numeric uid. In older versions this could lead to a crash (denial of
service) or other undefined behaviour, possibly including incorrect
authorization decisions if <policy group=...> is used.
Like Unix filesystems, D-Bus' model of identity cannot distinguish
between users of different names with the same numeric uid, so this
configuration is not advisable on systems where D-Bus will be used.
Thanks to Daniel Onaca.
(dbus#305, dbus!166; Simon McVittie)

that we do not overrun the buffer used for fd-passing, even if the
kernel tells us to.
(dbus#304, dbus!165; Andy Fiddaman)