[moderation] [serial?] KCSAN: data-race in n_tty_close / pty_close (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8282d5af7be8 Merge tag 'nfs-for-6.10-3' of git://git.linux..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13826d61980000
kernel config: https://syzkaller.appspot.com/x/.config?x=7e87b541dc1fc960
dashboard link: https://syzkaller.appspot.com/bug?extid=a678fcffb9af096f794a
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/90c1e907274a/disk-8282d5af.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4208061307e4/vmlinux-8282d5af.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6430245c6fa6/bzImage-8282d5af.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a678fc...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_close / pty_close

write to 0xffff888111b609d5 of 1 bytes by task 10488 on cpu 0:
pty_close+0x124/0x280 drivers/tty/pty.c:61
tty_release+0x20c/0x940 drivers/tty/tty_io.c:1760
__fput+0x2c2/0x660 fs/file_table.c:422
____fput+0x15/0x20 fs/file_table.c:450
task_work_run+0x13a/0x1a0 kernel/task_work.c:180
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0xbe/0x130 kernel/entry/common.c:218
do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888111b609d5 of 1 bytes by task 10498 on cpu 1:
n_tty_packet_mode_flush drivers/tty/n_tty.c:335 [inline]
n_tty_close+0x58/0x130 drivers/tty/n_tty.c:1896
tty_ldisc_close drivers/tty/tty_ldisc.c:455 [inline]
tty_ldisc_kill+0x90/0x140 drivers/tty/tty_ldisc.c:613
tty_ldisc_hangup+0x2f4/0x370 drivers/tty/tty_ldisc.c:729
__tty_hangup+0x3c6/0x540 drivers/tty/tty_io.c:630
tty_vhangup drivers/tty/tty_io.c:700 [inline]
tty_ioctl+0x613/0xbe0 drivers/tty/tty_io.c:2743
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xd3/0x150 fs/ioctl.c:893
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
x64_sys_call+0x1581/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x01 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 10498 Comm: syz.1.1959 Not tainted 6.10.0-rc5-syzkaller-00282-g8282d5af7be8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
==================================================================


---
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