display: port GdmDisplay to xcb

Xlib will kill the process if it notices the display connection has
gone away. This is suboptimal for the main gdm process!

This commit ports the Xlib code to xcb, so it won't have the above
fragility.

https://bugzilla.gnome.org/show_bug.cgi?id=776059

2 files changed, 121 insertions, 97 deletions

diff --git a/configure.ac b/configure.ac
index dd989928..fbf400e5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -84,6 +84,7 @@ PKG_CHECK_MODULES(DAEMON,
         gio-2.0 >= $GLIB_REQUIRED_VERSION
         gio-unix-2.0 >= $GLIB_REQUIRED_VERSION
         accountsservice >= $ACCOUNTS_SERVICE_REQUIRED_VERSION
+        xcb
 )
 AC_SUBST(DAEMON_CFLAGS)
 AC_SUBST(DAEMON_LIBS)
diff --git a/daemon/gdm-display.c b/daemon/gdm-display.c
index ee80c84b..4b035d6f 100644
--- a/daemon/gdm-display.c
+++ b/daemon/gdm-display.c
@@ -34,8 +34,7 @@
 #include <glib/gi18n.h>
 #include <glib-object.h>
 
-#include <X11/Xlib.h>
-#include <X11/Xatom.h>
+#include <xcb/xcb.h>
 
 #include "gdm-common.h"
 #include "gdm-display.h"
@@ -76,7 +75,8 @@ struct GdmDisplayPrivate
 
         guint                 finish_idle_id;
 
-        Display              *x11_display;
+        xcb_connection_t     *xcb_connection;
+        int                   xcb_screen_number;
 
         GDBusConnection      *connection;
         GdmDisplayAccessFile *user_access_file;
@@ -292,32 +292,17 @@ gdm_display_create_authority (GdmDisplay *self)
 }
 
 static void
-setup_xhost_auth (XHostAddress              *host_entries,
-                  XServerInterpretedAddress *si_entries)
-{
-        si_entries[0].type        = "localuser";
-        si_entries[0].typelength  = strlen ("localuser");
-        si_entries[1].type        = "localuser";
-        si_entries[1].typelength  = strlen ("localuser");
-        si_entries[2].type        = "localuser";
-        si_entries[2].typelength  = strlen ("localuser");
-
-        si_entries[0].value       = "root";
-        si_entries[0].valuelength = strlen ("root");
-        si_entries[1].value       = GDM_USERNAME;
-        si_entries[1].valuelength = strlen (GDM_USERNAME);
-        si_entries[2].value       = "gnome-initial-setup";
-        si_entries[2].valuelength = strlen ("gnome-initial-setup");
-
+setup_xhost_auth (XHostAddress              *host_entries)
+{
         host_entries[0].family    = FamilyServerInterpreted;
-        host_entries[0].address   = (char *) &si_entries[0];
-        host_entries[0].length    = sizeof (XServerInterpretedAddress);
+        host_entries[0].address   = "localuser\0root";
+        host_entries[0].length    = sizeof ("localuser\0root");
         host_entries[1].family    = FamilyServerInterpreted;
-        host_entries[1].address   = (char *) &si_entries[1];
-        host_entries[1].length    = sizeof (XServerInterpretedAddress);
+        host_entries[1].address   = "localuser\0" GDM_USERNAME;
+        host_entries[1].length    = sizeof ("localuser\0" GDM_USERNAME);
         host_entries[2].family    = FamilyServerInterpreted;
-        host_entries[2].address   = (char *) &si_entries[2];
-        host_entries[2].length    = sizeof (XServerInterpretedAddress);
+        host_entries[2].address   = "localuser\0gnome-initial-setup";
+        host_entries[2].length    = sizeof ("localuser\0gnome-initial-setup");
 }
 
 gboolean
@@ -331,8 +316,8 @@ gdm_display_add_user_authorization (GdmDisplay *self,
         gboolean              res;
 
         int                       i;
-        XServerInterpretedAddress si_entries[3];
         XHostAddress              host_entries[3];
+        xcb_void_cookie_t         cookies[3];
 
         g_return_val_if_fail (GDM_IS_DISPLAY (self), FALSE);
 
