[CVE-2026-68146][MODERATE REGULAR] ftrace: Add global mutex to serialize trace_parser access

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

CVE: CVE-2026-68146
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ftrace: Add global mutex to serialize trace_parser access
Commit: 3d0dd138a06c782f8b755cd1b6f9909494514ce1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d0dd138a06c782f8b755cd1b6f9909494514ce1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68146
Analysis date: Mon, 10 Aug 2026 12:41:25 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A local race in ftrace trace_parser handling can corrupt parser state when a shared trace file descriptor is written or released concurrently, causing undefined ftrace filter behavior or local DoS, with higher concern in deployments that delegate tracefs access to reduced-privilege users.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68146 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68146

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
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CVE-2026-68146	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:L/I:L/A:H';CWE-362;CWE-667;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'A race condition in ftrace can corrupt trace_parser state when the same trace file descriptor is shared across multiple userspace threads and concurrent write operations update parser idx, cont, and buffer without serialization. This can cause corrupted input parsing or undefined behavior in ftrace regex and graph filter handling. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate tracefs access to a reduced privilege tracing user, container root, or service account rather than full host administrator access. The issue is not network reachable and requires local access to ftrace control files. Impact is at least local denial of service or unintended tracing filter changes, and in worst case may allow limited confidentiality or integrity impact if parser buffer corruption is exploitable. Manual review is recommended because this is a race in kernel parser state with a possible memory corruption angle.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	WRITE OOB LOCK TRACE SIMPLEFIX RACE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. The race corrupts `trace_parser` state fields such as `idx`, `cont`, and `buffer`, but the patch does not show a concrete UAF, OOB write, arbitrary write, reclaim primitive, or callback corruption.
* Availability impact plausible: +1. Parser state corruption can cause undefined behavior or broken ftrace filter handling, but no reliable panic or Oops is shown.
* Hard or unreliable race / special timing required: -1. Trigger requires concurrent operations on a shared trace file descriptor.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. ftrace/tracefs control files are normally restricted to root or tracing-capable administrators.
* Broad/common subsystem: +1. ftrace is a common kernel tracing subsystem, but access is restricted.

Paranoid signals:

* Local low-privilege trigger in delegated setups: +1. Some systems may expose tracefs access to a tracing group, service account, container root, or reduced-capability administrator.
* Weak/indirect corruption candidate: +1. Concurrent parser updates can corrupt kernel parser state, but without a demonstrated strong memory corruption primitive.
* Integrity impact plausible: +1. Corrupted parsing can plausibly cause unintended ftrace regex or graph filter changes.
* Availability impact plausible: +1. Undefined parser behavior may cause local DoS or tracing subsystem disruption.
* Broad/common subsystem: +1. ftrace is widely present in Linux kernels.
* Hard race: -1. Exploitation depends on timing between concurrent write/release paths.

## 3. Reachability analysis

The bug is local only and is triggered through ftrace tracefs control files, not through network traffic. In typical deployments, access to these files requires root or CAP_SYS_ADMIN, so the conservative score is low. Namespace or container setups may reduce the effective privilege requirement if tracefs is exposed to a container root, tracing group, or service account, which justifies the paranoid PR:L interpretation. The path is common in kernels with tracing enabled, but it is not normally available to arbitrary unprivileged users.

Call-site confidence: high. The patch shows the affected write and release paths directly.

## 4. Severity interpretation

This behaves more like a borderline Moderate issue than an Important-class vulnerability. The patch shows a real race in kernel parser state, but it does not show UAF, double-free, controlled overwrite, arbitrary write, type confusion, refcount takeover, or attacker-controlled reclaim. The realistic impact is corrupted ftrace input parsing, unintended tracing filter changes, or local DoS. Theoretical memory corruption concern exists because `idx` and `buffer` are parser state used during kernel-side parsing, but exploitation evidence is weak.

## 5. One-sentence report phrase

A local race in ftrace trace_parser handling can corrupt parser state when a shared trace file descriptor is written or released concurrently, causing undefined ftrace filter behavior or local DoS, with higher concern in deployments that delegate tracefs access to reduced-privilege users.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a kernel race affecting parser state in ftrace control paths, with a possible but unproven memory corruption angle. It should not be treated as Important by default, but it also should not be blindly auto-closed if tracefs is delegated to non-root or containerized users.

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

Patch: ftrace: Add global mutex to serialize trace_parser access
Commit: 3d0dd138a06c782f8b755cd1b6f9909494514ce1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d0dd138a06c782f8b755cd1b6f9909494514ce1

Commit description:

In ftrace, the trace_parser structure is allocated and initialized when
a trace file is opened, and is subsequently used across write and release
handlers to parse user input.

The affected handler paths and their specific functions are:
  - Open paths: ftrace_regex_open(), ftrace_graph_open()
  - Write paths: ftrace_regex_write(), ftrace_graph_write()
  - Release paths: ftrace_regex_release(), ftrace_graph_release()

If userspace opens a trace file descriptor and shares it across multiple
threads, concurrent write calls will race on the parser's internal state,
specifically the 'idx', 'cont', and 'buffer' fields, leading to corrupted
input or undefined behavior.

Fix this by adding a global mutex, parser_lock, to serialize all access
to trace_parser across write and release paths, preventing concurrent
corruption of parser state.

Fixes: e704eff ("ftrace: Have set_graph_function handle multiple functions in one write")
Fixes: 689fd8b ("tracing: trace parser support for function and graph")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260725024721.1983675-1-wutengda@huaweicloud.com
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/trace/ftrace.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=3d0dd138a06c782f8b755cd1b6f9909494514ce1

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

The original Linux kernel CVE announcement for CVE-2026-68146 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68146

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:H/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 1
  Paranoid ActionableScore: 4

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).