Set XAUTHORITY environment variable if is unset

The way it works is that if XAUTHORITY is unset, then its default
value is $HOME/.Xauthority. But since we're changing user identity
this will not work since $HOME will now change. Therefore, if
XAUTHORITY is unset, just set its default value before changing
identity. This bug only affected login managers using X Window
Authorization but not explicitly setting the XAUTHORITY variable.

You can argue that XAUTHORITY is broken since it forces uid-changing
apps like pkexec(1) to do more work - and get involved in intimate
details of how X works and so on - but that doesn't change how things
work.

Based on a patch from Peter Wu <lekensteyn@gmail.com>.

https://bugs.freedesktop.org/show_bug.cgi?id=51623

Signed-off-by: David Zeuthen <zeuthen@gmail.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/programs/pkexec.c b/src/programs/pkexec.c
index 840eb3c..da9784a 100644
--- a/src/programs/pkexec.c
+++ b/src/programs/pkexec.c
@@ -608,6 +608,28 @@ main (int argc, char *argv[])
       g_ptr_array_add (saved_env, g_strdup (value));
     }
 
+  /* $XAUTHORITY is "special" - if unset, we need to set it to ~/.Xauthority. Yes,
+   * this is broken but it's unfortunately how things work (see fdo #51623 for
+   * details)
+   */
+  if (g_getenv ("XAUTHORITY") == NULL)
+    {
+      const gchar *home;
+
+      /* pre-2.36 GLib does not examine $HOME (it always looks in /etc/passwd) and
+       * this is not what we want
+       */
+      home = g_getenv ("HOME");
+      if (home == NULL)
+        home = g_get_home_dir ();
+
+      if (home != NULL)
+        {
+          g_ptr_array_add (saved_env, g_strdup ("XAUTHORITY"));
+          g_ptr_array_add (saved_env, g_build_filename (home, ".Xauthority", NULL));
+        }
+    }
+
   /* Nuke the environment to get a well-known and sanitized environment to avoid attacks
    * via e.g. the DBUS_SYSTEM_BUS_ADDRESS environment variable and similar.
    */