[SSSD] sssd.conf ownership

Stephen Gallagher sgallagh at redhat.com
Fri Nov 21 21:26:58 UTC 2014




On Fri, 2014-11-21 at 20:03 +0100, Jakub Hrozek wrote:
> Hi,
> 
> I was going through our design page that describes the rootless sssd and
> I'd like to discuss the default ownership of sssd.conf a bit more.
> 
> In the design document we proposed to change the default ownership to
> sssd.sssd. This wouldn't widen sssd.conf access as only root and the sssd
> user could read the config. One reason for the change was the dbus helper
> to change the config, which would otherwise run privileged.
> 
> But I wonder whether it's really the best approach. If we changed the
> ownership to sssd.sssd, then we'd have to be careful about chowning the
> file each time on startup because tools like authconfig or even customer's
> puppet modules or whatnot will keep writing out the file as root.root. We
> can't reasonably change all the external tools and chowning on each
> startup seems a bit fragile (as opposed to chowning the databases which
> is a one-time operation).
> 
> Also, if we kept the the config file owned by root, then making the
> confdb read-only for worker processes would mean the worker processes
> have no means of altering the config file even if they were taken over.
> 
> The downside of keeping the sssd.conf as root is that the augeas calls
> would have to be moved to a setuid process -- and a new setuid process is
> always a bit of a burden.
> 
> To sum up:
>     * sssd.sssd
>         (+) don't need any privileged code to access sssd.conf
>         (-) need to chown the file on each startup
>     * root.root
>         (+) config file is only writable by privileged processes
>         (+) we're able to make the confdb read-only
>         (-) need privileged code to perform sssd.conf changes
> 
> I do realize that the complexity of creating the setuid helpers is much
> larger than the complexity of writing a function to chown a file, but
> for some reason the chowning feels a bit fragile to me and my gut
> feeling is that the config file would better be only accessible by
> root...
> 
> What do the other developers think?

Why exactly would it need to be chown()ed? I'm unclear on that point.
Presumably, SSSD is still being launched as root and then dropping
privileges (otherwise it wouldn't be able to perform the chown). So to
me it seems like it makes sense to just open the file read-only prior to
dropping privileges, then pass the filehandle along. The sssd can then
generate the read-only confdb as the 'sssd' user.

So I guess I'm completely missing the need or advantage of chowning it.
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