[CVE-2026-46053][IMPORTANT] net: rds: fix MR cleanup on copy error

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

CVE: CVE-2026-46053
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net: rds: fix MR cleanup on copy error
Commit: 8fdbb6262a4a3ed44a0830a7793903b54bb27bdc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fdbb6262a4a3ed44a0830a7793903b54bb27bdc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46053
Analysis date: Wed, 27 May 2026 15:09:18 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-46053 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46053

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-2026-46053	IMPORTANT	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-415;*CWE-416;*CWE-664;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'RDS RDMA __rds_rdma_map() can duplicate cleanup after get_mr() has already transferred ownership of sg pages to the transport. If put_user() fails while copying the generated MR cookie to user space, the old error path can unpin pages and free sg before the final MR teardown handles the same resources, creating a double free or page lifetime corruption condition. For the CVSS the PR:L is used because a local process with access to the RDS RDMA interface can supply the failing user pointer and trigger the error path, while full administrator privileges are not inherently required. The issue is not directly network reachable because the vulnerable step is a local userspace copy failure. Impact is at least local denial of service and in the worst case may allow confidentiality or integrity impact due to kernel lifetime corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-46053  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	ERRORPATH LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6

1. ActionableScore
* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process with access to the RDS RDMA interface can trigger the `put_user()` failure path by supplying an invalid or faulting `cookie_addr`.
* Generic memory corruption, strong corruption primitive: +2. The old error path could `unpin_user_pages()` and `kfree(sg)` after ownership had already been transferred to MR teardown, creating a double cleanup condition.
* Real lifetime corruption: +1. The bug is explicitly about ownership and lifetime of `sg/pages` after `get_mr()` succeeds.
* Reliable kernel crash / strong DoS: +1. Double free or page lifetime corruption can plausibly crash the kernel.
* Local high-control kernel data-plane API: +1. RDMA MR registration lets local users influence pinned pages, scatterlists, and cleanup timing through a rich kernel interface.
* Availability impact realistic: +1. Kernel crash or corrupted MR teardown state is a realistic availability impact.
* Rare/configuration-dependent subsystem: -1. Practical exposure depends on RDS RDMA being enabled and usable, often requiring RDMA-capable environments.
* Paranoid additional weak LPE concern: +1. Double free and page refcount/lifetime corruption may be exploitable beyond DoS, but the patch does not show a controlled overwrite or reliable reclaim primitive.

3. Reachability analysis
The issue is locally reachable through the RDS RDMA memory registration path. It is not directly network-triggerable because the vulnerable failure occurs while copying the generated cookie back to local userspace with `put_user()`. Namespaces may matter if untrusted workloads can access RDS sockets and RDMA resources, but many deployments either do not enable RDS RDMA or restrict RDMA device access. Realistic exploitation requires a local process, RDS RDMA availability, successful `get_mr()`, and a controlled copy-to-user failure afterward.

4. Severity interpretation
This is not an ordinary cleanup bug. It is an ownership/lifetime bug with a plausible double free or page lifetime corruption primitive. Conservative handling is Actionable Moderate because local exploitation can likely produce kernel DoS. Paranoid handling reaches Strong Important candidate because kernel lifetime corruption in RDMA MR teardown may plausibly lead to confidentiality or integrity impact, although no reliable privilege escalation primitive is demonstrated by the patch alone.

5. One-sentence report phrase
An RDS RDMA MR cleanup bug can double free or double unpin pages after `get_mr()` transfers ownership, allowing a local process to trigger kernel lifetime corruption via a failing `put_user()` cookie copy.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This involves real memory lifetime corruption in a local kernel data-plane API, with plausible impact beyond simple DoS depending on RDS RDMA exposure and allocator/page-refcount behavior.

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

Patch: net: rds: fix MR cleanup on copy error
Commit: 8fdbb6262a4a3ed44a0830a7793903b54bb27bdc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8fdbb6262a4a3ed44a0830a7793903b54bb27bdc

Commit description:

__rds_rdma_map() hands sg/pages ownership to the transport after
get_mr() succeeds. If copying the generated cookie back to user space
fails after that point, the error path must not free those resources
again before dropping the MR reference.

Remove the duplicate unpin/free from the put_user() failure branch so
that MR teardown is handled only through the existing final cleanup
path.

Fixes: 0d4597c ("net/rds: Track user mapped pages through special API")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Ao Zhou <draw51280@163.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/79c8ef73ec8e5844d71038983940cc2943099baf.1776764247.git.draw51280@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/rds/rdma.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=8fdbb6262a4a3ed44a0830a7793903b54bb27bdc

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

The original Linux kernel CVE announcement for CVE-2026-46053 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46053

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: 6
  Paranoid ActionableScore: 7

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).