[CVE-2026-53304][LOW] scsi: sg: Resolve soft lockup issue when opening /dev/sgX [ Upstream

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

CVE: CVE-2026-53304
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: scsi: sg: Resolve soft lockup issue when opening /dev/sgX [ Upstream
Commit: 3d74e0654ac908c65a8f20373091826fe43b1363
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d74e0654ac908c65a8f20373091826fe43b1363
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53304
Analysis date: Fri, 26 Jun 2026 15:51:38 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
The sg driver allowed the root-writable def_reserved_size module parameter to be set outside its valid range, allowing an administrator to trigger a CPU soft lockup when opening /dev/sgX, resulting in local denial of service only.

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

The original Linux kernel CVE announcement for CVE-2026-53304 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53304

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-2026-53304	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';*CWE-20;**CWE-400;*CWE-835;BEST CVSS score: '4.4';DESCR 'The sg driver allowed the def_reserved_size module parameter to be set through sysfs without enforcing the documented range from 0 to 1 MB. Setting a negative value such as -1 can make a later open of /dev/sgX enter sg_build_reserve and trigger a CPU soft lockup, causing denial of service. For the CVSS the PR:H is selected because writing to /sys/module/sg/parameters/def_reserved_size is root writable and normally requires administrative control of kernel module parameters. The issue is not network reachable and is triggered through a local control interface rather than SCSI I/O from a remote peer. Impact is denial of service only, with no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0)	YES	DEADLOCK DANGER HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	guess

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

ActionableScore=0

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Reliable kernel crash / strong DoS: +1
  The commit shows a reproducible CPU soft lockup after setting `def_reserved_size` to `-1` and opening `/dev/sg0`.

Subtracted signals:

* Requires admin/root/CAP_SYS_ADMIN-like control in typical deployments: -2
  The dangerous write is to `/sys/module/sg/parameters/def_reserved_size`, which is root-writable via module parameter sysfs permissions.

Not triggered:

* Remote reachable: +0
  No network path is involved.

* Local unprivileged trigger: +0
  Opening `/dev/sgX` may be local, but the required invalid parameter setup needs administrative control.

* Generic memory corruption: +0
  The patch is validation-only and rejects invalid parameter values. No UAF, OOB write, double-free, refcount misuse, or type confusion is shown.

* Privilege escalation plausible: +0
  The attacker already needs root-level control over kernel module parameters, and no additional security boundary bypass is demonstrated.

* Confidentiality or integrity impact: +0
  The observed effect is availability-only.

## 3. Reachability analysis

The bug is locally triggered by first writing an invalid value such as `-1` into the `sg` module parameter and then opening `/dev/sgX`. In normal deployments, writing that sysfs parameter requires root or equivalent administrative privileges. Namespaces and containers do not usually make `/sys/module/.../parameters` writable to unprivileged container users unless the host has delegated unusually broad privileges. The affected `sg` driver can be present on many systems, but the vulnerable action is a privileged control-plane operation, not ordinary SCSI I/O from an untrusted user.

## 4. Severity interpretation

This behaves like a Low-like or ordinary Moderate availability issue rather than an actionable Moderate or Important kernel vulnerability. The patch fixes missing input validation for a module parameter and the demonstrated impact is a soft lockup. There is no evidence of memory corruption, object lifetime misuse, information disclosure, privilege escalation, or cross-boundary access.

## 5. One-sentence report phrase

The sg driver allowed the root-writable def_reserved_size module parameter to be set outside its valid range, allowing an administrator to trigger a CPU soft lockup when opening /dev/sgX, resulting in local denial of service only.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a validation-only fix for a root-writable module parameter with demonstrated DoS-only impact and no supported memory-corruption or privilege-escalation primitive.

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

Patch: scsi: sg: Resolve soft lockup issue when opening /dev/sgX [ Upstream
Commit: 3d74e0654ac908c65a8f20373091826fe43b1363
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d74e0654ac908c65a8f20373091826fe43b1363

Changed files:
  drivers/scsi/sg.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=3d74e0654ac908c65a8f20373091826fe43b1363

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

The original Linux kernel CVE announcement for CVE-2026-53304 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53304

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: unknown
  Paranoid ActionableScore: 0

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).