[gdm/wip/xserver-in-session: 10/12] util: add wrapper for launching X session



commit b3e89c99b0d013fabc7314adba42f78e2a753c2b
Author: Ray Strode <rstrode redhat com>
Date:   Mon Jan 19 14:39:51 2015 -0500

    util: add wrapper for launching X session
    
    This commit adds a utility for launching an X server and session
    together.
    
    This simple utility works a lot like xinit, but makes use of
    modern X features (like -displayfd) and has GDM specific integration
    (like reading from gdm configuration, and optionally running through
     /etc/gdm/Xsession)
    
    The eventual idea is to get the main GDM code out of the X server launching
    business and instead farm the logic off to an unprivileged helper
    that gets run within the logind session of the user.

 utils/Makefile.am     |   18 ++-
 utils/gdm-x-session.c |  547 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 563 insertions(+), 2 deletions(-)
---
diff --git a/utils/Makefile.am b/utils/Makefile.am
index 992ba6c..4772014 100644
--- a/utils/Makefile.am
+++ b/utils/Makefile.am
@@ -7,6 +7,8 @@ AM_CPPFLAGS = \
        -I$(top_builddir)                               \
        -I$(top_srcdir)/common                          \
        -I$(top_builddir)/common                        \
+       -DDATADIR=\"$(datadir)\"                        \
+       -DGDMCONFDIR=\"$(gdmconfdir)\"                  \
        -DLOCALSTATEDIR=\""$(localstatedir)"\"          \
        -DGDM_SCREENSHOT_DIR=\""$(GDM_SCREENSHOT_DIR)"\"\
        -DGNOMELOCALEDIR=\""$(datadir)/locale"\"        \
@@ -29,8 +31,20 @@ bin_PROGRAMS = \
        gdm-screenshot          \
        $(NULL)
 
-gdmflexiserver_SOURCES =       \
-       gdmflexiserver.c        \
+libexec_PROGRAMS = \
+       gdm-x-session           \
+       $(NULL)
+
+gdm_x_session_LDADD =          \
+       $(top_builddir)/common/libgdmcommon.la  \
+       $(GTK_LIBS)             \
+       $(COMMON_LIBS)          \
+       $(SYSTEMD_LIBS)         \
+       $(XLIB_LIBS)            \
+       $(NULL)
+
+gdm_x_session_SOURCES =        \
+       gdm-x-session.c \
        $(NULL)
 
