policycoreutils: sandbox: check for paths up front

When launching a sandbox x environment we should check up front to make
sure that the seunshare and sandboxsh files exist and bail politely if
they do not exist.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Dan Walsh <dwalsh@redhat.com>

policycoreutils/sandbox/sandbox

@@ -174,6 +174,15 @@ class Sandbox:
     def __x_callback(self, option, opt, value, parser):
            self.__mount = True
            setattr(parser.values, option.dest, True)
+           if not os.path.exists(SEUNSHARE):
+                  raise ValueError(_("""
+%s is required for the action you want to perform.
+""") % SEUNSHARE)
+
+           if not os.path.exists(SANDBOXSH):
+                  raise ValueError(_("""
+%s is required for the action you want to perform.
+""") % SANDBOXSH)
 
     def __validdir(self, option, opt, value, parser):
            if not os.path.isdir(value):