[CVE-2026-68164][LOW] mm/damon/core: disallow overlapping input ranges for damon_set_regions()

[CVE-2026-68164][LOW] mm/damon/core: disallow overlapping input ranges for damon_set_regions()

[AL-KERNEL]

CVE: CVE-2026-68164
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/damon/core: disallow overlapping input ranges for damon_set_regions()
Commit: 4b4a3e7ef7bb622237495db9ba4dfd7417d6530e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b4a3e7ef7bb622237495db9ba4dfd7417d6530e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68164
Analysis date: Mon, 10 Aug 2026 16:13:24 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
Overlapping DAMON input ranges can create invalid monitoring regions and, in specific update sequences, trigger a divide by zero in damon_merge_two_regions(), causing a local denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-68164 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68164

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-2026-68164	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-682;CWE-369;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'DAMON region setup can accept overlapping or otherwise invalid address ranges after validation was removed from damon_set_regions. This can create overlapping monitoring regions and may make DAMOS apply the same action multiple times, which can produce unexpected monitoring results and quota behavior. In a more serious setup dependent sequence, invalid ranges can create a negative size region and later trigger a divide by zero in damon_merge_two_regions, causing a local denial of service. For the CVSS the PR:L is used for paranoid scoring because some deployments may delegate DAMON sysfs control to a local service or reduced privilege account, although typical administration requires higher privileges. The issue is not network reachable and is triggered through local DAMON configuration rather than remote traffic. Impact is denial of service via warning, failed monitoring, or kernel crash, without a supported UAF or write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	OOB INIT UAF LINUS MEMORY  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Reliable kernel crash / strong DoS: +1
  The commit describes a possible divide by zero in `damon_merge_two_regions()` after invalid overlapping ranges create a negative-size DAMON region. This is a concrete crash-class outcome, but it is setup-dependent.

Negative signals:

* Requires admin/root/CAP_SYS_ADMIN-like control in typical deployments: -2
  DAMON region configuration through sysfs/debugfs-style control paths is normally administrator-controlled. A paranoid interpretation can treat delegated DAMON control by a local service account as lower privilege, but that is not the default.

* Rare or difficult-to-reach subsystem/configuration: -1
  DAMON/DAMOS is not a broad default data path. The more serious outcomes depend on DAMON being configured and on specific region update sequences.

Not awarded:

* No remote/network trigger.
* No generic memory corruption.
* No UAF, double-free, OOB write, arbitrary write, stale callback, refcount takeover, or page-cache corruption primitive.
* No confidentiality or integrity impact supported by the patch.
* No privilege escalation plausibility supported by the patch.

## 3. Reachability analysis

The bug is triggered through local DAMON region configuration by supplying overlapping or unsorted address ranges to `damon_set_regions()`. In normal deployments, this requires privileged access to DAMON control interfaces, so it is not reachable by an ordinary remote attacker and is not part of a default networking or filesystem data path.

Namespaces or containers could matter only if a product deliberately delegates DAMON control to a reduced-privilege service or container-like management context. That supports a paranoid PR:L-style view for CVSS, but not enough to make this an Important-class issue.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue. The patch restores input validation for a function that assumes sorted and non-overlapping ranges. The worst concrete outcome described is WARN_ONCE or divide by zero, not a memory lifetime bug or attacker-controlled corruption primitive.

Theoretical impact is limited to invalid DAMON state and crash conditions. Realistic exploitation evidence points to local configuration misuse rather than privilege escalation or cross-boundary compromise.

## 5. One-sentence report phrase

Overlapping DAMON input ranges can create invalid monitoring regions and, in specific update sequences, trigger a divide by zero in damon_merge_two_regions(), causing a local denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a validation-only fix with a concrete but limited local DoS outcome, typical privileged reachability, no network exposure, and no supported memory corruption or privilege escalation primitive.

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

Patch: mm/damon/core: disallow overlapping input ranges for damon_set_regions()
Commit: 4b4a3e7ef7bb622237495db9ba4dfd7417d6530e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b4a3e7ef7bb622237495db9ba4dfd7417d6530e

Commit description:

damon_set_regions() assumes the input ranges are sorted by the address and
don't overlap each other.  Hence the assumption was initially to be
explicitly validated.  But commit 97d482f ("mm/damon/sysfs: reuse
damon_set_regions() for regions setting") has mistakenly removed the
validation.

This can make DAMON behave in unexpected ways.  At the best, the
monitoring results snapshot will just look weird since there will be
overlapping regions.  DAMOS will also work weirdly, applying the same
action multiple times for overlapping regions, and make DAMOS quota weird.
More seriously, depending on the setup and regions updates sequence,
negative size regions can be made.  It will trigger WARN_ONCE() if the
kernel is built with CONFIG_DAMON_DEBUG_SANITY=y.  Depending on the
monitoring results, the negative size region can further trigger division
by zero in damon_merge_two_regions().

Note that some of the consequences including the WARN_ONCE() and the
divide by zero depend on commits that were introduced after the root cause
commit 97d482f ("mm/damon/sysfs: reuse damon_set_regions() for
regions setting").

Fix the problems by checking the assumption and returning an error if
the input ranges don't meet the assumption.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260703165610.92894-1-sj@kernel.org
Link: https://lore.kernel.org/20260630041806.151124-1-sj@kernel.org [1]
Fixes: 97d482f ("mm/damon/sysfs: reuse damon_set_regions() for regions setting")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.19.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=4b4a3e7ef7bb622237495db9ba4dfd7417d6530e

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

The original Linux kernel CVE announcement for CVE-2026-68164 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68164

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:H/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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  Paranoid ActionableScore: 1

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).