[CVE-2026-72040][LOW] ipmi: fix refcount leak in i_ipmi_request() [ Upstream commit a3f3859cecacb64f18fd446271ece9a3b3f2d4de ]

[CVE-2026-72040][LOW] ipmi: fix refcount leak in i_ipmi_request() [ Upstream commit a3f3859cecacb64f18fd446271ece9a3b3f2d4de ]

[AL-KERNEL]

CVE: CVE-2026-72040
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ipmi: fix refcount leak in i_ipmi_request() [ Upstream commit a3f3859cecacb64f18fd446271ece9a3b3f2d4de ]
Commit: 9409e18ffe7378d202efe1cf69989df9f67b0369
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9409e18ffe7378d202efe1cf69989df9f67b0369
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72040
Analysis date: Sun, 16 Aug 2026 03:38:24 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
`i_ipmi_request() can leak IPMI user message references on supplied_recv error paths, allowing repeated local failures to cause IPMI resource exhaustion or degraded service availability, but the patch does not indicate memory corruption or privilege escalation.`

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

The original Linux kernel CVE announcement for CVE-2026-72040 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72040

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-2026-72040	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-772;*CWE-401;CWE-404;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'i_ipmi_request() can leak IPMI user references when supplied_recv is used and a later error path is taken. The function increments nr_msgs and the user kref, but the old cleanup path only freed internally allocated recv messages and did not undo the reference operations for caller supplied messages. This can keep the IPMI user object referenced and can permanently consume message accounting entries, leading to local resource exhaustion or degraded IPMI service availability after repeated failures. For the CVSS the PR:L is used in the paranoid score because some deployments may expose IPMI management paths to local service accounts or delegated operators rather than only full administrators. The issue is not network reachable by itself and does not show a memory corruption primitive. Impact is denial of service through resource leakage, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-72040 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX LEAK ERRORPATH LINUS 	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered signals:

* Real lifetime corruption: +1
  The bug is a refcount lifetime leak. `i_ipmi_request()` increments `recv_msg->user->nr_msgs` and the user `kref`, but failed to undo those operations on error when `supplied_recv` is used.

* Availability impact realistic: +1
  Repeated failures can permanently consume message accounting references or keep IPMI user objects referenced, causing local IPMI resource exhaustion or degraded IPMI service availability.

Not triggered:

* No remote reachable signal.
  The patch affects the local IPMI message handler path and does not show a directly network-triggerable attack surface.

* No generic memory corruption signal.
  This is a leaked reference and accounting mismatch, not UAF, double-free, OOB write, type confusion, or arbitrary write.

* No privilege escalation plausible signal.
  The patch does not support a reclaim, overwrite, stale callback, object replacement, or refcount takeover primitive.

Subtracting or limiting factors:

* Special error-path condition: -1 for conservative interpretation.
  The leak requires the `supplied_recv` path and a later error path, not a simple always-triggered operation.

* No Important-class exposure bonus.
  IPMI is important on servers but this specific bug is a local resource leak in a management path, not a broad default kernel data-plane issue.

## 3. Reachability analysis

The most realistic trigger is a local process or kernel IPMI consumer that can reach `ipmi_request_supply_msgs()` or related IPMI request paths and repeatedly cause error handling after the supplied receive message has had its user reference accounting incremented. In typical deployments, IPMI access is restricted to root, an IPMI management service, or a delegated local operator group, so this is not a clean unprivileged-local issue. Namespaces do not obviously lower the requirement because the affected object is a host IPMI management interface, not a namespaced ordinary syscall path. There is no evidence that a remote network attacker can trigger this directly without already controlling a local IPMI management component or the relevant host-side interface.

Call-site confidence: medium. The patch and commit explicitly identify `ipmi_request_supply_msgs()` as the caller consequence, but the full caller graph and product-specific device permissions are not included.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local resource leak, not an Important-class vulnerability. The theoretical impact is local denial of service against IPMI message accounting or IPMI user lifetime cleanup after repeated failures. The realistic exploitation evidence does not show memory corruption, confidentiality impact, integrity impact, or privilege escalation. The paranoid score stays low because the bug class is refcount/resource leakage only.

## 5. One-sentence report phrase

`i_ipmi_request() can leak IPMI user message references on supplied_recv error paths, allowing repeated local failures to cause IPMI resource exhaustion or degraded service availability, but the patch does not indicate memory corruption or privilege escalation.`

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an auto-close or deferred Moderate-style issue unless the evaluated product exposes IPMI request paths to untrusted local users or has evidence of easy repeated triggering from a non-admin service account.

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

Patch: ipmi: fix refcount leak in i_ipmi_request() [ Upstream commit a3f3859cecacb64f18fd446271ece9a3b3f2d4de ]
Commit: 9409e18ffe7378d202efe1cf69989df9f67b0369
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9409e18ffe7378d202efe1cf69989df9f67b0369

Commit description:

When a caller provides a `supplied_recv` message to i_ipmi_request(),
the function increments the user's `nr_msgs` reference count. If an
error occurs later, the out_err cleanup path only frees the recv_msg
if the function allocated it itself (i.e., !supplied_recv). In the
supplied_recv case the cleanup is skipped, leaving the reference count
elevated. The caller ipmi_request_supply_msgs() does not release the
supplied_recv on error, so the reference is permanently leaked.

Fix this by explicitly reverting the reference count operations when a
supplied recv_msg with a valid user pointer is present in the error
path: decrement nr_msgs and drop the user's kref.

Cc: stable@vger.kernel.org
Fixes: b52da4054ee0 ("ipmi: Rework user message limit handling")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Message-ID: <20260603120634.3758747-1-vulab@iscas.ac.cn>
Signed-off-by: Corey Minyard <corey@minyard.net>
[ changed `free_ipmi_user` to `free_user` in the two added `kref_put()` calls ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- drivers/char/ipmi/ipmi_msghandler.c 8

Changed files:
  drivers/char/ipmi/ipmi_msghandler.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=9409e18ffe7378d202efe1cf69989df9f67b0369

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

The original Linux kernel CVE announcement for CVE-2026-72040 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72040

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:L
  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: 1
  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).