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