[CVE-2025-38106][MODERATE 7.0] io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo() [ Upstream

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

CVE: CVE-2025-38106
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo() [ Upstream
Commit: af8c13f9ee040b9a287ba246cf0055f7c77b7cc8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af8c13f9ee040b9a287ba246cf0055f7c77b7cc8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-38106
Analysis date: Mon, 06 Jul 2026 19:20:24 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Not a strong Important candidate on conservative evidence, but should not be auto-closed because this is a real task_struct UAF in io_uring.
Manual review required: YES

Summary:
A local race in the io_uring SQPOLL fdinfo path can leave sq->thread pointing to a freed task_struct, causing getrusage to dereference freed memory and potentially crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2025-38106 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-38106

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
======================================================================

CVE-2025-38106	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the io_uring SQPOLL fdinfo path because __io_uring_show_fdinfo can pass sq thread to getrusage after the sqpoll task_struct has already been released. A local process can trigger the race by using an io_uring SQPOLL instance and reading fdinfo while the sqpoll thread exits, causing getrusage to dereference freed task memory. For the CVSS the PR:L is used because local code execution is required, but full administrative privileges are not necessarily required in environments where io_uring SQPOLL is available to the user. The issue is not network reachable and is exposed through a local procfs fdinfo read path. Impact is at least local denial of service via kernel crash. In the paranoid interpretation the task_struct UAF may allow high confidentiality or integrity impact if freed task memory is reused in a controllable way, so this should not be autoclosed without manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) 	YES	READ OOB LOCK DANGER RACE UAF KERNEL_PANIC_PLUS_UAF HARDWARE IO_URING SYZBOT KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	YES	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**:: Actionable Moderate at minimum. Not a strong Important candidate on conservative evidence, but should not be auto-closed because this is a real task_struct UAF in io_uring.

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process can create or use an io_uring SQPOLL instance and read fdinfo while the SQPOLL thread exits. Some deployments may restrict io_uring or SQPOLL, but upstream-style reachability is local user context rather than remote.

* Memory corruption, weak primitive: +1
  This is a confirmed slab-use-after-free of task_struct, but the observed access is a stale read through getrusage. The patch does not show controlled reclaim, write-after-free, callback control, type confusion, or arbitrary write.

* Real lifetime corruption: +1
  sq->thread can point to a released task_struct. The fix uses RCU and get_task_struct to make the task lifetime valid during fdinfo reporting.

* Reliable kernel crash / strong DoS: +1
  syzbot provides a KASAN UAF trace in getrusage from the procfs fdinfo path. A non-KASAN kernel may still crash or behave unpredictably.

* Local high-control kernel API: +1
  io_uring is a rich local kernel API with user-controlled object lifetime and teardown behavior. This is counted only for configurations where io_uring SQPOLL is available to non-admin users.

* Broad/common subsystem exposure: +1
  io_uring is a common kernel subsystem and fdinfo is a normal procfs inspection path.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  Triggering depends on racing fdinfo reading against SQPOLL thread exit.

Applied cap:

* Race-UAF downgrade rule
  This is a syzbot race-dependent UAF with no demonstrated reclaim, write-after-free, type confusion, callback dispatch, or refcount takeover. Conservative score is capped at 4. Paranoid score is capped at 5.

Call-site confidence: high.
The relevant call site is present: __io_uring_show_fdinfo reads sq->thread and passes it to getrusage. The freeing path and fix clearly show missing task_struct lifetime protection.

## 3. Reachability analysis

The bug is local, not network reachable. The likely trigger is a local process using io_uring SQPOLL and reading the corresponding procfs fdinfo while the SQPOLL thread is exiting.

Privileges depend on product configuration. In upstream-like configurations where SQPOLL is usable by an unprivileged user, PR is effectively low. In hardened distributions where io_uring or SQPOLL is restricted by sysctl, LSM, seccomp, or capability checks, reachability may require a more privileged local process. Containers may matter if io_uring is exposed inside the container and procfs access allows fdinfo inspection.

The path is not a default network attack surface. Realistic exploitation requires local code execution and race timing. The demonstrated impact is UAF-triggered crash. Privilege escalation is not proven, but task_struct UAF is sensitive enough for manual review.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real lifetime bug and UAF in a common local kernel subsystem. Conservative interpretation is local DoS only because the stale access is a read in getrusage and no controlled reuse or write primitive is shown.

Paranoid interpretation reaches Actionable Moderate because task_struct UAFs can sometimes become more serious if object reuse becomes controllable, but the patch does not justify treating it as a strong Important candidate by itself.

## 5. One-sentence report phrase

A local race in the io_uring SQPOLL fdinfo path can leave sq->thread pointing to a freed task_struct, causing getrusage to dereference freed memory and potentially crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed UAF in task_struct lifetime handling. Conservative impact is DoS, but the object class and io_uring local attack surface make auto-closing unsafe without manual verification.

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

Patch: io_uring: fix use-after-free of sq->thread in __io_uring_show_fdinfo() [ Upstream
Commit: af8c13f9ee040b9a287ba246cf0055f7c77b7cc8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af8c13f9ee040b9a287ba246cf0055f7c77b7cc8

Changed files:
  io_uring/fdinfo.c
  io_uring/sqpoll.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=af8c13f9ee040b9a287ba246cf0055f7c77b7cc8

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

The original Linux kernel CVE announcement for CVE-2025-38106 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-38106

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:N/I:N/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: 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).