[CVE-2026-74629][MODERATE 7.0] net/dibs: Correct freeing of dmb_clientid_arr

[CVE-2026-74629][MODERATE 7.0] net/dibs: Correct freeing of dmb_clientid_arr

[AL-KERNEL]

CVE: CVE-2026-74629
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/dibs: Correct freeing of dmb_clientid_arr
Commit: ece6426b61241e9bfb41aa131f235168f55229b1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ece6426b61241e9bfb41aa131f235168f55229b1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74629
Analysis date: Sat, 22 Aug 2026 17:53:09 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A DIBS device lifetime bug can free `dmb_clientid_arr` before all users are gone, allowing an interrupt handler to access freed memory and also creating a double-free error path, with realistic local DoS impact and possible memory-corruption escalation concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74629 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74629

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-2026-74629	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-415;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free is possible in the DIBS device lifetime path because dmb_clientid_arr could be freed in dibs_dev_del while an interrupt handler may still access it after device deletion. A related error path in dibs_lo_dev_probe could also free the same array twice when dibs_dev_add fails, which makes this a memory lifetime issue rather than a simple leak. For the CVSS the PR:L is used in the paranoid score because a local actor with delegated device or driver control, such as a service account or reduced capability administrator, may be able to trigger add or delete paths without full host root privileges. The issue is not directly network reachable based on the patch context. Impact is at least denial of service via crash and in the worst case may allow confidentiality or integrity impact due to use after free or double free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74629 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER UAF HARDWARE LINUS KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, strong corruption primitive: +2. The patch explicitly describes UAF and double free involving `dmb_clientid_arr`.
* Real lifetime corruption: +1. Freeing is moved to `dibs_dev_release()` so the object is released only after the last device reference is gone.
* Reliable kernel crash / strong DoS: +1. An interrupt handler may access freed memory after `dibs_dev_del()`.
* Privileged kernel/device-management memory corruption path: +1. The affected code is driver/device lifetime management.
* Requires admin/root/CAP-like control in typical deployments: -2. Reliable triggering likely requires device add/delete/probe/remove or driver lifecycle control.
* Hard or unreliable race / special timing required: -1. The UAF depends on an interrupt handler remaining active after device deletion.

Paranoid additions:

* Weak LPE concern: +1. UAF and double-free in kernel heap lifetime management may be exploitable beyond DoS, but no reclaim or overwrite primitive is shown.
* Confidentiality impact plausible: +1. Only in the paranoid interpretation, due to generic UAF/double-free corruption risk.
* Integrity impact plausible: +1. Only in the paranoid interpretation, due to possible heap object corruption.
* Reduced privilege/device-control interpretation: +1 effective uplift. A service account, container root with delegated device control, or reduced-capability administrator may be able to reach lifecycle paths without full host-root equivalence.

Call-site confidence: high. The patch directly shows the relevant free sites in `dibs_dev_del()`, `dibs_lo_dev_probe()` error handling, and final release in `dibs_dev_release()`.

## 3. Reachability analysis

The issue is not directly network reachable based on the supplied patch. Triggering requires interaction with the DIBS device lifecycle, such as add, delete, probe failure, remove, or related driver/device-management paths. In normal deployments this is likely privileged host-local activity.

Namespaces or containers matter only if device management is delegated. If an untrusted service account, reduced-capability root, or containerized workload can cause DIBS device creation/removal or probe failure, the practical privilege requirement can drop from full admin to a PR:L-like local actor. The patch context does not show a default unprivileged user API.

The realistic impact is kernel crash or device/driver state corruption. Privilege escalation is technically plausible because UAF and double-free are real memory lifetime bugs, but exploitation evidence is not demonstrated.

## 4. Severity interpretation

This should not be treated as an ordinary low Moderate cleanup. It is a real lifetime bug with both UAF and double-free indicators, so manual review is justified.

Realistically, the most likely impact is local privileged DoS through a crash or device teardown race. The Important-class concern comes from the memory corruption class and the possibility that delegated device-control environments lower the required privileges. Without evidence of attacker-controlled reclaim, overwrite target control, callback control, or object replacement, it should be treated as Actionable Moderate by default and a Strong Important candidate only under the paranoid interpretation.

## 5. One-sentence report phrase

A DIBS device lifetime bug can free `dmb_clientid_arr` before all users are gone, allowing an interrupt handler to access freed memory and also creating a double-free error path, with realistic local DoS impact and possible memory-corruption escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The bug class includes explicit UAF and double-free in kernel device lifetime management. Even though triggering appears local and typically privileged, this is memory corruption and should not be auto-closed without confirming reachability, deployment exposure, and whether any delegated device-management path exists.

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

Patch: net/dibs: Correct freeing of dmb_clientid_arr
Commit: ece6426b61241e9bfb41aa131f235168f55229b1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ece6426b61241e9bfb41aa131f235168f55229b1

Commit description:

A dibs device interrupt handler can be active after dibs_dev_del() and
may still access dmb_clientid_arr. (UAF)

In case of a failure in dibs_dev_add() being called by dibs_lo_dev_probe()
dmb_clientid_arr is freed twice (double free).

Free dmb_clientid_arr in dibs_dev_release() after last reference is gone.
Note that allocating in dibs_dev_add() instead of dibs_dev_alloc() is ok
for now, because no dmbs can be registered before dibs_dev_add().

Fixes: cc21191 ("dibs: Move data path to dibs layer")
Cc: stable@vger.kernel.org
Co-developed-by: Hidayath Khan <hidayath@linux.ibm.com>
Signed-off-by: Hidayath Khan <hidayath@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/20260810111432.2334900-1-wintera@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/dibs/dibs_loopback.c
  drivers/dibs/dibs_main.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=ece6426b61241e9bfb41aa131f235168f55229b1

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

The original Linux kernel CVE announcement for CVE-2026-74629 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74629

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 6

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).