[PATCH V2] When "activating" systemd, handle its special case better

[Chengwei Yang]

When dbus-daemon receives a request to activate a service which
declaimed should be activated by systemd before systemd has
connected to it, it enqueues a fake request to "activate" systemd
itself (as a way to get a BusPendingActivationEntry to track the
process of waiting for systemd). When systemd later joins the bus,
dbus-daemon sends the actual activation message; any future
activation messages are sent directly to systemd.

In the "pending" code path, the activation messages are currently
dispatched as though they had been sent by the same process
that sent the original activation request, which is wrong:
the bus security policy probably doesn't allow that process
to talk to systemd directly. They should be dispatched as though
they had been sent by the dbus-daemon itself (connection == NULL),
the same as in the non-pending code path.

In the worst case, if the attempt to activate systemd
timed out, the dbus-daemon would crash with a (fatal) warning,
because in this special case, activation_message is a signal
with no serial number, whereas the code to send an error
reply is expecting a method call with a serial number.

For more details, please refer to freedesktop bugzilla below.
https://bugs.freedesktop.org/show_bug.cgi?id=50199

Signed-off-by: Chengwei Yang <chengwei.yang at intel.com>
Tested-by: Ma Yu <yu.ma at intel.com>
---
 bus/activation.c |   17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/bus/activation.c b/bus/activation.c
index 3dfba78..8de3997 100644
--- a/bus/activation.c
+++ b/bus/activation.c
@@ -80,7 +80,14 @@ typedef struct BusPendingActivationEntry BusPendingActivationEntry;
 
 struct BusPendingActivationEntry
 {
+  /* Normally a method call, but if connection is NULL, this is a signal
+   * instead.
+   */
   DBusMessage *activation_message;
+  /* NULL if this activation entry is for the dbus-daemon itself,
+   * waiting for systemd to start. In this case, auto_activation is always
+   * TRUE.
+   */
   DBusConnection *connection;
 
   dbus_bool_t auto_activation;
@@ -1106,7 +1113,8 @@ bus_activation_service_created (BusActivation  *activation,
       BusPendingActivationEntry *entry = link->data;
       DBusList *next = _dbus_list_get_next_link (&pending_activation->entries, link);
 
-      if (dbus_connection_get_is_connected (entry->connection))
+      /* entry->connection is NULL for activating systemd */
+      if (entry->connection && dbus_connection_get_is_connected (entry->connection))
         {
           /* Only send activation replies to regular activation requests. */
           if (!entry->auto_activation)
@@ -1175,7 +1183,7 @@ bus_activation_send_pending_auto_activation_messages (BusActivation  *activation
       BusPendingActivationEntry *entry = link->data;
       DBusList *next = _dbus_list_get_next_link (&pending_activation->entries, link);
 
-      if (entry->auto_activation && dbus_connection_get_is_connected (entry->connection))
+      if (entry->auto_activation && (entry->connection == NULL || dbus_connection_get_is_connected (entry->connection)))
         {
           DBusConnection *addressed_recipient;
 
@@ -1759,7 +1767,8 @@ bus_activation_activate_service (BusActivation  *activation,
   pending_activation_entry->activation_message = activation_message;
   dbus_message_ref (activation_message);
   pending_activation_entry->connection = connection;
-  dbus_connection_ref (connection);
+  if (connection)
+    dbus_connection_ref (connection);
 
   /* Check if the service is being activated */
   pending_activation = _dbus_hash_table_lookup_string (activation->pending_activations, service_name);
@@ -1972,7 +1981,7 @@ bus_activation_activate_service (BusActivation  *activation,
                                service_name,
                                entry->systemd_service);
               /* systemd is not around, let's "activate" it. */
-              retval = bus_activation_activate_service (activation, connection, activation_transaction, TRUE,
+              retval = bus_activation_activate_service (activation, NULL, activation_transaction, TRUE,
                                                         message, "org.freedesktop.systemd1", error);
             }
 
-- 
1.7.9.5