Re: [gentoo-dev] GLEP81 and /home

[Rich Freeman <rich0@gentoo.org>]

On Sun, Jan 19, 2020 at 10:49 AM Michael Orlitzky <mjo@gentoo.org> wrote:
>
> On 1/19/20 6:29 AM, Rich Freeman wrote:
> >
> > Daemons are local users.  There is no guarantee that /home is a local
> > filesystem.  Heck, there is no guarantee that /home is even mounted
> > when portage is running.  Portage shouldn't be touching /home at all.
> > With stuff like automounted or encrypted home directories and
> > systemd-homed and so on it seems like it is even more important to
> > avoid sticking stuff in /home (and this is hardly something started by
> > systemd - stuff in /home that is non-static has been a thing for some
> > time - certainly it was happening in the 90s on some IRIX workstations
> > I used).
>
> If you're sharing /home, you're also sharing users. At that point, the
> daemon user is no longer local.

Typically you wouldn't share service accounts across multiple hosts.
I'd think that something like amavisd is going to go on a mail server.
You're not going to be logging into that account to do typical
desktop-oriented functions.

If you had three mail servers, you probably would want to share
/home/mjo across all of them, but you probably wouldn't want to share
your amavisd config across them.  That is why the config goes in /etc.
I don't see how stuff it launches would be any different.

This is why /root is typically outside of /home as well.

> I like your /var/lib/amavis/{home,work} suggestion second-best, but the
> most appropriate place for the home directory of an account that will be
> used interactively by a human (even if it's also used to start a daemon)
> is under /home. For example I do want to back up that home directory,
> but I don't want to back up the working directory.

Honestly, since you're only using it for what amounts to configuration
it almost makes sense to put it in /etc, and back it up for that
reason.

You don't really want to be using it interactively as a human per-se
any more than you interactively log in as root or any other service
account.  There are rare occassions where I'll launch a shell as
apache or postfix or whatever, but that doesn't mean that you want it
to have a home in /home.

> > Portage should provide a safe mechanism to fix permissions.  Or we
> > should just avoid nesting user home directories inside directories
> > that will be written to by that user.
> >
> > If this is the same hard-linking concern as with tmpfiles.d then
> > somebody really just needs to fix POSIX.  :)  But as a workaround just
> > avoiding nesting seems like the simpler solution...
>
> Essentially yes, but hard links aren't the only problem. It's unsafe to
> do anything as root in a user-controlled directory. POSIX can't fix
> that, and that means that portage will never be able to fix permissions
> (or do anything else) within a user-controlled directory safely.

I mean, you're still doing stuff as root.  You're just not running chown.

POSIX certainly could fix it, though whether it could do it in a
manner that doesn't break everything in existence is another matter.
For example, if POSIX just got rid of hard links many of the issues
would just go away.

Obviously if the problem had a simple solution it would have been
implemented by now.

BTW, thanks to the recent QA post I can at least point you at
documentation for your issue.  Per the article if you want to change
it the procedure is to ask QA for an exception or change in policy,
and if you don't like the answer go to Council...

https://projects.gentoo.org/qa/policy-guide/filesystem.html#installation-paths

-- 
Rich