE-369;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'DAMON accepted empty or invalid monitoring ranges even though the core region logic assumes that zero length regions do not exist. A local actor able to configure DAMON regions can set start and end to the same aligned value and later trigger WARN_ONCE on CONFIG_DAMON_DEBUG_SANITY kernels or a divide by zero in damon_merge_two_regions. For the CVSS the PR:L is used only for the paranoid score because some deployments may delegate DAMON control to a service account or reduced capability administrator, while the typical base case requires administrative access to DAMON sysfs or related kernel controls. The issue is not network reachable and does not provide an obvious memory corruption primitive. Impact is denial of service through a kernel warning or divide by zero crash path, with no direct confidentiality or integrity impact indicated by the code change.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	UAF HARDWARE MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The commit explicitly mentions a possible divide-by-zero in `damon_merge_two_regions()`.
* Availability impact realistic: +1. A divide-by-zero in kernel context can plausibly cause an Oops or crash, depending on configuration and execution context.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. DAMON sysfs administration and DAMON_RECLAIM or DAMON_LRU_SORT configuration are normally privileged kernel tuning interfaces.

Conservative total: 0.

Paranoid signals:

* Reliable kernel crash / strong DoS: +1.
* Availability impact realistic: +1.
* No full admin penalty in paranoid interpretation. Some deployments may delegate DAMON control to a service account or reduced-capability admin context.

Paranoid total: 2.

Not counted:

* No remote/network trigger.
* No UAF, OOB write, double-free, refcount misuse, type confusion, page-cache corruption, or arbitrary write primitive.
* No confidentiality or integrity impact.
* No LPE signal.
* This is primarily an input-validation fix that rejects invalid zero-length or inverted ranges with `-EINVAL`.

Call-site confidence: high. The patch and commit identify the common API entry point `damon_set_regions()` and its downstream failure mode in `damon_merge_two_regions()`.

## 3. Reachability analysis

The bug is triggered by configuring DAMON monitoring ranges with an empty or invalid range, such as `start == end`. Typical access requires privileged control over DAMON sysfs or related DAMON kernel controls. It is not network reachable and is not triggered by ordinary memory access, packet traffic, or filesystem activity.

Namespaces and containers do not normally make this broadly unprivileged. A container or service account would need delegated access to DAMON control files or equivalent host-level management permissions. The affected feature is also not a universal default workload path, but it is reachable on systems where DAMON is enabled and administratively exposed.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue, not an Important-class vulnerability. The realistic impact is a warning or divide-by-zero crash path caused by invalid DAMON range input. The theoretical impact does not extend to memory corruption or privilege escalation based on the patch evidence.

The paranoid score accounts for delegated DAMON administration scenarios, but still remains low because the primitive is validation failure leading to DoS only.

## 5. One-sentence report phrase

DAMON accepted zero-length monitoring ranges through `damon_set_regions()`, allowing a privileged or delegated local actor to trigger a WARN_ONCE or divide-by-zero DoS path without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a validation-only fix for invalid range input with a concrete DoS failure mode and no supported memory corruption, security-boundary bypass, confidentiality impact, integrity impact, or network exposure.

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

Patch: mm/damon/core: validate ranges in damon_set_regions()
Commit: b585facbafbb5cf117b37b1c75819ac046646c27
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b585facbafbb5cf117b37b1c75819ac046646c27

Commit description:

DAMON core logic assumes zero length regions don't exist.  However, a few
DAMON API callers including DAMON_SYSFS, DAMON_RECLAIM and DAMON_LRU_SORT
allow users to set empty monitoring target regions.  This could result in
WARN_ONCE() on CONFIG_DAMON_DEBUG_SANITY enabled kernel, and
divide-by-zero from damon_merge_two_regions().

For example, the WANR_ONCE() can be triggered like below.

    # grep DAMON_DEBUG_SANITY /boot/config-$(uname -r)
    # CONFIG_DAMON_DEBUG_SANITY=y
    # damo start
    # cd /sys/kernel/mm/damon/admin/kdamonds/0
    # echo 0 > contexts/0/targets/0/regions/0/start
    # echo 0 > contexts/0/targets/0/regions/0/end
    # echo commit > state
    # dmesg
    [....]
    [   73.705780] ------------[ cut here ]------------
    [   73.707552] start 0 >= end 0
    [   73.708452] WARNING: mm/damon/core.c:359 at damon_new_region+0x6e/0x80, CPU#1: kdamond.0/758
    [...]

All DAMON API callers eventually use damon_set_regions() to setup the
regions.  Add the validation logic in the function.

Link: https://lore.kernel.org/20260630035221.146458-1-sj@kernel.org
Fixes: 43b0536 ("mm/damon: introduce DAMON-based Reclamation (DAMON_RECLAIM)")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Yang yingliang <yangyingliang@huawei.com>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/damon/core.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=b585facbafbb5cf117b37b1c75819ac046646c27

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

The original Linux kernel CVE announcement for CVE-2026-68165 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68165

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:L/PR:H/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: 0
  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).