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Lee Jones 036a8c320c can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF 
commit 68973f9db7 upstream.

Commit f1b4e32aca ("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.

Fixes: f1b4e32aca ("can: bcm: use call_rcu() instead of costly synchronize_rcu()")
Tested-by: Feng Xue <feng.xue@outlook.com>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260714-bcm_fixes-v15-1-562f7e3e42da@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>
History 2026-08-19 17:13:59 +02:00
arch powerpc/vtime: Initialize starttime at boot for native accounting 2026-08-19 17:13:54 +02:00
block partitions: aix: bound the pp_count scan to the ppe array 2026-07-24 15:51:24 +02:00
certs X.509: Fix validation of ASN.1 certificate header 2026-07-24 15:51:59 +02:00
crypto crypto: rsa-pkcs1pad: Don't WARN on an empty digest 2026-08-19 17:13:55 +02:00
Documentation PCI: Move Resizable BAR code to rebar.c 2026-07-24 15:51:58 +02:00
drivers net/mlx5e: Reject unsupported CB Shaper TSA in ETS validation 2026-08-19 17:13:59 +02:00
fs btrfs: free mapping node on duplicate reloc root insert 2026-08-19 17:13:56 +02:00
include raw: use more conventional iterators 2026-08-19 17:13:59 +02:00
init randomize_kstack: Maintain kstack_offset per task 2026-06-19 13:33:41 +02:00
io_uring io_uring/io-wq: re-check IO_WQ_BIT_EXIT for each linked work item 2026-07-24 15:51:21 +02:00
ipc ipc/shm: serialize orphan cleanup with shm_nattch updates 2026-06-19 13:33:38 +02:00
kernel bpf: Fix ld_{abs,ind} failure path analysis in subprogs 2026-08-19 17:13:56 +02:00
lib lib/test_meminit: use && for bools 2026-07-24 15:51:32 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/huge_memory: update file PMD counter before folio_put() 2026-06-19 13:33:49 +02:00
net
samples tracing/events: Fix to check the simple_tsk_fn creation 2026-07-24 15:51:42 +02:00
scripts kconfig: fix potential NULL pointer dereference in conf_askvalue 2026-07-24 15:51:28 +02:00
security apparmor: fix label can not be immediately before a declaration 2026-07-24 15:51:39 +02:00
sound ASoC: bt-sco: fix duplicate DAPM widget names for wideband DAI 2026-08-19 17:13:57 +02:00
tools bitops: make BYTES_TO_BITS() treewide-available 2026-07-24 15:51:56 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Move kvm_io_bus_get_dev() locking responsibilities to callers 2026-07-24 15:52:02 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:09:36 +09:00
Makefile Linux 5.15.215 2026-08-07 08:07:31 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.