[CVE-2026-52939][MODERATE REGULAR] net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion [ Upstream

[CVE-2026-52939][MODERATE REGULAR] net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52939
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion [ Upstream
Commit: a0148342badd8c9b2e46551766a27cb76c82e715
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a0148342badd8c9b2e46551766a27cb76c82e715
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52939
Analysis date: Wed, 24 Jun 2026 05:13:47 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An unprivileged local AF_RDS sender can trigger a NULL pointer dereference in the RDS/IB masked atomic completion path on configured RDMA systems, causing a host kernel panic.

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

The original Linux kernel CVE announcement for CVE-2026-52939 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52939

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 REGULAR
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-2026-52939	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-703;CWE-754;BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the RDS/IB send completion path occurs because masked atomic work request opcodes are not handled in rds_ib_send_unmap_op(). A local unprivileged user can trigger this through AF_RDS sendmsg() with an atomic cmsg over an active RDS/IB connection on hardware that accepts masked atomics. For the CVSS the PR:L value is used because the attacker needs local user or process access to issue the AF_RDS sendmsg() call, but does not need administrative privileges. The issue is not directly network reachable as a packet only remote trigger. Impact is denial of service via kernel panic in softirq context. The observed primitive is NULL pointer dereference, so confidentiality and integrity impact are not raised without evidence of UAF, OOB access, or arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)  SKIP CVE-2026-52939  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	KASAN NULLPTR HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The commit states that an unprivileged AF_RDS `sendmsg()` with an atomic cmsg can trigger the crash.

* Reliable kernel crash / strong DoS: +1
  The observed failure is a NULL pointer dereference in softirq context followed by kernel panic.

* Availability impact realistic: +1 in paranoid score only
  The crash is host-wide and appears directly reachable once an active RDS/IB connection and compatible hardware exist.

* Rare AND difficult-to-reach subsystem/configuration: -1 in conservative score
  The issue requires RDS over InfiniBand/RDMA, active RDS/IB connectivity, and hardware accepting masked atomics such as mlx4 or mlx5.

* Weak corruption / invalid pointer dereference: +0
  The primitive is a NULL pointer dereference, not UAF, OOB write, arbitrary write, or object lifetime corruption.

## 3. Reachability analysis

A local unprivileged user can trigger the bug if AF_RDS is available and an active RDS/IB connection exists. This is not directly packet-triggerable from the network by a remote attacker without local code execution. Namespaces may matter if an environment exposes AF_RDS or RDS/IB functionality to containerized or reduced-privilege users, but typical deployment still requires the RDS/IB stack and RDMA hardware to be configured. The path is not a default common networking path on most general-purpose systems.

## 4. Severity interpretation

This behaves like a strong local DoS, not an Important-class memory corruption issue. The theoretical impact is limited by the observed primitive: `rm == NULL` is dereferenced in `rds_ib_send_cqe_handler()`, causing a panic. There is no evidence in the patch of UAF reclaim, stale pointer reuse, OOB write, attacker-controlled overwrite, or privilege escalation. The issue is therefore more than an ordinary low-risk cleanup because it is unprivileged and panic-capable, but it remains below Important without a memory corruption or security-boundary bypass primitive.

## 5. One-sentence report phrase

An unprivileged local AF_RDS sender can trigger a NULL pointer dereference in the RDS/IB masked atomic completion path on configured RDMA systems, causing a host kernel panic.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.
Reason: unprivileged local kernel panic in a network subsystem, but current evidence supports DoS only and the required RDS/IB hardware/configuration limits exposure.

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

Patch: net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion [ Upstream
Commit: a0148342badd8c9b2e46551766a27cb76c82e715
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a0148342badd8c9b2e46551766a27cb76c82e715

Changed files:
  net/rds/ib_send.c
  net/rds/ib_cm.c
  kernel/softirq.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=a0148342badd8c9b2e46551766a27cb76c82e715

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

The original Linux kernel CVE announcement for CVE-2026-52939 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52939

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 3

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 REGULAR

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).