lsm: use 32-bit compatible data types in LSM syscalls

Change the size parameters in lsm_list_modules(), lsm_set_self_attr()
and lsm_get_self_attr() from size_t to u32. This avoids the need to
have different interfaces for 32 and 64 bit systems.

Cc: stable@vger.kernel.org
Fixes: a04a1198088a ("LSM: syscalls for current process attributes")
Fixes: ad4aff9ec25f ("LSM: Create lsm_list_modules system call")
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reported-and-reviewed-by: Dmitry V. Levin <ldv@strace.io>
[PM: subject and metadata tweaks, syscall.h fixes]
Signed-off-by: Paul Moore <paul@paul-moore.com>

LSM: selftests for Linux Security Module syscalls

Add selftests for the three system calls supporting the LSM
infrastructure. This set of tests is limited by the differences
in access policy enforced by the existing security modules.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Mickaël Salaün <mic@digikod.net>
Tested-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Paul Moore <paul@paul-moore.com>