[CVE-2026-72491][MODERATE 7.0] net/9p: fix race condition on rdma->state in trans_rdma.c [ Upstream

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

CVE: CVE-2026-72491
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/9p: fix race condition on rdma->state in trans_rdma.c [ Upstream
Commit: 4cee2b8766045059d5e0b8114837b4a8efe827ac
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cee2b8766045059d5e0b8114837b4a8efe827ac
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72491
Analysis date: Sat, 15 Aug 2026 08:42:32 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the 9p/RDMA transport can corrupt the RDMA connection state machine because `rdma->state` is updated without consistent `req_lock` protection, potentially causing use-after-free of request objects during teardown and leading at least to kernel crash DoS.

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

The original Linux kernel CVE announcement for CVE-2026-72491 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72491

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-2026-72491	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;CWE-667;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A race condition in the 9p/RDMA transport can occur because rdma state is modified without consistent req_lock protection in recv_done() and p9_cm_event_handler(), while rdma_request() reads and updates the same state under the lock. A lost FLUSHING or CLOSED transition can corrupt the RDMA connection state machine during teardown and may lead to use after free of RDMA request objects. For the CVSS the PR:N is used in the paranoid score because a malicious or compromised RDMA peer may influence disconnect and completion timing without an account on the victim, assuming the victim already uses a reachable 9p/RDMA mount. The attack is not Internet scale and is better modeled as AV:A because it depends on RDMA or a local storage fabric rather than ordinary remote IP exposure. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality and integrity impact due to UAF based memory corruption, so the issue should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-72491 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LOCK INIT RACE UAF IMPROVEONLY LINUS  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**. The affected path is 9p over RDMA, so triggering can involve an RDMA peer or RDMA fabric events, especially disconnect or completion timing. This is not Internet-scale remote exposure, but it is externally influenceable over an RDMA/storage fabric.
* **Local unprivileged trigger: +1**. If a 9p/RDMA mount is already configured and accessible, local users may generate file operations that enter `rdma_request()`.
* **Memory corruption, weak/indirect corruption candidate: +1**. The commit explicitly says the state-machine race can cause use-after-free on RDMA request objects, but the patch does not show attacker-controlled reclaim, controlled overwrite, callback control, or type confusion.
* **Real lifetime corruption: +1**. The bug is a race in teardown/request lifetime handling and can leave request objects in an unsafe lifetime state.
* **Reliable kernel crash / strong DoS: +1**. A UAF during RDMA teardown is a credible kernel crash condition.
* **Hard or unreliable race / special timing required: -1**. Exploitation depends on racing request submission, completion handling, and RDMA CM events.
* **Rare AND difficult-to-reach subsystem/configuration: -1**. 9p/RDMA requires RDMA-capable deployment and is not a broad default kernel attack surface.

Paranoid adjustment:

* **Weak LPE concern: +1**, but only for triage sensitivity. UAF is present in a kernel object lifetime path, but no practical reclaim or write primitive is demonstrated.
* **Confidentiality impact plausible: +1** and **Integrity impact plausible: +1** are defensible only in the paranoid interpretation because UAF-based memory corruption can sometimes be developed beyond DoS.
* **Race-UAF cap applied**. Because this is a race-dependent UAF without demonstrated reclaim, overwrite, type confusion, callback dispatch, or refcount takeover, the paranoid ActionableScore is capped at **5**.

Call-site confidence: **medium**. The patch shows the affected state writes and the commit describes the interaction with `rdma_request()`, but the full request teardown and object-freeing paths are not included.

## 3. Reachability analysis

The bug can be influenced by a local user performing operations on an already configured 9p/RDMA mount, and potentially by a malicious or compromised RDMA peer influencing disconnect and completion timing. Creating or configuring such a mount is normally privileged, but once exposed to users, ordinary file operations may participate in the race. Containers or namespaces do not automatically make this broadly reachable unless the host exposes the 9p/RDMA mount or RDMA device context to them.

The path is not default Internet-facing networking. It is best treated as adjacent or storage-fabric reachable, not ordinary AV:N public network exposure. Realistic exploitation requires a 9p/RDMA deployment, RDMA connectivity, and timing control over teardown or error paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the commit explicitly mentions use-after-free on RDMA request objects, not just a benign state mismatch. However, the demonstrated primitive is still weak: the patch does not show controlled reuse, write-after-free, type confusion, callback control, or an obvious privilege-escalation chain.

Conservatively, it is a **borderline/manual-review Moderate** with strong DoS potential. Paranoid triage should treat it as **Actionable Moderate at minimum** because kernel UAF in an externally influenced RDMA transport should not be auto-closed without review.

## 5. One-sentence report phrase

A race in the 9p/RDMA transport can corrupt the RDMA connection state machine because `rdma->state` is updated without consistent `req_lock` protection, potentially causing use-after-free of request objects during teardown and leading at least to kernel crash DoS.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the patch context explicitly identifies a race-driven UAF in a kernel RDMA transport path with possible adjacent-fabric influence. Practical LPE is not demonstrated, but the memory-lifetime class and teardown context justify manual review rather than automatic closure.

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

Patch: net/9p: fix race condition on rdma->state in trans_rdma.c [ Upstream
Commit: 4cee2b8766045059d5e0b8114837b4a8efe827ac
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cee2b8766045059d5e0b8114837b4a8efe827ac

Changed files:
  net/9p/trans_rdma.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=4cee2b8766045059d5e0b8114837b4a8efe827ac

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

The original Linux kernel CVE announcement for CVE-2026-72491 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72491

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:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).