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/include/linux/tty.h b/include/linux/tty.h
index 9f47ab5..7298385 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -553,7 +553,7 @@
 extern void tty_audit_tiocsti(struct tty_struct *tty, char ch);
 extern void tty_audit_push(struct tty_struct *tty);
 extern int tty_audit_push_task(struct task_struct *tsk,
-			       uid_t loginuid, u32 sessionid);
+			       kuid_t loginuid, u32 sessionid);
 #else
 static inline void tty_audit_add_data(struct tty_struct *tty,
 				      unsigned char *data, size_t size)
@@ -572,7 +572,7 @@
 {
 }
 static inline int tty_audit_push_task(struct task_struct *tsk,
-				      uid_t loginuid, u32 sessionid)
+				      kuid_t loginuid, u32 sessionid)
 {
 	return 0;
 }