[CVE-2026-64173][MODERATE 7.0] tracing: Do not call map->ops->elt_free() if elt_alloc() fails

[CVE-2026-64173][MODERATE 7.0] tracing: Do not call map->ops->elt_free() if elt_alloc() fails

[AL-KERNEL]

CVE: CVE-2026-64173
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tracing: Do not call map->ops->elt_free() if elt_alloc() fails
Commit: 49332e49ad5b20262cc719b03d4123b9362de701
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49332e49ad5b20262cc719b03d4123b9362de701
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64173
Analysis date: Sun, 19 Jul 2026 15:30:38 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A tracing_map allocation failure path could incorrectly call the map elt_free callback on a partially initialized element, potentially causing invalid cleanup or a local kernel crash, with higher concern in delegated tracing environments.

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

The original Linux kernel CVE announcement for CVE-2026-64173 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64173

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.

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

CVE-2026-64173	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-703;CWE-763;CWE-754;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A tracing_map element cleanup path can call map ops elt_free even when the matching elt_alloc callback did not complete successfully. This can expose the callback to a partially initialized element after an allocation failure and may lead to invalid cleanup, NULL pointer dereference, warning, or kernel crash. For the CVSS the PR:L value is used for the paranoid score because some systems may delegate tracing access to a non root local user or to a tracing service account, although typical deployments require administrator level tracing privileges. The issue is not network reachable and requires local access to tracing control paths plus a failure condition in element allocation. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to memory management misuse and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	INIT TRACE SIMPLEFIX  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1
  `map->ops->elt_free()` may be called on a partially initialized `tracing_map_elt` after `elt_alloc()` failed, so the callback may observe an object state it was not designed to handle.

* Real lifetime / cleanup contract violation: +1
  This is an alloc/free contract bug in an error path. The patch separates raw object cleanup from full callback-based cleanup.

* Reliable kernel crash / strong DoS: +1
  A NULL dereference, invalid cleanup, warning, or crash is plausible if the callback expects fields initialized by the successful `elt_alloc()` path.

* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2
  Tracing control paths are normally restricted to root or privileged tracing users.

Paranoid additional interpretation:

* Local lower-privilege trigger in delegated tracing setups: +1
  Some systems expose tracing through service accounts, debug environments, or delegated operational tooling, making PR:L defensible for triage.

* Weak LPE concern: +1
  Not because a concrete exploit primitive is shown, but because a callback is invoked on an object whose initialization contract failed. This is a memory-management misuse pattern that deserves manual review.

* Availability impact realistic: +1
  The most realistic impact remains local DoS through crash or warning-induced failure.

Call-site confidence: medium-high. The failed allocation path and incorrect callback call are visible, but the concrete behavior of all possible `elt_free` implementations is not shown in the supplied patch.

## 3. Reachability analysis

The issue is local and not network reachable. In normal deployments, creating and configuring tracing maps usually requires root or CAP_SYS_ADMIN through tracefs/debugfs, so the conservative interpretation treats this as privileged local access. A paranoid interpretation uses PR:L because tracing access may be delegated to a non-root tracing service account or available in specialized debug environments. Triggering also requires an allocation failure path, which makes exploitation less reliable than a normal direct syscall bug.

## 4. Severity interpretation

This behaves like an actionable Moderate rather than a clear Important issue. The patch shows a real cleanup/lifetime contract violation, but it does not demonstrate attacker-controlled reclaim, arbitrary write, type confusion, function pointer control, or a reliable privilege escalation primitive. Realistic impact is local DoS. The paranoid score keeps it visible for manual review because callback-based cleanup of partially initialized kernel objects can hide stronger impact depending on the callback implementation.

## 5. One-sentence report phrase

A tracing_map allocation failure path could incorrectly call the map elt_free callback on a partially initialized element, potentially causing invalid cleanup or a local kernel crash, with higher concern in delegated tracing environments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is not a simple leak or validation-only fix. It is an error-path cleanup bug involving a callback and partially initialized kernel object state, so the concrete `elt_free` implementations should be checked before auto-closing.

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

Patch: tracing: Do not call map->ops->elt_free() if elt_alloc() fails
Commit: 49332e49ad5b20262cc719b03d4123b9362de701
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49332e49ad5b20262cc719b03d4123b9362de701

Commit description:

In paths where tracing_map_elt_alloc() failed to allocate objects,
the map->ops->elt_alloc() call was never successful. In this case,
map->ops->elt_free() should not be called.

Link: https://sashiko.dev/#/patchset/20260520223101.34710-1-rosenp%40gmail.com

Cc: stable@vger.kernel.org
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Rosen Penev <rosenp@gmail.com>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 2734b62 ("tracing: Add per-element variable support to tracing_map")
Link: https://patch.msgid.link/177933895460.108746.5396070821443932634.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/trace/tracing_map.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=49332e49ad5b20262cc719b03d4123b9362de701

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

The original Linux kernel CVE announcement for CVE-2026-64173 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64173

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:N/A:H
  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: 2
  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).