[gdm/wip/laney/systemd-user: 95/97] manager: Find user's current graphical session, not session of caller

[Iain Lane <iainl src gnome org>]

commit 7bb3cb38f81038da277c82a09054d8f36d5da911
Author: Iain Lane <iain orangesquash org uk>
Date:   Fri Jan 5 11:53:34 2018 +0000

    manager: Find user's current graphical session, not session of caller
    
    If (e.g.) gnome-shell is started as a systemd --user unit, it won't be
    part of the login session. We should instead look through all of the
    user's sessions until we find the login session, and take that as our
    session.

 common/gdm-common.c         | 77 ++++++++++++++++++++++++++++++++++++++++++---
 common/gdm-common.h         |  5 +++
 daemon/gdm-manager.c        | 52 +++++++++++++++++++++++++++---
 libgdm/Makefile.am          |  1 +
 libgdm/gdm-user-switching.c |  8 ++---
 5 files changed, 129 insertions(+), 14 deletions(-)
---
diff --git a/common/gdm-common.c b/common/gdm-common.c
index 373d5b85..0beaf50c 100644
--- a/common/gdm-common.c
+++ b/common/gdm-common.c
@@ -484,6 +484,7 @@ goto_login_session (GDBusConnection  *connection,
         char           *our_session;
         char           *session_id;
         char           *seat_id;
+        GError         *local_error = NULL;
 
         ret = FALSE;
         session_id = NULL;
@@ -496,10 +497,8 @@ goto_login_session (GDBusConnection  *connection,
          * since the data allocated is from libsystemd-logind, which
          * does not use GLib's g_malloc (). */
 
-        res = sd_pid_get_session (0, &our_session);
-        if (res < 0) {
-                g_debug ("failed to determine own session: %s", strerror (-res));
-                g_set_error (error, GDM_COMMON_ERROR, 0, _("Could not identify the current session."));
+        if (!gdm_find_display_session_for_uid (getuid (), &our_session, &local_error)) {
+                g_propagate_prefixed_error (error, local_error, _("Could not identify the current session: 
"));
 
                 return FALSE;
         }
@@ -843,3 +842,73 @@ gdm_shell_expand (const char *str,
         }
         return g_string_free (s, FALSE);
 }
+
+gboolean
+gdm_find_display_session_for_uid (const uid_t uid,
+                                  char      **out_session_id,
+                                  GError    **error)
+{
+        const gchar * const graphical_session_types[] = { "wayland", "x11", "mir", NULL };
+        const gchar * const active_states[] = { "active", "online", NULL };
+        g_autofree gchar *local_session_id = NULL;
+        g_autofree gchar *type = NULL;
+        g_autofree gchar *state = NULL;
+        int saved_errno;
+
+        g_return_val_if_fail (out_session_id != NULL, FALSE);
+
+        if ((saved_errno = sd_uid_get_display (uid, &local_session_id)) < 0) {
+                g_set_error (error,
+                             GDM_COMMON_ERROR,
+                             0,
+                             "Couldn't get display: %s (%s)",
+                             g_strerror (-saved_errno),
+                             local_session_id);
+                return FALSE;
+        }
+
+        if ((saved_errno = sd_session_get_type (local_session_id, &type)) < 0) {
+                g_set_error (error,
+                             GDM_COMMON_ERROR,
+                             0,
+                             "Couldn't get type for session '%s': %s",
+                             local_session_id,
+                             g_strerror (-saved_errno));
+                return FALSE;
+        }
+
+        if (!g_strv_contains (graphical_session_types, type)) {
+                g_set_error (error,
+                             GDM_COMMON_ERROR,
+                             0,
+                             "Session '%s' is not a graphical session (type: '%s')",
+                             local_session_id,
+                             type);
+                return FALSE;
+        }
+
+        /* display sessions can be 'closing' if they are logged out but some
+         * processes are lingering; we shouldn't consider these */
+        if ((saved_errno = sd_session_get_state (local_session_id, &state)) < 0) {
+                g_set_error (error,
+                             GDM_COMMON_ERROR,
+                             0,
+                             "Couldn't get state for session '%s': %s",
+                             local_session_id,
+                             g_strerror (-saved_errno));
+                return FALSE;
+        }
+
+        if (!g_strv_contains (active_states, state)) {
+                g_set_error (error,
+                             GDM_COMMON_ERROR,
+                             0,
+                             "Session '%s' is not active",
+                             local_session_id);
+                return FALSE;
+        }
+
+        *out_session_id = g_steal_pointer (&local_session_id);
+
+        return TRUE;
+}
diff --git a/common/gdm-common.h b/common/gdm-common.h
index 07812b10..996c9153 100644
--- a/common/gdm-common.h
+++ b/common/gdm-common.h
@@ -46,6 +46,11 @@ int            gdm_wait_on_and_disown_pid (int pid,
                                            int timeout);
 int            gdm_signal_pid            (int pid,
                                           int signal);
+
+gboolean       gdm_find_display_session_for_uid (const uid_t uid,
+                                                 char      **out_session_id,
+                                                 GError    **error);
+
 gboolean       gdm_get_pwent_for_name    (const char     *name,
                                           struct passwd **pwentp);
 
diff --git a/daemon/gdm-manager.c b/daemon/gdm-manager.c
index 4d2ad9de..168eedbd 100644
--- a/daemon/gdm-manager.c
+++ b/daemon/gdm-manager.c
@@ -414,6 +414,34 @@ get_seat_id_for_session_id (const char  *session_id,
         return out_seat;
 }
 
