[CVE-2026-72118][LOW] can: bcm: fix CAN frame rx/tx statistics

[CVE-2026-72118][LOW] can: bcm: fix CAN frame rx/tx statistics

[AL-KERNEL]

CVE: CVE-2026-72118
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: can: bcm: fix CAN frame rx/tx statistics
Commit: 8b2783172d92edd650de6006ebd1c800937021ab
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b2783172d92edd650de6006ebd1c800937021ab
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72118
Analysis date: Sun, 16 Aug 2026 08:05:50 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72118 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72118

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: LOW
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-2026-72118	LOW	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:N/I:N/A:L';CWE-362;CWE-667;CWE-682;BEST CVSS score: '2.5';DESCR 'A data race in CAN BCM statistics handling can occur when multiple CPUs process received CAN frames for the same BCM operation and update frames_abs or frames_filtered concurrently. The race can make procfs statistics inconsistent, for example frames_filtered can become larger than frames_abs and produce a bogus negative reduction value. For the CVSS the PR:L is used because reliable triggering normally requires a local process that creates or controls a CAN BCM socket and receives matching CAN traffic. The issue is not directly reachable over an IP network. A CAN bus adjacent sender may influence traffic only when a local BCM subscription already exists. Impact is limited to low availability or observability degradation through inconsistent statistics, with no supported evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0)	YES	KASAN LOCK DISK RACE HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=0

1. ActionableScore
* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process may create or use a CAN BCM socket and receive matching CAN traffic.
* Hard or unreliable race / special timing required: -1. The issue requires concurrent processing of CAN frames for the same BCM operation on different CPUs.
* Rare AND difficult-to-reach subsystem/configuration: -1. CAN BCM is not a broad/default Internet-facing kernel path.
* Availability impact realistic: +0. The demonstrated impact is inconsistent procfs statistics, not a reliable kernel crash or system-wide DoS.
* Generic memory corruption: +0. The patch changes statistics counters to atomic_long_t and adjusts locking. No UAF, OOB write, double-free, stale pointer reuse, or controlled overwrite is shown.
* Privilege escalation plausible: +0. No exploit primitive supports LPE.

3. Reachability analysis
A local process using CAN BCM can plausibly trigger the affected code path if matching CAN frames are processed concurrently, especially for wildcard RX operations with ifindex == 0. A CAN-bus-adjacent sender may influence traffic, but only after a local BCM subscription exists, so this is not directly network-reachable over IP. Namespace or container effects do not materially increase severity unless untrusted tenants are explicitly allowed to use CAN BCM sockets and CAN devices. The path is specialized and not generally exposed on typical servers.

4. Severity interpretation
This behaves like a low-severity correctness/data-race issue rather than an actionable Moderate or Important kernel vulnerability. Theoretical race behavior exists, but the demonstrated consequence is bogus or negative statistics in procfs. There is no supported memory corruption, confidentiality impact, integrity impact, privilege escalation path, or reliable kernel crash.

5. One-sentence report phrase
A CAN BCM statistics data race can produce inconsistent procfs RX/TX counters under concurrent frame processing, but the demonstrated impact is limited to incorrect accounting with no evidence of memory corruption, information disclosure, privilege escalation, or reliable DoS.

6. Manual review recommendation
NO MANUAL CHECK NEEDED.
NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.
The issue is a KCSAN-reported statistics race with low practical security impact and no concrete exploit primitive beyond incorrect accounting.

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UPSTREAM PATCH SUMMARY
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Patch: can: bcm: fix CAN frame rx/tx statistics
Commit: 8b2783172d92edd650de6006ebd1c800937021ab
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b2783172d92edd650de6006ebd1c800937021ab

Commit description:

KCSAN detected a data race within the bcm_rx_handler() when two CAN frames
have been simultaneously received and processed in a single rx op by two
different CPUs.

Use atomic operations with (signed) long data types to access the
statistics in the hot path to fix the KCSAN complaint.

Additionally simplify the update and check of statistics overflow by
using the atomic operations in separate bcm_update_[rx|tx]_stats()
functions. The rx variant runs under bcm_rx_update_lock to prevent
races when resetting the two rx counters; the tx variant runs under
bcm_tx_lock and only needs to guard its own counter's overflow.

As the rx path resets its values already at LONG_MAX / 100, there is
no conflict between the two locking domains (bcm_rx_update_lock vs.
bcm_tx_lock) even for ops that use both paths.

The rx statistics update and the frames_filtered update in
bcm_rx_changed() were previously performed in two separate
bcm_rx_update_lock sections. For an rx op subscribed on all interfaces
(ifindex == 0), bcm_rx_handler() can run concurrently on different
CPUs, so a counter reset by one CPU between these two sections could
leave frames_filtered larger than frames_abs on another CPU, producing
a bogus (even negative) reduction percentage in procfs. Update the
statistics in the same critical section as bcm_rx_changed() to close
this gap, which also removes the now unneeded extra lock/unlock pair
around the traffic_flags calculation.

Fixes: ffd980f ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-4-562f7e3e42da@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>

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=8b2783172d92edd650de6006ebd1c800937021ab

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

The original Linux kernel CVE announcement for CVE-2026-72118 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72118

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 2.5

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: unknown
  Paranoid ActionableScore: 0

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).