[CVE-2026-45910][MODERATE 7.0] RDMA/rxe: Fix race condition in QP timer handlers [ Upstream

[CVE-2026-45910][MODERATE 7.0] RDMA/rxe: Fix race condition in QP timer handlers [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45910
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/rxe: Fix race condition in QP timer handlers [ Upstream
Commit: 756c93d6df7c3bc599f6590b8e5afead6a41de1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=756c93d6df7c3bc599f6590b8e5afead6a41de1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45910
Analysis date: Wed, 27 May 2026 09:24:31 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-45910 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45910

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45910	MODERATE	CHECK	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-362;*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in RDMA rxe QP timer callbacks can let retransmit_timer or rnr_nak_timer run while rxe_destroy_qp drops the QP reference count to zero. The timer then may continue using a QP whose lifetime is ending, causing refcount underflow and a real use-after-free in the software RDMA driver. For the CVSS the PR:L is used because a local user with RDMA uverbs access may create and destroy QPs and influence timer activity without full host root privileges. The issue is not directly Internet reachable, but peer behavior or packet loss may help make retransmit or RNR timers active. Impact is at least local denial of service via kernel warning or crash. In the paranoid interpretation, the real UAF warrants confidentiality and integrity impact for manual review sensitivity, even though no controlled reclaim or proven privilege escalation primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB RACE UAF NETWORK HARDWARE KPANIC 	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

2. Signal breakdown
* Generic memory corruption / UAF: +2. The commit explicitly reports refcount underflow and use-after-free when a QP timer races with QP destruction.
* Real lifetime corruption: +1. Timer callbacks can run while `rxe_destroy_qp()` drops the QP reference count to zero.
* Local unprivileged or low-privileged trigger: +1. If an RXE device is available, a local user with RDMA uverbs access may create and destroy QPs and influence timer activity.
* Local high-control kernel data-plane API: +1. RDMA uverbs exposes rich object lifetime and queue-pair control to userspace.
* Reliable kernel crash / strong DoS: +1. The observed warnings include refcount underflow and UAF, and realistic impact includes kernel warning or crash.
* Weak LPE concern: +1 in paranoid scoring. This is a real UAF on a userspace-reachable RDMA object, but no controlled reclaim, arbitrary write, or proven privilege escalation primitive is shown.
* Hard race / timing required: -1. Exploitation requires racing QP timer execution with QP destruction.
* Configuration-dependent exposure: -1. RXE must be enabled/configured and accessible, so this is not universal default exposure.

3. Reachability analysis
The bug is reachable through RDMA RXE Queue Pair lifetime handling. A local user with access to an RXE/uverbs device can potentially create and destroy QPs while retransmit or RNR timers are active. Creating or configuring the RXE device itself may require administrative privileges, but once exposed, QP operations may be available to non-root RDMA users depending on device permissions and deployment policy. Remote packets are not a direct standalone trigger, although peer behavior or packet loss can help make retransmit/RNR timers active.

4. Severity interpretation
This is more than an ordinary Moderate because it is an explicit race-based UAF with refcount underflow in a userspace-reachable RDMA object model. Realistic evidence supports local DoS via warning or crash. Privilege escalation is not demonstrated, but the object lifetime bug class is risky enough for actionable manual triage, especially where RXE/uverbs is available to untrusted users.

5. One-sentence report phrase
A race between RDMA RXE QP timer callbacks and QP destruction can drop the QP reference count to zero during timer execution, causing a real use-after-free reachable by local users with RXE/uverbs access.

6. Manual review recommendation
MANUAL CHECK REQUIRED
This is a real UAF in a local kernel data-plane API with user-controlled QP lifetimes, even though exploitation beyond DoS is not proven.

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

Patch: RDMA/rxe: Fix race condition in QP timer handlers [ Upstream
Commit: 756c93d6df7c3bc599f6590b8e5afead6a41de1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=756c93d6df7c3bc599f6590b8e5afead6a41de1c

Changed files:
  drivers/infiniband/sw/rxe/rxe_task.c
  lib/refcount.c
  drivers/infiniband/sw/rxe/rxe_comp.c
  drivers/infiniband/sw/rxe/rxe_req.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=756c93d6df7c3bc599f6590b8e5afead6a41de1c

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

The original Linux kernel CVE announcement for CVE-2026-45910 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45910

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: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: 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: 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).