[CVE-2026-72116][MODERATE REGULAR] can: bcm: fix stale rx/tx ops after device removal

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

CVE: CVE-2026-72116
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: bcm: fix stale rx/tx ops after device removal
Commit: 60d8a7942f4ed2d975207aaeba1adb576707e53d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=60d8a7942f4ed2d975207aaeba1adb576707e53d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72116
Analysis date: Sat, 15 Aug 2026 18:14:49 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate watchlist
Manual review required: YES

Summary:
A stale CAN BCM RX/TX operation after CAN device removal can cause lost receive delivery, a runaway cyclic TX timer, and possible CAN frame injection into a later reused ifindex, requiring local CAN_BCM access and device lifecycle conditions.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72116 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72116

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 REGULAR
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-2026-72116	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:L/A:H';*CWE-672;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '5.3';DESCR 'CAN BCM keeps per socket rx and tx operations across CAN device lifecycle events. In the RX path, an RX_SETUP update for an existing operation could skip re-registration after NETDEV_UNREGISTER had already removed the previous receive registration, causing silent loss of frame delivery for that filter. In the TX path, a device specific cyclic transmission could keep re-arming its hrtimer after the target device was unregistered, which can cause a runaway timer and may send CAN frames if the same ifindex is later reused. For the CVSS the PR:L is used for the paranoid score because a local user with access to CAN_BCM sockets may be able to create the stale operation while the unregister event can occur through hotplug, namespace teardown, or delegated network administration. The issue is not reachable over IP networks and requires local CAN socket access plus device lifecycle conditions. Impact is denial of service and possible limited integrity impact on CAN traffic, not known privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate watchlist (with actual score 4)	YES	DISK INIT TIMER HARDWARE LINUS 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **4**
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate watchlist**::

## 2. Signal breakdown

Triggered signals:

* **Local unprivileged trigger: +1**
  A local user may be able to create CAN_BCM socket operations if PF_CAN/CAN_BCM is available, though reliable full triggering also depends on CAN device unregister events.

* **Real lifetime / async timer mismatch: +1**
  The TX side leaves a cyclic tx op hrtimer active after NETDEV_UNREGISTER, so an operation tied to a removed device can continue executing asynchronously.

* **Reliable kernel crash / strong DoS: +1**
  The runaway hrtimer can repeatedly execute `bcm_tx_timeout_handler()`, producing a realistic local DoS condition.

* **Integrity impact plausible: +1**
  The commit explicitly mentions preventing injection into a later reused ifindex, so limited CAN traffic integrity impact is plausible.

* **Practical exploit chain strongly implied: +1, paranoid only**
  The TX path describes a concrete stale-ifindex scenario where cyclic transmission may affect a later reused interface index.

Subtracted signals:

* **Hard or unreliable race / special timing required: -1**
  The RX issue involves concurrent `RX_SETUP` and `NETDEV_UNREGISTER`, and the TX impact depends on device lifecycle timing and ifindex reuse.

Not awarded:

* **Remote reachable: +0**
  This is not IP-network remote. It requires local CAN socket interaction and CAN netdev lifecycle events.

* **Generic memory corruption: +0**
  The patch does not show UAF, OOB write, double free, type confusion, or attacker-controlled memory reuse.

* **Privilege escalation plausible: +0**
  No credible LPE primitive is shown. The main risks are DoS and limited CAN traffic integrity impact.

## 3. Reachability analysis

The bug is locally reachable through CAN BCM socket operations, assuming the CAN BCM protocol is enabled and usable. Reliable exploitation also requires CAN netdev removal or unregister activity, which is typically controlled by root or `CAP_NET_ADMIN`, but may be reachable in delegated network namespaces, container setups, hotplug scenarios, or test environments with virtual CAN devices.

The path is not broadly Internet-exposed and is not triggered by ordinary IP packet traffic. It is configuration-dependent because CAN is not a universal default workload, but it remains reachable through ordinary local socket APIs on systems using SocketCAN.

## 4. Severity interpretation

This behaves more like **borderline actionable Moderate** than Important. There is a real stale lifecycle/timer issue and a plausible limited integrity consequence through ifindex reuse, but the patch does not support memory corruption or privilege escalation.

The theoretical concern is higher than a pure cleanup bug because the stale TX operation can continue after device removal. Realistic exploitation still depends on local access, CAN availability, lifecycle timing, and possibly administrative or namespace-mediated control over device unregister events.

## 5. One-sentence report phrase

A stale CAN BCM RX/TX operation after CAN device removal can cause lost receive delivery, a runaway cyclic TX timer, and possible CAN frame injection into a later reused ifindex, requiring local CAN_BCM access and device lifecycle conditions.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Manual review is recommended because this is not a simple DoS-only cleanup. The patch explicitly references possible injection into a reused ifindex, which creates a limited integrity concern even though no memory corruption or privilege escalation primitive is evident.

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

Patch: can: bcm: fix stale rx/tx ops after device removal
Commit: 60d8a7942f4ed2d975207aaeba1adb576707e53d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=60d8a7942f4ed2d975207aaeba1adb576707e53d

Commit description:

RX: an RX_SETUP update(!) for an existing op skipped can_rx_register()
unconditionally, even when a concurrent NETDEV_UNREGISTER had already
torn down its registration (op->rx_reg_dev == NULL). This silently
did not re-enable frame delivery for that updated filter. bcm_rx_setup()
now re-registers in that case, while leaving rx_ops with ifindex = 0
(all CAN devices) which never carry a tracked rx_reg_dev registered as-is.

TX: bcm_notify() only handled bo->rx_ops on NETDEV_UNREGISTER, leaving
tx_ops with an active cyclic transmission re-arming its hrtimer
indefinitely to execute bcm_tx_timeout_handler(). Cancelling the hrtimer
prevents the runaway timer and any injection into a later reused ifindex,
since nothing else calls bcm_can_tx() for the op until an explicit
TX_SETUP update re-arms it.

Unlike bcm_rx_unreg(), which clears the tracked rx_reg_dev for rx_ops,
the ifindex is intentionally left unchanged for tx_ops. bcm_tx_setup()
always rejects ifindex 0, so clearing it would strand the op: neither a
later TX_SETUP (bcm_find_op()) nor TX_DELETE (bcm_delete_tx_op()) could
ever find it again, since both require an exact ifindex match.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/linux-can/20260708094536.DDF821F00A3A@smtp.kernel.org/
Closes: https://lore.kernel.org/linux-can/20260708154039.347ED1F000E9@smtp.kernel.org/
Fixes: ffd980f ("[CAN]: Add broadcast manager (bcm) protocol")
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-9-562f7e3e42da@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=60d8a7942f4ed2d975207aaeba1adb576707e53d

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

The original Linux kernel CVE announcement for CVE-2026-72116 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72116

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.3

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: 4

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 REGULAR

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).