Re: [Xen-devel] [systemd-devel] [PATCH v5 12/14] autoconf: xen: enable explicit preference option for xenstored preference

[Lennart Poettering <mzxreary@xxxxxxxxxxx>]

On Thu, 05.06.14 02:31, Luis R. Rodriguez (mcgrof@xxxxxxxx) wrote:

> On Sun, Jun 01, 2014 at 08:15:47AM +0200, Lennart Poettering wrote:
> > On Fri, 30.05.14 01:29, Luis R. Rodriguez (mcgrof@xxxxxxxx) wrote:
> > 
> > > I'm cc'ing a few security folks as I'd appreciate review on the ideas 
> > > here,
> > > in particular that of a launcher idea on system to replace alternatives 
> > > on the
> > > ExecStart= line of a systemd service unit file, alternative ideas are of
> > > course welcomed. I'm also Cc'ing systemd-devel as this subject was 
> > > reviewed
> > > a little while ago with nothing concrete being recommended but instead a 
> > > few
> > > options being now archived as possibilities. I'm looking for a bit wider
> > > review of the approaches and recomendations.
> > > 
> > > Some general background for non xen folks: old xen requires the launch of
> > > a daemon which implements supports of the xenstore, which is the database
> > > that xen uses for information about guests / dom0. There are two supported
> > > daemons, xenstored (C version) and oxenstored (Ocaml version) but they do 
> > > the
> > > same thing. Right now old init lets you override which one you pick 
> > > through
> > > an environment variable on /etc/{sysconfig,default}/xencommons, the script
> > > will use the appropriate on there. Systemd doesn't let you use variables 
> > > on
> > > the ExecStart line of a service unit file so alternatives are required.
> > > 
> > > The reason I'm being very careful here this could set a precedent and at
> > > least for the launcher idea it'd require the usage of getenv() and 
> > > execve(),
> > > and secure alternatives for these (secure_getenv(), execve_nosecurity())
> > > have either been merged or suggested before for Linux. The systemd 
> > > discussion
> > > is only specific to Linux but if we have a launcher we could consider it 
> > > for
> > > other supported OSes. All that said I'd like proper review of the security
> > > implications of *all* strategies but obviously in particular the launcher
> > > idea. I want to tread carefuly before setting precedents.
> > 
> > You can also just invoke a shell script from ExecStart=. I mean, we try
> > to deemphesize them in the boot process, but there's nothing wrong with
> > using shell, if you need to parse shell configuraiton fragments and just
> > want to execute on ot another program...
> 
> I tried this and it didn't work given that systemd expects sd_notify()
> to be called from the parent process, in this case the shell script.

Hmm? You should "exec" the real daemon binary at the end, not just fork
it off. That wait the shell script process is replaced by the daemon
binary, which is what you want.

Lennart

-- 
Lennart Poettering, Red Hat

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