Authentication, authorization and filtering of messages.

[janderholm]

Hello!

I'm trying to add in application authentication of dbus calls. My initial attempt uses Sender in the header, see the following pseudo rust code.

#[dbus_interface(name = "org.zbus.MyGreeter1")]
impl Greeter {
    async fn say_hello(
        &self,
        name: &str,
        #[zbus(header)] hdr: zbus::message::Header<'_>,
    ) -> String {
        if authorized(hdr.sender()) {
            format!("Hello {}!", name)
        } else {
            format!("You are not allowed to make this call at this time")
        }
    }
}

This breaks down when it comes to properties, because of #218. I started implementing support for the ZBUS parameters but quickly ran into the same issues as this earlier attempt:
Draft: Allow #[zbus(...)] args in dbus_interface properties

So now I'm left scratching my head thinking of alternative approaches. If this was sd_bus I would have used sd_bus_add_filter which lets you filter messages.

I haven't been able to figure out a way of doing this with zbus. Is it possible? I think it would probably be an easier solution since the filtering could be done in one place instead of having to implement it in every method and property.

Any ideas?

[zeenix]

I'm trying to add in application authentication of dbus calls.

Why? The authentication is (and should be) handled by the bus.

This breaks down when it comes to properties, because of #218. I started implementing support for the ZBUS parameters but quickly ran into the same issues as this earlier attempt:
Draft: Allow #[zbus(...)] args in dbus_interface properties

I know it's hard to edit macro code (I myself dread it each time I've to do it) but this is still a matter of figuring out the code and making it happen.

I haven't been able to figure out a way of doing this with zbus. Is it possible?

Just FYI, if the high-level API is not cutting it for you, there is always the (slightly) low-level API, via MessageStream. So your choice is either to fix the small limitation in the high-level API or use MessageStream. So yeah, it's very much possible.

[zeenix]

There's plenty of times where you do auth in the service itself. One example would be systemd which does this a lot:

Right, sorry I got confused by your very simple sample code and thought you may be doing something you shouldn't. :)

I have been looking into the macros and made some progress and am willing to give it a shot.

Cool!

But I was disheartened by your comment in the draft

The effort mainly died because the contributor in question lost interest and/or ran out of time.

and though it would be quite difficult to make something acceptable?

It depends. Probably best if you first describe your solution in the issue so we can discuss it before you work hard on making it happen. Looking back at that MR, I think my comments might have sounded like judgements but I was mostly just thinking out loud. For example this part:

that will be very inconvenient though to have to unwrap the Option but OTOH keeping it only wrapped in Option for setter/getter would be inconsistent and strange.

Thinking now, I think this inconsistency might be OK, as long as it's documented well.

[zeenix]

Looking quickly in to the macro code, I realized that this will likely need API break as Interface::{get*, set*} will need a Message (or Option<Message>) argument.

[zeenix]

Ughh.. hit "enter" too quickly. The thing is that we're right now in an API break so if you can get this done soon, it's the best time for this. Otherwise, it'll have to wait for the next API break. I'd suggest first making the trivial Interface changes in a separate PR. For now the macros can ignore that argument. That way you won't have to rush your real PR and can be handled after 4.x is out.

[janderholm]

Let's see if I understand this corrertly. If I add Message to Interface::{get*, set*}, I also need a way to insert the message into a method call. Since those methods are implemented here:

https://github.com/dbus2/zbus/blob/main/zbus/src/fdo.rs#L129

Is that how you envision things?

[zeenix]

Let's see if I understand this corrertly. If I add Message to Interface::{get*, set*}, I also need a way to insert the message into a method call. Since those methods are implemented here:

https://github.com/dbus2/zbus/blob/main/zbus/src/fdo.rs#L129

Ah, I see what you mean. Actually we should instead add a header argument (we only need that in the end anyway) to Interface::get*, set*}.