polkit: Allow password-less access for 'libvirt' group

Many users, who admin their own machines, want to be able to access
system libvirtd via tools like virt-manager without having to enter
a root password. Just google 'virt-manager without password' and
you'll find many hits. I've read at least 5 blog posts over the years
describing slightly different ways of achieving this goal.

Let's finally add official support for this.

Install a polkit-1 rules file granting password-less auth for any user
in the new 'libvirt' group. Create the group on RPM install

https://bugzilla.redhat.com/show_bug.cgi?id=957300

daemon/Makefile.am

@@ -53,6 +53,7 @@ EXTRA_DIST =						\
 	libvirtd.init.in				\
 	libvirtd.upstart				\
 	libvirtd.policy.in				\
+	libvirt.rules					\
 	libvirtd.sasl					\
 	libvirtd.service.in				\
 	libvirtd.socket.in				\
@@ -233,6 +234,8 @@ policyauth = auth_admin_keep_session
 else ! WITH_POLKIT0
 policydir = $(datadir)/polkit-1/actions
 policyauth = auth_admin_keep
+rulesdir = $(datadir)/polkit-1/rules.d
+rulesfile = libvirt.rules
 endif ! WITH_POLKIT0
 endif WITH_POLKIT
 
@@ -263,9 +266,19 @@ if WITH_POLKIT
 install-data-polkit::
 	$(MKDIR_P) $(DESTDIR)$(policydir)
 	$(INSTALL_DATA) libvirtd.policy $(DESTDIR)$(policydir)/org.libvirt.unix.policy
+if ! WITH_POLKIT0
+	$(MKDIR_P) $(DESTDIR)$(rulesdir)
+	$(INSTALL_DATA) $(srcdir)/$(rulesfile) $(DESTDIR)$(rulesdir)/50-libvirt.rules
+endif ! WITH_POLKIT0
+
 uninstall-data-polkit::
 	rm -f $(DESTDIR)$(policydir)/org.libvirt.unix.policy
 	rmdir $(DESTDIR)$(policydir) || :
+if ! WITH_POLKIT0
+	rm -f $(DESTDIR)$(rulesdir)/50-libvirt.rules
+	rmdir $(DESTDIR)$(rulesdir) || :
+endif ! WITH_POLKIT0
+
 else ! WITH_POLKIT
 install-data-polkit::
 uninstall-data-polkit::

daemon/libvirt.rules

+// Allow any user in the 'libvirt' group to connect to system libvirtd
+// without entering a password.
+
+polkit.addRule(function(action, subject) {
+    if (action.id == "org.libvirt.unix.manage" &&
+        subject.isInGroup("libvirt")) {
+        return polkit.Result.YES;
+    }
+});

libvirt.spec.in

@@ -1645,9 +1645,9 @@ then
 fi
 
 %if %{with_libvirtd}
+%pre daemon
     %if ! %{with_driver_modules}
         %if %{with_qemu}
-%pre daemon
             %if 0%{?fedora} || 0%{?rhel} >= 6
 # We want soft static allocation of well-known ids, as disk images
 # are commonly shared across NFS mounts by id rather than name; see
@@ -1661,11 +1661,21 @@ if ! getent passwd qemu >/dev/null; then
     useradd -r -g qemu -G kvm -d / -s /sbin/nologin -c "qemu user" qemu
   fi
 fi
-exit 0
             %endif
         %endif
     %endif
 
+    %if %{with_polkit}
+        %if 0%{?fedora} || 0%{?rhel} >= 6
+# 'libvirt' group is just to allow password-less polkit access to
+# libvirtd. The uid number is irrelevant, so we use dynamic allocation
+# described at the above link.
+getent group libvirt >/dev/null || groupadd -r libvirt
+        %endif
+    %endif
+
+exit 0
+
 %post daemon
 
     %if %{with_systemd}
@@ -1939,6 +1949,7 @@ exit 0
         %if 0%{?fedora} || 0%{?rhel} >= 6
 %{_datadir}/polkit-1/actions/org.libvirt.unix.policy
 %{_datadir}/polkit-1/actions/org.libvirt.api.policy
+%{_datadir}/polkit-1/rules.d/50-libvirt.rules
         %else
 %{_datadir}/PolicyKit/policy/org.libvirt.unix.policy
         %endif