[PATCH] selinux: fix tty locking

Take tty_mutex when accessing ->signal->tty in selinux code.  Noted by Alan
Cox.  Longer term, we are looking at refactoring the code to provide better
encapsulation of the tty layer, but this is a simple fix that addresses the
immediate bug.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Alan Cox <alan@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>