[CVE-2026-80710][MODERATE 7.0] s390/dasd: Fix undersized format-check buffer

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

CVE: CVE-2026-80710
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/dasd: Fix undersized format-check buffer
Commit: aca18289c86f22d3fc2f3f6ff615286e7b1702f6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aca18289c86f22d3fc2f3f6ff615286e7b1702f6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80710
Analysis date: Fri, 28 Aug 2026 04:18:49 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An integer truncation in s390 DASD format checking can cause an undersized kernel allocation followed by an out-of-bounds write during channel-program buffer construction, making local DoS likely and privilege escalation plausible if an attacker can access the affected DASD ioctl path.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80710 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80710

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-2026-80710	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:H/I:H/A:H';CWE-190;CWE-131;*CWE-787;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'An integer truncation in s390/DASD format checking can allocate a buffer that is smaller than the amount of track metadata later written by the channel program setup. The bug is caused by storing the computed trkcount * rpt_max * sizeof(struct eckd_count) size in a 32-bit int after a wider calculation, so a large caller controlled track range can produce an undersized kzalloc() result. This is a local attack surface through the DASD BIODASDCHECKFMT ioctl on s390/ECKD devices and is not network reachable. For the CVSS the PR:L value is used for the paranoid score because a local non-root user or service account with access to the DASD block device ioctl could supply the affected range parameters. Impact can include kernel crash and potential privilege escalation because this is an out-of-bounds write into kernel allocated memory, not only a warning or resource leak.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	SIMPLEFIX  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The patch explicitly describes undersized allocation followed by writes past the end of `fmt_buffer`.
* Weak LPE concern: +1. The primitive is an OOB write in kernel memory, but payload and target control are not clearly demonstrated.
* Privileged kernel/device-management memory corruption path: +1. The affected path is s390 DASD storage device handling and channel-program related buffer construction.
* Reliable kernel crash / strong DoS: +1. OOB writes in this path can plausibly crash the kernel.
* Confidentiality impact plausible: +1. Kernel memory corruption can potentially expose or influence adjacent objects, but no direct leak is shown.
* Integrity impact plausible: +1. Kernel heap overwrite can corrupt kernel state.
* Important filesystem/storage path: +1. DASD is a block storage subsystem.
* Requires admin/root/CAP-like access in typical deployments: -2. Access to DASD block ioctls is normally restricted.
* Corruption primitive constrained or target/payload not fully controlled: -1. The overflow content appears tied to format-check or channel-program data rather than an arbitrary attacker payload.
* Rare hardware / platform-specific exposure: -1. This is s390/ECKD DASD specific.

Paranoid signals:

* Local trigger with reduced-privilege device access: +1. If a non-root user, service account, or storage-management process has access to the DASD device node or ioctl path, the caller-controlled range may be supplied without full host-root.
* Strong memory corruption primitive: +2. The commit directly states that an undersized allocation is followed by writes past the end of the allocated buffer.
* Privilege escalation plausible: +2. A kernel heap OOB write is a plausible LPE candidate even though exploitability is not proven.
* Privileged kernel/device-management memory corruption path: +1.
* Confidentiality impact plausible: +1.
* Integrity impact plausible: +1.
* Availability impact realistic: +1.
* Important filesystem/storage path: +1.
* Constrained overwrite uncertainty: -1.
* Rare s390/ECKD DASD exposure: -2.

Paranoid total: 7.

## 3. Reachability analysis

The bug is local and is not network reachable. Triggering requires access to the DASD `BIODASDCHECKFMT` ioctl path and caller-controlled `start_unit` / `stop_unit` values. In typical deployments this likely means root, a privileged storage-management tool, or access to a restricted block device node. Namespaces do not normally make raw host DASD management available to unprivileged containers, but reduced-capability service accounts or delegated storage administration may make PR:L a defensible paranoid interpretation. The affected platform is specialized: s390 with ECKD DASD devices, so exposure is much narrower than common x86 block-layer or filesystem bugs.

Call-site confidence: medium. The patch and commit message clearly describe the vulnerable allocation and later OOB write, but the exact downstream overwrite target and payload controllability are not fully shown in the provided diff.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or warning fix. The core issue is an integer truncation that causes an undersized kernel allocation followed by an out-of-bounds write. Realistically, exploitation may be constrained by platform specificity, device permissions, and limited control over the overwritten data. However, because the primitive is kernel memory corruption in a storage driver, it should be treated as Actionable Moderate at minimum and a Strong Important candidate under the paranoid interpretation.

## 5. One-sentence report phrase

An integer truncation in s390 DASD format checking can cause an undersized kernel allocation followed by an out-of-bounds write during channel-program buffer construction, making local DoS likely and privilege escalation plausible if an attacker can access the affected DASD ioctl path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: the patch explicitly describes kernel OOB write memory corruption, and the practical risk depends on device-node permissions, s390/DASD deployment details, and how much control the caller has over the overflow length, payload, and adjacent kernel objects.

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

Patch: s390/dasd: Fix undersized format-check buffer
Commit: aca18289c86f22d3fc2f3f6ff615286e7b1702f6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aca18289c86f22d3fc2f3f6ff615286e7b1702f6

Commit description:

fmt_buffer_size in dasd_eckd_check_device_format() is declared as
int, even though one of the multiplicands, sizeof(struct eckd_count),
is a size_t. The expression

    trkcount * rpt_max * sizeof(struct eckd_count)

is therefore correctly evaluated at 64-bit width, but the result is
silently truncated when it is stored back into the 32-bit
fmt_buffer_size variable. For a sufficiently large track range
(start_unit/stop_unit are caller-controlled) this truncation
yields a buffer size far smaller than the number of tracks actually
requested. kzalloc() then succeeds with an undersized allocation,
while the subsequent channel program build still operates on the
untruncated track count and writes past the end of that buffer.

Compute the buffer size with check_mul_overflow() and keep it in a
size_t, so that a value that no longer fits results in -EINVAL
instead of a silently truncated allocation size.

Fixes: 8fd5752 ("s390/dasd: Add new ioctl BIODASDCHECKFMT")
Cc: stable@vger.kernel.org #4.7
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260727142840.567286-4-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/s390/block/dasd_eckd.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=aca18289c86f22d3fc2f3f6ff615286e7b1702f6

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

The original Linux kernel CVE announcement for CVE-2026-80710 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80710

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:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 5
  Paranoid ActionableScore: 7

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: YES
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).