[systemd-devel] D-feet displays an error message when using sd-bus

[Mantas Mikulėnas]

On Tue, Oct 19, 2021, 18:29 yves baumes <ybaumes at gmail.com> wrote:

> Hello,
>
> First I am not sure it is the correct place to ask questions about lib
> sd-bus. Is it? Here is my issues:
>
> I am trying to use the lib sd-bus, following this blog post:
> http://0pointer.net/blog/the-new-sd-bus-api-of-systemd.html .
>
> I am able to launch my own service on the *user* bus.
> When I launch it on the *system* bus, problems appear.
> First I had a permission denied issue, and to correct it I had to create a
> configuration file in /etc/dbus-1/system.d/net.poettering.Calculator.conf .
> As stated in
> https://stackoverflow.com/questions/32828468/sd-bus-api-sd-bus-request-name-returns-permission-denied
> .
> Thus the executable launches perfectly (no more 'permission denied'
> errors).
>

This is normal as the system bus is "deny everything by default", to make
sure unprivileged users can't impersonate a service.


> Now I am trying to inspect the service with D-feet. The service is well
> listed on the left pane: net.poettering.Calculator, but when I click on it,
> I get an error window stating :
> 'net.poettering.Calculator: g-dbus-error-quark:
> GDBus.Error:org.freedesktop.DBus.Error.AccessDenied: Rejected send message,
> 1 matched rules; type="method_call", sender=":-1.1996" (uid=1000
> pid=3110822 comm="/usr/bin/python3 /usr/bin/d-feet" label"unconfined")
> interface="org.freedesktop.DBus.Introspectable" member="Introspect" error
> name ="(unset)" requested_reply="0" destination=net.poettering.Calculator"
> (uid=0 pid=3110595 comm="./-bus-service" label="unconfined")(9)' .
>

This also means you need to allow things in the dbus-daemon policy. Not
only does the service need permissions to claim a name, but everyone also
needs permissions to send it messages (and receive replies).

In many cases you can copy a basic policy that just allows everything from
any UID to your service (possibly still limited by interface), like how
UDisks2.conf does it.
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