[CVE-2026-72117][LOW] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()

[CVE-2026-72117][LOW] can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()

[AL-KERNEL]

CVE: CVE-2026-72117
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
Commit: 5f246b96ab47523ec9b8ea870b5c567a3cb1eb1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f246b96ab47523ec9b8ea870b5c567a3cb1eb1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72117
Analysis date: Sat, 15 Aug 2026 21:44:25 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A CAN BCM data race can cause userspace to receive a CAN frame with timestamp or interface metadata from a different concurrently processed frame, but the patch does not indicate memory corruption, privilege escalation, or reliable denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-72117 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72117

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: 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-2026-72117	LOW	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:N';CWE-362;CWE-667;CWE-662;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3.6';DESCR 'A data race in CAN BCM can occur when one rx operation is subscribed to all interfaces and bcm_rx_handler runs concurrently on different CPUs for frames from different CAN devices. The race can update rx_stamp and rx_ifindex outside the same locked section that compares and delivers the CAN frame content, so userspace may receive a frame with timestamp or interface metadata belonging to another frame. On 32 bit platforms the 64 bit timestamp store may also be torn. For the CVSS the PR:L is used because reliable triggering normally requires a local user or process that can create or influence CAN BCM socket state and local CAN traffic. The issue is not directly network reachable in the usual IP network sense, but it may be influenced by access to local CAN buses or virtual CAN devices. Impact is mainly low integrity impact for reported metadata, with at most low confidentiality impact in the paranoid interpretation due to mixed timing or origin metadata.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	WRITE OOB SIMPLEFIX RACE SKB HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process can normally create CAN BCM socket state if CAN sockets and a CAN interface are available.
* Integrity impact plausible: +1. Userspace may receive CAN frame content with mismatched timestamp or interface metadata.
* Hard or unreliable race / special timing required: -1. The issue requires concurrent bcm_rx_handler execution on different CPUs for the same wildcard rx op.

Paranoid additional signal:

* Confidentiality impact plausible: +1. Mixed timestamp or ifindex metadata from another frame could be treated as a low metadata disclosure concern.

Not counted:

* No generic memory corruption. The race affects scalar metadata fields rx_stamp and rx_ifindex, not object lifetime, bounds, callback pointers, or attacker controlled overwrite targets.
* No privilege escalation plausible. There is no UAF, OOB write, type confusion, stale callback, refcount abuse, or reclaim primitive.
* No reliable kernel crash / strong DoS. The patch describes incorrect metadata bundling and torn 64 bit store on 32 bit platforms, not panic or oops.
* No remote reachable score. CAN bus influence is not equivalent to ordinary IP network reachability.

## 3. Reachability analysis

A local user or process with access to CAN BCM sockets and relevant CAN traffic can potentially trigger the race by using an rx operation subscribed to all interfaces with ifindex 0. The bug is not directly reachable from a normal remote IP network. It may be influenced by local CAN, virtual CAN, or attached CAN devices, but exploitation requires local CAN subsystem access and a concurrent traffic pattern. Namespaces may matter if CAN devices or vcan are delegated, but creating or managing CAN interfaces usually requires CAP_NET_ADMIN.

## 4. Severity interpretation

This behaves like a low severity data race and metadata integrity issue, not an Important class kernel vulnerability. The theoretical concern is inconsistent or torn metadata reported to userspace. Realistic exploitation evidence does not show kernel memory corruption, privilege escalation, sensitive data theft, or reliable DoS. It should not be treated as Actionable Moderate unless the product has safety critical dependence on CAN timestamp or interface metadata correctness.

## 5. One-sentence report phrase

A CAN BCM data race can cause userspace to receive a CAN frame with timestamp or interface metadata from a different concurrently processed frame, but the patch does not indicate memory corruption, privilege escalation, or reliable denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for ordinary security triage because the issue is a constrained metadata race with low impact and no supported memory corruption or LPE primitive.

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

Patch: can: bcm: fix data race on rx_stamp/rx_ifindex in bcm_rx_handler()
Commit: 5f246b96ab47523ec9b8ea870b5c567a3cb1eb1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5f246b96ab47523ec9b8ea870b5c567a3cb1eb1c

Commit description:

For an rx op subscribed on all interfaces (ifindex == 0), the same op
is registered once in the shared per-netns wildcard filter list, so
bcm_rx_handler() can run concurrently on different CPUs for frames
arriving on different net devices.

op->rx_stamp and op->rx_ifindex were written before bcm_rx_update_lock was
taken, allowing concurrent writers to race each other - including a torn
store of the 64-bit rx_stamp on 32-bit platforms.

Beyond a torn store bcm_send_to_user() must report the timestamp/ifindex
of the very same frame whose content it is delivering. So the assignment
is placed in the same unbroken bcm_rx_update_lock section as the content
comparison.

As a side effect, the RTR-request frame feature (which never reach
bcm_send_to_user()) no longer updates rx_stamp/rx_ifindex, since only
the notification path needs them.

Fixes: ffd980f ("[CAN]: Add broadcast manager (bcm) protocol")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-can/20260707145135.5BC831F00A3A@smtp.kernel.org/
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-10-562f7e3e42da@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=5f246b96ab47523ec9b8ea870b5c567a3cb1eb1c

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

The original Linux kernel CVE announcement for CVE-2026-72117 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72117

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:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
  The Best / paranoid CVSS score: 3.6

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: 2

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).