[glib/benzea/systemd-transient-scope: 313/314] gdesktopappinfo: Move launched applications into transient scope

[Benjamin Berg <bberg src gnome org>]

commit fc0eb98b81b532d5310df61abda8495954389299
Author: Benjamin Berg <bberg redhat com>
Date:   Mon Jul 27 22:22:32 2020 +0200

    gdesktopappinfo: Move launched applications into transient scope
    
    Try to move the spawned executable into its own systemd scope. To avoid
    possible race conditions and ensure proper accounting, we delay the
    execution of the real command until after the DBus call to systemd has
    finished.
    
    From the two approaches we can take here, this is better in the sense
    that we have a child that the API consumer can watch. API consumers
    should not be doing this, however, gnome-session needs to watch children
    during session startup. Until gnome-session is fixed, we will not be
    able to change this.
    
    The alternative approach is to delegate launching itself to systemd by
    creating a transient .service unit instead. This is cleaner and has e.g.
    the advantage that systemd will take care of log redirection and similar
    issues.
    
    Note that this patch is incomplete. The DBus call is done in a "fire and
    forget" manner, which is fine in most cases, but means that "gio open"
    will fail to move the child into the new scope as gio quits before the
    DBus call finishes.

 gio/gdesktopappinfo.c | 296 ++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 261 insertions(+), 35 deletions(-)
---
diff --git a/gio/gdesktopappinfo.c b/gio/gdesktopappinfo.c
index 229e62143..0d1943b2a 100644
--- a/gio/gdesktopappinfo.c
+++ b/gio/gdesktopappinfo.c
@@ -2733,6 +2733,167 @@ notify_desktop_launch (GDBusConnection  *session_bus,
 
 #define _SPAWN_FLAGS_DEFAULT (G_SPAWN_SEARCH_PATH)
 
