[moderation] [serial?] KCSAN: data-race in n_tty_receive_char / n_tty_write (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9bacdd8996c7 Merge tag 'for-6.7-rc1-tag' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14186fdf680000
kernel config: https://syzkaller.appspot.com/x/.config?x=a91f789b98394377
dashboard link: https://syzkaller.appspot.com/bug?extid=b9fb1de8724719df2e7e
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/be70757ec048/disk-9bacdd89.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/45e8c725b4dc/vmlinux-9bacdd89.xz
kernel image: https://storage.googleapis.com/syzbot-assets/82e551f976a9/bzImage-9bacdd89.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b9fb1d...@syzkaller.appspotmail.com

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

write to 0xffffc90000659028 of 8 bytes by task 7092 on cpu 1:
commit_echoes drivers/tty/n_tty.c:758 [inline]
n_tty_receive_char+0x4be/0x670 drivers/tty/n_tty.c:1437
n_tty_receive_buf_standard+0x4bd/0x2e20 drivers/tty/n_tty.c:1606
__receive_buf drivers/tty/n_tty.c:1630 [inline]
n_tty_receive_buf_common+0x7e5/0xbc0 drivers/tty/n_tty.c:1729
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1775
tty_ldisc_receive_buf+0x60/0xe0 drivers/tty/tty_buffer.c:386
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x1ca/0x400 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:2630 [inline]
process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2703
worker_thread+0x525/0x730 kernel/workqueue.c:2784
kthread+0x1d7/0x210 kernel/kthread.c:388
ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

read to 0xffffc90000659028 of 8 bytes by task 25548 on cpu 0:
process_echoes drivers/tty/n_tty.c:784 [inline]
n_tty_write+0x161/0xb60 drivers/tty/n_tty.c:2365
iterate_tty_write drivers/tty/tty_io.c:1021 [inline]
file_tty_write+0x382/0x680 drivers/tty/tty_io.c:1092
tty_write+0x28/0x30 drivers/tty/tty_io.c:1113
call_write_iter include/linux/fs.h:2020 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x48a/0x790 fs/read_write.c:584
ksys_write+0xeb/0x1a0 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__x64_sys_write+0x42/0x50 fs/read_write.c:646
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x00000000000001fa -> 0x0000000000000200

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25548 Comm: syz-executor.4 Tainted: G W 6.7.0-rc1-syzkaller-00012-g9bacdd8996c7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
==================================================================


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