[moderation] [serial?] KCSAN: data-race in ppp_asynctty_receive / tty_set_termios (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2c4a1f3fe03e Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12fd6d70580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f437300db311c188
dashboard link: https://syzkaller.appspot.com/bug?extid=3f6682fe2bea300dcde6
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
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/655e44254540/disk-2c4a1f3f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0b107f49d633/vmlinux-2c4a1f3f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1ae745fedaa8/bzImage-2c4a1f3f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3f6682...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ppp_asynctty_receive / tty_set_termios

write to 0xffff8881469fc108 of 44 bytes by task 12946 on cpu 0:
tty_set_termios+0xc0/0x8c0 drivers/tty/tty_ioctl.c:335
set_termios+0x496/0x4e0 drivers/tty/tty_ioctl.c:512
tty_mode_ioctl+0x379/0x5c0 drivers/tty/tty_ioctl.c:-1
ppp_asynctty_ioctl+0x13f/0x2d0 drivers/net/ppp/ppp_async.c:324
tty_ioctl+0x845/0xb80 drivers/tty/tty_io.c:2801
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:893
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881469fc108 of 4 bytes by task 5417 on cpu 1:
ppp_async_input drivers/net/ppp/ppp_async.c:905 [inline]
ppp_asynctty_receive+0x75c/0xd40 drivers/net/ppp/ppp_async.c:342
tty_ldisc_receive_buf+0xbc/0xf0 drivers/tty/tty_buffer.c:391
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+0x144/0x360 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3321
worker_thread+0x582/0x770 kernel/workqueue.c:3402
kthread+0x486/0x510 kernel/kthread.c:464
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000500 -> 0x00038000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5417 Comm: kworker/u8:55 Not tainted 6.16.0-rc1-syzkaller-00010-g2c4a1f3fe03e #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events_unbound flush_to_ldisc
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.