[CVE-2026-72107][MODERATE 7.0] dm era: fix out-of-bounds memory access for non-zero start sector

[CVE-2026-72107][MODERATE 7.0] dm era: fix out-of-bounds memory access for non-zero start sector

[AL-KERNEL]

CVE: CVE-2026-72107
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: dm era: fix out-of-bounds memory access for non-zero start sector
Commit: fe94a0b14010a3c267ff9a2508afb4f27ff1c5bf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fe94a0b14010a3c267ff9a2508afb4f27ff1c5bf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72107
Analysis date: Sun, 16 Aug 2026 02:59:31 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
dm-era may calculate writeset blocks before applying the target offset, allowing local I/O on a non-zero-start dm-era mapping to trigger an out-of-bounds in-core bitset access and possible kernel crash or metadata tracking inconsistency.

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

The original Linux kernel CVE announcement for CVE-2026-72107 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72107

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 7.0
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-2026-72107	MODERATE	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:L/I:L/A:H';CWE-125;CWE-129;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'dm-era can perform an out-of-bounds bitset access when a target is configured with a non-zero start sector because the era block is calculated before applying the target-relative offset. Local I/O to such a mapped device can pass an absolute mapped-device block into the writeset lookup, causing writeset_marked to test memory past the end of the in-core bitset. For the CVSS the PR:L is used for the paranoid score because an unprivileged local user or service may be able to trigger I/O after an administrator has already created the affected dm-era mapping. The issue is not directly network reachable. Impact is at least local denial of service via kernel crash, with limited confidentiality or integrity impact possible from an out-of-bounds read affecting metadata decisions. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	WRITE KASAN OOB DISK SIMPLEFIX HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. If an affected dm-era mapping already exists and is exposed through a mounted filesystem or writable block device, ordinary local I/O can reach `era_map()`.
* Weak/indirect corruption candidate: +1. The bug is an out-of-bounds bitset access in kernel memory, but the patch indicates a read/test past the in-core bitset rather than an attacker-controlled overwrite.
* Important filesystem/storage path: +1. dm-era is a device-mapper storage target and the bug affects write tracking metadata decisions.
* Rare AND difficult-to-reach configuration: -1. The issue requires a dm-era target with a non-zero start sector, which is not a broad default path.
* Requires admin/root for setup in typical deployments: -1. Creating the affected device-mapper table is privileged, but triggering I/O may be possible by less privileged users after setup, so I use -1 rather than -2.

Paranoid additional signals:

* Reliable kernel crash / strong DoS: +1. KASAN reports vmalloc-out-of-bounds access, and such kernel OOB reads can plausibly produce an oops or panic depending on layout and hardening.
* Confidentiality impact plausible: +1. The primitive is read-only OOB and not a direct leak, but out-of-bounds bit tests may observe adjacent kernel memory state.
* Integrity impact plausible: +1. A wrong writeset marked/unmarked decision may affect dm-era tracking semantics, although no direct arbitrary metadata write is shown.

Not awarded:

* No remote reachable score. This is local storage I/O, not a network protocol path.
* No strong LPE score. The patch does not show UAF reclaim, writable stale object reuse, arbitrary write, callback control, or type confusion.
* No Dirty-Pipe-like ownership/COW violation. There is no evidence of writes crossing a page-cache, reflink, or COW ownership boundary.

Call-site confidence: high. The relevant call path is visible: `era_map()` remaps the bio and then calls `get_block()` after the patch.

## 3. Reachability analysis

The vulnerable path is reached through I/O submitted to a dm-era device. The affected configuration requires a non-zero target start sector, which normally must be created by root or another process with device-mapper administration privileges. However, once such a mapping is active, local users or services that can cause writes through the mapped block device or mounted filesystem may trigger the vulnerable lookup without having device-mapper administration rights themselves.

Namespaces and containers matter only if the container or delegated environment can access the affected mapped device or cause I/O through a host-provided mount. The path is not network reachable by itself. Realistic exploitation requires a specific dm-era deployment, but the trigger is ordinary I/O once the device exists.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary low-risk correctness fix. The demonstrated primitive is an out-of-bounds kernel memory read/test in a storage metadata path, with realistic DoS potential and possible limited metadata-decision impact. It is not an Important-class issue based on the supplied patch alone because there is no demonstrated write primitive, UAF reclaim, object replacement, type confusion, or privilege escalation path.

The conservative score stays low-to-borderline because setup is privileged and configuration-dependent. The paranoid score reaches actionable Moderate because kernel OOB access in a storage target should not be auto-closed without manual review.

## 5. One-sentence report phrase

dm-era may calculate writeset blocks before applying the target offset, allowing local I/O on a non-zero-start dm-era mapping to trigger an out-of-bounds in-core bitset access and possible kernel crash or metadata tracking inconsistency.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should be reviewed manually because it is a kernel out-of-bounds access in a device-mapper storage path, with plausible DoS and limited C/I concerns, even though the current evidence does not support strong LPE or remote reachability.

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

Patch: dm era: fix out-of-bounds memory access for non-zero start sector
Commit: fe94a0b14010a3c267ff9a2508afb4f27ff1c5bf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fe94a0b14010a3c267ff9a2508afb4f27ff1c5bf

Commit description:

dm-era tracks writes in target-relative blocks, but era_map() calculates
the writeset block before applying the target offset.  Tables with a
non-zero start sector can therefore pass an absolute mapped-device block
to metadata_current_marked().

If the absolute block is beyond the current writeset size,
writeset_marked() tests past the end of the in-core bitset.  KASAN reports
this as a vmalloc-out-of-bounds access.

Apply the target offset before calculating the era block so writeset
lookups use the target-relative block number.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
Reviewed-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Fixes: eec4057 ("dm: add era target")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/md/dm-era-target.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=fe94a0b14010a3c267ff9a2508afb4f27ff1c5bf

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

The original Linux kernel CVE announcement for CVE-2026-72107 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72107

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 5

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 7.0

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).