audit: avoid missing-prototype warnings

Building with 'make W=1' reveals two function definitions without
a previous prototype in the audit code:

lib/compat_audit.c:32:5: error: no previous prototype for 'audit_classify_compat_syscall' [-Werror=missing-prototypes]
kernel/audit.c:1813:14: error: no previous prototype for 'audit_serial' [-Werror=missing-prototypes]

The first one needs a declaration from linux/audit.h but cannot
include that header without causing conflicting (compat) syscall number
definitions, so move the it into linux/audit_arch.h.

The second one is declared conditionally based on CONFIG_AUDITSYSCALL
but needed as a local function even when that option is disabled, so
move the declaration out of the #ifdef block.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Moore <paul@paul-moore.com>

audit: add support for the openat2 syscall

The openat2(2) syscall was added in kernel v5.6 with commit
fddb5d430ad9 ("open: introduce openat2(2) syscall").

Add the openat2(2) syscall to the audit syscall classifier.

Link: https://github.com/linux-audit/audit-kernel/issues/67
Link: https://lore.kernel.org/r/f5f1a4d8699613f8c02ce762807228c841c2e26f.1621363275.git.rgb@redhat.com
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
[PM: merge fuzz due to previous header rename, commit line wraps]
Signed-off-by: Paul Moore <paul@paul-moore.com>

audit: replace magic audit syscall class numbers with macros

Replace audit syscall class magic numbers with macros.

This required putting the macros into new header file
include/linux/audit_arch.h since the syscall macros were
included for both 64 bit and 32 bit in any compat code, causing
redefinition warnings.

Link: https://lore.kernel.org/r/2300b1083a32aade7ae7efb95826e8f3f260b1df.1621363275.git.rgb@redhat.com
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
[PM: renamed header to audit_arch.h after consulting with Richard]
Signed-off-by: Paul Moore <paul@paul-moore.com>