 gdmflexiserver_LDADD =         \
diff --git a/utils/gdm-x-session.c b/utils/gdm-x-session.c
new file mode 100644
index 0000000..47ce7e4
--- /dev/null
+++ b/utils/gdm-x-session.c
@@ -0,0 +1,547 @@
+/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 8 -*-
+ *
+ * Copyright (C) 2015 Red Hat, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+#include "config.h"
+
+#include <locale.h>
+#include <sysexits.h>
+
+#include "gdm-common.h"
+#include "gdm-settings-direct.h"
+#include "gdm-settings-keys.h"
+#include "gdm-log.h"
+
+#include <glib/gi18n.h>
+#include <glib/gstdio.h>
+#include <glib-unix.h>
+#include <glib.h>
+#include <gio/gunixinputstream.h>
+#include <glib-unix.h>
+#include <X11/Xauth.h>
+
+#define DISPLAY_FD (STDERR_FILENO + 1)
+
+typedef struct
+{
+        GdmSettings  *settings;
+        GCancellable *cancellable;
+        GSubprocess  *x_subprocess;
+        GSubprocess  *session_subprocess;
+        char         *session_command;
+        char         *auth_file;
+        char         *display_name;
+
+        int           session_exit_status;
+
+        GMainLoop    *main_loop;
+
+        guint32       debug_enabled : 1;
+} State;
+
+static FILE *
+create_auth_file (char **filename)
+{
+        char *auth_dir = NULL;
+        char *auth_file = NULL;
+        int fd;
+        FILE *fp = NULL;
+
+        auth_dir = g_build_filename (g_get_user_runtime_dir (),
+                                     "gdm",
+                                     NULL);
+
+        g_mkdir_with_parents (auth_dir, 0711);
+        auth_file = g_build_filename (auth_dir, "Xauthority", NULL);
+        g_clear_pointer (&auth_dir, g_free);
+
+        fd = g_open (auth_file, O_RDWR | O_CREAT | O_TRUNC, 0700);
+
+        if (fd < 0) {
+                g_debug ("could not open %s to store auth cookie: %m",
+                         auth_file);
+                g_clear_pointer (&auth_file, g_free);
+                goto out;
+        }
+
+        fp = fdopen (fd, "w+");
+
+        if (fp == NULL) {
+                g_debug ("could not set up stream for auth cookie file: %m");
+                g_clear_pointer (&auth_file, g_free);
+                close (fd);
+                goto out;
+        }
+
+        *filename = auth_file;
+out:
+        return fp;
+}
+
+static char *
+prepare_auth_file (void)
+{
+        FILE     *fp = NULL;
+        char     *filename = NULL;
+        GError   *error = NULL;
+        gboolean  prepared = FALSE;
+        Xauth     auth_entry = { 0 };
+        char      localhost[HOST_NAME_MAX + 1] = "";
+
+        g_debug ("Preparing auth file for X server");
+
+        fp = create_auth_file (&filename);
+
+        if (fp == NULL) {
+                return NULL;
+        }
+
+        if (gethostname (localhost, HOST_NAME_MAX) < 0) {
+                strncpy (localhost, "localhost", sizeof (localhost) - 1);
+        }
+
+        auth_entry.family = FamilyLocal;
+        auth_entry.address = localhost;
+        auth_entry.address_length = strlen (auth_entry.address);
+        auth_entry.name = "MIT-MAGIC-COOKIE-1";
+        auth_entry.name_length = strlen (auth_entry.name);
+
+        auth_entry.data_length = 16;
+        auth_entry.data = gdm_generate_random_bytes (auth_entry.data_length, &error);
+
+        if (error != NULL) {
+                goto out;
+        }
+
+        if (!XauWriteAuth (fp, &auth_entry) || fflush (fp) == EOF) {
+                goto out;
+        }
+
+        auth_entry.family = FamilyWild;
+        if (!XauWriteAuth (fp, &auth_entry) || fflush (fp) == EOF) {
+                goto out;
+        }
+
+        prepared = TRUE;
+
+out:
+        g_clear_pointer (&auth_entry.data, g_free);
+        g_clear_pointer (&fp, fclose);
+
+        if (!prepared) {
+                g_clear_pointer (&filename, g_free);
+        }
+
+        return filename;
+}
+
+static void
+on_x_server_finished (GSubprocess  *subprocess,
+                      GAsyncResult *result,
+                      State        *state)
+{
+        gboolean cancelled;
+
+        cancelled = !g_subprocess_wait_finish (subprocess, result, NULL);
+
+        if (cancelled) {
+                goto out;
+        }
+
+        if (g_subprocess_get_if_exited (subprocess)) {
+                int exit_status;
+
+                exit_status = g_subprocess_get_exit_status (subprocess);
+
+                g_debug ("X server exited with status %d", exit_status);
+        } else {
+                int signal_number;
+
+                signal_number = g_subprocess_get_term_sig (subprocess);
+                g_debug ("X server was killed with status %d", signal_number);
+        }
+
+out:
+        g_clear_object (&state->x_subprocess);
+        g_main_loop_quit (state->main_loop);
+}
+
+static gboolean
+spawn_x_server (State        *state,
+                GCancellable *cancellable)
+{
+        GPtrArray           *arguments;
+        GSubprocessLauncher *launcher;
+        GSubprocess         *subprocess;
+        GInputStream        *input_stream;
+        GDataInputStream    *data_stream;
+        GError              *error = NULL;
+
+        char     *auth_file;
+        gboolean  is_running = FALSE;
+        int       ret;
+        int       pipe_fds[2];
+        char     *display_fd_string = NULL;
+        char     *vt_string = NULL;
+        char     *display_number;
+        gsize     display_number_size;
+
+        auth_file = prepare_auth_file ();
+
+        g_debug ("Running X server");
+
+        ret = g_unix_open_pipe (pipe_fds, FD_CLOEXEC, &error);
+
+        if (!ret) {
