[systemd-bugs] [Bug 77005] New: bus-driverd racing external requests

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=77005

          Priority: medium
            Bug ID: 77005
          Assignee: systemd-bugs at lists.freedesktop.org
           Summary: bus-driverd racing external requests
        QA Contact: systemd-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: dh.herrmann at gmail.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: general
           Product: systemd

Ryan just made me aware of this. The following sequence works reliably with
dbus1, but not with kdbus + bus-driverd:

ADD_MATCH to=org.freedesktop.DBus
METHOD_CALL to=someone.else

If both calls are async, with dbus1, the ADD_MATCH is guaranteed to be finished
before METHOD_CALL is forwarded to someone.else. With bus-driverd, there's no
such guarantee.

I'm not really sure how to fix it. Some ideas:
 * make any org.freedesktop.DBus call synchronous in the kernel (ugh, ugly!)
 * support org.freedesktop.DBus only when called through bus-proxyd and make it
synchronous inside of bus-proxyd (hm, still ugly?)
 * make sd-bus inspect any outgoing messages and make them synchronous if
they're targeted as org.freedesktop.DBus
 * document it, but it ignore it and make people wait for ADD_MATCH to actually
finish

With "synchronous" I obviously mean just delaying any other outgoing message
until we got the response. That "waiting" can still be async.. (like HELO)

I'm actually not sure whether _any_ of the bus-driverd calls is still needed
with kdbus, but if it is, we probably need to review the other ones, too.

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