[systemd-devel] Work on adding polkit support to systemd1

[Lennart Poettering]

On Fri, 15.08.14 19:28, Stef Walter (stefw at redhat.com) wrote:

> 
> On 15.08.2014 18:56, Lennart Poettering wrote:
> > On Fri, 15.08.14 18:25, Stef Walter (stefw at redhat.com) wrote:
> > 
> >>
> >> On 13.08.2014 20:27, Lennart Poettering wrote:
> >>> On Wed, 06.08.14 13:23, Stef Walter (stefw at redhat.com) wrote:
> >>>
> >>>> I've done initial work on adding polkit support to systemd1 DBus
> >>>> methods. You can see it here:
> >>
> >> Thanks for the review. Worked on this a bit more.
> >>
> >> I might drop off the face of the earth for a couple weeks. In case I do,
> >> I thought I'd update my public branch. But if I'm around, I'll test and
> >> prepare a patch set early next week.
> >>
> >>>> https://github.com/stefwalter/systemd/commits/polkit-systemd1
> > 
> > Hmm, yuck. There's a security issue here... Reading the capabilities
> > from the sender on dbus1 is racy, since we have to read it from
> > /proc/$PID/stat and don't get it sent along with the message, like we do
> > on kdbus. A rogue client could send a message, quickly invoke some suid
> > binary, and we'd consider the client trusted.
> > 
> > Now for the low-level implementation of the vtable bit we are actually
> > smart, and check by UID on dbus1, and by cap on kdbus, in order to avoid
> > the vulnerability.
> > 
> > Hmm, now I wonder how to best handle this for cases like this, we
> > probably need some generic way how clients can make this decision in an
> > always safe way...
> > 
> > I need to think more about this...
> 
> By the way, there's some similar problematic code in the modified
> KillUnit() method implementation ... changed from specifying the
> CAP_KILL in the vtable, and now it does a manual check.
> 
> > Patch set looks great otherwise. I'll come up with something for the
> > security issue, then adapt your patch, and merge it.
> 
> I haven't tested the updated branch at all :) So it may go boom...

I have now pushed this, after reworking this on top some major changes
to bus_verify_polkit(), which avoids having to pass the original
callbacks through to the function that ultimately does the verification.

While merging I also made another change, you are probably not going to
like: I turned of the interactivity for the polkit checks. Interactivity
needs to be optional, and it currently is for all out polkit-enabled bus
methods. And we should do the same for the PID 1 offered methods.

Now, of course, we should open this up for inetractive (after all,
that's what polkit is good for), but we probably need a new set of
methods for that, which take the original arguments but also take a
boolean argument to enable ineractivity. Hence, we probably should have
StartUnit2() in addition to StartUnit().

Lennart

-- 
Lennart Poettering, Red Hat