From dd45295425c5a843c30aa8797b02d59ff488acb8 Mon Sep 17 00:00:00 2001
From: Iain Lane <iainl@gnome.org>
Date: Mon, 4 Feb 2019 15:12:38 +0000
Subject: [PATCH] GdmManager: Don't perform timed login if session gets started

At the moment it's possible for the login screen to initiate
a timed login operation shortly after a user successfully starts
their session.

GDM won't complete the timed login operation, since a session is
already running, but will erroneously overwrite the username
associated with the session, misattributing the users session
to the timed login user.

Later, attempts to log in as the timed user will instead unlock the
session for the other user, since that session is now associated
with the timed login user.

This commit refuses timed login requests on sessions that are
already running, so the username doesn't get corrupted.

CVE-2019-3825

Closes https://gitlab.gnome.org/GNOME/gdm/issues/460
---
 daemon/gdm-manager.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/daemon/gdm-manager.c b/daemon/gdm-manager.c
index 1e5719558..b8619fbba 100644
--- a/daemon/gdm-manager.c
+++ b/daemon/gdm-manager.c
@@ -1947,6 +1947,14 @@ on_session_client_connected (GdmSession      *session,
 
         g_debug ("GdmManager: client with pid %d connected", (int) pid_of_client);
 
+        if (gdm_session_is_running (session)) {
+                const char *session_username;
+                session_username = gdm_session_get_username (session);
+                g_debug ("GdmManager: ignoring connection, since session already running (for user %s)",
+                         session_username);
+                return;
+        }
+
         display = get_display_for_user_session (session);
 
         if (display == NULL) {
-- 
GitLab

