---
id: CVE-2026-72123
title: 'can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF

  Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly
  synchronize_rcu()") replaced synch…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 85cd41070df992d3c0dfd828866fdd243d3b774a <
    de5fce46637de05bef56ec08528127676eb6fc9b
  - >-
    Linux >= f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1 <
    036a8c320ca11bc912e8027adcfad14b326f067e
  - >-
    Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 <
    3cf4fd5316f449811d8baf1bc6978ef5a7b743a9
  - >-
    Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 <
    4177762f70646ac48a2af382e45a795cbd295198
  - >-
    Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 <
    6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f
  - >-
    Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 <
    cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5
  - >-
    Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 <
    ce2d4b121fb7545e1ed588e860c8e5fd5ad45224
  - >-
    Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 <
    68973f9db76144825e4f35dfdc80fb8279eb2d57
  - Linux fbac09a3b8890003c0c55294c00709f3ae5501bb
  - Linux 5b48f5711f1c630841ab78dcc061de902f0e37bf
  - Linux edb4baffb9483141a50fb7f7146cfe4a4c0c2db8
  - Linux >= 5.10.130 < 5.10.265
  - Linux >= 5.15.54 < 5.15.216
  - Linux >= 4.19.252 < 4.20
  - Linux >= 5.4.205 < 5.5
  - Linux >= 5.18.11 < 5.19
  - Linux 5.19
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T18:42:12.952847Z'
published: '2026-08-15'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T18:44:57.598Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-72123'
references:
  - url: 'https://git.kernel.org/stable/c/de5fce46637de05bef56ec08528127676eb6fc9b'
  - url: 'https://git.kernel.org/stable/c/036a8c320ca11bc912e8027adcfad14b326f067e'
  - url: 'https://git.kernel.org/stable/c/3cf4fd5316f449811d8baf1bc6978ef5a7b743a9'
  - url: 'https://git.kernel.org/stable/c/4177762f70646ac48a2af382e45a795cbd295198'
  - url: 'https://git.kernel.org/stable/c/6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f'
  - url: 'https://git.kernel.org/stable/c/cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5'
  - url: 'https://git.kernel.org/stable/c/ce2d4b121fb7545e1ed588e860c8e5fd5ad45224'
  - url: 'https://git.kernel.org/stable/c/68973f9db76144825e4f35dfdc80fb8279eb2d57'
tags:
  - cve.org
epss: 0.00169
epssPercentile: 0.05786
ingestedAt: '2026-10-16T19:46:24.431Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF

Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly
synchronize_rcu()") replaced synchronize_rcu() in bcm_delete_rx_op()
with call_rcu() and introduced the RX_NO_AUTOTIMER flag.

However, this flag check was omitted for thrtimer in the packet rx
fast-path. During BCM RX operation teardown, a concurrent RCU reader
(bcm_rx_handler) can race and re-arm thrtimer via
bcm_rx_update_and_send() after call_rcu() has been scheduled.  Once
the RCU grace period elapses, bcm_op is freed.  The subsequently
firing thrtimer then dereferences the deallocated op, causing a UAF.

Adding flag checks to the rx fast-path (bcm_rx_update_and_send) does not
fully close the TOCTOU race and introduces latency for every CAN frame.
Conversely, calling hrtimer_cancel() directly inside the RCU callback
(softirq context) is fatal as hrtimer_cancel() can sleep, triggering
a "scheduling while atomic" panic.

Resolve this by deferring the timer cancellation and memory free to a
dedicated unbound workqueue (bcm_wq).  The RCU callback now queues a
work item to bcm_wq, which safely cancels both timers and deallocates
memory in sleepable process context.  A dedicated workqueue is used to
prevent system-wide WQ saturation and is cleanly flushed/destroyed
on module unload to avoid rmmod page faults.

Since the deferred work can now outlive the calling context by an
unbounded amount, also take a reference on op->sk when it is assigned
and drop it only once the deferred work has cancelled both timers, so a
socket can no longer be freed out from under a still-armed timer whose
callback (bcm_send_to_user()) dereferences op->sk.

## Affected

- `Linux >= 85cd41070df992d3c0dfd828866fdd243d3b774a < de5fce46637de05bef56ec08528127676eb6fc9b`
- `Linux >= f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1 < 036a8c320ca11bc912e8027adcfad14b326f067e`
- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 3cf4fd5316f449811d8baf1bc6978ef5a7b743a9`
- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 4177762f70646ac48a2af382e45a795cbd295198`
- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f`
- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5`
- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < ce2d4b121fb7545e1ed588e860c8e5fd5ad45224`
- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 68973f9db76144825e4f35dfdc80fb8279eb2d57`
- `Linux fbac09a3b8890003c0c55294c00709f3ae5501bb`
- `Linux 5b48f5711f1c630841ab78dcc061de902f0e37bf`
- `Linux edb4baffb9483141a50fb7f7146cfe4a4c0c2db8`
- `Linux >= 5.10.130 < 5.10.265`
- `Linux >= 5.15.54 < 5.15.216`
- `Linux >= 4.19.252 < 4.20`
- `Linux >= 5.4.205 < 5.5`
- `Linux >= 5.18.11 < 5.19`
- `Linux 5.19`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.