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/audit.h b/include/linux/audit.h
index ca019bb..12367cb 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -527,7 +527,7 @@
 extern unsigned int audit_serial(void);
 extern int auditsc_get_stamp(struct audit_context *ctx,
 			      struct timespec *t, unsigned int *serial);
-extern int  audit_set_loginuid(uid_t loginuid);
+extern int  audit_set_loginuid(kuid_t loginuid);
 #define audit_get_loginuid(t) ((t)->loginuid)
 #define audit_get_sessionid(t) ((t)->sessionid)
 extern void audit_log_task_context(struct audit_buffer *ab);
@@ -639,7 +639,7 @@
 #define audit_core_dumps(i) do { ; } while (0)
 #define audit_seccomp(i,s,c) do { ; } while (0)
 #define auditsc_get_stamp(c,t,s) (0)
-#define audit_get_loginuid(t) (-1)
+#define audit_get_loginuid(t) (INVALID_UID)
 #define audit_get_sessionid(t) (-1)
 #define audit_log_task_context(b) do { ; } while (0)
 #define audit_ipc_obj(i) ((void)0)
@@ -705,7 +705,7 @@
 extern int audit_filter_user(void);
 extern int audit_filter_type(int type);
 extern int  audit_receive_filter(int type, int pid, int seq,
-				void *data, size_t datasz, uid_t loginuid,
+				void *data, size_t datasz, kuid_t loginuid,
 				u32 sessionid, u32 sid);
 extern int audit_enabled;
 #else