[CVE-2026-53133][MODERATE 7.0] RDMA/umem: Fix truncation for block sizes >= 4G [ Upstream

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

CVE: CVE-2026-53133
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/umem: Fix truncation for block sizes >= 4G [ Upstream
Commit: 2ff4b7817e5b78070c30f5fb5e678e452a2628b3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ff4b7817e5b78070c30f5fb5e678e452a2628b3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53133
Analysis date: Thu, 25 Jun 2026 19:17:50 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A 32 bit truncation in the RDMA umem block iterator can compute wrong DMA addresses for IOMMU mappings with blocks >= 4G split across SG entries, creating a plausible DMA data corruption or disclosure risk and requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53133 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53133

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-2026-53133	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-190;CWE-681;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A 32 bit truncation bug in the RDMA umem block iterator can occur when IOMMU mapping linearization creates a logically contiguous DMA block of 4G or larger split across multiple SG entries. The iterator used unsigned int for block_offset and delta, so reassembling the split entries could wrap the intermediate values and compute wrong DMA addresses for later blocks. For the CVSS the PR:L is used because reliable triggering requires local code with access to RDMA verbs or a service context that can register large RDMA memory regions, but it does not require full administrator privileges in deployments where RDMA device access is delegated. The issue is not directly network reachable by ordinary packet traffic, although a remote RDMA peer may interact with incorrectly registered memory after a local or service side registration has occurred. Impact is at least denial of service or data corruption through invalid DMA addressing, and in the paranoid interpretation may include confidentiality and integrity impact because wrong DMA addresses can point the device at unintended DMA mapped memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)  SKIP CVE-2026-53133  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX NETWORK DMAorINTERRUPT KPANIC MEMORY 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged or service-context trigger: +1. Triggering likely requires local code or a local service with RDMA verbs access and ability to register large memory regions.
* Memory corruption, weak or indirect corruption candidate: +1. The bug is a 32 bit truncation in DMA address arithmetic, causing wrong DMA addresses, but the patch does not show an arbitrary kernel write primitive.
* Privileged kernel/device-management memory corruption path: +1. The affected code is RDMA umem DMA mapping iteration, which is DMA-adjacent and runs in a highly trusted kernel/device context.
* Confidentiality impact plausible: +1. Wrong DMA addresses may cause access to unintended DMA mapped memory, depending on IOMMU layout and RDMA operation direction.
* Integrity impact plausible: +1. Incorrect DMA addresses can plausibly corrupt unintended mapped memory or application data.
* Availability impact realistic: +1. Invalid DMA addressing can cause IOMMU faults, failed RDMA operations, data-path disruption, or crashes in dependent workloads.
* Important storage or memory data path exposure: +1. RDMA umem is used by high-performance storage and memory access stacks such as RDMA verbs and potentially storage transports.
* Weak LPE concern in paranoid score: +1. Privilege escalation is not demonstrated, but wrong DMA address calculation is a security-sensitive primitive worth manual review.
* Special triggering conditions: -1. Requires IOMMU mapping behavior, block sizes >= 4G, and split SG entries.
* Constrained primitive uncertainty: -1. The patch does not show attacker-controlled arbitrary target selection or attacker-chosen kernel overwrite payload.

## 3. Reachability analysis

The likely trigger is a local process or service that can use RDMA verbs and register a sufficiently large memory region. This is not directly reachable through ordinary network packets. A remote RDMA peer may interact with the affected memory after registration, but the vulnerable address computation is controlled by local RDMA setup and kernel mapping behavior.

Typical systems require explicit RDMA device access, group membership, container/device delegation, or a privileged service using RDMA. In environments where RDMA devices are exposed to containers or non-root users, PR:L is a reasonable practical interpretation. The path is not default-exposed on general-purpose Linux systems, but it is relevant in RDMA, HPC, storage, and data-center deployments.

## 4. Severity interpretation

This is stronger than an ordinary Moderate correctness bug because it affects DMA address calculation, not just accounting or cleanup. Realistic exploitation conditions are narrow, and the patch does not prove arbitrary kernel memory corruption or reliable LPE. However, DMA misaddressing can plausibly cause data corruption, disclosure of unintended DMA mapped memory, or severe availability impact, so it should be treated as Actionable Moderate at minimum and a borderline Strong Important candidate under paranoid triage.

## 5. One-sentence report phrase

A 32 bit truncation in the RDMA umem block iterator can compute wrong DMA addresses for IOMMU mappings with blocks >= 4G split across SG entries, creating a plausible DMA data corruption or disclosure risk and requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is not a simple DoS-only issue. It affects DMA address arithmetic in RDMA memory registration paths, and the security impact depends on IOMMU layout, RDMA access delegation, and whether the wrong DMA addresses can reach sensitive or cross-boundary mapped memory.

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

Patch: RDMA/umem: Fix truncation for block sizes >= 4G [ Upstream
Commit: 2ff4b7817e5b78070c30f5fb5e678e452a2628b3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ff4b7817e5b78070c30f5fb5e678e452a2628b3

Changed files:
  drivers/infiniband/core/iter.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=2ff4b7817e5b78070c30f5fb5e678e452a2628b3

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

The original Linux kernel CVE announcement for CVE-2026-53133 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53133

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:L/I:L/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: 5
  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).