userns: Convert the audit loginuid  to be a kuid

Always store audit loginuids in type kuid_t.

Print loginuids by converting them into uids in the appropriate user
namespace, and then printing the resulting uid.

Modify audit_get_loginuid to return a kuid_t.

Modify audit_set_loginuid to take a kuid_t.

Modify /proc/<pid>/loginuid on read to convert the loginuid into the
user namespace of the opener of the file.

Modify /proc/<pid>/loginud on write to convert the loginuid
rom the user namespace of the opener of the file.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: Paul Moore <paul@paul-moore.com> ?
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/net/netlabel/netlabel_user.c b/net/netlabel/netlabel_user.c
index 9fae63f..9650c4a 100644
--- a/net/netlabel/netlabel_user.c
+++ b/net/netlabel/netlabel_user.c
@@ -109,7 +109,7 @@
 		return NULL;
 
 	audit_log_format(audit_buf, "netlabel: auid=%u ses=%u",
-			 audit_info->loginuid,
+			 from_kuid(&init_user_ns, audit_info->loginuid),
 			 audit_info->sessionid);
 
 	if (audit_info->secid != 0 &&