[gvfs/gnome-3-30] admin: Prevent access if any authentication agent isn't available

[Ondrej Holy <oholy src gnome org>]

commit e4eec2bc863e85e2b6b47e4d1c3bdd90ab36dc93
Author: Ondrej Holy <oholy redhat com>
Date:   Wed Jan 2 17:13:27 2019 +0100

    admin: Prevent access if any authentication agent isn't available
    
    The backend currently allows to access and modify files without prompting
    for password if any polkit authentication agent isn't available. This seems
    isn't usually problem, because polkit agents are integral parts of
    graphical environments / linux distributions. The agents can't be simply
    disabled without root permissions and are automatically respawned. However,
    this might be a problem in some non-standard cases.
    
    This affects only users which belong to wheel group (i.e. those who are
    already allowed to use sudo). It doesn't allow privilege escalation for
    users, who don't belong to that group.
    
    Let's return permission denied error also when the subject can't be
    authorized by any polkit agent to prevent this behavior.
    
    Closes: https://gitlab.gnome.org/GNOME/gvfs/issues/355

 daemon/gvfsbackendadmin.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/daemon/gvfsbackendadmin.c b/daemon/gvfsbackendadmin.c
index ec0f2392..0f849008 100644
--- a/daemon/gvfsbackendadmin.c
+++ b/daemon/gvfsbackendadmin.c
@@ -130,8 +130,7 @@ check_permission (GVfsBackendAdmin *self,
       return FALSE;
     }
 
-  is_authorized = polkit_authorization_result_get_is_authorized (result) ||
-    polkit_authorization_result_get_is_challenge (result);
+  is_authorized = polkit_authorization_result_get_is_authorized (result);
 
   g_object_unref (result);