[CVE-2026-64297][LOW] module: decompress: check return value of module_extend_max_pages()

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

CVE: CVE-2026-64297
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: module: decompress: check return value of module_extend_max_pages()
Commit: e7f174715f9f0cbcb9e87b52e4fc4ef149baac98
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7f174715f9f0cbcb9e87b52e4fc4ef149baac98
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64297
Analysis date: Sat, 25 Jul 2026 10:50:36 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like auto-close candidate
Manual review required: NO

Summary:
A missing error check in module_decompress() can turn an allocation failure into a ZERO_SIZE_PTR dereference during compressed module loading, causing a local kernel oops or DoS, normally requiring privileged module-loading capability.

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

The original Linux kernel CVE announcement for CVE-2026-64297 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64297

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64297	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-252;CWE-690;**CWE-476;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A missing error check in module_decompress() allows module_extend_max_pages() allocation failure to leave the module page array uninitialized. Later module_get_next_page() can try to grow the array from zero pages, causing kvrealloc(NULL, 0) to return ZERO_SIZE_PTR and leading to a kernel oops when that value is dereferenced. The direct trigger is local and normally requires the ability to load a compressed kernel module or to cause a kernel assisted module load under memory pressure. For the CVSS the PR:L is used for the paranoid score because an unprivileged local process may be able to combine memory pressure with an automatic module load path, while direct module loading normally requires administrative privileges. The issue is not network reachable. Impact is denial of service via kernel crash or oops, with no supported evidence of information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like auto-close candidate (with actual score 1)	YES	SIMPLEFIX IMPROVEONLY 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
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The commit describes a ZERO_SIZE_PTR dereference leading to kernel oops.
* Requires admin/root/CAP_SYS_MODULE in typical deployments: -2. Direct triggering normally requires loading a compressed kernel module.
* Broad/default/common subsystem: +1. Kernel module loading is a common kernel facility, but the vulnerable path is privileged.

Conservative total: 0.

Paranoid additional interpretation:

* Local unprivileged trigger: +1. A local unprivileged process might indirectly trigger automatic module loading while creating memory pressure, but this is not a reliable direct trigger.
* Hard or unreliable condition: -1. The crash depends on allocation failure and a specific compressed-module loading path.
* Reliable kernel crash / strong DoS: +1.
* Broad/default/common subsystem: +1.

Paranoid total: 2.

No memory corruption, UAF, OOB write, refcount takeover, page-cache corruption, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The direct trigger is local and normally requires administrative control over module loading, typically CAP_SYS_MODULE or root. A weaker paranoid path exists if an unprivileged local process can cause kernel-assisted module autoloading while also inducing memory pressure, but this is indirect and reliability is low. Containers and namespaces usually do not lower this to a practical unprivileged trigger unless module autoloading is exposed by host policy. The path is not network reachable.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue. The bug is an unchecked allocation failure followed by ZERO_SIZE_PTR dereference, not a reclaimable UAF or attacker-controlled overwrite. Theoretical availability impact is real, but realistic exploitation requires privileged module loading or an unreliable autoload plus memory-pressure scenario. There is no evidence of confidentiality impact, integrity impact, or LPE.

## 5. One-sentence report phrase

A missing error check in module_decompress() can turn an allocation failure into a ZERO_SIZE_PTR dereference during compressed module loading, causing a local kernel oops or DoS, normally requiring privileged module-loading capability.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an auto-close candidate unless external information shows an unprivileged reliable autoload trigger or a corruption primitive beyond ZERO_SIZE_PTR dereference.

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

Patch: module: decompress: check return value of module_extend_max_pages()
Commit: e7f174715f9f0cbcb9e87b52e4fc4ef149baac98
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7f174715f9f0cbcb9e87b52e4fc4ef149baac98

Commit description:

module_extend_max_pages() calls kvrealloc() internally and returns
-ENOMEM on allocation failure. The return value is never checked.

If the initial allocation fails, info->pages remains NULL and
info->max_pages remains 0. Subsequent calls to module_get_next_page()
will attempt to dynamically grow the array by calling
module_extend_max_pages(info, 0) since info->used_pages is 0. This
results in kvrealloc(NULL, 0) returning ZERO_SIZE_PTR, which is treated
as a success, leading to a dereference of ZERO_SIZE_PTR and a kernel
oops.

Fix: add the missing error check after module_extend_max_pages() and
return immediately on failure. This matches the pattern used by every
other kvrealloc() caller in the module loading path.

Fixes: b1ae6dc ("module: add in-kernel support for decompressing")
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Andrii Kuchmenko <capyenglishlite@gmail.com>
Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
[Sami: Corrected the analysis in the commit message.]
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/module/decompress.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=e7f174715f9f0cbcb9e87b52e4fc4ef149baac98

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

The original Linux kernel CVE announcement for CVE-2026-64297 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64297

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: 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).