[CVE-2026-53274][LOW] net/smc: fix sleep-inside-lock in __smc_setsockopt() causing local DoS

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

CVE: CVE-2026-53274
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/smc: fix sleep-inside-lock in __smc_setsockopt() causing local DoS
Commit: 35a22117839602bb52283de08894c5a7dde92420
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=35a22117839602bb52283de08894c5a7dde92420
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53274
Analysis date: Thu, 25 Jun 2026 09:42:07 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local unprivileged user can trigger a sleep-inside-lock condition in `__smc_setsockopt()` by blocking `copy_from_sockptr()` on controlled userspace memory, causing SMC socket teardown workers to hang and resulting in local denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-53274 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53274

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-53274	LOW	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-667;**CWE-400;*CWE-833;BEST CVSS score: '5.5';DESCR 'A sleep inside lock issue in __smc_setsockopt can occur because copy_from_sockptr is executed while lock_sock holds the SMC socket lock. A local process can pass an optval pointer backed by userfaultfd controlled memory or by FUSE backed memory and make the user copy block for a long time. This keeps the socket lock held and can block asynchronous shutdown or teardown work on lock_sock_nested, leading to kworker exhaustion and hung task warnings. For the CVSS the PR:L is used because triggering requires local code execution as an unprivileged user with control over an SMC socket and the optval memory. The issue is not network reachable because remote traffic alone cannot supply the blocking userspace pointer to setsockopt. Impact is denial of service only through local resource exhaustion and blocked kernel workers.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	INIT WARNONLY LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local unprivileged process can call `setsockopt()` on an SMC socket and pass an `optval` pointer that can block during `copy_from_sockptr()`.

* Reliable kernel crash / strong DoS: +1
  The bug can hold `lock_sock(sk)` indefinitely and block asynchronous teardown paths such as `smc_shutdown()`, leading to kworker exhaustion and hung task watchdog reports.

Not triggered:

* Remote reachable: +0
  Remote traffic alone cannot provide the blocking userspace pointer to `setsockopt()`.

* Generic memory corruption: +0
  The patch shows a sleep-inside-lock / locking design bug, not UAF, OOB write, double-free, refcount misuse, or type confusion.

* Privilege escalation plausible: +0
  No reclaim primitive, write primitive, stale callback, object confusion, or credential/security-boundary bypass is indicated.

* Confidentiality / Integrity: +0
  The impact is resource exhaustion only.

Potential reduction:

* Rare / configuration-dependent subsystem: could be -1, but not applied in the main score because AF_SMC is still reachable through an ordinary local socket API when enabled.

## 3. Reachability analysis

The bug is locally reachable by a process that can create or use an SMC socket and call `setsockopt()` with `SMC_LIMIT_HS`. The attacker does not need administrative privileges in the described scenario, so PR is effectively local unprivileged. The blocking copy can be arranged with `userfaultfd` where available, or with FUSE-backed memory on systems where unprivileged `userfaultfd` is disabled.

Namespaces and containers may matter only if AF_SMC is available inside the container and the relevant socket operations are not restricted. This does not make the issue remotely reachable. The affected path is not a central TCP/IP receive path and SMC is less commonly exposed than mainstream networking APIs, but the trigger is simple once the local API is available.

## 4. Severity interpretation

This behaves like an ordinary Moderate local DoS, not an Important-class vulnerability. The realistic impact is blocked socket teardown, kworker exhaustion, and hung task warnings. There is no concrete memory corruption primitive and no demonstrated path to privilege escalation.

Theoretical escalation is not supported by the patch context. The fix simply moves `copy_from_sockptr()` outside the `lock_sock()` critical section, confirming that the vulnerable condition is sleeping while holding a socket lock rather than corrupting memory or bypassing an access-control boundary.

## 5. One-sentence report phrase

A local unprivileged user can trigger a sleep-inside-lock condition in `__smc_setsockopt()` by blocking `copy_from_sockptr()` on controlled userspace memory, causing SMC socket teardown workers to hang and resulting in local denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a clear local DoS-only locking/resource-exhaustion issue with no memory corruption, no information disclosure, no integrity impact, and no plausible privilege-escalation primitive shown by the patch.

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

Patch: net/smc: fix sleep-inside-lock in __smc_setsockopt() causing local DoS
Commit: 35a22117839602bb52283de08894c5a7dde92420
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=35a22117839602bb52283de08894c5a7dde92420

Commit description:

A logic flaw in __smc_setsockopt() allows a local unprivileged user to
cause a Denial of Service (DoS) by holding the socket lock indefinitely.

The function __smc_setsockopt() calls copy_from_sockptr() while holding
lock_sock(sk). By passing a userfaultfd-monitored memory page (or
FUSE-backed memory on systems where unprivileged userfaultfd is disabled)
as the optval, an attacker can halt execution during the copy operation,
keeping the lock held.

Combined with asynchronous tear-down operations like shutdown(), this
exhausts the kernel wq (kworkers) and triggers the hung task watchdog.

[  240.123456] INFO: task kworker/u8:2 blocked for more than 120 seconds.
[  240.123489] Call Trace:
[  240.123501]  smc_shutdown+...
[  240.123512]  lock_sock_nested+...

This patch moves the user-space copy outside the lock_sock() critical
section to prevent the issue.

Fixes: a6a6fe2 ("net/smc: Dynamic control handshake limitation by socket options")
Signed-off-by: Nicolò Coccia <n.coccia96@gmail.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Tested-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/smc/af_smc.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=35a22117839602bb52283de08894c5a7dde92420

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

The original Linux kernel CVE announcement for CVE-2026-53274 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53274

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: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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).