File gdm-look-for-session-based-on-pid-first.patch of Package gdm

From 82c3c9bbe924c43e93e74cd622207a54bc44962c Mon Sep 17 00:00:00 2001
From: Benjamin Berg <bberg@redhat.com>
Date: Thu, 23 Jan 2020 14:32:38 +0100
Subject: [PATCH] manager: Try looking up session based on PID first

Unfortunately, GDM may be running multiple greeters, and each greeter is
currently using the same user. So while in a lot of setups each user
should only have one graphical session and also only one DBus session
bus, this is not true for the gdm greeter.

Lacking another solution (e.g. separate users), we need to be able to
correctly lookup the session information for all greeter instances. We
can do so by using sd_pid_get_session and using this information is safe
if it does return something.

See: #526
---
 common/gdm-common.c         | 30 ++++++++++++++++++++++++++----
 common/gdm-common.h         |  7 ++++---
 daemon/gdm-manager.c        |  2 +-
 libgdm/gdm-user-switching.c |  2 +-
 4 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/common/gdm-common.c b/common/gdm-common.c
index 41bdb389..d13cf618 100644
--- a/common/gdm-common.c
+++ b/common/gdm-common.c
@@ -497,7 +497,7 @@ goto_login_session (GDBusConnection  *connection,
          * since the data allocated is from libsystemd-logind, which
          * does not use GLib's g_malloc (). */
 
-        if (!gdm_find_display_session_for_uid (getuid (), &our_session, &local_error)) {
+        if (!gdm_find_display_session (0, getuid (), &our_session, &local_error)) {
                 g_propagate_prefixed_error (error, local_error, _("Could not identify the current session: "));
 
                 return FALSE;
@@ -898,16 +898,38 @@ _systemd_session_is_active (const char *session_id)
 }
 
 gboolean
-gdm_find_display_session_for_uid (const uid_t uid,
-                                  char      **out_session_id,
-                                  GError    **error)
+gdm_find_display_session (int         pid,
+                          const uid_t uid,
+                          char      **out_session_id,
+                          GError    **error)
 {
         char *local_session_id = NULL;
         g_auto(GStrv) sessions = NULL;
         int n_sessions;
+        int res;
 
         g_return_val_if_fail (out_session_id != NULL, FALSE);
 
+        /* First try to look up the session using the pid. We need this
+         * at least for the greeter, because it currently runs multiple
+         * sessions under the same user.
+         * See also commit 2b52d8933c8ab38e7ee83318da2363d00d8c5581
+         * which added an explicit dbus-run-session for all but seat0.
+         */
+        res = sd_pid_get_session (pid, &local_session_id);
+        if (res >= 0) {
+                g_debug ("Found session %s for PID %d, using", local_session_id, pid);
+
+                *out_session_id = g_strdup (local_session_id);
+                g_free (local_session_id);
+
+                return TRUE;
+        } else {
+                if (res != -ENODATA)
+                        g_warning ("Failed to retrieve session information for pid %d: %s",
+                                   pid, strerror (-res));
+        }
+
         g_debug ("Finding a graphical session for user %d", uid);
 
         n_sessions = sd_uid_get_sessions (uid,
diff --git a/common/gdm-common.h b/common/gdm-common.h
index 5c3fe137..3d037d68 100644
--- a/common/gdm-common.h
+++ b/common/gdm-common.h
@@ -51,9 +51,10 @@ int            gdm_wait_on_and_disown_pid (int pid,
 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_find_display_session (int         pid,
+                                         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 907eca37..d8dfa843 100644
--- a/daemon/gdm-manager.c
+++ b/daemon/gdm-manager.c
@@ -501,7 +501,7 @@ get_display_and_details_for_bus_sender (GdmManager       *self,
                 goto out;
         }
 
-        ret = gdm_find_display_session_for_uid (caller_uid, &session_id, &error);
+        ret = gdm_find_display_session (pid, caller_uid, &session_id, &error);
 
         if (!ret) {
                 g_debug ("GdmManager: Unable to find display session for uid %d: %s",
diff --git a/libgdm/gdm-user-switching.c b/libgdm/gdm-user-switching.c
index 3a33fcbb..20235fd8 100644
--- a/libgdm/gdm-user-switching.c
+++ b/libgdm/gdm-user-switching.c
@@ -203,7 +203,7 @@ 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 (). */
-        if (!gdm_find_display_session_for_uid (getuid (), &our_session, &local_error)) {
+        if (!gdm_find_display_session (0, getuid (), &our_session, &local_error)) {
                 g_propagate_prefixed_error (error, local_error, _("Could not identify the current session: "));
 
                 return FALSE;
-- 
2.24.1