Re: [ptxdist] Resend: Home dir fixup for root in systemd

[David Jander <david@protonic.nl>]

Dear Guillermo,

Thanks for your reply.

On Tue, 26 Jul 2016 15:19:59 +0200
Guillermo Rodriguez Garcia <guille.rodriguez@gmail.com> wrote:

> Wouldn't it be easier to either use a custom /etc/passwd, or create a /root
> dir in the filesystem ? That sounds better than patching systemd.

Maybe it would be better to change the default /etc/passwd (and everywhere
else) in ptxdist then...

The problem is that what /etc/passwd says is mandatory. The home directory has
a special meaning to the user. You can get to the home directory via $HOME
passed in the environment, or via the NS-switch (getent) lookup. They are
supposed to be the same.
systemd has hardcoded defaults in source-code, which by definition is ugly as
hell, but the reason is clearly to avoid potentially expensive, blocking
NSS-lookups in the early boot stages, so it is understandable. It would be a
lot better if there was some configuration setting read from a file I guess,
but alas.
On PTXdist now (with the default, shipped /etc/passwd), a user logging in as
"root" via, say a serial console getty, will have a different $HOME than a
systemd service started with User=root. This is bad, and can potentially do
funny things people will not like.
To solve the problem, there are really only two options AFAICS:

 1.- Change PTXdist and all places in it that assume the $HOME=/home for root.
 No idea how many places that are, nor how many users already depend on this
 historic assumption.

or

 2.- Patch systemd to adapt to the reality of PTXdist.

I agree that option 1 is probably better if PTXdist is more or less the only
place on earth left where $HOME != /root for uid=0. Historically on Unix it
used to be "/", but that is just way too ugly (guess where the name "root"
came from?).

Using a custom /etc/passwd is not an option, because the default PTXdist stays
broken this way.

Creating a /root dir is also broken, because like I explained above, the root
user will become schizophrenic when logging in and running services from
systemd alternately. Think about a user logging in, starting a tool that
writes a config files to ~/.bla, and then configuring the same tool to run as a
system service. I would (did!) get slightly mad when finding the tool to run
with a totally different configuration in the latter case.

> Guillermo
> 
> 2016-07-26 14:09 GMT+02:00 David Jander <david.jander@protonic.nl>:
> 
> >
> > Dear Michael,
> >
> > I have prepared a patch against ptxdist git for the package systemd-230.
> > I would like to know the right way to proceed to submit this patch, since
> > I am
> > not a ptxdist developer and am not familiar with how tools like
> > git-ptxdist-patch are supposed to be used (to generate the correct series
> > file
> > in this case).
> >
> > The patch is really trivial and I don't know if it deserves so much work (I
> > suspect that I have to clone the git repository of systemd first and apply
> > all
> > patches there, right?).
> >
> > What I am trying to fix here is the notion that systemd has about what the
> > $HOME directory of the user 'root' (uid=0) should be. As it seems, in
> > systemd
> > this is hardcoded to be "/root", while ptxdist by default seems to insist
> > in
> > "/home" for some reason (according to shipped /etc/passwd). Here's the gist
> > of what the patch does:
> >
> > --- systemd-230.orig/src/basic/user-util.c
> > +++ systemd-230/src/basic/user-util.c
> > @@ -123,7 +123,7 @@ int get_user_creds(
> >                          *gid = 0;
> >
> >                  if (home)
> > -                        *home = "/root";
> > +                        *home = "/home";
> >
> >                  if (shell)
> >                          *shell = "/bin/sh";
> >
> > Without this patch, things like services that declare "User=root" get
> > screwed
> > up with the wrong home directory for example.
> >
> > Thanks.
> >
> > Best regards,
> >
> > --
> > David Jander
> > Protonic Holland.
> >
> > _______________________________________________
> > ptxdist mailing list
> > ptxdist@pengutronix.de  
> 
> 
> 
> 

Best regards,

-- 
David Jander
Protonic Holland.
tel.: +31 (0) 229 212928
fax.: +31 (0) 229 210930
Factorij 36 / 1689 AL Zwaag

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