+static char *
+find_greeter_session_for_uid (uid_t uid)
+{
+        g_autofree gchar *class = NULL;
+        gchar *session_id = NULL;
+        g_auto(GStrv) sessions = NULL;
+        int n_sessions;
+        int saved_errno;
+
+        n_sessions = sd_uid_get_sessions (uid, 1, &sessions);
+
+        for (int i = 0; i < n_sessions; ++i) {
+                if ((saved_errno = sd_session_get_class (sessions[i], &class)) < 0) {
+                        g_critical ("Couldn't get class for session '%s': %s",
+                                    sessions[i],
+                                    g_strerror (-saved_errno));
+                        continue;
+                }
+
+                if (g_strcmp0 (class, "greeter") == 0) {
+                        session_id = g_strdup (sessions[i]);
+                        break;
+                }
+        }
+
+        return session_id;
+}
+
 static char *
 get_tty_for_session_id (const char  *session_id,
                         GError     **error)
@@ -483,15 +511,29 @@ get_display_and_details_for_bus_sender (GdmManager       *self,
                 goto out;
         }
 
-        session_id = get_session_id_for_pid (pid, &error);
+        ret = gdm_find_display_session_for_uid (caller_uid, &session_id, &error);
 
         if (session_id == NULL) {
-                g_debug ("GdmManager: Error while retrieving session id for sender: %s",
+                g_debug ("GdmManager: Error while retrieving session id for sender: %s, trying fallback.",
                          error->message);
-                g_error_free (error);
-                goto out;
+                g_clear_pointer (&error, g_error_free);
+
+                /* No display session for the user - we're probably the
+                 * greeter; look for a greeter session */
+                session_id = find_greeter_session_for_uid (caller_uid);
+                if (session_id == NULL) {
+                        /* Hmm, no, OK, let's look at the PID */
+                        g_debug ("GdmManager: Error while retrieving session id for user %d, looking at 
pid.",
+                                 caller_uid);
+                        session_id = get_session_id_for_pid (pid, &error);
+                        if (session_id == NULL) {
+                                g_debug ("GdmManager: Error while retrieving session id for pid %d, 
failing.",
+                                         pid);
+                                goto out;
+                        }
+                }
         }
- 
+
         if (out_session_id != NULL) {
                 *out_session_id = g_strdup (session_id);
         }
diff --git a/libgdm/Makefile.am b/libgdm/Makefile.am
index 2f7d7b61..ccd739bb 100644
--- a/libgdm/Makefile.am
+++ b/libgdm/Makefile.am
@@ -66,6 +66,7 @@ libgdm_la_LDFLAGS =                                                    \
         $(END_OF_LIST)
 
 libgdm_la_LIBADD =                                                     \
+        $(top_builddir)/common/libgdmcommon.la                         \
         $(LIBGDM_LIBS)                                                 \
         $(SYSTEMD_LIBS)                                                \
         $(END_OF_LIST)
diff --git a/libgdm/gdm-user-switching.c b/libgdm/gdm-user-switching.c
index 3d4303e3..3a33fcbb 100644
--- a/libgdm/gdm-user-switching.c
+++ b/libgdm/gdm-user-switching.c
@@ -191,6 +191,7 @@ goto_login_session (GDBusConnection  *connection,
         char           *our_session;
         char           *session_id;
         char           *seat_id;
+        GError         *local_error = NULL;
 
         ret = FALSE;
         session_id = NULL;
@@ -202,11 +203,8 @@ goto_login_session (GDBusConnection  *connection,
         /* Note that we mostly use free () here, instead of g_free ()
          * since the data allocated is from libsystemd-logind, which
          * does not use GLib's g_malloc (). */
-
-        res = sd_pid_get_session (0, &our_session);
-        if (res < 0) {
-                g_debug ("failed to determine own session: %s", strerror (-res));
-                g_set_error (error, GDM_CLIENT_ERROR, 0, _("Could not identify the current session."));
+        if (!gdm_find_display_session_for_uid (getuid (), &our_session, &local_error)) {
+                g_propagate_prefixed_error (error, local_error, _("Could not identify the current session: 
"));
 
                 return FALSE;
         }