[moderation] [can?] KCSAN: data-race in _copy_from_iter / bcm_can_tx

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7ca6d1cfec80 Merge tag 'powerpc-7.0-4' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13b359f6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=f43fec8e098b30e6fbac
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/22943b1048bd/disk-7ca6d1cf.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/36afcbebeb04/vmlinux-7ca6d1cf.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3088e4f4695f/bzImage-7ca6d1cf.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f43fec...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_from_iter / bcm_can_tx

read to 0xffff88810cf825f8 of 72 bytes by interrupt on cpu 1:
skb_put_data include/linux/skbuff.h:2800 [inline]
bcm_can_tx+0x1b3/0x4c0 net/can/bcm.c:327
bcm_tx_timeout_handler+0xe5/0x290 net/can/bcm.c:478
__run_hrtimer kernel/time/hrtimer.c:1785 [inline]
__hrtimer_run_queues+0x218/0x4f0 kernel/time/hrtimer.c:1849
hrtimer_run_softirq+0xe0/0x2c0 kernel/time/hrtimer.c:1866
handle_softirqs+0xb9/0x2a0 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+0x37/0x80 arch/x86/kernel/apic/apic.c:1056
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697

write to 0xffff88810cf825f8 of 72 bytes by task 5344 on cpu 0:
instrument_copy_from_user_before include/linux/instrumented.h:147 [inline]
copy_from_user_iter lib/iov_iter.c:66 [inline]
iterate_iovec include/linux/iov_iter.h:52 [inline]
iterate_and_advance2 include/linux/iov_iter.h:304 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
__copy_from_iter lib/iov_iter.c:261 [inline]
_copy_from_iter+0x258/0xea0 lib/iov_iter.c:272
copy_from_iter include/linux/uio.h:228 [inline]
copy_from_iter_full include/linux/uio.h:245 [inline]
memcpy_from_msg include/linux/skbuff.h:4273 [inline]
bcm_tx_setup+0xae5/0xdd0 net/can/bcm.c:966
bcm_sendmsg+0x357/0x4a0 net/can/bcm.c:1434
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
____sys_sendmsg+0x563/0x5b0 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+0x194c/0x3020 arch/x86/include/generated/asm/syscalls_64.h:47
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 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: 5344 Comm: syz.3.483 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup