KCSAN: data-race in __stop_tty / pty_write (16)

KCSAN: data-race in __stop_tty / pty_write (16)

Status: moderation: reported on 2025/12/27 04:05
Subsystems: serial
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+9c3ef9da49a12d7bbc27@syzkaller.appspotmail.com
First crash: 173d, last: 7d18h

▶ ▼ ✨ AI Jobs (3)

ID	Workflow	Result	Correct	Bug	Created	Started	Finished	Revision	Error
d74c47cf-c17d-44f7-8e39-7fb039b7a637	assessment-security	DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌	❓	KCSAN: data-race in __stop_tty / pty_write (16)	2026/05/19 20:23	2026/05/19 20:23	2026/05/19 20:45	1d9407ad5a662c921fc0d659cf022b438c0bde91
e8a9d68b-3db4-4e66-a3df-1abbef210f10	repro		💥	KCSAN: data-race in __stop_tty / pty_write (16)	2026/03/09 22:34	2026/03/09 22:34	2026/03/09 22:57	6972f30219093b03bcc1a54487e12a7097245c01	Error 504, Message: Deadline expired before operation could complete., Status: DEADLINE_EXCEEDED, Details: [map[@type:type.googleapis.com/google.rpc.DebugInfo detail:[ORIGINAL ERROR] generic::deadline... truncated to first 200 bytes; open job for full error
4f8bda19-d56a-49f6-879d-185e0fb1c438	assessment-kcsan	Benign: ✅	❓	KCSAN: data-race in __stop_tty / pty_write (16)	2026/01/10 08:14	2026/01/10 08:14	2026/01/10 08:38	7519916073b761ced56a7b15fdeeb4674e8dc125

▶ ▼ Similar bugs (15)

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in __stop_tty / pty_write serial	6				1	1799d	1799d	0/29	auto-closed as invalid on 2021/08/19 13:20
upstream	KCSAN: data-race in __stop_tty / pty_write (6) serial	6				1	1492d	1492d	0/29	auto-closed as invalid on 2022/06/22 11:40
upstream	KCSAN: data-race in __stop_tty / pty_write (8) serial	6				4	1152d	1168d	0/29	auto-obsoleted due to no activity on 2023/05/28 07:29
upstream	KCSAN: data-race in __stop_tty / pty_write (9) serial	6				3	1061d	1092d	0/29	auto-obsoleted due to no activity on 2023/08/26 21:27
upstream	KCSAN: data-race in __stop_tty / pty_write (2) serial	6				1	1716d	1716d	0/29	auto-closed as invalid on 2021/11/09 20:04
upstream	KCSAN: data-race in __stop_tty / pty_write (4) serial	6				1	1589d	1589d	0/29	auto-closed as invalid on 2022/03/17 12:14
upstream	KCSAN: data-race in __stop_tty / pty_write (3) serial	6				1	1676d	1676d	0/29	auto-closed as invalid on 2021/12/20 07:00
upstream	KCSAN: data-race in __stop_tty / pty_write (13) serial	6				19	641d	820d	0/29	auto-obsoleted due to no activity on 2024/10/19 22:07
upstream	KCSAN: data-race in __stop_tty / pty_write (5) serial	6				1	1545d	1545d	0/29	auto-closed as invalid on 2022/04/30 10:57
upstream	KCSAN: data-race in __stop_tty / pty_write (10) serial	6				1	1013d	1013d	0/29	auto-obsoleted due to no activity on 2023/10/14 11:29
upstream	KCSAN: data-race in __stop_tty / pty_write (11) serial	6				3	969d	972d	0/29	auto-obsoleted due to no activity on 2023/11/26 18:07
upstream	KCSAN: data-race in __stop_tty / pty_write (14) serial	6				1	602d	602d	0/29	auto-obsoleted due to no activity on 2024/12/18 17:29
upstream	KCSAN: data-race in __stop_tty / pty_write (12) serial	6				7	856d	918d	0/29	auto-obsoleted due to no activity on 2024/03/18 19:09
upstream	KCSAN: data-race in __stop_tty / pty_write (7) serial	6				1	1351d	1351d	0/29	auto-obsoleted due to no activity on 2022/11/10 14:49
upstream	KCSAN: data-race in __stop_tty / pty_write (15) serial	6				12	311d	543d	0/29	auto-obsoleted due to no activity on 2025/10/05 23:38

Sample crash report:

==================================================================
BUG: KCSAN: data-race in __stop_tty / pty_write

write to 0xffff88810e103194 of 1 bytes by task 30605 on cpu 1:
 __stop_tty+0x36/0x90 drivers/tty/tty_io.c:744
 n_tty_ioctl_helper+0x2d1/0x370 drivers/tty/tty_ioctl.c:951
 n_tty_ioctl+0x101/0x220 drivers/tty/n_tty.c:2496
 tty_ioctl+0x83e/0xb80 drivers/tty/tty_io.c:2801
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
 x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810e103194 of 1 bytes by task 401 on cpu 0:
 pty_write+0x24/0x90 drivers/tty/pty.c:113
 tty_put_char+0x8f/0xc0 drivers/tty/tty_io.c:3154
 n_tty_process_echo_ops drivers/tty/n_tty.c:644 [inline]
 __process_echoes+0x309/0x6b0 drivers/tty/n_tty.c:689
 flush_echoes drivers/tty/n_tty.c:785 [inline]
 __receive_buf drivers/tty/n_tty.c:1618 [inline]
 n_tty_receive_buf_common+0x8d3/0xc00 drivers/tty/n_tty.c:1715
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
 tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:394
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:452 [inline]
 flush_to_ldisc+0x148/0x340 drivers/tty/tty_buffer.c:502
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
 worker_thread+0x58a/0x780 kernel/workqueue.c:3478
 kthread+0x22a/0x280 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 401 Comm: kworker/u8:7 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound flush_to_ldisc
==================================================================

Crashes (5):
Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Assets (help?)	Manager	Title
2026/06/10 20:45	upstream	acb7500801e9	f79bac11	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci2-upstream-kcsan-gce	KCSAN: data-race in __stop_tty / pty_write
2026/05/01 06:20	upstream	26fd6bff2c05	753c55b9	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci2-upstream-kcsan-gce	KCSAN: data-race in __stop_tty / pty_write
2026/03/19 00:59	upstream	8a30aeb0d1b4	0199f9a1	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci2-upstream-kcsan-gce	KCSAN: data-race in __stop_tty / pty_write
2026/02/02 01:57	upstream	9f2693489ef8	6b8752f2	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci2-upstream-kcsan-gce	KCSAN: data-race in __stop_tty / pty_write
2025/12/27 04:04	upstream	3f0e9c8cefa9	d6526ea3	.config	console log	report			info	[disk image] [vmlinux] [kernel image]	ci2-upstream-kcsan-gce	KCSAN: data-race in __stop_tty / pty_write

* ~~Struck through~~ repros no longer work on HEAD.