This patch for adds dynamic context transition support to SELinux via writes
to the existing /proc/pid/attr/current interface.

Previously, SELinux only supported exec-based context transitions.  This
functionality allows privileged applications to apply privilege bracketing
without necessarily being refactored to an exec-based model (although such a
model has advantages in least privilege and isolation).

A process must have setcurrent permission to use this mechanism at all, and
the dyntransition permission must be granted between the old and new security
contexts.  Multi-threaded processes are not allowed to use this operation, as
it will yield an inconsistency among the security contexts of the threads
sharing the same mm.

Ptrace permission is revalidated against the new context if the process is
being ptraced.

Author:  Darrel Goeddel <dgoeddel@trustedcs.com>
Signed-off-by: Stephen Smalley <sds@epoch.ncsc.mil>
Signed-off-by: James Morris <jmorris@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>