@@ -382,14 +367,25 @@ gdm_display_add_user_authorization (GdmDisplay *self,
         /* Remove access for the programs run by greeter now that the
          * user session is starting.
          */
-        setup_xhost_auth (host_entries, si_entries);
-        gdm_error_trap_push ();
+        setup_xhost_auth (host_entries);
+
         for (i = 0; i < G_N_ELEMENTS (host_entries); i++) {
-                XRemoveHost (self->priv->x11_display, &host_entries[i]);
+                cookies[i] = xcb_change_hosts_checked (self->priv->xcb_connection,
+                                                       XCB_HOST_MODE_DELETE,
+                                                       host_entries[i].family,
+                                                       host_entries[i].length,
+                                                       (uint8_t *) host_entries[i].address);
         }
-        XSync (self->priv->x11_display, False);
-        if (gdm_error_trap_pop ()) {
-                g_warning ("Failed to remove greeter program access to the display. Trying to proceed.");
+
+        for (i = 0; i < G_N_ELEMENTS (cookies); i++) {
+                xcb_generic_error_t *xcb_error;
+
+                xcb_error = xcb_request_check (self->priv->xcb_connection, cookies[i]);
+
+                if (xcb_error != NULL) {
+                        g_warning ("Failed to remove greeter program access to the display. Trying to proceed.");
+                        free (xcb_error);
+                }
         }
 
         return TRUE;
@@ -652,7 +648,7 @@ gdm_display_finish (GdmDisplay *self)
 static void
 gdm_display_disconnect (GdmDisplay *self)
 {
-        g_clear_pointer (&self->priv->x11_display, XCloseDisplay);
+        g_clear_pointer (&self->priv->xcb_connection, xcb_disconnect);
 }
 
 gboolean
@@ -951,7 +947,7 @@ gdm_display_get_property (GObject        *object,
                 g_value_set_boolean (value, self->priv->is_local);
                 break;
         case PROP_IS_CONNECTED:
-                g_value_set_boolean (value, self->priv->x11_display != NULL);
+                g_value_set_boolean (value, self->priv->xcb_connection != NULL);
                 break;
         case PROP_LAUNCH_ENVIRONMENT:
                 g_value_set_object (value, self->priv->launch_environment);
@@ -1601,70 +1597,78 @@ gdm_display_stop_greeter_session (GdmDisplay *self)
         }
 }
 
+static xcb_window_t
+get_root_window (xcb_connection_t *connection,
+                 int               screen_number)
+{
+        xcb_screen_t *screen = NULL;
+        xcb_screen_iterator_t iter;
+
+        iter = xcb_setup_roots_iterator (xcb_get_setup (connection));
+        while (iter.rem) {
+                if (screen_number == 0)
+                        screen = iter.data;
+                screen_number--;
+                xcb_screen_next (&iter);
+        }
+
+        if (screen != NULL) {
+                return screen->root;
+        }
+
+        return XCB_WINDOW_NONE;
+}
+
 static void
 gdm_display_set_windowpath (GdmDisplay *self)
 {
         /* setting WINDOWPATH for clients */
-        Atom prop;
-        Atom actualtype;
-        int actualformat;
-        unsigned long nitems;
-        unsigned long bytes_after;
-        unsigned char *buf;
+        xcb_intern_atom_cookie_t atom_cookie;
+        xcb_intern_atom_reply_t *atom_reply = NULL;
+        xcb_get_property_cookie_t get_property_cookie;
+        xcb_get_property_reply_t *get_property_reply = NULL;
+        xcb_window_t root_window = XCB_WINDOW_NONE;
         const char *windowpath;
         char *newwindowpath;
-        unsigned long num;
+        uint32_t num;
         char nums[10];
         int numn;
 
-        prop = XInternAtom (self->priv->x11_display, "XFree86_VT", False);
-        if (prop == None) {
+        atom_cookie = xcb_intern_atom (self->priv->xcb_connection, 0, strlen("XFree86_VT"), "XFree86_VT");
+        atom_reply = xcb_intern_atom_reply (self->priv->xcb_connection, atom_cookie, NULL);
+
+        if (atom_reply == NULL) {
                 g_debug ("no XFree86_VT atom\n");
-                return;
-        }
-        if (XGetWindowProperty (self->priv->x11_display,
-                DefaultRootWindow (self->priv->x11_display), prop, 0, 1,
-                False, AnyPropertyType, &actualtype, &actualformat,
-                &nitems, &bytes_after, &buf)) {
-                g_debug ("no XFree86_VT property\n");
-                return;
+                goto out;
         }
 
-        if (nitems != 1) {
-                g_debug ("%lu items in XFree86_VT property!\n", nitems);
-                XFree (buf);
-                return;
+        root_window = get_root_window (self->priv->xcb_connection,
+                                       self->priv->xcb_screen_number);
+
+        if (root_window == XCB_WINDOW_NONE) {
+                g_debug ("couldn't find root window\n");
+                goto out;
         }
 
