[CVE-2026-74334][MODERATE 7.0] RDMA/nldev: Fix locking when accessing mr->pd [ Upstream

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

CVE: CVE-2026-74334
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/nldev: Fix locking when accessing mr->pd [ Upstream
Commit: 1a132ee4e655288d9a0937ea5109a0d038431ae9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1a132ee4e655288d9a0937ea5109a0d038431ae9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74334
Analysis date: Sat, 15 Aug 2026 19:57:11 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
RDMA nldev resource dumps can race with MR reregistration and read a stale `mr->pd` pointer after the old protection domain reference is dropped, creating a local UAF-style kernel crash risk and a paranoid privilege-escalation concern that requires manual review.

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

The original Linux kernel CVE announcement for CVE-2026-74334 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74334

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-2026-74334	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'RDMA/nldev resource dumps can race with ib_uverbs_rereg_mr when a memory region is moved to another protection domain. The dump path may read mr pd while the reregistration path replaces that pointer and later drops the old protection domain reference, creating a stale pointer and use-after-free candidate in kernel memory. For the CVSS the PR:L is used because reliable triggering requires a local user or process with access to RDMA uverbs and netlink resource dump interfaces, not full administrator privileges in all deployments. The issue is not directly network reachable and is driven by local control plane operations rather than RDMA packet traffic. Impact is at least local denial of service via kernel crash and in the paranoid case may allow confidentiality or integrity impact due to UAF style memory corruption, so it should be manually reviewed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	READ LOCK DANGER INIT NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process with access to RDMA uverbs and RDMA netlink resource dump paths can potentially race `ib_uverbs_rereg_mr()` against `nldev` MR dumping.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch addresses racy access to `mr->pd`, which can change during `rereg_mr`. The old PD can be dropped while `nldev` is still reading through the stale pointer. This is a UAF candidate, but the patch does not show attacker-controlled reclaim, overwrite, callback control, or type confusion.

* Real lifetime corruption: +1
  The new `rdma_restrack_sync()` acts as a lifetime fence, waiting for old netlink dump users before the old PD reference is dropped. That strongly indicates a real object lifetime race rather than a pure bookkeeping issue.

* Reliable kernel crash / strong DoS: +1
  A stale `mr->pd` dereference in the kernel resource dump path can plausibly crash the kernel.

* Local device object lifetime API concern: +1 paranoid only
  RDMA uverbs plus nldev exposes user-created kernel objects and this patch specifically involves object lifetime and reference ordering. This is enough for paranoid manual-review elevation, but not enough to infer strong LPE.

* Hard or unreliable race / special timing required: -1 conservative
  Exploitation requires racing MR reregistration with concurrent netlink resource dumping. There is no demonstrated reclaim or stable exploitation primitive in the patch.

## 3. Reachability analysis

The bug is locally reachable on systems with RDMA support and accessible `/dev/infiniband/uverbs*` plus RDMA netlink resource interfaces. It is not directly network reachable through RDMA packet traffic. In many deployments RDMA uverbs access may be granted to non-root HPC, storage, or service users, so PR:L is more realistic than PR:H when such users can create and reregister MRs. Namespaces and containers may matter if RDMA devices are passed through or delegated, but typical host exposure still depends on device permissions and RDMA stack availability.

## 4. Severity interpretation

This is more than an ordinary Moderate cleanup because it fixes a real lifetime race around `mr->pd` and introduces an explicit synchronization primitive to fence old netlink users. Realistic impact is most clearly local kernel crash / DoS. Theoretical escalation is not proven because the patch does not show attacker-controlled reclaim, writable stale access, callback dispatch, or type confusion. Therefore this is best treated as Actionable Moderate at minimum, with manual review required due to UAF-style lifetime corruption.

## 5. One-sentence report phrase

RDMA nldev resource dumps can race with MR reregistration and read a stale `mr->pd` pointer after the old protection domain reference is dropped, creating a local UAF-style kernel crash risk and a paranoid privilege-escalation concern that requires manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a race-dependent lifetime bug with a plausible stale pointer / UAF path in kernel memory, even though the provided patch does not demonstrate a strong exploit primitive beyond DoS.

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

Patch: RDMA/nldev: Fix locking when accessing mr->pd [ Upstream
Commit: 1a132ee4e655288d9a0937ea5109a0d038431ae9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1a132ee4e655288d9a0937ea5109a0d038431ae9

Changed files:
  drivers/infiniband/core/nldev.c
  drivers/infiniband/core/restrack.c
  drivers/infiniband/core/restrack.h
  drivers/infiniband/core/uverbs_cmd.c
  include/rdma/ib_verbs.h

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=1a132ee4e655288d9a0937ea5109a0d038431ae9

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

The original Linux kernel CVE announcement for CVE-2026-74334 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74334

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: 4
  Paranoid ActionableScore: 5

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 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).