+                g_debug ("could not open pipe: %s", error->message);
+                goto out;
+        }
+
+        arguments = g_ptr_array_new ();
+        launcher = g_subprocess_launcher_new (G_SUBPROCESS_FLAGS_STDIN_INHERIT);
+        g_subprocess_launcher_take_fd (launcher, pipe_fds[1], DISPLAY_FD);
+
+        if (g_getenv ("XDG_VTNR") != NULL) {
+                int vt;
+
+                vt = atoi (g_getenv ("XDG_VTNR"));
+
+                if (vt > 0 && vt < 64) {
+                        vt_string = g_strdup_printf ("vt%d", vt);
+                }
+        }
+
+        display_fd_string = g_strdup_printf ("%d", DISPLAY_FD);
+
+        g_ptr_array_add (arguments, X_SERVER);
+
+        if (vt_string != NULL) {
+                g_ptr_array_add (arguments, vt_string);
+        }
+
+        g_ptr_array_add (arguments, "-displayfd");
+        g_ptr_array_add (arguments, display_fd_string);
+
+        g_ptr_array_add (arguments, "-auth");
+        g_ptr_array_add (arguments, auth_file);
+
+        g_ptr_array_add (arguments, "-nolisten");
+        g_ptr_array_add (arguments, "tcp");
+
+        g_ptr_array_add (arguments, "-background");
+        g_ptr_array_add (arguments, "none");
+
+        g_ptr_array_add (arguments, "-noreset");
+        g_ptr_array_add (arguments, "-keeptty");
+        g_ptr_array_add (arguments, "-novtswitch");
+
+        g_ptr_array_add (arguments, "-verbose");
+        if (state->debug_enabled) {
+                g_ptr_array_add (arguments, "7");
+        } else {
+                g_ptr_array_add (arguments, "3");
+        }
+
+        if (state->debug_enabled) {
+                g_ptr_array_add (arguments, "-core");
+        }
+        g_ptr_array_add (arguments, NULL);
+
+        subprocess = g_subprocess_launcher_spawnv (launcher,
+                                                   (const char * const *) arguments->pdata,
+                                                   &error);
+        g_free (display_fd_string);
+        g_clear_object (&launcher);
+        g_ptr_array_free (arguments, TRUE);
+
+        if (subprocess == NULL) {
+                g_debug ("could not start X server: %s", error->message);
+                goto out;
+        }
+
+        input_stream = g_unix_input_stream_new (pipe_fds[0], TRUE);
+        data_stream = g_data_input_stream_new (input_stream);
+        g_clear_object (&input_stream);
+
+        display_number = g_data_input_stream_read_line (data_stream,
+                                                        &display_number_size,
+                                                        cancellable,
+                                                        &error);
+
+        if (error != NULL) {
+                g_debug ("could not read display string from X server: %s", error->message);
+                goto out;
+        }
+
+        if (display_number == NULL) {
+                g_debug ("X server did not write display string");
+                goto out;
+        }
+
+        state->display_name = g_strdup_printf (":%s", display_number);
+        g_clear_pointer (&display_number, g_free);
+
+        state->auth_file = g_strdup (auth_file);
+        state->x_subprocess = g_object_ref (subprocess);
+
+        g_subprocess_wait_async (state->x_subprocess,
+                                 cancellable,
+                                 (GAsyncReadyCallback)
+                                 on_x_server_finished,
+                                 state);
+
+        is_running = TRUE;
+out:
+        g_clear_pointer (&auth_file, g_free);
+        g_clear_object (&data_stream);
+        g_clear_object (&subprocess);
+        g_clear_object (&launcher);
+        g_clear_error (&error);
+
+        return is_running;
+}
+
+static void
+on_session_finished (GSubprocess  *subprocess,
+                     GAsyncResult *result,
+                     State        *state)
+{
+        gboolean cancelled;
+
+        cancelled = !g_subprocess_wait_finish (subprocess, result, NULL);
+
+        if (cancelled) {
+                goto out;
+        }
+
+        if (g_subprocess_get_if_exited (subprocess)) {
+                int exit_status;
+
+                exit_status = g_subprocess_get_exit_status (subprocess);
+
+                g_debug ("session exited with status %d", exit_status);
+
+                state->session_exit_status = exit_status;
+        } else {
+                int signal_number;
+
+                signal_number = g_subprocess_get_term_sig (subprocess);
+                g_debug ("session was killed with status %d", signal_number);
+        }
+
+out:
+        g_clear_object (&state->session_subprocess);
+        g_main_loop_quit (state->main_loop);
+}
+
+static gboolean
+spawn_session (State        *state,
+               gboolean      run_script,
+               GCancellable *cancellable)
+{
+        GSubprocessLauncher *launcher;
+        GSubprocess         *subprocess;
+        GError              *error = NULL;
+        gboolean             is_running = FALSE;
+
+        g_debug ("Running X session");
+
+        launcher = g_subprocess_launcher_new (G_SUBPROCESS_FLAGS_NONE);
+        g_subprocess_launcher_setenv (launcher, "DISPLAY", state->display_name, TRUE);
+        g_subprocess_launcher_setenv (launcher, "XAUTHORITY", state->auth_file, TRUE);
+
+        if (run_script) {
+                subprocess = g_subprocess_launcher_spawn (launcher,
+                                                          &error,
+                                                          GDMCONFDIR "/Xsession",
