ima: instantiate the bprm_creds_for_exec() hook

ima: instantiate the bprm_creds_for_exec() hook

Like direct file execution (e.g. ./script.sh), indirect file execution
(e.g. sh script.sh) needs to be measured and appraised.  Instantiate
the new security_bprm_creds_for_exec() hook to measure and verify the
indirect file's integrity.  Unlike direct file execution, indirect file
execution is optionally enforced by the interpreter.

Differentiate kernel and userspace enforced integrity audit messages.

Co-developed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241212174223.389435-9-mic@digikod.net
Signed-off-by: Kees Cook <kees@kernel.org>