KCSAN: data-race in __process_echoes / n_tty_write (16)

Status: moderation: reported on 2026/08/24 18:41
Subsystems: serial
Labels: race:benign prio:low
[Documentation on labels]
Reported-by: syzbot+07379f00afb16a33fa0d@syzkaller.appspotmail.com
First crash: 1d09h, last: 1d09h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
e3d356b8 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KCSAN: data-race in __process_echoes / n_tty_write (16) 2026/08/26 00:09 2026/08/26 00:09 2026/08/26 00:40 ee98d2fd
1987efb2 assessment-kcsan Benign: ✅ ❓ KCSAN: data-race in __process_echoes / n_tty_write (16) 2026/08/24 18:40 2026/08/24 18:41 2026/08/24 19:03 23caa175
▶ ▼ Similar bugs (15)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __process_echoes / n_tty_write (14) serial 6 13 226d 417d 0/29 auto-obsoleted due to no activity on 2026/03/08 20:00
upstream KCSAN: data-race in __process_echoes / n_tty_write (9) serial 6 4 1135d 1181d 0/29 auto-obsoleted due to no activity on 2023/08/21 10:01
upstream KCSAN: data-race in __process_echoes / n_tty_write serial 6 3 2200d 2241d 0/29 auto-closed as invalid on 2020/09/20 17:41
upstream KCSAN: data-race in __process_echoes / n_tty_write (3) serial 6 7 1913d 1978d 0/29 auto-closed as invalid on 2021/07/04 10:36
upstream KCSAN: data-race in __process_echoes / n_tty_write (11) serial 6 13 866d 944d 0/29 auto-obsoleted due to no activity on 2024/05/16 20:06
upstream KCSAN: data-race in __process_echoes / n_tty_write (10) serial 6 10 989d 990d 0/29 auto-obsoleted due to no activity on 2024/01/14 04:02
upstream KCSAN: data-race in __process_echoes / n_tty_write (4) serial 6 1 1871d 1871d 0/29 auto-closed as invalid on 2021/08/15 21:06
upstream KCSAN: data-race in __process_echoes / n_tty_write (6) serial 6 41 1422d 1717d 0/29 auto-obsoleted due to no activity on 2022/11/07 20:53
upstream KCSAN: data-race in __process_echoes / n_tty_write (2) serial 6 4 2068d 2087d 0/29 auto-closed as invalid on 2021/01/30 23:25
upstream KCSAN: data-race in __process_echoes / n_tty_write (15) serial 6 1 161d 161d 0/29 auto-obsoleted due to no activity on 2026/05/12 22:47
upstream KCSAN: data-race in __process_echoes / n_tty_write (7) serial 6 2 1366d 1367d 0/29 auto-obsoleted due to no activity on 2023/01/13 20:09
upstream KCSAN: data-race in __process_echoes / n_tty_write (5) serial 6 1 1791d 1791d 0/29 auto-closed as invalid on 2021/11/04 02:47
upstream KCSAN: data-race in __process_echoes / n_tty_write (12) serial 6 2 799d 805d 0/29 auto-obsoleted due to no activity on 2024/07/22 07:47
upstream KCSAN: data-race in __process_echoes / n_tty_write (13) serial 6 4 567d 631d 0/29 auto-obsoleted due to no activity on 2025/04/01 20:34
upstream KCSAN: data-race in __process_echoes / n_tty_write (8) serial 6 3 1229d 1282d 0/29 auto-obsoleted due to no activity on 2023/05/19 15:46

Sample crash report:
==================================================================
BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc90001365280 of 8 bytes by task 13974 on cpu 0:
 __process_echoes+0x63e/0x6b0 drivers/tty/n_tty.c:726
 flush_echoes drivers/tty/n_tty.c:785 [inline]
 __receive_buf drivers/tty/n_tty.c:1618 [inline]
 n_tty_receive_buf_common+0x90f/0xc10 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+0x13a/0x330 drivers/tty/tty_buffer.c:502
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3470
 worker_thread+0x569/0x750 kernel/workqueue.c:3551
 kthread+0x223/0x270 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

read to 0xffffc90001365280 of 8 bytes by task 10657 on cpu 1:
 process_echoes drivers/tty/n_tty.c:762 [inline]
 n_tty_write+0x18a/0xb00 drivers/tty/n_tty.c:2352
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x392/0x6a0 drivers/tty/tty_io.c:1054
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1075
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x57f/0x9a0 fs/read_write.c:687
 ksys_write+0xdc/0x1a0 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:747
 x64_sys_call+0x154e/0x2550 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000004320 -> 0x0000000000004326

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10657 Comm: syz.1.6700 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/24 18:40 upstream 0a0d1d55dad5 b55bd4c3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __process_echoes / n_tty_write
* Struck through repros no longer work on HEAD.