[CVE-2026-72105][MODERATE REGULAR] dm-log: fix a bitset_size overflow on 32bit machines commit 9743132a41f4d9d0e54c5f2adcb821b04796bab1 upstream.

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

CVE: CVE-2026-72105
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dm-log: fix a bitset_size overflow on 32bit machines commit 9743132a41f4d9d0e54c5f2adcb821b04796bab1 upstream.
Commit: cdc4ddf9db2cb79f4ab86b1a509b7ac21b0b6cf5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cdc4ddf9db2cb79f4ab86b1a509b7ac21b0b6cf5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72105
Analysis date: Sun, 16 Aug 2026 01:09:04 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A 32-bit integer overflow in dm-log bitmap size calculation can make `bitset_size` wrap to zero for a valid large `region_count`, causing local device-mapper dirty-log creation failure and requiring manual review for possible allocation-size side effects.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72105 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72105

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: MODERATE REGULAR
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
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CVE-2026-72105	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-190;CWE-131;*CWE-787;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'dm-log calculates bitset_size from region_count on 32-bit systems and the rounding step can wrap to zero when the rounded bit count becomes 2 to the power of 32. This can make the dirty log bitmap size incorrect for an otherwise valid region_count, causing valid device mapper log creation to fail and potentially causing severe availability impact if such a mapping is required for storage recovery or mirroring. For the CVSS the PR:L is used for the paranoid score because delegated dm management or a reduced capability root context may make the trigger reachable to a less than full host administrator in some environments. The issue is local and is not network reachable. Impact is primarily denial of service or storage configuration failure, with no strong evidence of direct information disclosure or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)  SKIP CVE-2026-72105 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: c20e36b7631d83e7535877f08af8b0af72c44b1a YES  NO NO unknown 	MAYBE	WRITE OOB DISK LOG HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Memory layout invariant restoration: +1
  The patch restores consistency between `region_count`, rounded bitmap bit count, and `bitset_size` used for dm-log bitmap allocation.
* Availability impact realistic: +1
  On 32-bit systems, a valid large `region_count` can make `bitset_size` wrap to zero and cause dirty-log creation failure.
* Important filesystem/storage path: +1
  Device-mapper dirty logs are part of storage reliability and recovery paths.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2
  Creating or configuring dm targets normally requires privileged device-mapper access.

Paranoid additional interpretation:

* Memory corruption, weak/indirect corruption candidate: +1
  This is an integer overflow in allocation-size computation for a kernel bitmap, and the surrounding history references an earlier OOB-write fix. The supplied patch does not prove an OOB write here, so this remains weak and manual-review oriented.
* Privilege penalty refinement: -1 instead of -2
  In some environments, dm management may be delegated to reduced-capability root, container root, initramfs tooling, or storage management services, so the trigger may not always equal full host-root control.

## 3. Reachability analysis

The bug is local and not network reachable. Triggering it requires creating a device-mapper configuration with parameters that produce a very large valid `region_count` on a 32-bit kernel. In typical deployments this requires `CAP_SYS_ADMIN` or equivalent access to device-mapper control interfaces. Namespace or container setups may reduce the effective privilege requirement if dm control is delegated, but ordinary unprivileged users normally cannot reach this path.

The affected condition is also architecture-dependent. It requires a 32-bit `size_t` environment and a sufficiently large region count near the rollover boundary.

## 4. Severity interpretation

This behaves mostly like an ordinary Moderate or Low-like privileged storage configuration failure. The realistic impact is local availability loss or failure to create a valid dirty log. The paranoid concern is that allocation-size integer overflows in kernel storage code can sometimes hide later bitmap OOB access, especially given the nearby history of an OOB-write fix. However, this patch itself does not demonstrate attacker-controlled overwrite, UAF, arbitrary write, information disclosure, or privilege escalation.

## 5. One-sentence report phrase

A 32-bit integer overflow in dm-log bitmap size calculation can make `bitset_size` wrap to zero for a valid large `region_count`, causing local device-mapper dirty-log creation failure and requiring manual review for possible allocation-size side effects.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is an allocation-size integer overflow in kernel storage code, but it should not be treated as an Important-class candidate without evidence of a concrete OOB write, memory corruption primitive, or unprivileged trigger.

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

Patch: dm-log: fix a bitset_size overflow on 32bit machines commit 9743132a41f4d9d0e54c5f2adcb821b04796bab1 upstream.
Commit: cdc4ddf9db2cb79f4ab86b1a509b7ac21b0b6cf5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cdc4ddf9db2cb79f4ab86b1a509b7ac21b0b6cf5

Commit description:

Commit c20e36b7631d ("dm log: fix out-of-bounds write due to
region_count overflow") made sure that region_count could fit in an
unsigned int. But the bitmap memory isn't allocated based on
region_count. It uses bitset_size (a size_t variable). The first step of
calculating bitset_size is to set it to region_count, rounded up to a
multiple of BITS_PER_LONG. If region_size is less than BITS_PER_LONG
smaller than UINT_MAX, it will get rounded up to 2^32. On a 32bit
architecture, this will make bitset_size wrap around to 0 and fail,
despite region_count being valid.

Since bitset_size gets divided by 8, it can hold any valid region_count.
It just needs a special case to handle the rollover. If it is 0, the
value rolled over, and bitset size should be set to the number of bytes
needed to hold 2^32 bits.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: c20e36b7631d ("dm log: fix out-of-bounds write due to region_count overflow")
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- drivers/md/dm-log.c 3

Changed files:
  drivers/md/dm-log.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=cdc4ddf9db2cb79f4ab86b1a509b7ac21b0b6cf5

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

The original Linux kernel CVE announcement for CVE-2026-72105 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72105

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:L
  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: 1
  Paranoid ActionableScore: 3

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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).