[moderation] [serial?] KCSAN: data-race in n_tty_ioctl_helper / n_tty_receive_char (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8cd26fd90c1a Merge tag 'for-6.9-rc4-tag' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1243190b180000
kernel config: https://syzkaller.appspot.com/x/.config?x=eaea34ec4c9b6fb6
dashboard link: https://syzkaller.appspot.com/bug?extid=e872aa09b96e5dbe6106
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7dd0084db5fd/disk-8cd26fd9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ab71121fac45/vmlinux-8cd26fd9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/76f6c8730574/bzImage-8cd26fd9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e872aa...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_ioctl_helper / n_tty_receive_char

write to 0xffff8881157c41bd of 1 bytes by task 17655 on cpu 0:
n_tty_ioctl_helper+0x102/0x240 drivers/tty/tty_ioctl.c:962
n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2511
tty_ioctl+0x886/0xbe0 drivers/tty/tty_io.c:2812
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:904 [inline]
__se_sys_ioctl+0xd3/0x150 fs/ioctl.c:890
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:890
x64_sys_call+0x155d/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881157c41bd of 1 bytes by task 27 on cpu 1:
n_tty_receive_char+0x5e/0x680 drivers/tty/n_tty.c:1427
n_tty_receive_buf_standard+0x4bd/0x2e30 drivers/tty/n_tty.c:1606
__receive_buf drivers/tty/n_tty.c:1630 [inline]
n_tty_receive_buf_common+0x7e5/0xbd0 drivers/tty/n_tty.c:1729
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1775
tty_ldisc_receive_buf+0x63/0x100 drivers/tty/tty_buffer.c:387
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x1ce/0x410 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0x465/0x990 kernel/workqueue.c:3335
worker_thread+0x526/0x730 kernel/workqueue.c:3416
kthread+0x1d1/0x210 kernel/kthread.c:388
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0x01 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 27 Comm: kworker/u8:1 Not tainted 6.9.0-rc4-syzkaller-00038-g8cd26fd90c1a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound flush_to_ldisc
==================================================================


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