[mutter/wip/pwithnall/meta-xwayland-fd-leaks] xwayland: Fix some FD leaks on error paths

[Philip Withnall <pwithnall src gnome org>]

commit bec456ba0a3a9aa54c09052c0b1591b4b81e1ed5
Author: Philip Withnall <pwithnall endlessos org>
Date:   Fri Feb 19 18:04:25 2021 +0000

    xwayland: Fix some FD leaks on error paths
    
    If `meta_xwayland_start_xserver()` returned via an error path, some of
    the socket FDs were leaked.
    
    Fix that, and add `steal_fd()` calls to make it clearer that FDs passed
    to `g_subprocess_launcher_take_fd()` are transferred to it. There were
    no bugs with how `GSubprocessLauncher` was being used.
    
    Spotted while working on
    https://gitlab.gnome.org/GNOME/glib/-/issues/2332.
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1738>

 src/wayland/meta-xwayland.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)
---
diff --git a/src/wayland/meta-xwayland.c b/src/wayland/meta-xwayland.c
index 7abcb5def2..48fabbfb33 100644
--- a/src/wayland/meta-xwayland.c
+++ b/src/wayland/meta-xwayland.c
@@ -837,6 +837,14 @@ on_displayfd_ready (int          fd,
   return G_SOURCE_REMOVE;
 }
 
+static int
+steal_fd (int *fd_ptr)
+{
+  int fd = *fd_ptr;
+  *fd_ptr = -1;
+  return fd;
+}
+
 void
 meta_xwayland_start_xserver (MetaXWaylandManager *manager,
                              GCancellable        *cancellable,
@@ -880,6 +888,9 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
 
   if (socketpair (AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, displayfd) < 0)
     {
+      close (xwayland_client_fd[0]);
+      close (xwayland_client_fd[1]);
+
       g_task_return_new_error (task,
                                G_IO_ERROR,
                                g_io_error_from_errno (errno),
@@ -903,11 +914,16 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
 
   launcher = g_subprocess_launcher_new (flags);
 
-  g_subprocess_launcher_take_fd (launcher, xwayland_client_fd[1], 3);
-  g_subprocess_launcher_take_fd (launcher, manager->public_connection.abstract_fd, 4);
-  g_subprocess_launcher_take_fd (launcher, manager->public_connection.unix_fd, 5);
-  g_subprocess_launcher_take_fd (launcher, displayfd[1], 6);
-  g_subprocess_launcher_take_fd (launcher, manager->private_connection.abstract_fd, 7);
+  g_subprocess_launcher_take_fd (launcher,
+                                 steal_fd (&xwayland_client_fd[1]), 3);
+  g_subprocess_launcher_take_fd (launcher,
+                                 steal_fd (&manager->public_connection.abstract_fd), 4);
+  g_subprocess_launcher_take_fd (launcher,
+                                 steal_fd (&manager->public_connection.unix_fd), 5);
+  g_subprocess_launcher_take_fd (launcher,
+                                 steal_fd (&displayfd[1]), 6);
+  g_subprocess_launcher_take_fd (launcher,
+                                 steal_fd (&manager->private_connection.abstract_fd), 7);
 
   g_subprocess_launcher_setenv (launcher, "WAYLAND_SOCKET", "3", TRUE);
 
@@ -954,6 +970,9 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
 
   if (!manager->proc)
     {
+      close (displayfd[0]);
+      close (xwayland_client_fd[0]);
+
       g_task_return_error (task, error);
       return;
     }