linux-kernel - Re: PROBLEM: with daemon.c after y2038 on 32-bits Kernel

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Date:   Tue, 31 May 2022 10:33:05 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Arnaud Panaïotis <arnaud.panaiotis@....fr>
Cc:     linux-kernel@...r.kernel.org, y2038@...ts.linaro.org,
        libc-alpha@...rceware.org
Subject: Re: PROBLEM: with daemon.c after y2038 on 32-bits Kernel

(cc correct libc-alpha list, sorry for the typo)

On Tue, May 31, 2022 at 10:24 AM Arnd Bergmann <arnd@...nel.org> wrote:
> On 17/05/2022 09:51, Arnaud Panaïotis wrote:
> > I'm working for a client to generate embedded 32-bits Linux Kernel working after y2038 issue.
> >
> > I generated a 5.15 Kernel thought Buildroot with Coreutils 9.0, GCC 11.2.0, Binutils 2.37, Glibc 2.34-9 and CFLAGS  -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64  -D_TIME_BITS=64.
> >
> > I encounter an issue while working with OpenSSH (I initially contacted them before).
>
> To clarify: did you build just openssh with  -D_TIME_BITS=64, or did
> you build the entire user space this way?
>
> > After 2038, /usr/sbin/sshd does not create an error but it child does generate this one:
> > daemon() failed: Value too large for defined data type
> >
> > This happend here in sshd.c:
> >
> > 2019         /*
> > 2020          * If not in debugging mode, not started from inetd and not already
> > 2021          * daemonized (eg re-exec via SIGHUP), disconnect from the controlling
> > 2022          * terminal, and fork.  The original process exits.
> > 2023          */
> > 2024         already_daemon = daemonized();
> > 2025         if (!(debug_flag || inetd_flag || no_daemon_flag || already_daemon)) {
> > 2026
> > 2027                 if (daemon(0, 0) == -1)
> > 2028                         fatal("daemon() failed: %.200s", strerror(errno));
>
> My guess is that there are parts of glibc that are not fully
> y2038-safe at the moment, but
> merely provide the interfaces for time64 applications.
>
>
> In the glibc code, I see
>
> int
> daemon (int nochdir, int noclose)
> {
> ...
>                 if ((fd = __open_nocancel(_PATH_DEVNULL, O_RDWR, 0)) != -1
>                     && (__builtin_expect (__fstat64 (fd, &st), 0)
>                         == 0)) {
> ...
>                              } else {
>                         __close_nocancel_nostatus (fd);
>                         return -1;
>                 }
>      return (0);
> }
>
> __fstatat64 (int fd, const char *file, struct stat64 *buf, int flags)
> {
>   struct __stat64_t64 st_t64;
>   return __fstatat64_time64 (fd, file, &st_t64, flags)
>          ?: __cp_stat64_t64_stat64 (&st_t64, buf);
> }
>
> If I'm reading this correctly, daemon() internally uses the time32
> version of 'stat', which fails for files with out-of-range timestamps.
> Are you able to rebuild the ssh binary (or your entire distro, if that's
> easier) against musl-1.2.x instead of glibc to see if the same thing
> happens there?
>
>        Arnd
>
> > To reproduce:
> >
> > # date -s "2040-05-12"
> > # hwclock --systohc
> > # reboot
> > # /usr/sbin/sshd
> >
> > Note this error occurs only after the reboot, and setting a date before 2038 also require a reboot to remove the error.
> >
> > strace and gdb trace linked.
> >
> > Let me know if you need additional information.