[moderation] [can?] KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e84d960149e7 Merge tag 'for-6.19-rc5-tag' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=134d53fa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=676c6f0212d0c041
dashboard link: https://syzkaller.appspot.com/bug?extid=54ac9a66066e25a8973f
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [linu...@vger.kernel.org linux-...@vger.kernel.org m...@pengutronix.de sock...@hartkopp.net]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e2c3723b9ab1/disk-e84d9601.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5790bc964aa6/vmlinux-e84d9601.xz
kernel image: https://storage.googleapis.com/syzbot-assets/023ce82e3277/bzImage-e84d9601.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+54ac9a...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send

write to 0xffff88811ab24050 of 16 bytes by task 5054 on cpu 1:
bcm_rx_setup+0x7dd/0xe00 net/can/bcm.c:1260
bcm_sendmsg+0x1bb/0x4a0 net/can/bcm.c:1427
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x145/0x170 net/socket.c:742
____sys_sendmsg+0x31e/0x4a0 net/socket.c:2592
___sys_sendmsg+0x195/0x1e0 net/socket.c:2646
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2683 [inline]
__se_sys_sendmsg net/socket.c:2681 [inline]
__x64_sys_sendmsg+0xd4/0x160 net/socket.c:2681
x64_sys_call+0x17ba/0x3000 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811ab24050 of 16 bytes by interrupt on cpu 0:
bcm_rx_changed net/can/bcm.c:501 [inline]
bcm_rx_update_and_send+0x392/0x420 net/can/bcm.c:553
bcm_rx_handler+0x2b0/0x580 net/can/bcm.c:739
deliver net/can/af_can.c:575 [inline]
can_rcv_filter+0x3c6/0x4f0 net/can/af_can.c:636
can_receive+0xfb/0x1c0 net/can/af_can.c:662
canfd_rcv+0xed/0x190 net/can/af_can.c:705
__netif_receive_skb_one_core net/core/dev.c:6152 [inline]
__netif_receive_skb+0x120/0x270 net/core/dev.c:6265
process_backlog+0x228/0x420 net/core/dev.c:6617
__napi_poll+0x5f/0x300 net/core/dev.c:7681
napi_poll net/core/dev.c:7744 [inline]
net_rx_action+0x452/0x930 net/core/dev.c:7896
handle_softirqs+0xb9/0x280 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0x39/0xc0 kernel/softirq.c:723
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
sysvec_apic_timer_interrupt+0x74/0x80 arch/x86/kernel/apic/apic.c:1056
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
finish_task_switch+0x82/0x280 kernel/sched/core.c:5114
context_switch kernel/sched/core.c:5259 [inline]
__schedule+0x82d/0xc90 kernel/sched/core.c:6863
__schedule_loop kernel/sched/core.c:6945 [inline]
schedule+0x5e/0xd0 kernel/sched/core.c:6960
futex_do_wait kernel/futex/waitwake.c:358 [inline]
__futex_wait+0x121/0x260 kernel/futex/waitwake.c:687
futex_wait+0x9c/0x1d0 kernel/futex/waitwake.c:715
do_futex+0x2bf/0x380 kernel/futex/syscalls.c:130
__do_sys_futex kernel/futex/syscalls.c:207 [inline]
__se_sys_futex+0x2f6/0x370 kernel/futex/syscalls.c:188
__x64_sys_futex+0x78/0x90 kernel/futex/syscalls.c:188
x64_sys_call+0x2bc2/0x3000 arch/x86/include/generated/asm/syscalls_64.h:203
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5056 Comm: syz.4.451 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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