Subject: Re: bug#35996: User account password got locked when booting old generation

From: "pelzflorian (Florian Pelz)" <[email-masked]>
Date: Sun, 2 Jun 2019 12:21:22 +0200

On Sun, Jun 02, 2019 at 11:38:36AM +0200, Ludovic Courtès wrote:
> Hi Florian,
> 
> "pelzflorian (Florian Pelz)" <[email-masked]> skribis:
> 
> > On Sat, Jun 01, 2019 at 11:37:51PM +0200, Ludovic Courtès wrote:
> >> This is definitely not a problem when booting.  It could be a problem if
> >> you’re concurrently running ‘guix system reconfigure’ (which runs
> >> activation snippets, including the account updating code) and some other
> >> program, such as ‘passwd’, that assumes it holds an exclusive lock on
> >> the file.  Though in that case, the worst that could happen is that the
> >> changes made by Guix would be undoed by that other program.
> 
> Actually, another thing that could happen is that Guix reads an
> incomplete /etc/shadow because some other program is writing to it.
> 
> In that case, suppose Guix reads a partial /etc/shadow where user
> “florian” is missing.  It would then create a new /etc/shadow where the
> password for “florian” is uninitialized (or set to the initial value
> that appears in config.scm.)
> 
> Could it be what happened to you?  You’d have to be running ‘passwd’ or
> ‘usermod’ or whatever at exactly the same time as ‘guix system
> reconfigure’ (and you’d have to be “lucky”).
>

No, I did not change my password in a very long time.

Is there no proper cross-application locking mechanism for
/etc/passwd?  elogind uses

struct flock flock = {
  .l_type = F_WRLCK,
  .l_whence = SEEK_SET,
  .l_start = 0,
  .l_len = 0,
};
[…]
fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW, 0600);
[…]
r = fcntl(fd, F_SETLKW, &flock;

Should Guix adopt something similar for shadow/passwd/… database
reads?

> > error: '/gnu/store/h5bi85lgnpqcjx2avy126lwiss01idsj-grub-efi-2.02/sbin/grub-install --boot-directory //boot --bootloader-id=Guix --efi-directory //boot/efi' exited with status 1; output follows:
> >
> >   Installing for x86_64-efi platform.
> >   Could not prepare Boot variable: No such file or directory
> >   /gnu/store/h5bi85lgnpqcjx2avy126lwiss01idsj-grub-efi-2.02/sbin/grub-install: error: efibootmgr failed to register the boot entry: Input/output error.
> 
> Maybe you’ve exhausted the room for those EFI “variables” or something?
> 
> Thanks for your debugging work!
> 
> Ludo’.

Maybe exhausted, maybe it is an error with the NVRAM.  I will try
making grub-install execute like when installing on external USB
drives so it writes nothing to the motherboard.

Regards,
Florian