[CVE-2026-17523][LOW] can: bcm: switch timer to HRTIMER_MODE_SOFT and remove hrtimer_tasklet

[CVE-2026-17523][LOW] can: bcm: switch timer to HRTIMER_MODE_SOFT and remove hrtimer_tasklet

[AL-KERNEL]

CVE: CVE-2026-17523
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: can: bcm: switch timer to HRTIMER_MODE_SOFT and remove hrtimer_tasklet
Commit: 79305a826f872fe446c6fbf8450f515053ef6951
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79305a826f872fe446c6fbf8450f515053ef6951
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-17523
Analysis date: Wed, 09 Sep 2026 03:50:14 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-17523 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-17523

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-17523	LOW	https://www.kernelcve.org/list/?q=CVE-2026-17523 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:N/A:L';CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N';BEST CVSS score: '2.5';DESCR 'The CAN BCM timer path is changed so hrtimer callbacks run in softirq context instead of scheduling separate tasklets. The visible patch mainly removes the intermediate tasklet layer and moves TX timeout, RX timeout, and RX throttle work into soft hrtimer callbacks. For the CVSS the PR:L is used only as a conservative local interface assumption because a local process would need access to CAN BCM socket operations to exercise this path. The patch context does not show a concrete memory corruption primitive, NULL pointer dereference, information leak, or confirmed crash. The issue is not network reachable from a remote IP attacker and should be treated as cleanup or hardening unless external evidence links it to a real exploitable race. Impact is none for the base assessment and at most low availability impact for a paranoid tracking score.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	DANGER INIT TIMER LINUS TEST  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS	NO	YES	guess

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

Awarded signals:

* +0. No concrete vulnerability primitive is established. The patch changes CAN BCM timer execution from tasklet based handling to soft hrtimer callbacks.
* +0. No Real UAF is established. The diff removes tasklets and simplifies cancellation, but does not show a stale object dereference after free.
* +0. No reliable kernel crash is established. The supplied commit message does not report an Oops, panic, lockup, KASAN finding, or syzbot crash.
* +0. No authorization bypass, COW violation, arbitrary write, OOB access, information leak, or repeated release/refcount operation is established.

Non-awarded material signals:

* Remote reachability not awarded. CAN BCM socket operations are local socket/control operations, not remote IP packet processing.
* Local unprivileged trigger not awarded. Even if PF_CAN sockets may be usable by local users in some systems, there is no concrete vulnerable behavior to trigger.
* Race/timing penalty not applied. The patch involves timers and tasklets, but no concrete hard race vulnerability is described.
* Structured stale-object leverage not awarded. struct bcm_op is active structured state, but no stale post-lifetime consumption is established.
* Weak LPE or strong LPE not awarded. There is no controlled reclaim, callback hijack, refcount takeover, arbitrary R/W, or privilege boundary consequence.
* Extra availability not awarded. No actual crash, hang, persistent resource exhaustion, or host-wide DoS is shown.
* Concrete repeated release/refcount not awarded. No first release that can end lifetime, surviving exact reference, or second lifetime mutation is visible.

3. Reachability analysis

The relevant code is in net/can/bcm.c and is exercised through local CAN BCM socket setup and timer operations. A local process may be able to create BCM operations if CAN support and a CAN or virtual CAN device are available, but the supplied evidence does not establish a complete security-relevant trigger below host-admin privilege. Prior setup of CAN interfaces such as vcan often requires administrative configuration, but that is deployment dependent and not enough to set HostAdminRequired=YES for the nonexistent vulnerability path.

Namespace-scoped privilege is unresolved. The mere fact that CAN networking can interact with network namespaces does not establish that the complete operation is namespace-scoped and attacker reachable. No remote network trigger is established. No special physical hardware is required by the code path in principle because vcan may exist, but no vulnerability impact depends on hardware.

4. Primitive and severity interpretation

The exact patch primitive is a timer execution model change: hrtimer callbacks are moved to HRTIMER_MODE_SOFT and tasklets are removed. This appears to be cleanup, modernization, and possibly PREEMPT_RT oriented hardening. It does not establish memory corruption, UAF, double free, refcount misuse, OOB access, information disclosure, or security-boundary bypass.

The affected object is an active structured CAN BCM operation object, but the patch does not show post-free use of that object. The old code explicitly cancelled hrtimers and killed tasklets in bcm_remove_op, while the new code cancels soft hrtimers directly. That simplification may reduce lifetime complexity, but it is not enough to classify the change as a confirmed lifetime vulnerability.

PrimitiveClass=NONE because no meaningful security primitive is established. RealUAF=NO because no actual or directly implied use-after-free is shown. ImportantCandidate=NO because there is no unresolved kernel corruption primitive requiring Important-vs-Moderate review. AutoDowngradeAllowed=YES because this can be treated as cleanup or non-security hardening unless external advisory evidence connects it to a concrete crash, UAF, or security consequence.

5. One-sentence report phrase

The CAN BCM patch switches timer callbacks to soft hrtimer context and removes tasklets, but the supplied evidence does not establish a concrete memory corruption, crash, information leak, or privilege escalation primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the supplied patch and commit message do not establish a concrete vulnerability primitive or security consequence. Reopen only if an external CVE/advisory links this commit to a real crash, UAF, or exploitable race.

7. Call-site confidence

Call-site confidence: medium

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

Patch: can: bcm: switch timer to HRTIMER_MODE_SOFT and remove hrtimer_tasklet
Commit: 79305a826f872fe446c6fbf8450f515053ef6951
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79305a826f872fe446c6fbf8450f515053ef6951

Commit description:

This patch switches the timer to HRTIMER_MODE_SOFT, which executed the
timer callback in softirq context and removes the hrtimer_tasklet.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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=79305a826f872fe446c6fbf8450f515053ef6951

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

The original Linux kernel CVE announcement for CVE-2026-17523 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-17523

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:N
  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).