exec: introduce finalize_exec() before start_thread()

exec: introduce finalize_exec() before start_thread()

Provide a final callback into fs/exec.c before start_thread() takes
over, to handle any last-minute changes, like the coming restoration of
the stack limit.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Ben Hutchings <[email protected]>
Cc: Ben Hutchings <[email protected]>
Cc: Brad Spengler <[email protected]>
Cc: Greg KH <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: "Jason A. Donenfeld" <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Willy Tarreau <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>