authz-pam: Check that 'service' property is set

If the 'service' property is not set, we'll call pam_start() with a NULL
pointer for the service name. This fails and leaves a message like this
in the syslog:

qemu-storage-daemon[294015]: PAM pam_start: invalid argument: service == NULL

Make specifying the property mandatory and catch the error already
during the creation of the object.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

authz/pamacct.c

@@ -84,6 +84,12 @@ qauthz_pam_prop_get_service(Object *obj,
 static void
 qauthz_pam_complete(UserCreatable *uc, Error **errp)
 {
+    QAuthZPAM *pauthz = QAUTHZ_PAM(uc);
+
+    if (!pauthz->service) {
+        error_setg(errp, "The 'service' property must be set");
+        return;
+    }
 }