[moderation] [kernel?] KCSAN: data-race in ktime_get_real_ts64 / timekeeping_update_from_shadow

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dd6c438c3e64 Merge tag 'vfs-7.1-rc1.fixes' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16d37702580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9bed1befe3a428bc
dashboard link: https://syzkaller.appspot.com/bug?extid=d24e7c020d64b98f1003
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [jst...@google.com linux-...@vger.kernel.org sb...@kernel.org tg...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cd551d2b03e4/disk-dd6c438c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aaf0bde313fe/vmlinux-dd6c438c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/45ce1d7bcda4/bzImage-dd6c438c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d24e7c...@syzkaller.appspotmail.com

af_packet: tpacket_rcv: packet too big, clamped from 32818 to 3966. macoff=82
==================================================================
BUG: KCSAN: data-race in ktime_get_real_ts64 / timekeeping_update_from_shadow

write to 0xffffffff895d9488 of 304 bytes by interrupt on cpu 0:
timekeeping_update_from_shadow+0x40d/0x440 kernel/time/timekeeping.c:829
__timekeeping_advance+0xa5d/0xc10 kernel/time/timekeeping.c:2532
timekeeping_advance kernel/time/timekeeping.c:2540 [inline]
update_wall_time+0x21/0x50 kernel/time/timekeeping.c:2550
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+0x8d/0x3d0 kernel/time/tick-sched.c:312
__run_hrtimer kernel/time/hrtimer.c:1930 [inline]
__hrtimer_run_queues+0x276/0x4f0 kernel/time/hrtimer.c:1994
hrtimer_interrupt+0x261/0x850 kernel/time/hrtimer.c:2113
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
__sysvec_apic_timer_interrupt+0x5f/0x1c0 arch/x86/kernel/apic/apic.c:1067
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
sysvec_apic_timer_interrupt+0x6f/0x80 arch/x86/kernel/apic/apic.c:1061
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
kcsan_setup_watchpoint+0x404/0x410 kernel/kcsan/core.c:705
scm_set_cred include/net/scm.h:73 [inline]
unix_skb_to_scm net/unix/af_unix.c:2005 [inline]
__unix_dgram_recvmsg+0x5ca/0x870 net/unix/af_unix.c:2638
unix_dgram_recvmsg+0x7e/0x90 net/unix/af_unix.c:2686
sock_recvmsg_nosec+0xc2/0xf0 net/socket.c:1137
____sys_recvmsg+0x26f/0x280 net/socket.c:2916
___sys_recvmsg+0x11f/0x3b0 net/socket.c:2960
do_recvmmsg+0x1ef/0x560 net/socket.c:3055
__sys_recvmmsg net/socket.c:3129 [inline]
__do_sys_recvmmsg net/socket.c:3152 [inline]
__se_sys_recvmmsg net/socket.c:3145 [inline]
__x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3145
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+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff895d9498 of 8 bytes by task 1037 on cpu 1:
timekeeping_cycles_to_ns kernel/time/timekeeping.c:426 [inline]
timekeeping_get_ns kernel/time/timekeeping.c:449 [inline]
ktime_get_real_ts64+0xee/0x300 kernel/time/timekeeping.c:946
prb_open_block net/packet/af_packet.c:857 [inline]
prb_dispatch_next_block net/packet/af_packet.c:936 [inline]
__packet_lookup_frame_in_block net/packet/af_packet.c:1094 [inline]
packet_current_rx_frame net/packet/af_packet.c:1120 [inline]
tpacket_rcv+0xe93/0x1c10 net/packet/af_packet.c:2350
packet_rcv_fanout+0x2a7/0x2d0 net/packet/af_packet.c:1505
dev_queue_xmit_nit+0x4cc/0x510 net/core/dev.c:2606
xmit_one net/core/dev.c:3884 [inline]
dev_hard_start_xmit+0xd8/0x3a0 net/core/dev.c:3904
__dev_queue_xmit+0xbd5/0x1ec0 net/core/dev.c:4870
dev_queue_xmit include/linux/netdevice.h:3421 [inline]
neigh_hh_output include/net/neighbour.h:540 [inline]
neigh_output include/net/neighbour.h:554 [inline]
ip_finish_output2+0x705/0x8c0 net/ipv4/ip_output.c:237
__ip_finish_output net/ipv4/ip_output.c:-1 [inline]
ip_finish_output+0x112/0x290 net/ipv4/ip_output.c:325
NF_HOOK_COND include/linux/netfilter.h:307 [inline]
ip_output+0xbd/0x1c0 net/ipv4/ip_output.c:438
dst_output include/net/dst.h:470 [inline]
ip_local_out net/ipv4/ip_output.c:131 [inline]
__ip_queue_xmit+0xb68/0xba0 net/ipv4/ip_output.c:534
ip_queue_xmit+0x39/0x50 net/ipv4/ip_output.c:548
__tcp_transmit_skb+0x1c2a/0x20b0 net/ipv4/tcp_output.c:1715
tcp_transmit_skb net/ipv4/tcp_output.c:1733 [inline]
tcp_write_xmit+0x129e/0x36a0 net/ipv4/tcp_output.c:3060
__tcp_push_pending_frames+0x6d/0x1b0 net/ipv4/tcp_output.c:3243
tcp_push+0x311/0x330 net/ipv4/tcp.c:776
mptcp_push_release net/mptcp/protocol.c:1569 [inline]
__mptcp_push_pending+0x3d5/0x550 net/mptcp/protocol.c:1709
mptcp_release_cb+0x49c/0x7f0 net/mptcp/protocol.c:3671
release_sock+0x168/0x180 net/core/sock.c:3819
mptcp_worker+0xa41/0xd60 net/mptcp/protocol.c:3007
process_one_work kernel/workqueue.c:3302 [inline]
process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3385
worker_thread+0x58a/0x780 kernel/workqueue.c:3466
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: 0x000000831bc8e013 -> 0x000000831d189180

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 1037 Comm: kworker/1:2 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: events mptcp_worker
==================================================================


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