[CVE-2026-74470][MODERATE 7.0] scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write

[CVE-2026-74470][MODERATE 7.0] scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write

[AL-KERNEL]

CVE: CVE-2026-74470
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write
Commit: 49e5b25a0b74dbac595f122e5608fdce2918cc4e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49e5b25a0b74dbac595f122e5608fdce2918cc4e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74470
Analysis date: Sat, 15 Aug 2026 17:43:10 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A crafted REPORT ZONES allocation length in scsi_debug can cause a 4 GB allocation size to truncate to kzalloc(0) on 32-bit systems, leading to an out-of-bounds write and likely local kernel crash when raw SCSI command access is available.

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

The original Linux kernel CVE announcement for CVE-2026-74470 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74470

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
======================================================================

CVE-2026-74470	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-787;CWE-190;CWE-131;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'scsi_debug REPORT ZONES can compute a 4 GB response buffer length from a large alloc_len value on 32-bit systems. The 4 GB size can truncate to 0 for kzalloc, so kzalloc(0) returns ZERO_SIZE_PTR and later descriptor writes are made past that pointer in resp_report_zones. A local actor that can issue raw SCSI commands to an affected scsi_debug zoned device can trigger a kernel OOB write and likely panic. For the CVSS the PR:L is used in the paranoid score because reliable triggering may only require local access to the scsi_debug device or an account allowed to send SG_IO style commands, while loading or configuring the debug device itself is usually administrative. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the paranoid interpretation may include limited confidentiality or integrity impact because the failure mode is an OOB write rather than a pure NULL dereference.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	WRITE OOB DANGER LOG HARDWARE  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

Paranoid score signals:

* Local unprivileged trigger: +1
  If scsi_debug is already loaded and the device node allows SG_IO or raw SCSI command access, a local non-root user may be able to issue REPORT ZONES with a crafted allocation length.

* Generic memory corruption: +2
  The patch description explicitly states out-of-bounds write / panic. This is not just a warning or validation cleanup.

* Memory layout invariant restoration: +1
  The fix restores consistency between alloc_len, rep_max_zones, arr_len, and the real device zone count.

* Reliable kernel crash / strong DoS: +1
  kzalloc(0) returns ZERO_SIZE_PTR, then desc = arr + 64 is written through, making panic/Oops realistic.

* Weak LPE concern: +1
  The primitive is an OOB write, so manual review is justified, but there is no demonstrated reclaim, controlled target, arbitrary write, or object replacement.

* Integrity impact plausible: +1
  Limited integrity concern is defensible because the failure mode is an OOB write, not a pure NULL dereference.

Subtract:

* Corruption primitive constrained / no attacker-controlled target: -1
  The overwrite appears near ZERO_SIZE_PTR and the payload is mostly kernel-generated report-zone descriptor data.

* Rare / non-default condition: -1
  Requires 32-bit truncation behavior and scsi_debug zoned REPORT ZONES exposure. scsi_debug is a debug/test driver, not a default production storage path.

Conservative score is lower because loading/configuring scsi_debug normally requires administrative privileges.

## 3. Reachability analysis

The bug is local, not network reachable. In the conservative deployment model, triggering requires root or administrative control to load and configure scsi_debug, so the issue is lower priority. In the paranoid model, if an affected scsi_debug zoned device already exists and local users can issue SG_IO-style commands to it, PR:L is reasonable. Namespaces do not automatically make this reachable, but container or service configurations that expose raw SCSI devices could lower the practical privilege requirement. Call-site confidence: high, because the vulnerable allocation and later descriptor write are described directly in the patch context.

## 4. Severity interpretation

This is not a Strong Important candidate by default because the affected driver is non-default/debug-oriented, the condition is 32-bit-specific, and the OOB write appears highly constrained. However, it should not be auto-closed as an ordinary low-risk DoS because the patch documents an explicit kernel OOB write, not only a crash or resource leak. Realistic impact is likely local kernel crash. Theoretical impact beyond DoS is limited but deserves manual review due to memory corruption semantics.

## 5. One-sentence report phrase

A crafted REPORT ZONES allocation length in scsi_debug can cause a 4 GB allocation size to truncate to kzalloc(0) on 32-bit systems, leading to an out-of-bounds write and likely local kernel crash when raw SCSI command access is available.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit OOB write candidate, PR:L is plausible when the debug device is already exposed, and paranoid scoring reaches actionable Moderate even though practical exploitation beyond DoS is constrained.

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

Patch: scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write
Commit: 49e5b25a0b74dbac595f122e5608fdce2918cc4e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49e5b25a0b74dbac595f122e5608fdce2918cc4e

Commit description:

resp_report_zones() sizes the reply buffer from the CDB allocation
length. The v3 fix rounds alloc_len up with ALIGN() before deriving the
descriptor count:

	rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) -
			 RZONES_DESC_HD) >> ilog2(RZONES_DESC_HD);
	arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1);

For alloc_len in 0xFFFFFFC1..0xFFFFFFFF, ALIGN() rounds up to
0x100000000, so arr_len is 4 GB. On 32-bit, kzalloc()'s size_t is 32-bit
and truncates 0x100000000 to 0; kzalloc(0) returns ZERO_SIZE_PTR, which
passes the !arr check, and desc = arr + 64 is then dereferenced in the
loop -> out-of-bounds write / panic.

Clamp rep_max_zones to devip->nr_zones. The loop already stops at
sdebug_capacity (after nr_zones zones), so a report can never hold more
than nr_zones descriptors; the clamp does not change the report, it only
bounds arr_len to (nr_zones + 1) * RZONES_DESC_HD, a real device
property that can never reach 0x100000000.

Fixes: 7db0e0c ("scsi: scsi_debug: Fix buffer size of REPORT ZONES command")
Suggested-by: Damien Le Moal <dlemoal@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Assisted-by: AuditCode-AI:2026.07
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20260712183739.83915-1-security@auditcode.ai
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/scsi/scsi_debug.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=49e5b25a0b74dbac595f122e5608fdce2918cc4e

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

The original Linux kernel CVE announcement for CVE-2026-74470 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74470

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:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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).