syzbot


KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4)

Status: upstream: reported on 2026/05/18 12:55
Subsystems: kernel
Labels: race:harmful prio:high
[Documentation on labels]
Reported-by: syzbot+72789cd1697965e714ca@syzkaller.appspotmail.com
First crash: 53d, last: 10d
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
7ad0cab3-ac3a-43ca-ba5d-f27a03108284 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ✅ NetworkTrigger: ✅ PeripheralTrigger: ✅ RemoteTrigger: ✅ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ✅ KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4) 2026/06/01 21:00 2026/06/01 21:00 2026/06/01 21:02 386cc6dacdf7e3ebce9507beed6755d7e999554d

			
		
7af8d9b4-b6f3-433e-b0e6-f5734a9b6ef3 assessment-kcsan Benign: ❌ KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4) 2026/05/18 12:23 2026/05/18 12:23 2026/05/18 12:54 55156e845761fb36809c4b3701a920dddce23332

			
		
Discussions (3)
Title Replies (including bot) Last reply
Re: [PATCH] timekeeping: Use data_race() and READ_ONCE() in ktime_get_real_seconds() 2 (2) 2026/06/21 13:17
[PATCH] timekeeping: Use data_race() and READ_ONCE() in ktime_get_real_seconds() 2 (2) 2026/06/02 09:46
[syzbot] [kernel?] KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (4) 0 (1) 2026/05/18 12:55
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (2) kernel 6 2 351d 369d 0/29 auto-obsoleted due to no activity on 2025/09/18 01:57
upstream KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow (3) kernel 6 2 200d 247d 0/29 auto-obsoleted due to no activity on 2026/02/16 08:50
upstream KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow kernel 6 1 434d 434d 0/29 auto-obsoleted due to no activity on 2025/06/27 01:56

Sample crash report:
==================================================================
BUG: KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow

write to 0xffffffff893d04c8 of 304 bytes by interrupt on cpu 1:
 timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:835
 __timekeeping_advance+0xa68/0xc10 kernel/time/timekeeping.c:2614
 timekeeping_advance kernel/time/timekeeping.c:2622 [inline]
 update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2632
 tick_do_update_jiffies64+0x169/0x1c0 kernel/time/tick-sched.c:149
 tick_sched_do_timer kernel/time/tick-sched.c:253 [inline]
 tick_nohz_handler+0x88/0x380 kernel/time/tick-sched.c:310
 __run_hrtimer kernel/time/hrtimer.c:2032 [inline]
 __hrtimer_run_queues+0x1f8/0x510 kernel/time/hrtimer.c:2096
 hrtimer_interrupt+0x257/0x810 kernel/time/hrtimer.c:2215
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x5f/0x1c0 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1062
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
 should_watch kernel/kcsan/core.c:280 [inline]
 check_access kernel/kcsan/core.c:752 [inline]
 __tsan_memset+0x17f/0x1f0 kernel/kcsan/core.c:1335
 ____sys_recvmsg+0x59/0x280 net/socket.c:2886
 ___sys_recvmsg+0x11f/0x3a0 net/socket.c:2946
 do_recvmmsg+0x1e5/0x560 net/socket.c:3041
 __sys_recvmmsg net/socket.c:3115 [inline]
 __do_sys_recvmmsg net/socket.c:3138 [inline]
 __se_sys_recvmmsg net/socket.c:3131 [inline]
 __x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3131
 x64_sys_call+0x80f/0x3020 arch/x86/include/generated/asm/syscalls_64.h:300
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff893d0500 of 8 bytes by task 16961 on cpu 0:
 ktime_get_real_seconds+0x15/0x30 kernel/time/timekeeping.c:1162
 lookup_user_key+0x5fe/0xd60 security/keys/process_keys.c:807
 keyctl_revoke_key security/keys/keyctl.c:385 [inline]
 __do_sys_keyctl security/keys/keyctl.c:1903 [inline]
 __se_sys_keyctl+0x457/0xb70 security/keys/keyctl.c:1886
 __x64_sys_keyctl+0x67/0x80 security/keys/keyctl.c:1886
 x64_sys_call+0x1d12/0x3020 arch/x86/include/generated/asm/syscalls_64.h:251
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000006a43ba6b -> 0x000000006a43ba6c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16961 Comm: syz.1.3500 Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/30 12:37 upstream dc59e4fea9d8 fff8d0a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow
2026/05/29 20:14 upstream 8fde5d1d47f6 6b4a8443 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow
2026/05/22 13:26 upstream 6779b50faa56 5f091fcc .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow
2026/05/18 12:20 upstream 5200f5f493f7 55156e84 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in ktime_get_real_seconds / timekeeping_update_from_shadow
* Struck through repros no longer work on HEAD.