[syzbot] [kernel?] KMSAN: uninit-value in timespec64_add_safe

[syzbot] [kernel?] KMSAN: uninit-value in timespec64_add_safe

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    e2bd1b136926 Merge tag 'core-debugobjects-2026-03-01' of g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1307a202580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=10f867da86e38691
dashboard link: https://syzkaller.appspot.com/bug?extid=5fca9514ef36ad94d973
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dc98e5be9809/disk-e2bd1b13.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8b4eb1704ccf/vmlinux-e2bd1b13.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6016576769b8/bzImage-e2bd1b13.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5fca9514ef36ad94d973@syzkaller.appspotmail.com

udevd[5131]: starting eudev-3.2.14
=====================================================
BUG: KMSAN: uninit-value in set_normalized_timespec64 kernel/time/time.c:492 [inline]
BUG: KMSAN: uninit-value in timespec64_add_safe+0x4b4/0x520 kernel/time/time.c:846
 set_normalized_timespec64 kernel/time/time.c:492 [inline]
 timespec64_add_safe+0x4b4/0x520 kernel/time/time.c:846
 ep_timeout_to_timespec fs/eventpoll.c:1872 [inline]
 __do_sys_epoll_wait fs/eventpoll.c:2471 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2465 [inline]
 __x64_sys_epoll_wait+0x1fa/0x3a0 fs/eventpoll.c:2465
 x64_sys_call+0x2ece/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:233
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable now.i.i.i created at:
 ep_timeout_to_timespec fs/eventpoll.c:1857 [inline]
 __do_sys_epoll_wait fs/eventpoll.c:2471 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2465 [inline]
 __x64_sys_epoll_wait+0xcf/0x3a0 fs/eventpoll.c:2465
 x64_sys_call+0x2ece/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:233

CPU: 0 UID: 0 PID: 5131 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================
Kernel panic - not syncing: kmsan.panic set ...
CPU: 0 UID: 0 PID: 5131 Comm: udevd Tainted: G    B               syzkaller #0 PREEMPT(full) 
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 __dump_stack+0x26/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x50/0x1c0 lib/dump_stack.c:120
 dump_stack+0x1e/0x25 lib/dump_stack.c:129
 vpanic+0x7b4/0x1430 kernel/panic.c:650
 panic+0x15d/0x160 kernel/panic.c:787
 kmsan_report+0x31a/0x320 mm/kmsan/report.c:218
 __msan_warning+0x1b/0x30 mm/kmsan/instrumentation.c:315
 set_normalized_timespec64 kernel/time/time.c:492 [inline]
 timespec64_add_safe+0x4b4/0x520 kernel/time/time.c:846
 ep_timeout_to_timespec fs/eventpoll.c:1872 [inline]
 __do_sys_epoll_wait fs/eventpoll.c:2471 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2465 [inline]
 __x64_sys_epoll_wait+0x1fa/0x3a0 fs/eventpoll.c:2465
 x64_sys_call+0x2ece/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:233
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd5f3ea7407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffec9f715a0 EFLAGS: 00000202 ORIG_RAX: 00000000000000e8
RAX: ffffffffffffffda RBX: 00007fd5f456c880 RCX: 00007fd5f3ea7407
RDX: 0000000000000008 RSI: 00007ffec9f71700 RDI: 000000000000000b
RBP: 00000000000000b0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000bb8 R11: 0000000000000202 R12: 0000000000000000
R13: 000055fdbce5d100 R14: 000055fddbf24b30 R15: 0000000000000000
 </TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [kernel?] KMSAN: uninit-value in timespec64_add_safe

[Thomas Gleixner]

On Thu, Mar 05 2026 at 18:52, syzbot wrote:
> udevd[5131]: starting eudev-3.2.14
> =====================================================
> BUG: KMSAN: uninit-value in set_normalized_timespec64 kernel/time/time.c:492 [inline]
> BUG: KMSAN: uninit-value in timespec64_add_safe+0x4b4/0x520 kernel/time/time.c:846
>  set_normalized_timespec64 kernel/time/time.c:492 [inline]
>  timespec64_add_safe+0x4b4/0x520 kernel/time/time.c:846
>  ep_timeout_to_timespec fs/eventpoll.c:1872 [inline]
>  __do_sys_epoll_wait fs/eventpoll.c:2471 [inline]
>  __se_sys_epoll_wait fs/eventpoll.c:2465 [inline]
>  __x64_sys_epoll_wait+0x1fa/0x3a0 fs/eventpoll.c:2465
>  x64_sys_call+0x2ece/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:233
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Local variable now.i.i.i created at:
>  ep_timeout_to_timespec fs/eventpoll.c:1857 [inline]
>  __do_sys_epoll_wait fs/eventpoll.c:2471 [inline]
>  __se_sys_epoll_wait fs/eventpoll.c:2465 [inline]
>  __x64_sys_epoll_wait+0xcf/0x3a0 fs/eventpoll.c:2465
>  x64_sys_call+0x2ece/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:233

This lacks:

Local variable now.i.i.i initialized at:

        ktime_get_ts64(&now);                   <---- HERE

Right before the timespec64_add_safe() invocation
        
        *to = timespec64_add_safe(now, *to);

KMSAN confused itself....

Thanks,

        tglx