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

[syzbot <syzbot+71cffbc1f77596292d08@syzkaller.appspotmail.com>]

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=71cffbc1f77596292d08
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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+71cffbc1f77596292d08@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
==================================================================


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