[CVE-2026-72119][MODERATE 7.0] can: bcm: extend bcm_tx_lock usage for data and timer updates commit 12ce799f7ab1e05bd8fbf79e46f403bfe5597ebc upstream.

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

CVE: CVE-2026-72119
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: bcm: extend bcm_tx_lock usage for data and timer updates commit 12ce799f7ab1e05bd8fbf79e46f403bfe5597ebc upstream.
Commit: 52f06e7603780de100233713ddaf971d422e10ef
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=52f06e7603780de100233713ddaf971d422e10ef
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72119
Analysis date: Sat, 15 Aug 2026 04:01:33 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A local CAN_BCM user can race TX operation updates with timer driven transmission, allowing the kernel to observe partially updated or unvalidated frame and timer state, which may cause incorrect CAN transmission or local denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-72119 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72119

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: NO

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-2026-72119	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-367;CWE-252;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'CAN BCM TX operation updates can race with bcm_can_tx and bcm_tx_timeout_handler because frame data and timer fields were updated without consistently holding bcm_tx_lock. A local process using CAN_BCM sockets can update an existing TX operation while the timer path is transmitting, so the kernel may observe partially updated or not yet validated CAN frame content and inconsistent timer state. For the CVSS the PR:L because triggering requires local code execution with access to CAN_BCM socket operations, but not full administrative privileges in deployments where CAN interfaces are already available. The issue is not directly reachable over an IP network and is triggered through the local CAN socket control path rather than by remote packet traffic. Impact is at least incorrect CAN frame transmission or local denial of service. In the paranoid case limited confidentiality or integrity impact is kept for manual review sensitivity because the race exposes kernel TX paths to inconsistent validated state, but the patch does not show a strong arbitrary write or UAF primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-72119 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: c2aba69d0c36a496ab4f2e81e9c2b271f2693fd7 YES  NO NO unknown 	MAYBE	LOCK NOMEMCHK ERRORPATH TIMER LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process can use CAN_BCM socket operations if CAN or vcan access is available.
* Integrity impact plausible: +1. The race can expose partially updated or not yet validated CAN frame content to the transmit path, causing unintended CAN frame transmission.
* Availability impact realistic: +1. Inconsistent timer state or invalid frame state can plausibly cause local DoS or malfunction in the CAN BCM transmit path.
* Hard or unreliable race / special timing required: -1. The problematic behavior depends on racing bcm_tx_setup() with bcm_can_tx() or bcm_tx_timeout_handler().
* Local unprivileged high-control kernel data-plane API refinement: +1. CAN_BCM lets local users shape kernel-managed frame buffers and timer driven transmission state with relatively fine control.

Paranoid additional signals:

* Memory corruption, weak/indirect corruption candidate: +1. The patch prevents kernel TX paths from observing inconsistent or unvalidated in-kernel frame state, but it does not show UAF, OOB write, arbitrary write, or controlled reclaim.
* Reliable kernel crash / strong DoS: +1 in paranoid interpretation only. Torn 64-bit ktime_t reads on 32-bit platforms and inconsistent timer state may cause stronger availability failures, but the patch does not demonstrate a reliable panic.

Not awarded:

* No strong LPE plausibility. There is no demonstrated UAF reclaim, object replacement, callback control, type confusion, refcount takeover, or arbitrary write.
* No remote reachable signal. This is not triggered by IP network traffic and requires local CAN socket control.
* No strong generic memory corruption. The update is bounded and targets the intended op->frames buffer, with the main issue being publication before validation and inconsistent locking.

## 3. Reachability analysis

The likely trigger is a local process that creates or updates an existing CAN_BCM TX operation while the BCM timer path is active. This generally requires local code execution and access to CAN_BCM sockets, but not necessarily full host root if CAN interfaces are already configured and available to the user. Namespaces or containers may matter if a container is given access to CAN networking or vcan devices, which can make PR:L the practical assumption rather than PR:H. The path is not a common Internet exposed network path. It is configuration dependent on SocketCAN and CAN_BCM usage, but it is reachable through ordinary local socket APIs on systems using CAN.

Call-site confidence: high. The patch shows both the update path bcm_tx_setup() and the concurrent timer/transmit paths bcm_tx_set_expiry(), bcm_tx_timeout_handler(), and bcm_can_tx() interaction.

## 4. Severity interpretation

This is more than an ordinary low-risk correctness fix because it affects a local asynchronous kernel transmit path where user-provided frame data and timer state can be observed concurrently before consistent validation and publication. Realistic impact is mainly local DoS or incorrect CAN frame transmission. Theoretical escalation remains weak because the patch does not show a concrete memory corruption primitive such as UAF, OOB write, type confusion, arbitrary write, or attacker-controlled reclaim. The conservative score is borderline manual review. The paranoid score reaches Actionable Moderate because the affected API is locally reachable, race based, and controls kernel-managed TX state.

## 5. One-sentence report phrase

A local CAN_BCM user can race TX operation updates with timer driven transmission, allowing the kernel to observe partially updated or unvalidated frame and timer state, which may cause incorrect CAN transmission or local denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a race in an asynchronous kernel networking subsystem with user-controlled frame and timer state, but the patch does not demonstrate a strong memory corruption or privilege escalation primitive.

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

Patch: can: bcm: extend bcm_tx_lock usage for data and timer updates commit 12ce799f7ab1e05bd8fbf79e46f403bfe5597ebc upstream.
Commit: 52f06e7603780de100233713ddaf971d422e10ef
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=52f06e7603780de100233713ddaf971d422e10ef

Commit description:

Stage new CAN frame content for an existing tx op into a kmalloc()'d
buffer and validate it there, mirroring the approach already used in
bcm_rx_setup(). Only copy the validated data into op->frames while
holding op->bcm_tx_lock, so bcm_can_tx() and bcm_tx_timeout_handler()
can no longer observe a partially updated or unvalidated frame.

Add a missing error path for memcpy_from_msg() when copying CAN frame
data from userspace.

Also move the kt_ival1/kt_ival2/ival1/ival2 updates in bcm_tx_setup()
under op->bcm_tx_lock, and read kt_ival1/kt_ival2/count under the same
lock in bcm_tx_set_expiry() and bcm_tx_timeout_handler(), closing the
torn 64-bit ktime_t read on 32-bit platforms.

Fixes: c2aba69d0c36 ("can: bcm: add locking for bcm_op runtime updates")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-6-562f7e3e42da@hartkopp.net
Cc: stable@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat -rw-r--r-- net/can/bcm.c 104

Changed files:
  net/can/bcm.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=52f06e7603780de100233713ddaf971d422e10ef

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

The original Linux kernel CVE announcement for CVE-2026-72119 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72119

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: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: 3
  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).