exec: Promised cleanups after introducing exec_update_mutex

In the patchset that introduced exec_update_mutex there were a few last
minute discoveries and fixes that left the code in a state that can
be very easily be improved.

During the merge window we discussed the first three of these patches
and I promised I would resend them.

What the first patch does is it makes the the calls in the binfmts:
	flush_old_exec();
        /* set the personality */
        setup_new_exec();
        install_exec_creds();

With no sleeps or anything in between.

At the conclusion of this set of changes the the calls in the binfmts
are:
	begin_new_exec();
        /* set the personality */
        setup_new_exec();

The intent is to make the code easier to follow and easier to change.

Eric W. Biederman (7):
      binfmt: Move install_exec_creds after setup_new_exec to match binfmt_elf
      exec: Make unlocking exec_update_mutex explict
      exec: Rename the flag called_exec_mmap point_of_no_return
      exec: Merge install_exec_creds into setup_new_exec
      exec: In setup_new_exec cache current in the local variable me
      exec: Move most of setup_new_exec into flush_old_exec
      exec: Rename flush_old_exec begin_new_exec

 Documentation/trace/ftrace.rst |   2 +-
 arch/x86/ia32/ia32_aout.c      |   4 +-
 fs/binfmt_aout.c               |   3 +-
 fs/binfmt_elf.c                |   3 +-
 fs/binfmt_elf_fdpic.c          |   3 +-
 fs/binfmt_flat.c               |   4 +-
 fs/exec.c                      | 162 ++++++++++++++++++++---------------------
 include/linux/binfmts.h        |  10 +--
 kernel/events/core.c           |   2 +-
 9 files changed, 92 insertions(+), 101 deletions(-)

Link: https://lkml.kernel.org/r/87h7wujhmz.fsf@x220.int.ebiederm.org


Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>