[CVE-2026-46043][MODERATE 7.0] RDMA/rxe: Validate pad and ICRC before payload_size() in rxe_rcv

[CVE-2026-46043][MODERATE 7.0] RDMA/rxe: Validate pad and ICRC before payload_size() in rxe_rcv

[AL-KERNEL]

CVE: CVE-2026-46043
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/rxe: Validate pad and ICRC before payload_size() in rxe_rcv
Commit: 2fd4f8b749309a61c3f3f88ee8891d94f79e1240
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2fd4f8b749309a61c3f3f88ee8891d94f79e1240
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46043
Analysis date: Wed, 27 May 2026 15:35:18 -0400
ActionableScore: 6
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-2026-46043 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46043

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-2026-46043	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-191;*CWE-20;CWE-125;CWE-754;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.6';DESCR 'RDMA rxe validates only the fixed header length before payload_size() subtracts the attacker controlled BTH pad and RXE_ICRC_SIZE from pkt paylen. A malformed short packet can therefore make payload_size() underflow and pass an oversized payload length to later receive path code, causing a kernel crash or possible limited out of bounds access. For the CVSS the PR:N is used because no local privileges are required on the victim once the RXE interface is reachable by RDMA traffic. The issue is treated as AV:A because Soft RoCE is normally exposed on local storage or data center fabrics rather than the public Internet. Impact is primarily denial of service, with limited confidentiality and integrity concern kept for the paranoid score because the bug is an attacker controlled length underflow in a packet receive path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	OOB SIMPLEFIX NETWORK SKB KPANIC PACKET  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=6
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

2. Signal breakdown
* Network-triggerable on RDMA fabric: +2. A malformed incoming RXE packet can reach `rxe_rcv()` when Soft RoCE is configured and reachable. This is better treated as adjacent or datacenter fabric exposure, not public Internet exposure.
* Weak or indirect corruption candidate: +1. The attacker-controlled BTH pad can cause `payload_size()` integer underflow and pass an oversized length to later receive-path users, but the patch does not prove an OOB write or controlled overwrite.
* Reliable kernel crash / strong DoS: +1. An underflowed payload size in packet receive processing can plausibly crash or stall the kernel receive path.
* Availability impact realistic: +1. The primary realistic impact is denial of service.
* Confidentiality impact plausible in paranoid view: +1. A later OOB read or oversized receive operation is plausible, but not demonstrated.
* Integrity impact plausible in paranoid view: +1. Integrity impact is possible only as a conservative manual-review concern from malformed length propagation, not as a proven write primitive.
* Rare/configuration-dependent exposure: -1. RXE or Soft RoCE must be enabled and reachable, usually inside storage or datacenter networks.

3. Reachability analysis
The bug is reachable by a remote peer on the same RDMA or Soft RoCE reachable network that can send malformed RXE packets. No local privileges are required on the victim once the RXE interface is exposed. Containers and namespaces do not materially change the remote packet path, but system exposure depends on whether RXE is configured and bound to a reachable interface. This is not normally Internet-facing, but it is realistic in storage, HPC, or datacenter fabrics.

4. Severity interpretation
This is more serious than an ordinary local Moderate because it is attacker-controlled packet parsing in a kernel receive path. The demonstrated impact is primarily DoS from an integer underflow and oversized payload length. The theoretical memory impact is limited to possible downstream OOB access, with no demonstrated arbitrary write, UAF, or privilege escalation primitive. This fits Actionable Moderate and should not be auto-closed.

5. One-sentence report phrase
A malformed RXE packet with a forged BTH pad can make `payload_size()` underflow in `rxe_rcv()`, potentially causing kernel DoS and limited downstream OOB-access risk on reachable Soft RoCE deployments.

6. Manual review recommendation
MANUAL CHECK REQUIRED. The issue is network-triggerable within RDMA fabrics and involves attacker-controlled length underflow in a kernel receive path, even though no strong memory-corruption primitive is proven.

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

Patch: RDMA/rxe: Validate pad and ICRC before payload_size() in rxe_rcv
Commit: 2fd4f8b749309a61c3f3f88ee8891d94f79e1240
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2fd4f8b749309a61c3f3f88ee8891d94f79e1240

Commit description:

rxe_rcv() currently checks only that the incoming packet is at least
header_size(pkt) bytes long before payload_size() is used.

However, payload_size() subtracts both the attacker-controlled BTH pad
field and RXE_ICRC_SIZE from pkt->paylen:

  payload_size = pkt->paylen - offset[RXE_PAYLOAD] - bth_pad(pkt)
                 - RXE_ICRC_SIZE

This means a short packet can still make payload_size() underflow even
if it includes enough bytes for the fixed headers. Simply requiring
header_size(pkt) + RXE_ICRC_SIZE is not sufficient either, because a
packet with a forged non-zero BTH pad can still leave payload_size()
negative and pass an underflowed value to later receive-path users.

Fix this by validating pkt->paylen against the full minimum length
required by payload_size(): header_size(pkt) + bth_pad(pkt) +
RXE_ICRC_SIZE.

Cc: stable@vger.kernel.org
Fixes: 8700e3e ("Soft RoCE driver")
Link: https://patch.msgid.link/r/20260401121907.1468366-1-hkbinbinbin@gmail.com
Signed-off-by: hkbinbin <hkbinbinbin@gmail.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/sw/rxe/rxe_recv.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=2fd4f8b749309a61c3f3f88ee8891d94f79e1240

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

The original Linux kernel CVE announcement for CVE-2026-46043 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46043

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7.6

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).