+#if defined(__linux__) && !defined(__BIONIC__)
+typedef struct {
+  int pipe[2];
+  GSpawnChildSetupFunc user_setup;
+  gpointer             user_setup_data;
+} SpawnWrapperData;
+
+static void
+launch_uris_with_spawn_delay_exec (gpointer user_data)
+{
+  SpawnWrapperData *data = user_data;
+
+  /* Clear CLOEXEC again, as that was set due to
+   * %G_SPAWN_LEAVE_DESCRIPTORS_OPEN not being set. */
+  fcntl (data->pipe[0], F_SETFD, 0);
+
+  /* No need to close read side, we have CLOEXEC set. */
+
+  if (data->user_setup)
+    data->user_setup (data->user_setup_data);
+}
+
+static gchar *
+systemd_unit_name_escape (const gchar *in)
+{
+  /* Adapted from systemd's unit_name_escape found in src/basic/unit-name.c */
+  GString * str = g_string_sized_new (strlen (in));
+
+  for (; *in; in++)
+    {
+      if (g_ascii_isalnum (*in) || *in == ':' || *in == '_' || *in == '.')
+        g_string_append_c (str, *in);
+      else
+        g_string_append_printf (str, "\\x%02x", *in);
+    }
+  return g_string_free (str, FALSE);
+}
+
+static void
+create_systemd_scope (GDBusConnection    *session_bus,
+                      GDesktopAppInfo    *info,
+                      gint                pid,
+                      GAsyncReadyCallback callback,
+                      gpointer            user_data)
+{
+  GVariantBuilder builder;
+  const char *app_name = g_get_application_name ();
+  const char *source_path = NULL;
+  char *source_path_utf8 = NULL;
+  char *appid = NULL;
+  char *appid_escaped = NULL;
+  char *snid_escaped = NULL;
+  char *unit_name = NULL;
+
+  /* In this order:
+   *  1. Actual application ID from file
+   *  2. Stripping the .desktop from the desktop ID
+   *  3. Fall back to using the binary name
+   */
+  if (info->app_id)
+    appid = g_strdup (info->app_id);
+  else if (info->desktop_id && g_str_has_suffix (info->desktop_id, ".desktop"))
+    appid = g_strndup (info->desktop_id, strlen (info->desktop_id) - strlen (".desktop"));
+  else
+    appid = g_path_get_basename (info->binary);
+
+  appid_escaped = systemd_unit_name_escape (appid);
+
+  /* Generate a name conforming to
+   *   https://systemd.io/DESKTOP_ENVIRONMENTS/
+   * We use the PID to disambiguate, as that should be unique enough.
+   */
+  unit_name = g_strdup_printf ("app-glib-%s-%d.scope", appid_escaped, pid);
+
+  source_path = g_desktop_app_info_get_filename (info);
+  if (source_path)
+    source_path_utf8 = g_filename_to_utf8 (source_path, -1, NULL, NULL, NULL);
+
+  g_variant_builder_init (&builder, G_VARIANT_TYPE ("(ssa(sv)a(sa(sv)))"));
+  g_variant_builder_add (&builder, "s", unit_name);
+  g_variant_builder_add (&builder, "s", "fail"); /* job-mode */
+
+  g_variant_builder_open (&builder, G_VARIANT_TYPE ("a(sv)"));
+
+  /* Add a generic human readable description, can be changed at will. */
+  if (app_name)
+    g_variant_builder_add (&builder,
+                           "(sv)",
+                           "Description",
+                           g_variant_new_take_string (g_strdup_printf ("Application launched by %s",
+                                                                       app_name)));
+
+  /* If we have a .desktop file, document that the scope has been "generated"
+   * from it.
+   */
+  if (source_path_utf8)
+    g_variant_builder_add (&builder,
+                           "(sv)",
+                           "SourcePath",
+                           g_variant_new_take_string (source_path_utf8));
+
+  g_variant_builder_add (&builder,
+                         "(sv)",
+                         "PIDs",
+                          g_variant_new_fixed_array (G_VARIANT_TYPE_UINT32, &pid, 1, sizeof(guint32)));
+  /* Default to let systemd garbage collect failed applications we launched. */
+  g_variant_builder_add (&builder,
+                         "(sv)",
+                         "CollectMode",
+                          g_variant_new_string ("inactive-or-failed"));
+
+  g_variant_builder_close (&builder);
+
+  g_variant_builder_open (&builder, G_VARIANT_TYPE ("a(sa(sv))"));
+  g_variant_builder_close (&builder);
+
+  /* It is intentionally to not allow cancellation as cancellation could result
+   * in the created process to not be moved into a separate systemd unit.
+   */
+  g_dbus_connection_call (session_bus,
+                          "org.freedesktop.systemd1",
+                          "/org/freedesktop/systemd1",
+                          "org.freedesktop.systemd1.Manager",
+                          "StartTransientUnit",
+                          g_variant_builder_end (&builder),
+                          G_VARIANT_TYPE ("(o)"),
+                          G_DBUS_CALL_FLAGS_NO_AUTO_START,
+                          -1,
+                          NULL,
+                          callback,
+                          user_data);
+
+  g_free (appid);
+  g_free (appid_escaped);
+  g_free (snid_escaped);
+  g_free (unit_name);
+}
+
+static void
+systemd_scope_created_cb (GObject      *object,
+                          GAsyncResult *result,
+                          gpointer      user_data)
+{
+  GVariant *res = NULL;
+  GError *error = NULL;
+
+  res = g_dbus_connection_call_finish (G_DBUS_CONNECTION (object), result, &error);
+  if (error != NULL)
+    {
+      g_debug ("Failed to move new child into scope: %s", error->message);
+      g_error_free (error);
+    }
+
+  /* Unblock the waiting wrapper binary. */
+  close (GPOINTER_TO_INT (user_data));
+
+  if (res)
+    g_variant_unref (res);
+}
+#endif
+
 static gboolean
 g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
                                            GDBusConnection            *session_bus,
@@ -2747,19 +2908,17 @@ g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
                                            gint                        stdin_fd,
                                            gint                        stdout_fd,
                                            gint                        stderr_fd,
-                                           GError                    **error)
+                                           GError                    **error_out)
 {
   gboolean completed = FALSE;
-  GList *old_uris;
   GList *dup_uris;
-
-  char **argv, **envp;
+  GStrv envp = NULL;
+  GError *error = NULL;
+  char *sn_id = NULL;
   int argc;
 
   g_return_val_if_fail (info != NULL, FALSE);
 
