[gnome-session/wip/blacklist-session-specific-variables: 21/21] util: Blacklist some session-specific variables

[Ray Strode <halfline src gnome org>]

commit 646b9bc0584d02033ab9600c39b77d6f99bfc4a6
Author: Iain Lane <iainl gnome org>
Date:   Thu Aug 15 11:21:49 2019 +0100

    util: Blacklist some session-specific variables
    
    Things like XDG_SESSION_ID should not be uploaded to the environment.
    For example this is broken currently:
    
      1. SSH to your machine
      2. Log in to GNOME Shell
      3. Log out
      4. Log in again
      5. Lock the screen
      6. Try to unlock
    
    You can't, and this is because the XDG_SESSION_ID from the first session
    (step 2) has leaked through to the second one (step 4), and so GNOME
    Shell is listening to the `logind` `UnlockSession` signal for the wrong
    session. The SSH session established in step 1 serves to keep the
    `systemd --user` instance alive, so that the state is not torn down
    between logins.

 gnome-session/gsm-util.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)
---
diff --git a/gnome-session/gsm-util.c b/gnome-session/gsm-util.c
index dc0f138d..f6ddefc3 100644
--- a/gnome-session/gsm-util.c
+++ b/gnome-session/gsm-util.c
@@ -35,6 +35,13 @@
 static gchar *_saved_session_dir = NULL;
 static gchar **child_environment;
 
+static const char * const variable_blacklist[] = {
+    "XDG_SEAT",
+    "XDG_SESSION_ID",
+    "XDG_VTNR",
+    NULL
+};
+
 char *
 gsm_util_find_desktop_file_for_app_name (const char *name,
                                          gboolean    look_in_saved_session,
@@ -532,6 +539,9 @@ gsm_util_export_activation_environment (GError     **error)
                 const char *entry_name = entry_names[i];
                 const char *entry_value = g_getenv (entry_name);
 
+                if (g_strv_contains (variable_blacklist, entry_name))
+                    continue;
+
                 if (!g_utf8_validate (entry_name, -1, NULL))
                     continue;
 
@@ -603,8 +613,13 @@ gsm_util_export_user_environment (GError     **error)
                 return FALSE;
         }
 
+        entries = g_get_environ ();
+
+        for (; variable_blacklist[i] != NULL; i++)
+                entries = g_environ_unsetenv (entries, variable_blacklist[i]);
+
         g_variant_builder_init (&builder, G_VARIANT_TYPE ("as"));
-        for (entries = g_get_environ (); entries[i] != NULL; i++) {
+        for (i = 0; entries[i] != NULL; i++) {
                 const char *entry = entries[i];
 
                 if (!g_utf8_validate (entry, -1, NULL))