-        switch (actualtype) {
-        case XA_CARDINAL:
-        case XA_INTEGER:
-        case XA_WINDOW:
-                switch (actualformat) {
-                case  8:
-                        num = (*(uint8_t  *)(void *)buf);
-                        break;
-                case 16:
-                        num = (*(uint16_t *)(void *)buf);
-                        break;
-                case 32:
-                        num = (*(long *)(void *)buf);
-                        break;
-                default:
-                        g_debug ("format %d in XFree86_VT property!\n", actualformat);
-                        XFree (buf);
-                        return;
-                }
-                break;
-        default:
-                g_debug ("type %lx in XFree86_VT property!\n", actualtype);
-                XFree (buf);
-                return;
+        get_property_cookie = xcb_get_property (self->priv->xcb_connection,
+                                                FALSE,
+                                                root_window,
+                                                atom_reply->atom,
+                                                XCB_ATOM_INTEGER,
+                                                0,
+                                                1);
+
+        get_property_reply = xcb_get_property_reply (self->priv->xcb_connection, get_property_cookie, NULL);
+
+        if (get_property_reply == NULL) {
+                g_debug ("no XFree86_VT property\n");
+                goto out;
         }
-        XFree (buf);
+
+        num = ((uint32_t *) xcb_get_property_value (get_property_reply))[0];
 
         windowpath = getenv ("WINDOWPATH");
-        numn = snprintf (nums, sizeof (nums), "%lu", num);
+        numn = snprintf (nums, sizeof (nums), "%u", num);
         if (!windowpath) {
                 newwindowpath = malloc (numn + 1);
                 sprintf (newwindowpath, "%s", nums);
@@ -1674,11 +1678,15 @@ gdm_display_set_windowpath (GdmDisplay *self)
         }
 
         g_setenv ("WINDOWPATH", newwindowpath, TRUE);
+out:
+        g_clear_pointer (&atom_reply, free);
+        g_clear_pointer (&get_property_reply, free);
 }
 
 gboolean
 gdm_display_connect (GdmDisplay *self)
 {
+        xcb_auth_info_t *auth_info = NULL;
         gboolean ret;
 
         ret = FALSE;
@@ -1687,21 +1695,26 @@ gdm_display_connect (GdmDisplay *self)
 
         /* Get access to the display independent of current hostname */
         if (self->priv->x11_cookie != NULL) {
-                XSetAuthorization ("MIT-MAGIC-COOKIE-1",
-                                   strlen ("MIT-MAGIC-COOKIE-1"),
-                                   (gpointer)
-                                   self->priv->x11_cookie,
-                                   self->priv->x11_cookie_size);
+                auth_info = g_alloca (sizeof (xcb_auth_info_t));
+
+                auth_info->namelen = strlen ("MIT-MAGIC-COOKIE-1");
+                auth_info->name = "MIT-MAGIC-COOKIE-1";
+                auth_info->datalen = self->priv->x11_cookie_size;
+                auth_info->data = self->priv->x11_cookie;
+
         }
 
-        self->priv->x11_display = XOpenDisplay (self->priv->x11_display_name);
+        self->priv->xcb_connection = xcb_connect_to_display_with_auth_info (self->priv->x11_display_name,
+                                                                            auth_info,
+                                                                            &self->priv->xcb_screen_number);
 
-        if (self->priv->x11_display == NULL) {
+        if (xcb_connection_has_error (self->priv->xcb_connection)) {
+                g_clear_pointer (&self->priv->xcb_connection, xcb_disconnect);
                 g_warning ("Unable to connect to display %s", self->priv->x11_display_name);
                 ret = FALSE;
         } else if (self->priv->is_local) {
-                XServerInterpretedAddress si_entries[3];
                 XHostAddress              host_entries[3];
+                xcb_void_cookie_t         cookies[3];
                 int                       i;
 
                 g_debug ("GdmDisplay: Connected to display %s", self->priv->x11_display_name);
@@ -1709,17 +1722,27 @@ gdm_display_connect (GdmDisplay *self)
 
                 /* Give programs access to the display independent of current hostname
                  */
-                setup_xhost_auth (host_entries, si_entries);
-
-                gdm_error_trap_push ();
+                setup_xhost_auth (host_entries);
 
                 for (i = 0; i < G_N_ELEMENTS (host_entries); i++) {
-                        XAddHost (self->priv->x11_display, &host_entries[i]);
+                        cookies[i] = xcb_change_hosts_checked (self->priv->xcb_connection,
+                                                               XCB_HOST_MODE_INSERT,
+                                                               host_entries[i].family,
+                                                               host_entries[i].length,
+                                                               (uint8_t *) host_entries[i].address);
                 }
 
-                XSync (self->priv->x11_display, False);
-                if (gdm_error_trap_pop ()) {
-                        g_debug ("Failed to give some system users access to the display. Trying to proceed.");
+                for (i = 0; i < G_N_ELEMENTS (cookies); i++) {
+                        xcb_generic_error_t *xcb_error;
+
+                        xcb_error = xcb_request_check (self->priv->xcb_connection, cookies[i]);
+
+                        if (xcb_error != NULL) {
+                                g_debug ("Failed to give system user '%s' access to the display. Trying to proceed.", host_entries[i].address + sizeof ("localuser"));
+                                free (xcb_error);
+                        } else {
+                                g_debug ("Gave system user '%s' access to the display.", host_entries[i].address + sizeof ("localuser"));
+                        }
                 }
 
                 gdm_display_set_windowpath (self);