-  argv = NULL;
-
   if (launch_context)
     envp = g_app_launch_context_get_environment (launch_context);
   else
@@ -2772,13 +2931,26 @@ g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
   dup_uris = uris;
   do
     {
+      GList *old_uris;
+      GStrv argv = NULL;
+      GList *launched_uris = NULL;
       GPid pid;
-      GList *launched_uris;
       GList *iter;
-      char *sn_id = NULL;
-      char **wrapped_argv;
       int i;
-      gsize j;
+#if defined(__linux__) && !defined(__BIONIC__)
+      SpawnWrapperData wrapper_data;
+      gchar *wrapper_fd_arg = NULL;
+      const gchar * const wrapper_argv[] =
+        {
+          "/bin/sh",
+          "-e",
+          "-u",
+          /* The "cat" will hang until the write side is closed, "$signal_fd<&-" closes the read side */
+          "-c", "export GIO_LAUNCHED_DESKTOP_FILE_PID=$$; signal_fd=$1; shift; cat <&$signal_fd; exec \"$@\" 
$signal_fd<&-",
+          "sh",  /* argv[0] for sh */
+          NULL, /* Placeholder for signaling FD, must be last in the array */
+        };
+#else
       const gchar * const wrapper_argv[] =
         {
           "/bin/sh",
@@ -2787,20 +2959,23 @@ g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
           "-c", "export GIO_LAUNCHED_DESKTOP_FILE_PID=$$; exec \"$@\"",
           "sh",  /* argv[0] for sh */
         };
+#endif
+      GStrv wrapped_argv = NULL;
+      GSpawnChildSetupFunc setup = user_setup;
+      gpointer             setup_data = user_setup_data;
 
       old_uris = dup_uris;
-      if (!expand_application_parameters (info, exec_line, &dup_uris, &argc, &argv, error))
+      if (!expand_application_parameters (info, exec_line, &dup_uris, &argc, &argv, &error))
         goto out;
 
       /* Get the subset of URIs we're launching with this process */
-      launched_uris = NULL;
       for (iter = old_uris; iter != NULL && iter != dup_uris; iter = iter->next)
         launched_uris = g_list_prepend (launched_uris, iter->data);
       launched_uris = g_list_reverse (launched_uris);
 
       if (info->terminal && !prepend_terminal_to_vector (&argc, &argv))
         {
-          g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+          g_set_error_literal (&error, G_IO_ERROR, G_IO_ERROR_FAILED,
                                _("Unable to find terminal required for application"));
           goto out;
         }
@@ -2811,7 +2986,6 @@ g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
                                  info->filename,
                                  TRUE);
 
-      sn_id = NULL;
       if (launch_context)
         {
           GList *launched_files = create_files_for_uris (launched_uris);
@@ -2841,37 +3015,85 @@ g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
        * `gio-launch-desktop` for an example of this which could be
        * resurrected). */
       wrapped_argv = g_new (char *, argc + G_N_ELEMENTS (wrapper_argv) + 1);
+      wrapped_argv[argc + G_N_ELEMENTS (wrapper_argv)] = NULL;
 
-      for (j = 0; j < G_N_ELEMENTS (wrapper_argv); j++)
-        wrapped_argv[j] = g_strdup (wrapper_argv[j]);
+      for (i = 0; i < G_N_ELEMENTS (wrapper_argv); i++)
+        wrapped_argv[i] = g_strdup (wrapper_argv[i]);
       for (i = 0; i < argc; i++)
-        wrapped_argv[i + G_N_ELEMENTS (wrapper_argv)] = g_steal_pointer (&argv[i]);
+        wrapped_argv[i + G_N_ELEMENTS (wrapper_argv)] = (gchar*) argv[i];
+
+#if defined(__linux__) && !defined(__BIONIC__)
+      /* Create pipes, if we use a setup func, then set cloexec,
+       * otherwise our wrapper script will close both sides. */
+      if (!g_unix_open_pipe (wrapper_data.pipe, 0, NULL))
+        {
+          g_set_error_literal (&error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                               _("Unable to create pipe for systemd synchronization"));
+          goto out;
+        }
 
