* Beginning of secure multi-user Nix stores. If Nix is started as

root (or setuid root), then builds will be performed under one of
  the users listed in the `build-users' configuration variables.  This
  is to make it impossible to influence build results externally,
  allowing locally built derivations to be shared safely between
  users (see ASE-2005 paper).

  To do: only one builder should be active per build user.

src/libmain/shared.cc

@@ -334,6 +334,11 @@ void switchToNixUser()
         exit(1);
     }
 
+    /* !!! for setuid operation, we should: 1) wipe the environment;
+       2) verify file descriptors 0, 1, 2; 3) etc.
+       See: http://www.daemon-systems.org/man/setuid.7.html
+    */
+
     haveSwitched = true;
     
 #endif