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qapi: fix double free in qmp_output_visitor_cleanup()

Stack entries in QmpOutputVisitor are navigation links (weak references),
except the bottom (ie. least recently added) entry, which owns the root
QObject [1]. Make qmp_output_visitor_cleanup() drop the stack entries,
then release the QObject tree by the root.

Attempting to serialize an invalid enum inside a dictionary is an example
for triggering the double free.

[1] http://lists.nongnu.org/archive/html/qemu-devel/2012-03/msg03276.html

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
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1 parent 8a22565 commit f24582d6ad8a080e008974c000bf0ae635d036ac @lersek lersek committed with Luiz Capitulino Mar 20, 2012
Showing with 5 additions and 3 deletions.
  1. +5 −3 qapi/qmp-output-visitor.c
@@ -199,14 +199,16 @@ void qmp_output_visitor_cleanup(QmpOutputVisitor *v)
{
QStackEntry *e, *tmp;
+ /* The bottom QStackEntry, if any, owns the root QObject. See the
+ * qmp_output_push_obj() invocations in qmp_output_add_obj(). */
+ QObject *root = QTAILQ_EMPTY(&v->stack) ? NULL : qmp_output_first(v);
+
QTAILQ_FOREACH_SAFE(e, &v->stack, node, tmp) {
QTAILQ_REMOVE(&v->stack, e, node);
- if (e->value) {
- qobject_decref(e->value);
- }
g_free(e);
}
+ qobject_decref(root);
g_free(v);
}

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