[CVE-2026-53187][MODERATE REGULAR] RDMA/core: Validate cpu_id against nr_cpu_ids in DMAH alloc

[CVE-2026-53187][MODERATE REGULAR] RDMA/core: Validate cpu_id against nr_cpu_ids in DMAH alloc

[AL-KERNEL]

CVE: CVE-2026-53187
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/core: Validate cpu_id against nr_cpu_ids in DMAH alloc
Commit: bd5e818be7964c1689fba2dad9e6bd3a827fee74
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd5e818be7964c1689fba2dad9e6bd3a827fee74
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53187
Analysis date: Thu, 25 Jun 2026 06:53:15 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended, not Important-class by default
Manual review required: YES

Summary:
A local RDMA uverbs user can pass an out-of-range DMAH cpu_id that reaches cpumask_test_cpu and may cause an OOB cpumask read or a panic_on_warn reboot on debug checked kernels, making this primarily a local DoS issue rather than a demonstrated privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53187 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53187

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.

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

CVE-2026-53187	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-125;CWE-129;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.5';DESCR 'An out-of-bounds read can occur in the RDMA DMAH allocation path because a user supplied cpu_id is passed to cpumask_test_cpu without checking it against nr_cpu_ids. The helper can index past the valid cpumask bitmap and on kernels with CONFIG_DEBUG_PER_CPU_MAPS it can also trigger a WARN path that becomes a system reboot when panic_on_warn is enabled. For the CVSS the PR:L is used because a local process needs access to the RDMA uverbs device interface, but full administrator privileges are not necessarily required in deployments that grant RDMA device access to users or service accounts. The issue is not directly network reachable and is triggered through a local device ioctl style control path. Impact is primarily denial of service, with only limited confidentiality concern from the invalid read and no clear integrity or privilege escalation primitive shown by the code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended, not Important-class by default (with actual score 3)	YES	OOB DANGER SIMPLEFIX NETWORK HARDWARE BOOT TEST  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended, not Important-class by default**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process with access to the RDMA uverbs device can supply `UVERBS_ATTR_ALLOC_DMAH_CPU_ID`.
* Availability impact realistic: +1. The patch states that with `CONFIG_DEBUG_PER_CPU_MAPS` and `panic_on_warn`, invalid input can cause a machine reboot.
* Limited OOB read only: +0. The issue is an out-of-bounds read from a cpumask bitmap via `cpumask_test_cpu()`, but no user-visible disclosure or controlled write primitive is shown.
* No privilege escalation signal: +0. The patch does not show UAF, write-after-free, object replacement, callback corruption, arbitrary write, or refcount takeover.
* No remote reachability: +0. This is a local uverbs control path, not a network-triggerable RDMA packet path.

Paranoid additional signal:

* Reliable kernel crash / strong DoS in affected debug or hardened configurations: +1. If `panic_on_warn` is enabled with the relevant debug check, the bad input can become a host reboot.

Not awarded:

* Generic memory corruption: not awarded. This is read-only bitmap over-indexing, not OOB write or lifetime corruption.
* Confidentiality impact: not awarded in the paranoid score. The OOB read result is not shown to disclose kernel memory to userspace.
* Integrity impact: not awarded. No write primitive or security-boundary bypass is demonstrated.
* High-control RDMA API bonus: not awarded. The patch shows object configuration input, not attacker control over memory layout, lifetime, DMA mappings, callbacks, or page ownership.

## 3. Reachability analysis

The bug is reachable by a local process that can open and use the RDMA uverbs interface and issue DMAH allocation with a malformed `cpu_id`. This usually means local access plus permission to the relevant `/dev/infiniband/uverbs*` device. It does not require full host root if RDMA device access is granted to users, containers, or service accounts.

Namespaces or containers can matter if the RDMA device is delegated into a container or exposed to non-root workloads. In that case, PR:L is the practical interpretation. If RDMA devices are not exposed to untrusted users, the practical reachability is much lower.

The affected path is not a normal network receive path. It is not remotely triggerable merely because RDMA is a networking-related subsystem. Realistic exploitation is mostly a local DoS concern, especially on kernels where `panic_on_warn` converts the debug warning into a reboot.

## 4. Severity interpretation

This behaves like an ordinary Moderate to borderline actionable Moderate issue. The concrete primitive is a local invalid/OOB read from a cpumask bitmap plus a conditional WARN-to-panic path. There is no demonstrated privilege escalation primitive, no write primitive, no UAF, no object lifetime corruption, and no direct information disclosure path.

The paranoid score is raised to 3 because the patch explicitly describes a reboot condition under `CONFIG_DEBUG_PER_CPU_MAPS` combined with `panic_on_warn`. However, this should not be treated as an Important-class kernel vulnerability without additional evidence of memory disclosure, corruption, or privilege escalation.

## 5. One-sentence report phrase

A local RDMA uverbs user can pass an out-of-range DMAH cpu_id that reaches cpumask_test_cpu and may cause an OOB cpumask read or a panic_on_warn reboot on debug checked kernels, making this primarily a local DoS issue rather than a demonstrated privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: manual review is recommended because the bug has an explicit OOB read from untrusted local input and a documented panic_on_warn reboot path, but it does not currently show enough evidence for Important-class handling or mandatory escalation.

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

Patch: RDMA/core: Validate cpu_id against nr_cpu_ids in DMAH alloc
Commit: bd5e818be7964c1689fba2dad9e6bd3a827fee74
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd5e818be7964c1689fba2dad9e6bd3a827fee74

Commit description:

The cpu_id attribute supplied by user space through
UVERBS_ATTR_ALLOC_DMAH_CPU_ID is passed directly to cpumask_test_cpu()
without first verifying that the value is within the valid CPU range.

Passing such untrusted data to cpumask_test_cpu() may lead to an
out-of-bounds read of the underlying cpumask bitmap: the helper expands
to a test_bit() that indexes the bitmap by cpu_id / BITS_PER_LONG with
no bound check.

In addition, on kernels built with CONFIG_DEBUG_PER_CPU_MAPS it trips
the WARN_ON_ONCE() in cpumask_check(); combined with panic_on_warn this
turns a bad user input into a machine reboot.

Reject any cpu_id that is not smaller than nr_cpu_ids with -EINVAL
before it is used.

Reported by Smatch.

Fixes: d83edab ("RDMA/core: Introduce a DMAH object and its alloc/free APIs")
Link: https://patch.msgid.link/r/20260525142136.28165-1-yishaih@nvidia.com
Cc: stable@vger.kernel.org
Reported-by: Dan Carpenter <error27@gmail.com>
Closes: https://lore.kernel.org/r/ag68qoAW3P04J7pT@stanley.mountain/
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/core/uverbs_std_types_dmah.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=bd5e818be7964c1689fba2dad9e6bd3a827fee74

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

The original Linux kernel CVE announcement for CVE-2026-53187 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53187

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:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  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).