From ef2be42998e3fc10299055a5a01f7c791538174c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Mon, 3 Feb 2020 15:38:28 +0200
Subject: [PATCH] GMainContext - Fix GSource iterator if iteration can modify
 the list

We first have to ref the next source and then unref the previous one.
This might be the last reference to the previous source, and freeing the
previous source might unref and free the next one which would then leave
use with a dangling pointer here.

Fixes https://gitlab.gnome.org/GNOME/glib/issues/2031

Upstream-Status: Backport [https://gitlab.gnome.org/GNOME/glib/-/commit/b06c48de7554607ff3fb58d6c0510cfa5088e909]

---
 glib/gmain.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/glib/gmain.c b/glib/gmain.c
index af979c8..a9a287d 100644
--- a/glib/gmain.c
+++ b/glib/gmain.c
@@ -969,13 +969,17 @@ g_source_iter_next (GSourceIter *iter, GSource **source)
    * GSourceList to be removed from source_lists (if iter->source is
    * the only source in its list, and it is destroyed), so we have to
    * keep it reffed until after we advance iter->current_list, above.
+   *
+   * Also we first have to ref the next source before unreffing the
+   * previous one as unreffing the previous source can potentially
+   * free the next one.
    */
+  if (next_source && iter->may_modify)
+    g_source_ref (next_source);

   if (iter->source && iter->may_modify)
     g_source_unref_internal (iter->source, iter->context, TRUE);
   iter->source = next_source;
-  if (iter->source && iter->may_modify)
-    g_source_ref (iter->source);

   *source = iter->source;
   return *source != NULL;