[CVE-2026-72120][MODERATE 7.0] can: bcm: add missing rcu list annotations and operations commit 7b2c3eabc4dafc062a25e10711154f2107526a78 upstream.

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

CVE: CVE-2026-72120
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: bcm: add missing rcu list annotations and operations commit 7b2c3eabc4dafc062a25e10711154f2107526a78 upstream.
Commit: 8357255e56dc1aaa437e3c53ee9385de984e0d57
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8357255e56dc1aaa437e3c53ee9385de984e0d57
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72120
Analysis date: Sat, 15 Aug 2026 05:53:11 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
CAN BCM RCU list misuse can expose partially initialized or stale `bcm_op` objects during procfs traversal, allowing a local user with CAN BCM access to trigger a kernel crash and creating a weak UAF based privilege escalation concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72120 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72120

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
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CVE-2026-72120	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-362;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'CAN BCM uses RCU protected lists for tx_ops and rx_ops, but new bcm_op entries could be linked before full initialization and release paths could pass still linked ops to call_rcu based freeing. A local user process that can use CAN BCM sockets may race setup or release with procfs traversal in bcm_proc_show(), which can expose partially initialized or stale bcm_op objects. For the CVSS the PR:L is used because reliable triggering requires local code execution and access to the CAN BCM interface, but not full administrative control in typical threat modeling. The issue is not network reachable in the IP sense and is triggered through local socket and procfs activity. Impact is at least local denial of service via kernel crash. In the paranoid interpretation, limited confidentiality or integrity impact is kept because the RCU list misuse is a use-after-free candidate, but the patch context does not support a strong arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-72120 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: dac5e6249159ac255dad9781793dbe5908ac9ddb YES  NO NO unknown 	MAYBE	DISK INIT HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK 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. CAN BCM sockets can be reachable by local users when CAN support and relevant interfaces are available.
* Memory corruption, weak/indirect corruption candidate: +1. The bug involves RCU list misuse, partially initialized `bcm_op` publication, and stale list entries.
* Real lifetime corruption: +1. `bcm_remove_op()` frees objects via `call_rcu()`, while the old release path could leave them linked.
* Hard or unreliable race / special timing required: -1. Practical triggering requires racing setup or release against procfs traversal.
* Reliable kernel crash / strong DoS: +1. A stale or partially initialized `bcm_op` dereference during procfs traversal can plausibly crash the kernel.

Paranoid additional signal:

* Weak LPE concern: +1. The stale RCU list entry creates a UAF candidate, but the patch does not show attacker-controlled reclaim, callback control, arbitrary write, or reliable object replacement.

## 3. Reachability analysis

The likely attacker is a local process that can create or manipulate CAN BCM sockets and concurrently read CAN BCM procfs state. This is not IP-network reachable and should not be treated as a remote network attack. CAP_NET_ADMIN may be needed to create or configure CAN or vcan interfaces in some environments, but the vulnerable BCM socket and procfs activity may be reachable with lower privileges once CAN infrastructure exists. Namespaces can matter because container or delegated network setups may reduce the practical privilege requirement from full host root to a less privileged local actor.

Call-site confidence: high. The patch shows the relevant publication path, procfs traversal path, and release/free path.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary low-priority DoS. The realistic impact is local kernel crash or instability from RCU list lifetime misuse. The theoretical concern is UAF-style stale object traversal, but the patch does not demonstrate a strong privilege escalation primitive such as controlled reclaim, overwrite, callback hijack, or type confusion. Therefore it should be manually reviewed, but it is not a Strong Important candidate on the supplied evidence alone.

## 5. One-sentence report phrase

CAN BCM RCU list misuse can expose partially initialized or stale `bcm_op` objects during procfs traversal, allowing a local user with CAN BCM access to trigger a kernel crash and creating a weak UAF based privilege escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is an RCU lifetime bug with a UAF candidate in a local kernel networking subsystem. The demonstrated impact is mainly DoS, but stale object traversal makes it unsafe to auto-close without manual review.

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

Patch: can: bcm: add missing rcu list annotations and operations commit 7b2c3eabc4dafc062a25e10711154f2107526a78 upstream.
Commit: 8357255e56dc1aaa437e3c53ee9385de984e0d57
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8357255e56dc1aaa437e3c53ee9385de984e0d57

Commit description:

sashiko-bot remarked the missing use of list_add_rcu() in
bcm_[rx|tx]_setup() to have a proper initialized bcm_op structure
when bcm_proc_show() traverses the bcm_op's under rcu_read_lock().

To cover all initial settings of the bcm_op's the list_add_rcu() calls
are moved to the end of the setup code.

While at it, also fix the mirroring removal side: bcm_release() called
bcm_remove_op() - which frees the op via call_rcu() - on ops that were
still linked in bo->tx_ops/bo->rx_ops, without list_del_rcu() first.
Unlink each op with list_del_rcu() before handing it to bcm_remove_op(),
matching the existing pattern in bcm_delete_tx_op()/bcm_delete_rx_op().

Reported-by: sashiko-reviews@lists.linux.dev
Closes: https://lore.kernel.org/linux-can/20260610094654.A1FFE1F00893@smtp.kernel.org/
Fixes: dac5e6249159 ("can: bcm: add missing rcu read protection for procfs content")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-5-562f7e3e42da@hartkopp.net
Cc: stable@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- net/can/bcm.c 25

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=8357255e56dc1aaa437e3c53ee9385de984e0d57

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

The original Linux kernel CVE announcement for CVE-2026-72120 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72120

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: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).