[CVE-2026-64268][IMPORTANT] RDMA/siw: bound Read Response placement to the RREAD length

[CVE-2026-64268][IMPORTANT] RDMA/siw: bound Read Response placement to the RREAD length

[AL-KERNEL]

CVE: CVE-2026-64268
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: RDMA/siw: bound Read Response placement to the RREAD length
Commit: a31b6d18ded3cc32d9ee85a6ff0726d4274887b2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a31b6d18ded3cc32d9ee85a6ff0726d4274887b2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64268
Analysis date: Sat, 25 Jul 2026 12:00:10 -0400
ActionableScore: 9
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A connected remote SIW peer can send oversized cumulative Read Response DDP segments for an RREAD operation and cause siw_rx_data() to write past the validated sink buffer, creating a remote out-of-bounds write with DoS and potential privilege-escalation impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64268 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64268

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: IMPORTANT
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-2026-64268	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-119;BEST CVSS score: '9.8';DESCR 'An out-of-bounds write in the RDMA/siw Read Response receive path occurs because siw_proc_rresp places each inbound DDP segment at sge laddr plus wqe processed without bounding the accumulated placement offset against the requested RREAD length on continuation segments. A connected remote siw peer can trigger this by replying to an outstanding RREAD with Read Response segments that keep the DDP Last flag clear and carry more total payload than requested, causing siw_rx_data to write past the validated sink buffer. For the CVSS the PR:N value is used because no local account or local code execution on the target is needed when the attacker can act as the remote RDMA peer over the exposed siw TCP connection. The issue is network reachable because siw implements iWARP over ordinary routable TCP, although real deployments often restrict RDMA traffic to trusted storage or data center networks. Impact is memory corruption with potential confidentiality, integrity, and availability impact, including kernel crash and possible privilege escalation depending on the corrupted memory layout.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 9)	YES	WRITE OOB INIT NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=9
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: 7
* Paranoid score: 9
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. SIW is iWARP over ordinary TCP, and the attacker can be the connected remote RDMA peer.
* Memory corruption, strong corruption primitive: +2. The patch prevents an attacker-controlled Read Response payload from being written past the validated RREAD sink buffer.
* Privilege escalation plausible: +2. This is a remote controlled out-of-bounds write in a kernel-mediated RDMA receive path, so LPE or broader compromise is plausible enough for manual review, even if not demonstrated.
* Reliable kernel crash / strong DoS: +1. An out-of-bounds write from siw_rx_data can realistically crash or corrupt the kernel or RDMA process context.
* Integrity impact plausible: +1. The primitive is a write beyond intended bounds.
* Rare/config-dependent RDMA SIW exposure: -1. The affected path requires SIW/RDMA use and an established RDMA connection, and is usually not Internet-facing.

Paranoid additions/interpretation:

* Confidentiality impact plausible: +1. Not directly shown, but kernel memory corruption can plausibly lead to disclosure in worst-case exploit development.
* Availability impact realistic: +1. The trigger is protocol-level and can cause repeatable corruption or crash when the SIW service is reachable.
* No rare/config penalty in paranoid scoring because SIW uses routable TCP and the bug is remotely triggerable within exposed RDMA deployments.

## 3. Reachability analysis

The bug is triggerable by a connected remote SIW peer that responds to an outstanding RREAD with continuation Read Response DDP segments whose cumulative payload exceeds the requested RREAD length. No local account on the target is required if the attacker can act as the RDMA peer. Namespaces are not the main gating factor here. The main exposure condition is whether RDMA/siw is enabled and reachable over TCP. In practice, SIW/RDMA is usually deployed in storage, HPC, or data-center networks rather than exposed publicly, but within those networks the trigger is realistic.

Call-site confidence: high. The patch shows the missing bound check immediately before siw_rx_data() writes to sge->laddr + wqe->processed.

## 4. Severity interpretation

This behaves more like an Important-class kernel vulnerability than an ordinary Moderate. The key issue is not merely a protocol error or DoS condition, but a remote attacker-influenced out-of-bounds write in the RDMA receive path. Realistic exploitability depends on SIW deployment, RDMA connection setup, memory registration layout, and whether the overwrite reaches useful kernel or process-owned memory. However, the primitive is strong enough that auto-closing as ordinary Moderate would be unsafe.

## 5. One-sentence report phrase

A connected remote SIW peer can send oversized cumulative Read Response DDP segments for an RREAD operation and cause siw_rx_data() to write past the validated sink buffer, creating a remote out-of-bounds write with DoS and potential privilege-escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: remote reachable RDMA protocol path plus attacker-influenced out-of-bounds write is a strong memory-corruption primitive, even though practical exploitation depends on SIW deployment and memory layout.

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

Patch: RDMA/siw: bound Read Response placement to the RREAD length
Commit: a31b6d18ded3cc32d9ee85a6ff0726d4274887b2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a31b6d18ded3cc32d9ee85a6ff0726d4274887b2

Commit description:

In drivers/infiniband/sw/siw/siw_qp_rx.c, siw_proc_rresp() places each
inbound Read Response DDP segment at sge->laddr + wqe->processed and then
accumulates wqe->processed, but it never checks the running total against
the sink buffer length on continuation segments. siw_check_sge() resolves
and validates the sink memory only on the first fragment (the if (!*mem)
branch), and siw_rresp_check_ntoh() compares the cumulative length against
wqe->bytes only on the final segment (the !frx->more_ddp_segs guard).

A connected siw peer that answers an outstanding RREAD with Read Response
segments that keep the DDP Last flag clear, carrying more total payload
than the RREAD requested, drives wqe->processed past the validated sink
buffer; the next siw_rx_data() call writes out of bounds at
sge->laddr + wqe->processed. siw runs iWARP over ordinary routable TCP,
so the peer is the remote end of an established RDMA connection and needs
no local privilege.

Bound every segment before placement, exactly as siw_proc_send() and
siw_proc_write() already do for their tagged and untagged paths, and
terminate the connection with a base-or-bounds DDP error when the
Read Response would overrun the sink buffer.

This is the second receive-path length fix for this file. A separate
change rejects an MPA FPDU length that underflows the per-fragment
remainder in the header decode; that guard does not cover this case,
because here each individual segment length is self-consistent and only
the accumulated placement offset overruns the buffer.

Fixes: 8b6a361 ("rdma/siw: receive path")
Link: https://patch.msgid.link/r/20260602194700.2273758-1-michael.bommarito@gmail.com
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/sw/siw/siw_qp_rx.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=a31b6d18ded3cc32d9ee85a6ff0726d4274887b2

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

The original Linux kernel CVE announcement for CVE-2026-64268 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64268

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:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 9.8

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: 7
  Paranoid ActionableScore: 9

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).