+                                                          state->session_command,
+                                                          NULL);
+        } else {
+                subprocess = g_subprocess_launcher_spawn (launcher,
+                                                          &error,
+                                                          state->session_command,
+                                                          NULL);
+        }
+
+        if (subprocess == NULL) {
+                g_debug ("could not start session: %s", error->message);
+                goto out;
+        }
+
+        state->session_subprocess = g_object_ref (subprocess);
+
+        g_subprocess_wait_async (state->session_subprocess,
+                                 cancellable,
+                                 (GAsyncReadyCallback)
+                                 on_session_finished,
+                                 state);
+
+        is_running = TRUE;
+out:
+        g_clear_object (&subprocess);
+        return is_running;
+}
+
+static void
+signal_subprocesses (State *state)
+{
+        if (state->session_subprocess != NULL) {
+                g_subprocess_send_signal (state->session_subprocess, SIGTERM);
+        }
+
+        if (state->x_subprocess != NULL) {
+                g_subprocess_send_signal (state->x_subprocess, SIGTERM);
+        }
+}
+
+static void
+wait_on_subprocesses (State *state)
+{
+        if (state->x_subprocess != NULL) {
+                g_subprocess_wait (state->x_subprocess, NULL, NULL);
+        }
+
+        if (state->session_subprocess != NULL) {
+                g_subprocess_wait (state->session_subprocess, NULL, NULL);
+        }
+}
+
+static void
+init_state (State **state)
+{
+        static State state_allocation;
+
+        *state = &state_allocation;
+}
+
+static void
+clear_state (State **out_state)
+{
+        State *state = *out_state;
+
+        g_clear_object (&state->cancellable);
+        g_clear_object (&state->session_subprocess);
+        g_clear_object (&state->x_subprocess);
+        g_clear_pointer (&state->auth_file, g_free);
+        g_clear_pointer (&state->display_name, g_free);
+        g_clear_pointer (&state->main_loop, g_main_loop_unref);
+        *out_state = NULL;
+}
+
+static gboolean
+on_sigterm (State *state)
+{
+        g_cancellable_cancel (state->cancellable);
+
+        if (g_main_loop_is_running (state->main_loop)) {
+                g_main_loop_quit (state->main_loop);
+        }
+
+        return G_SOURCE_CONTINUE;
+}
+
+int
+main (int    argc,
+      char **argv)
+{
+        State           *state;
+        GOptionContext  *context;
+        static char    **args = NULL;
+        static gboolean  run_script = FALSE;
+        gboolean         debug = FALSE;
+        gboolean         ret;
+        int              exit_status = EX_OK;
+        static GOptionEntry entries []   = {
+                /* todo add authentication and add bypass for Xsession script */
+                { "run-script", 'r', 0, G_OPTION_ARG_NONE, &run_script, N_("Run program through 
/etc/gdm/Xsession wrapper script"), NULL },
+                { G_OPTION_REMAINING, 0, 0, G_OPTION_ARG_STRING_ARRAY, &args, "", "" },
+                { NULL }
+        };
+
+        bindtextdomain (GETTEXT_PACKAGE, GNOMELOCALEDIR);
+        textdomain (GETTEXT_PACKAGE);
+        setlocale (LC_ALL, "");
+
+        gdm_log_init ();
+
+        context = g_option_context_new (_("GNOME Display Manager X Session Launcher"));
+        g_option_context_add_main_entries (context, entries, NULL);
+
+        g_option_context_parse (context, &argc, &argv, NULL);
+        g_option_context_free (context);
+
+        if (args == NULL || args[0] == NULL || args[1] != NULL) {
+                g_warning ("gdm-x-session takes one argument (the session)");
+                exit_status = EX_USAGE;
+                goto out;
+        }
+
+        init_state (&state);
+
+        state->session_command = args[0];
+
+        state->settings = gdm_settings_new ();
+        ret = gdm_settings_direct_init (state->settings, DATADIR "/gdm/gdm.schemas", "/");
+
+        if (!ret) {
+                g_printerr ("Unable to initialize settings");
+                exit_status = EX_DATAERR;
+                goto out;
+        }
+
+        gdm_settings_direct_get_boolean (GDM_KEY_DEBUG, &debug);
+        state->debug_enabled = debug;
+
+        gdm_log_set_debug (debug);
+
+        state->main_loop = g_main_loop_new (NULL, FALSE);
+        state->cancellable = g_cancellable_new ();
+
+        g_unix_signal_add (SIGTERM, (GSourceFunc) on_sigterm, state);
+
+        ret = spawn_x_server (state, state->cancellable);
+
+        if (!ret) {
+                g_printerr ("Unable to run X server");
+                exit_status = EX_SOFTWARE;
+                goto out;
+        }
+
+        ret = spawn_session (state, run_script, state->cancellable);
+
+        if (!ret) {
+                g_printerr ("Unable to run session");
+                exit_status = EX_SOFTWARE;
+                goto out;
+        }
+
+        g_main_loop_run (state->main_loop);
+
+        /* Only use exit status of session if we're here because it exit */
+
+        if (state->session_subprocess == NULL) {
+                exit_status = state->session_exit_status;
+        }
+
+        signal_subprocesses (state);
+        wait_on_subprocesses (state);
+out:
+        clear_state (&state);
+
+        return exit_status;
+}


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