lib/config: don't set destructor until iterator is initialized.

As diagnosed by Olivier Taïbi in
id:20201027100916.emry3k2wujod4xnl@galois.lan, if an exception is
thrown while the initialization is happening (e.g. if the function is
called on a closed database), then the destructor is (sometimes)
invoked on an uninitialized Xapian object.

Solve the problem by moving the setting of the destructor until after
the placement new successfully completes. It is conceivable this might
cause a memory leak, but that seems preferable to crashing, and in any
case, there seems to be nothing better to be done if the
initialization is failing things are in an undefined state by
definition.

diff --git a/lib/config.cc b/lib/config.cc
index dae0ff0e7f92d3e70681bff9589c38a9a814f6d4..efab01e400708fde51470b85eee3102482f59a4e 100644 (file)
--- a/lib/config.cc
+++ b/lib/config.cc
@@ -113,7 +113,6 @@ notmuch_database_get_config_list (notmuch_database_t *notmuch,
        goto DONE;
     }
 
-    talloc_set_destructor (list, _notmuch_config_list_destroy);
     list->notmuch = notmuch;
     list->current_key = NULL;
     list->current_val = NULL;
@@ -122,6 +121,7 @@ notmuch_database_get_config_list (notmuch_database_t *notmuch,
 
        new(&(list->iterator)) Xapian::TermIterator (notmuch->xapian_db->metadata_keys_begin
                                                         (CONFIG_PREFIX + (prefix ? prefix : "")));
+       talloc_set_destructor (list, _notmuch_config_list_destroy);
 
     } catch (const Xapian::Error &error) {
        _notmuch_database_log (notmuch, "A Xapian exception occurred getting metadata iterator: %s.\n",