[CVE-2026-72104][LOW] dm-pcache: reject option groups without values commit d9c631e3fbd44246a2be781d26cfacbb9b8ec127 upstream.

[CVE-2026-72104][LOW] dm-pcache: reject option groups without values commit d9c631e3fbd44246a2be781d26cfacbb9b8ec127 upstream.

[AL-KERNEL]

CVE: CVE-2026-72104
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dm-pcache: reject option groups without values commit d9c631e3fbd44246a2be781d26cfacbb9b8ec127 upstream.
Commit: 1247615aadb74c89c1b2f01a6de7df9dab92ecb3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1247615aadb74c89c1b2f01a6de7df9dab92ecb3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72104
Analysis date: Sat, 15 Aug 2026 16:06:26 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A malformed dm-pcache device-mapper table can omit the value for cache_mode or data_crc, causing a NULL pointer dereference during option parsing and a local denial of service, typically requiring administrative device-mapper control.

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

The original Linux kernel CVE announcement for CVE-2026-72104 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72104

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-2026-72104	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-476;*CWE-20;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 'A NULL pointer dereference in dm_pcache option parsing can occur when a malformed device mapper table declares an optional argument but provides only the option name without its value. The parser can consume cache_mode or data_crc and then call dm_shift_arg for the missing value, which returns NULL and is later passed to strcmp. For the CVSS the PR:L is used in the paranoid interpretation because some environments delegate device mapper control to storage services, containers, or reduced capability administrators, although normal dmsetup table loading usually requires CAP_SYS_ADMIN. The issue is local and is not network reachable. Impact is denial of service via kernel oops or crash during target construction, with no supported confidentiality or integrity primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-72104 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DISK HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	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 malformed dm-pcache table can cause dm_shift_arg() to return NULL, followed by strcmp(NULL, ...), producing a NULL pointer dereference during target construction.

* Important filesystem/storage path: +1 in paranoid view only
  The affected code is in device-mapper storage target setup, but the bug is limited to parsing invalid target options and does not affect storage metadata integrity or data-plane writes.

Subtracted signals:

* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2
  Loading or changing device-mapper tables normally requires root or CAP_SYS_ADMIN via dmsetup or equivalent access to /dev/mapper/control.

* Rare / non-default target path: -1 in conservative view
  dm-pcache is a specific device-mapper target and the trigger requires constructing a malformed table for that target.

Not triggered:

* No local unprivileged trigger in typical deployments.
* No remote or network reachability.
* No UAF, double-free, OOB write, arbitrary write, refcount abuse, type confusion, or page-cache corruption.
* No confidentiality or integrity primitive.
* No plausible privilege escalation from the patch context.

Call-site confidence: high. The vulnerable parser path and the NULL dereference condition are directly described by the commit and visible in the patch.

## 3. Reachability analysis

The bug is triggered by submitting a malformed dm-pcache device-mapper table where a recognized option such as cache_mode or data_crc is provided without its required value. In normal deployments, this requires administrative storage management privileges, typically root or CAP_SYS_ADMIN. A reduced-capability storage service or containerized environment with delegated device-mapper control could lower the practical privilege boundary, but this is not the default model and does not make the issue broadly unprivileged. The path is local only and not network-triggerable.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue. The realistic impact is a kernel oops or crash during invalid target construction. Theoretical impact does not extend beyond DoS because the patch shows a NULL pointer dereference from missing argument validation, not a memory corruption primitive with attacker-controlled reuse, overwrite, disclosure, or privilege escalation potential.

## 5. One-sentence report phrase

A malformed dm-pcache device-mapper table can omit the value for cache_mode or data_crc, causing a NULL pointer dereference during option parsing and a local denial of service, typically requiring administrative device-mapper control.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a validation-only NULL pointer dereference in a privileged local storage configuration path, with no supported confidentiality, integrity, or privilege-escalation primitive.

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

Patch: dm-pcache: reject option groups without values commit d9c631e3fbd44246a2be781d26cfacbb9b8ec127 upstream.
Commit: 1247615aadb74c89c1b2f01a6de7df9dab92ecb3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1247615aadb74c89c1b2f01a6de7df9dab92ecb3

Commit description:

The pcache target parses optional arguments as name/value pairs.  A
table that advertises one optional argument and supplies only a
recognized option name, for example "cache_mode", reaches
parse_cache_opts() with argc == 1.  The parser consumes the name,
decrements argc to zero, then calls dm_shift_arg() again for the value.
dm_shift_arg() returns NULL when no arguments remain, and the following
strcmp() dereferences that NULL pointer.

Check that each recognized option has a value before consuming it.  This
keeps valid "cache_mode writeback" and "data_crc true/false" tables
unchanged while making malformed tables fail during target construction
with a precise missing-value error.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
Reviewed-by:  Zheng Gu <cengku@gmail.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 1d57628ff95b ("dm-pcache: add persistent cache target in device-mapper")
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- drivers/md/dm-pcache/dm_pcache.c 8

Changed files:
  drivers/md/dm-pcache/dm_pcache.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=1247615aadb74c89c1b2f01a6de7df9dab92ecb3

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

The original Linux kernel CVE announcement for CVE-2026-72104 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72104

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: 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).