-      wrapped_argv[i + G_N_ELEMENTS (wrapper_argv)] = NULL;
-      g_free (argv);
-      argv = NULL;
+      /* Set CLOEXEC on the write pipe, so we don't need to deal with it in the child. */
+      fcntl (wrapper_data.pipe[1], F_SETFD, FD_CLOEXEC);
+
+      if (!(spawn_flags & G_SPAWN_LEAVE_DESCRIPTORS_OPEN))
+        {
+          /* In this case, we use a setup function (which could probably also
+           * overwrite envp to set GIO_LAUNCHED_DESKTOP_FILE_PID).
+           *
+           * Note that this does not incur an additional cost because
+           * %G_SPAWN_LEAVE_DESCRIPTORS_OPEN must be set in order to use
+           * posix_spawn. */
+          wrapper_data.user_setup = setup;
+          wrapper_data.user_setup_data = setup_data;
+
+          setup = launch_uris_with_spawn_delay_exec;
+          setup_data = &wrapper_data;
+        }
+
+      /* The last item is the placeholder for the FD, overwrite it (so far it is NULL). */
+      g_assert (wrapped_argv[G_N_ELEMENTS(wrapper_argv) - 1] == NULL);
+      wrapper_fd_arg = g_strdup_printf ("%d", wrapper_data.pipe[0]);
+      wrapped_argv[G_N_ELEMENTS(wrapper_argv) - 1] = wrapper_fd_arg;
+#endif
 
       if (!g_spawn_async_with_fds (info->path,
                                    wrapped_argv,
                                    envp,
                                    spawn_flags,
-                                   user_setup,
-                                   user_setup_data,
+                                   setup,
+                                   setup_data,
                                    &pid,
                                    stdin_fd,
                                    stdout_fd,
                                    stderr_fd,
-                                   error))
+                                   &error))
         {
+#if defined(__linux__) && !defined(__BIONIC__)
+          close (wrapper_data.pipe[0]);
+          close (wrapper_data.pipe[1]);
+#endif
+
           if (sn_id)
             g_app_launch_context_launch_failed (launch_context, sn_id);
 
-          g_free (sn_id);
-          g_list_free (launched_uris);
-
           goto out;
         }
 
+#if defined(__linux__) && !defined(__BIONIC__)
+      /* We close write side asynchronously later on when the dbus call
+       * to systemd finishes. */
+      close (wrapper_data.pipe[0]);
+
+      if (session_bus)
+        create_systemd_scope (session_bus,
+                              info,
+                              pid,
+                              systemd_scope_created_cb,
+                              GINT_TO_POINTER (wrapper_data.pipe[1]));
+      else
+        close (wrapper_data.pipe[1]);
+#endif
+
       if (pid_callback != NULL)
         pid_callback (info, pid, pid_callback_data);
 
@@ -2896,19 +3118,23 @@ g_desktop_app_info_launch_uris_with_spawn (GDesktopAppInfo            *info,
                              sn_id,
                              launched_uris);
 
-      g_free (sn_id);
-      g_list_free (launched_uris);
-
-      g_strfreev (wrapped_argv);
-      wrapped_argv = NULL;
+    out:
+      g_clear_pointer (&sn_id, g_free);
+      g_clear_pointer (&launched_uris, g_list_free);
+      g_clear_pointer (&wrapped_argv, g_free);
+      g_clear_pointer (&argv, g_strfreev);
+#if defined(__linux__) && !defined(__BIONIC__)
+      g_clear_pointer (&wrapper_fd_arg, g_free);
+#endif
     }
-  while (dup_uris != NULL);
+  while (dup_uris != NULL && !error);
 
-  completed = TRUE;
+  if (dup_uris == NULL)
+    completed = TRUE;
 
- out:
-  g_strfreev (argv);
   g_strfreev (envp);
+  if (error)
+    g_propagate_error (error_out, error);
 
   return completed;
 }