From 5be6e7b18e179a6979b19866d9512389efb3aaef Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Mon, 9 Jan 2023 15:35:52 +0100
Subject: [PATCH] settings: Add Xwayland byte-swapped clients

Recent versions of Xwayland can allow or disallow X11 clients from
different endianess to connect.

Add a setting to configure this feature from mutter, who spawns
Xwayland.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2785>
---
 data/org.gnome.mutter.wayland.gschema.xml.in | 24 ++++++++++++++++++++
 src/backends/meta-settings-private.h         |  2 ++
 src/backends/meta-settings.c                 | 23 +++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/data/org.gnome.mutter.wayland.gschema.xml.in b/data/org.gnome.mutter.wayland.gschema.xml.in
index 8a1878e10..3c3e54498 100644
--- a/data/org.gnome.mutter.wayland.gschema.xml.in
+++ b/data/org.gnome.mutter.wayland.gschema.xml.in
@@ -125,6 +125,30 @@
       </description>
     </key>
 
+    <key name="xwayland-allow-byte-swapped-clients" type="b">
+      <default>false</default>
+      <summary>Allow X11 clients with a different endianess to connect to Xwayland</summary>
+      <description>
+        Allow connections from clients with an endianess different to that
+	of Xwayland.
+
+	The X server byte-swapping code is a huge attack surface, much of
+	that code in Xwayland is prone to security issues.
+
+	The use-case of byte-swapped clients is very niche, and disabled by
+	default in Xwayland.
+
+	Enable this option to instruct Xwayland to accept connections from
+	X11 clients with a different endianess.
+
+        This option has no effect if Xwayland does not support the command
+	line option +byteswappedclients/-byteswappedclients to control that
+	setting.
+
+        Xwayland needs to be restarted for this setting to take effect.
+      </description>
+    </key>
+
   </schema>
 
 </schemalist>
diff --git a/src/backends/meta-settings-private.h b/src/backends/meta-settings-private.h
index 47d2d6074..87af21515 100644
--- a/src/backends/meta-settings-private.h
+++ b/src/backends/meta-settings-private.h
@@ -77,6 +77,8 @@ gboolean meta_settings_are_xwayland_grabs_allowed (MetaSettings *settings);
 
 int meta_settings_get_xwayland_disable_extensions (MetaSettings *settings);
 
+gboolean meta_settings_are_xwayland_byte_swapped_clients_allowed (MetaSettings *settings);
+
 gboolean meta_settings_is_privacy_screen_enabled (MetaSettings *settings);
 
 void meta_settings_set_privacy_screen_enabled (MetaSettings *settings,
diff --git a/src/backends/meta-settings.c b/src/backends/meta-settings.c
index 414ca48e8..aead64ccb 100644
--- a/src/backends/meta-settings.c
+++ b/src/backends/meta-settings.c
@@ -74,6 +74,9 @@ struct _MetaSettings
 
   /* A bitmask of MetaXwaylandExtension enum */
   int xwayland_disable_extensions;
+
+  /* Whether Xwayland should allow X11 clients from different endianess */
+  gboolean xwayland_allow_byte_swapped_clients;
 };
 
 G_DEFINE_TYPE (MetaSettings, meta_settings, G_TYPE_OBJECT)
@@ -428,6 +431,15 @@ update_privacy_settings (MetaSettings *settings)
                             settings);
 }
 
+static void
+update_xwayland_allow_byte_swapped_clients (MetaSettings *settings)
+{
+
+  settings->xwayland_allow_byte_swapped_clients =
+    g_settings_get_flags (settings->wayland_settings,
+                          "xwayland-allow-byte-swapped-clients");
+}
+
 static void
 wayland_settings_changed (GSettings    *wayland_settings,
                           gchar        *key,
@@ -446,6 +458,10 @@ wayland_settings_changed (GSettings    *wayland_settings,
     {
       update_xwayland_disable_extensions (settings);
     }
+  else if (g_str_equal (key, "xwayland-allow-byte-swapped-clients"))
+    {
+      update_xwayland_allow_byte_swapped_clients (settings);
+    }
 }
 
 void
@@ -469,6 +485,13 @@ meta_settings_get_xwayland_disable_extensions (MetaSettings *settings)
   return (settings->xwayland_disable_extensions);
 }
 
+gboolean
+meta_settings_are_xwayland_byte_swapped_clients_allowed (MetaSettings *settings)
+{
+
+  return settings->xwayland_allow_byte_swapped_clients;
+}
+
 gboolean
 meta_settings_is_privacy_screen_enabled (MetaSettings *settings)
 {