config-parser: Fail on impossible send_broadcast/send_destination pair

If we add a rule like

    <allow send_destination="com.example" send_broadcast="true"/>

then it cannot possibly match anything, because to be a broadcast, the
message would have to have no destination. The only value of
send_destination that can be combined with send_broadcast="true" is
the wildcard "*", but by this point in the function we already
replaced "*" with NULL.

Adapted from an earlier implementation of send_broadcast by
Alban Crequy.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Bug: https://bugs.freedesktop.org/92853
Reviewed-by: Philip Withnall <withnall@endlessm.com>

diff --git a/bus/config-parser.c b/bus/config-parser.c
index 7f095bd..be27d38 100644 (file)
--- a/bus/config-parser.c
+++ b/bus/config-parser.c
@@ -1554,6 +1554,19 @@ append_rule_from_element (BusConfigParser   *parser,
           return FALSE;
         }
 
+      if (send_destination != NULL &&
+          send_broadcast != NULL &&
+          strcmp (send_broadcast, "true") == 0)
+        {
+          /* Broadcast messages have no destination, so this cannot
+           * possibly match */
+          dbus_set_error (error, DBUS_ERROR_FAILED,
+                          "Rule with send_broadcast=\"true\" and "
+                          "send_destination=\"%s\" cannot match anything",
+                          send_destination);
+          return FALSE;
+        }
+
       if (send_requested_reply &&
           !(strcmp (send_requested_reply, "true") == 0 ||
             strcmp (send_requested_reply, "false") == 0))